This page is for anything related to McIntosh amplifiers.Photos will be periodicaly added showing McIntosh Unity Coupled Output transformers being wound and assembled.MC75 transformer with tri-filar windings will be shown durring winding process, banding t.
The 300 Watt vacuum tube amp in the MC901 uses McIntosh's patented Unity Coupled Circuit output transformer – the same technology McIntosh was founded on in 1949 – to deliver its full 300 Watts into almost any speaker regardless if it has 2, 4 or 8 Ohm impedance. The 300 Watt vacuum tube amp in the MC901 uses our patented Unity Coupled Circuit output transformer – the same technology McIntosh was founded on in 1949 – to deliver its full 300 Watts into almost any speaker regardless if it has 2, 4 or 8 Ohm impedance.
Contributors include: Peter Breuninger, Neil Gader, Robert E. Greene, Robert Harley, Dick Olsher, Harry Pearson, Paul Seydor, and Jonathan Valin.
Peter Breuninger
Dynaco ST-70
Along with Avery Fisher’s 500c, David Hafler’s ST-70 put high performance audio in the American home. Introduced in 1959, the ST-70 is the world’s most prolific stand alone amplifier with over 300,000 units manufactured. Amazingly, its clear, three-dimensional sound is comparable to many amplifiers made today.
Along with Avery Fisher’s 500c, David Hafler’s ST-70 put high performance audio in the American home. Introduced in 1959, the ST-70 is the world’s most prolific stand alone amplifier with over 300,000 units manufactured. Amazingly, its clear, three-dimensional sound is comparable to many amplifiers made today.
McIntosh MC3500
While the MC2505 put the signature big blue meters in the market, many people consider this the greatest amplifier ever made. Released in 1968 (as the MI350) for commercial applications, it eclipsed any amplifier of the day with an extraordinary 350 watts per channel. The consumer version, MC3500 established McIntosh as the premier audio company of the day.
While the MC2505 put the signature big blue meters in the market, many people consider this the greatest amplifier ever made. Released in 1968 (as the MI350) for commercial applications, it eclipsed any amplifier of the day with an extraordinary 350 watts per channel. The consumer version, MC3500 established McIntosh as the premier audio company of the day.
Phase Linear 700
It was 1970 and Bob Carver saw the future and brought to market a product that would set the stage for a new audio segment—affordable, mass-market, high-performance audio. Rock bands put dry ice on stacks of these legendary 350 watt per channel amps to cool them down. The Series One is the one to have.
It was 1970 and Bob Carver saw the future and brought to market a product that would set the stage for a new audio segment—affordable, mass-market, high-performance audio. Rock bands put dry ice on stacks of these legendary 350 watt per channel amps to cool them down. The Series One is the one to have.
Krell KSA-100
Arguably, the first high-end solid-state super-amp. The year was 1980 and who would know that the KSA 100, right out-of-the-box, would establish Krell as one of the greatest brands of all time. Dan D’Agostino proved to the world that solid-state output devices could actually reproduce music. To this day, Krell sets the benchmark for military build-quality and outstanding sonics.
Arguably, the first high-end solid-state super-amp. The year was 1980 and who would know that the KSA 100, right out-of-the-box, would establish Krell as one of the greatest brands of all time. Dan D’Agostino proved to the world that solid-state output devices could actually reproduce music. To this day, Krell sets the benchmark for military build-quality and outstanding sonics.
Mark Levinson ML2
This John Curl designed amplifier established Mark Levinson, the man, as a driving force in the audiophile marketplace. The 25-watt ML2 monoblock, Levinson’s first power amp, was designed for wide-swing-impedance speakers such as the legendary HQD system (Hartley, stacked Quads, Decca Ribbon).
This John Curl designed amplifier established Mark Levinson, the man, as a driving force in the audiophile marketplace. The 25-watt ML2 monoblock, Levinson’s first power amp, was designed for wide-swing-impedance speakers such as the legendary HQD system (Hartley, stacked Quads, Decca Ribbon).
Audio Research Reference 610T
In the late 1960s, William Zane Johnson, began building and selling modified (Dynaco) ST-70s. Several solid-state designs emerged in the 70s but it was the all tube D70 in 1983 that established forever the hallmark “high definition” sound of an Audio Research amplifier. In 1995, Johnson designed his lifetime achievement product, the Reference 600. Refined into the 610T (tall), it’s 600 watts of breathtaking thermionic power that has no peer.
In the late 1960s, William Zane Johnson, began building and selling modified (Dynaco) ST-70s. Several solid-state designs emerged in the 70s but it was the all tube D70 in 1983 that established forever the hallmark “high definition” sound of an Audio Research amplifier. In 1995, Johnson designed his lifetime achievement product, the Reference 600. Refined into the 610T (tall), it’s 600 watts of breathtaking thermionic power that has no peer.
Conrad Johnson Premier One
Introduced in 1981, two years after CJ’s first amp, the MV75, the Premier One was the first super-output modern-day tube amp. It eclipsed Audio Research’s 50- and 75-watt tube amps of the 70s with an amazing 200 watts per channel. It’s still a reference for many collectors when recapped (including me).
Introduced in 1981, two years after CJ’s first amp, the MV75, the Premier One was the first super-output modern-day tube amp. It eclipsed Audio Research’s 50- and 75-watt tube amps of the 70s with an amazing 200 watts per channel. It’s still a reference for many collectors when recapped (including me).
Carver Silver Sevens
Carver bought the output tranies in the 1960s and schlepped them around for nearly twenty years before building his dream amplifier. The audacity of the “Carver challenge” still fresh in the public mind, he shocked the world with the most expensive ($17,000) and esoteric conventional tube amplifier ever (till then). Its 375 watts per channel, four gleaming chassis, and 15 KT88s per side (14 as outputs) were mind blowing. BTW, I have the very first pair ever made in for audition!
Carver bought the output tranies in the 1960s and schlepped them around for nearly twenty years before building his dream amplifier. The audacity of the “Carver challenge” still fresh in the public mind, he shocked the world with the most expensive ($17,000) and esoteric conventional tube amplifier ever (till then). Its 375 watts per channel, four gleaming chassis, and 15 KT88s per side (14 as outputs) were mind blowing. BTW, I have the very first pair ever made in for audition!
Audio Note Ongaku
It shocked the audio world. $60,000 for an amplifier! In 1988, Hiroyasu Kondo’s, minuscule-powered, 27Wpc SET integrated amplifier set the mark for luxury pricing of audio components. This was the first production amplifier to use handmade silver electronic components (transformers, caps, and wire).
It shocked the audio world. $60,000 for an amplifier! In 1988, Hiroyasu Kondo’s, minuscule-powered, 27Wpc SET integrated amplifier set the mark for luxury pricing of audio components. This was the first production amplifier to use handmade silver electronic components (transformers, caps, and wire).
Cary CAD-805
The poster child for single-ended triodes. Dennis Had’s Cary CAD-805 was the amplifier that put SETs on magazine covers. It had the build-quality of a McIntosh and established the phrase “SET midrange magic.” The CAD-805 has been in production since 1992.
The poster child for single-ended triodes. Dennis Had’s Cary CAD-805 was the amplifier that put SETs on magazine covers. It had the build-quality of a McIntosh and established the phrase “SET midrange magic.” The CAD-805 has been in production since 1992.
Neil Gader
Plinius 8150
The 8150 represented the leading edge of a new breed of high-power integrated amplifiers that challenged the hegemony of separates. Part of the trick was its use of an extra dose of Class A bias, lack of compression, and superb channel separation.
The 8150 represented the leading edge of a new breed of high-power integrated amplifiers that challenged the hegemony of separates. Part of the trick was its use of an extra dose of Class A bias, lack of compression, and superb channel separation.
Dynaco ST-70
Insanely popular, the David Hafler designed 35Wpc was introduced in 1959 yet kept on truckin’ for about 30 years. Easy to modify and renown for its personable midrange, it was often affectionately referenced as the “poor Man’s McIntosh.”
Insanely popular, the David Hafler designed 35Wpc was introduced in 1959 yet kept on truckin’ for about 30 years. Easy to modify and renown for its personable midrange, it was often affectionately referenced as the “poor Man’s McIntosh.”
Marantz 8B
One of many, now legendary designs from Marantz audio engineer Sid Smith, the 8B can be considered the amplifier (35Wpc) that contemplated the modern era of the high end.
One of many, now legendary designs from Marantz audio engineer Sid Smith, the 8B can be considered the amplifier (35Wpc) that contemplated the modern era of the high end.
McIntosh MC275
Using an implementation of Mac’s original unity-coupled circuit, the MC275 set new standards for low distortion. Able to run as a 150W mono amp or as a 75Wpc stereo amp, it proved so popular that it returned for an encore years after ceased production.
Using an implementation of Mac’s original unity-coupled circuit, the MC275 set new standards for low distortion. Able to run as a 150W mono amp or as a 75Wpc stereo amp, it proved so popular that it returned for an encore years after ceased production.
Audio Research D-150
ARC’s D-150 did everything big in 1975. Huge meters on a massive chassis, high heat output from the 6550s, and the kind of power that made them the amplifier of choice for the then speaker of choice, the Magneplanar Timpani 1D.
ARC’s D-150 did everything big in 1975. Huge meters on a massive chassis, high heat output from the 6550s, and the kind of power that made them the amplifier of choice for the then speaker of choice, the Magneplanar Timpani 1D.
Rotel RB-1090
Blue plate manna from audio heaven, the RB-1090 was the go-to amp for low-sensitivity speakers that presented tractor-sized loads. Rated at 380Wpc with 1kW peaks at 2 ohms, it combined price/power and performance like few amps on the market.
Blue plate manna from audio heaven, the RB-1090 was the go-to amp for low-sensitivity speakers that presented tractor-sized loads. Rated at 380Wpc with 1kW peaks at 2 ohms, it combined price/power and performance like few amps on the market.
NAD-3020 Integrated
Born in the late 1970s, it was the little integrated amp that could. By keeping it clean and minimalist, blessing it with a sweet midrange and dynamics out of proportion to its modest power, NAD kept buyers coming back for more. And they still are.
Born in the late 1970s, it was the little integrated amp that could. By keeping it clean and minimalist, blessing it with a sweet midrange and dynamics out of proportion to its modest power, NAD kept buyers coming back for more. And they still are.
Phase Linear 700/400
Bob Carver’s 1970 designs demonstrated that mega-amps driving lower-sensitivity loudspeakers could perform on the same field with lower-powered competitors. Unique for its time were the transformers and output transistors placed on the outside the chassis–an innovation that eased serviceability and reduced operating temperatures.
Bob Carver’s 1970 designs demonstrated that mega-amps driving lower-sensitivity loudspeakers could perform on the same field with lower-powered competitors. Unique for its time were the transformers and output transistors placed on the outside the chassis–an innovation that eased serviceability and reduced operating temperatures.
Mark Levinson ML-2
Before Lexus and corporate branding, before Kim Cattrall, there was Mark Levinson, the man—an original who pioneered a second wave of high-status boutique amplifiers like the ML-2 that defied corporate culture. Levinson help to raise the bar on resolution and power cost and led the way for dozens of wannabes.
Before Lexus and corporate branding, before Kim Cattrall, there was Mark Levinson, the man—an original who pioneered a second wave of high-status boutique amplifiers like the ML-2 that defied corporate culture. Levinson help to raise the bar on resolution and power cost and led the way for dozens of wannabes.
Heathkit amps
A right of passage—there was more hair pulled out trying to finish these DIY amps. The parts often changed and kits sometimes arrived incomplete but a generation of teenage hobbyists cut their teeth building these components and moving on to their own cutting-edge designs.
A right of passage—there was more hair pulled out trying to finish these DIY amps. The parts often changed and kits sometimes arrived incomplete but a generation of teenage hobbyists cut their teeth building these components and moving on to their own cutting-edge designs.
Robert E. Greene
The Williamson Amplifier (1947-1949)
Not the first tube amplifier with feedback nor the first with low distortion—Peter Walker had a feedback prototype in the late 1930s and Leak a hi-fi amp before Williamson—Williamson’s designs published in Wireless World in the late 1940s showed once and for all that low-distortion amplification was possible and practical. Along with the McIntosh M50W1, the beginning of modern high fidelity.
Not the first tube amplifier with feedback nor the first with low distortion—Peter Walker had a feedback prototype in the late 1930s and Leak a hi-fi amp before Williamson—Williamson’s designs published in Wireless World in the late 1940s showed once and for all that low-distortion amplification was possible and practical. Along with the McIntosh M50W1, the beginning of modern high fidelity.
McIntosh M50W1
This amplifier, developed by Gordon Gow for McIntosh in the late 1940s, was the American analogue of the British accomplishments. With bandwidth from 20Hz to 20kHz and less than 1% harmonic distortion, it had high fidelity in a strong sense and set the stage for the American tube amplifier industry of the 1950s and early 60s.
This amplifier, developed by Gordon Gow for McIntosh in the late 1940s, was the American analogue of the British accomplishments. With bandwidth from 20Hz to 20kHz and less than 1% harmonic distortion, it had high fidelity in a strong sense and set the stage for the American tube amplifier industry of the 1950s and early 60s.
Dynaco ST-70
The amplifier that brought high-fidelity stereo to the masses in the USA. Marantz, Harmon Kardon Citation, and McIntosh amplifiers may have been better, but the Stereo 70, with 300,000 unit sales, was 35Wpc of power to the people.
The amplifier that brought high-fidelity stereo to the masses in the USA. Marantz, Harmon Kardon Citation, and McIntosh amplifiers may have been better, but the Stereo 70, with 300,000 unit sales, was 35Wpc of power to the people.
Quad 303
Not the first transistor amplifier, but arguably the first to show that transistor amplifiers could sound as good as, or indeed better than, tube amplifiers. Even today, it is startling how good the 303 sounds, if played within its power limits. Even in the late 60s, a transistor amplifier could, as the 303 showed, sound really wonderful.
Not the first transistor amplifier, but arguably the first to show that transistor amplifiers could sound as good as, or indeed better than, tube amplifiers. Even today, it is startling how good the 303 sounds, if played within its power limits. Even in the late 60s, a transistor amplifier could, as the 303 showed, sound really wonderful.
Phase Linear
Carver the man and the company would produce better amplifiers later and more powerful ones, too, but the Phase Linear 700 and the more popular 400 were the amplifiers that put high power on the map. After their 350 and 200 watts per channel, there was no going back to things like 25 watts—or there should not have been, anyway. 6 Audio Research D series and Conrad Johnson Premiere series: Arguably, none of these were really all that interesting as circuit design in principle, but they put tube amplifiers back in the center of things in American High End in the 1970’s and ‘80’s, for better or worse.
Carver the man and the company would produce better amplifiers later and more powerful ones, too, but the Phase Linear 700 and the more popular 400 were the amplifiers that put high power on the map. After their 350 and 200 watts per channel, there was no going back to things like 25 watts—or there should not have been, anyway. 6 Audio Research D series and Conrad Johnson Premiere series: Arguably, none of these were really all that interesting as circuit design in principle, but they put tube amplifiers back in the center of things in American High End in the 1970’s and ‘80’s, for better or worse.
Hafler XL-280
Hafler’s line of MOSFET amps begun in the 1970s, though very popular, did not quite dominate the American scene as had Dynaco. But Hafler could prove by his differential input-output test that the XL-280 was close to perfect and probably did not worry much that high end was largely preferring tubes, which were demonstrably less accurate by comparison.
Hafler’s line of MOSFET amps begun in the 1970s, though very popular, did not quite dominate the American scene as had Dynaco. But Hafler could prove by his differential input-output test that the XL-280 was close to perfect and probably did not worry much that high end was largely preferring tubes, which were demonstrably less accurate by comparison.
Carver Sunfire, Lightstar, and A Series
Carver the man and the company, separate by that time, shared the remarkable power-supply technology that gave these compact and not very heavy amplifiers enormous power. The Sunfire Signature could produce 2500 watt pulses! And the Carver A Series, designed by Jim Croft, had the all but unique feature of no output network, for flat response into any load at all. Capabilities beyond the wildest dreams of decades past.
Carver the man and the company, separate by that time, shared the remarkable power-supply technology that gave these compact and not very heavy amplifiers enormous power. The Sunfire Signature could produce 2500 watt pulses! And the Carver A Series, designed by Jim Croft, had the all but unique feature of no output network, for flat response into any load at all. Capabilities beyond the wildest dreams of decades past.
Tact Millennium
Digital amplification in some form or another was bound to show up eventually and there were earlier tries at something like “digital” amplification. The Tact Millennium was the first digital amplifier to realize the full sonic promise of keeping the signal in digital form almost up to the last instant. The future had arrived, or at least one version of the future.
Digital amplification in some form or another was bound to show up eventually and there were earlier tries at something like “digital” amplification. The Tact Millennium was the first digital amplifier to realize the full sonic promise of keeping the signal in digital form almost up to the last instant. The future had arrived, or at least one version of the future.
Sanders Magtech
Not around long enough yet to have had much influence, but give it time. This amplifier offers a unique mode of operation and not just the promise but the reality of an all but unprecedented ability to drive difficult loads playing demanding music with uncompromised sound quality. Analog amplification lives!
Not around long enough yet to have had much influence, but give it time. This amplifier offers a unique mode of operation and not just the promise but the reality of an all but unprecedented ability to drive difficult loads playing demanding music with uncompromised sound quality. Analog amplification lives!
Robert Harley
Dynaco ST-70
The David-Hafler-designed ST-70 not only sold in huge numbers, it became the blueprint (literally and figuratively) for generations of mid-powered tubed amplifiers. The circuit sounded so good that many of today’s tubed amplifiers are based on the ST-70’s fundamental topology. Perhaps the best-selling high-performance amplifier of all time.
The David-Hafler-designed ST-70 not only sold in huge numbers, it became the blueprint (literally and figuratively) for generations of mid-powered tubed amplifiers. The circuit sounded so good that many of today’s tubed amplifiers are based on the ST-70’s fundamental topology. Perhaps the best-selling high-performance amplifier of all time.
Threshold 800A
Nelson Pass’ first power amplifier under the Threshold name (1975), the 800A signaled to the world that Pass was a designer of uncommon talent and original thinking. The 800A introduced active biasing that allowed the 800A to deliver far more Class A power than conventionally biased Class A/B amplifiers of similar size and heat dissipation. The triple-series, triple-parallel output stage was also groundbreaking. The 800A was the first product in a lifetime of creative approaches to amplifier design that continues to this day in Pass Labs’ products. I could have chosen several other Pass designs that would be worthy of this list.
Nelson Pass’ first power amplifier under the Threshold name (1975), the 800A signaled to the world that Pass was a designer of uncommon talent and original thinking. The 800A introduced active biasing that allowed the 800A to deliver far more Class A power than conventionally biased Class A/B amplifiers of similar size and heat dissipation. The triple-series, triple-parallel output stage was also groundbreaking. The 800A was the first product in a lifetime of creative approaches to amplifier design that continues to this day in Pass Labs’ products. I could have chosen several other Pass designs that would be worthy of this list.
Audio Research D150
The ARC D150 represented a turning point in tubed amplifier design at its 1975 introduction. Although it followed in the footsteps of the groundbreaking 76A, the D150 took the idea of high resolution (and high power) in a tubed design to another level. The D150 proved that transparency, resolution, and low coloration were not the exclusive province of solid-state amplifiers.
The ARC D150 represented a turning point in tubed amplifier design at its 1975 introduction. Although it followed in the footsteps of the groundbreaking 76A, the D150 took the idea of high resolution (and high power) in a tubed design to another level. The D150 proved that transparency, resolution, and low coloration were not the exclusive province of solid-state amplifiers.
Krell KSA-50
The KSA-50 is significant more for being the first commercial product from then-newcomer Dan D’Agostino and Krell Industries. It established the “dreadnought” build-quality of massive power supplies, lots of output devices relative to the output power, and the ability to drive the world’s most challenging loudspeaker loads. The KSA-50 was the antecedent of a long string of great power amplifiers from Krell, and the product that forced other manufacturers to step up their games with regard to bottom-end slam and bulletproof construction.
The KSA-50 is significant more for being the first commercial product from then-newcomer Dan D’Agostino and Krell Industries. It established the “dreadnought” build-quality of massive power supplies, lots of output devices relative to the output power, and the ability to drive the world’s most challenging loudspeaker loads. The KSA-50 was the antecedent of a long string of great power amplifiers from Krell, and the product that forced other manufacturers to step up their games with regard to bottom-end slam and bulletproof construction.
Phase Linear 700
Although not nearly as popular as the smaller 400, the 700’s claim to fame is that it was the first truly high-powered amplifier. Remember that when the 350Wpc Phase Linear 700 was introduced in 1970, 50Wpc was considered a powerhouse. Bob Carver’s 700 paved the way for the modern era of high-powered amplifiers, both tubed and solid-state. This trend toward high-powered amplifiers gave loudspeaker designers more latitude in their designs, unleashing the wave of loudspeaker innovation that began a few years later.
Although not nearly as popular as the smaller 400, the 700’s claim to fame is that it was the first truly high-powered amplifier. Remember that when the 350Wpc Phase Linear 700 was introduced in 1970, 50Wpc was considered a powerhouse. Bob Carver’s 700 paved the way for the modern era of high-powered amplifiers, both tubed and solid-state. This trend toward high-powered amplifiers gave loudspeaker designers more latitude in their designs, unleashing the wave of loudspeaker innovation that began a few years later.
Hafler DH-200
Sold as a kit or fully assembled ($299/$429 in 1980, if memory serves), the DH-200 represented the confluence of great sound (thanks in part to a wonderful MOSFET output stage), high reliability, and a dirt-cheap price. The DH-200 made a high-end powerhouse amplifier affordable to many.
Sold as a kit or fully assembled ($299/$429 in 1980, if memory serves), the DH-200 represented the confluence of great sound (thanks in part to a wonderful MOSFET output stage), high reliability, and a dirt-cheap price. The DH-200 made a high-end powerhouse amplifier affordable to many.
NAD 3020
This unassuming little integrated amplifier brought true high-end sound to a mass-market price, and in the process, exposed a whole generation of music lovers to high-end audio. The 3020 was simply the “go-to” amplifier for an entry-level high-end system. There are many more audiophiles today because of the 3020.
This unassuming little integrated amplifier brought true high-end sound to a mass-market price, and in the process, exposed a whole generation of music lovers to high-end audio. The 3020 was simply the “go-to” amplifier for an entry-level high-end system. There are many more audiophiles today because of the 3020.
Audio Research Reference 600/610T
The forerunner of the 610T, the massive Reference 600 (34 tubes per side) not only set a new standard in timbral purity and realism, it opened my eyes to the virtues of tube regulation (6550’s as the series-pass elements). Completely devoid of grain and grit, the Reference 600 was revelatory in its seductive liquidity. The Reference 600 combined this exquisite delicacy with iron-fisted dynamic authority.
The forerunner of the 610T, the massive Reference 600 (34 tubes per side) not only set a new standard in timbral purity and realism, it opened my eyes to the virtues of tube regulation (6550’s as the series-pass elements). Completely devoid of grain and grit, the Reference 600 was revelatory in its seductive liquidity. The Reference 600 combined this exquisite delicacy with iron-fisted dynamic authority.
NAD M2
Although not the first amplifier to accept digital signals and directly convert PCM audio data to the pulse-width-modulated signal that drives a switching output stage (that was the Tact Millennium), the M2 is more significant in many ways. It sounds far better than any previous switching amplifier, accepts high-resolution digital audio, is affordable, fundamentally changes audio-system architecture, and is the forerunner of what is likely to be a long line of future NAD products based on the topology.
Although not the first amplifier to accept digital signals and directly convert PCM audio data to the pulse-width-modulated signal that drives a switching output stage (that was the Tact Millennium), the M2 is more significant in many ways. It sounds far better than any previous switching amplifier, accepts high-resolution digital audio, is affordable, fundamentally changes audio-system architecture, and is the forerunner of what is likely to be a long line of future NAD products based on the topology.
BAlabo BP-1 Mk.II
The Bridge Audio Laboratories BP-1 Mk.II hasn’t stood the test of time as others on this list have, but it’s surely worthy of inclusion by virtue of its sonic merits, which are singular in my experience. The BP-1 Mk.II’s core triumph is combining high resolution of musical information with an utterly relaxed and unfatiguing sense of ease. This amplifier doesn’t force you to choose between resolution and musicality.
The Bridge Audio Laboratories BP-1 Mk.II hasn’t stood the test of time as others on this list have, but it’s surely worthy of inclusion by virtue of its sonic merits, which are singular in my experience. The BP-1 Mk.II’s core triumph is combining high resolution of musical information with an utterly relaxed and unfatiguing sense of ease. This amplifier doesn’t force you to choose between resolution and musicality.
Dick Olsher Ipa installer cydia serial key.
Futterman H3 OTL
Julius Futterman was the first to realize the dream of a commercial output-transformerless tube amplifier, albeit for a brief period. Its life span was extended for a few more years by New York Audio Labs.
Julius Futterman was the first to realize the dream of a commercial output-transformerless tube amplifier, albeit for a brief period. Its life span was extended for a few more years by New York Audio Labs.
Dynaco ST-70
A simple, yet elegant 35Wpc Ultra-Linear design which turned out to be the perfect confluence of performance and value for the dollar. Wildly popular; sales are estimated in excess of 300,00 units.
A simple, yet elegant 35Wpc Ultra-Linear design which turned out to be the perfect confluence of performance and value for the dollar. Wildly popular; sales are estimated in excess of 300,00 units.
Marantz 8B
Introduced in 1962, this Sid Smith design represented the pinnacle of Class A Ultra-Linear design, delivering a sweet 30Wpc from a pair of EL-34 power pentodes operating in fixed bias.
Introduced in 1962, this Sid Smith design represented the pinnacle of Class A Ultra-Linear design, delivering a sweet 30Wpc from a pair of EL-34 power pentodes operating in fixed bias.
Harman Kardon Citation II
Leave it to Stewart Hegeman to bring speed to tube power amplification; claimed by H-K to be the world's first ultra-wide bandwidth tube power amplifier. Still competitive today, this chocolate-colored beauty is seriously collectible.
Leave it to Stewart Hegeman to bring speed to tube power amplification; claimed by H-K to be the world's first ultra-wide bandwidth tube power amplifier. Still competitive today, this chocolate-colored beauty is seriously collectible.
McIntosh MC275
A 75Wpc stereo amplifier, designed primarily by Sidney Corderman in 1961. It comprises a perfect setting for the McIntosh Unity-Coupled output stage. Vintage tube sound at its best.
A 75Wpc stereo amplifier, designed primarily by Sidney Corderman in 1961. It comprises a perfect setting for the McIntosh Unity-Coupled output stage. Vintage tube sound at its best.
Audio Research 76A
Featuring a complex, regulated power supply, and a pentode output stage, it coaxed 75Wpc from a pair of 6550 beam power tubes. The start of modern tube sound and its emphasis on detail resolution.
Featuring a complex, regulated power supply, and a pentode output stage, it coaxed 75Wpc from a pair of 6550 beam power tubes. The start of modern tube sound and its emphasis on detail resolution.
GAS Ampzilla II
Jim Bongiorno’s masterpiece and one of the first genuinely great solid-state amplifiers possessing not only killer bass, but also huge dynamics and a major boogie factor. Said to be the world’s first servo-controlled power amplifier.
Jim Bongiorno’s masterpiece and one of the first genuinely great solid-state amplifiers possessing not only killer bass, but also huge dynamics and a major boogie factor. Said to be the world’s first servo-controlled power amplifier.
Threshold 400A
A seminal design that nudged high-end forward and almost perfectly highlighted the virtues of Class A operation. It essentially started Nelson Pass’s phenomenal power amp creative spree.
A seminal design that nudged high-end forward and almost perfectly highlighted the virtues of Class A operation. It essentially started Nelson Pass’s phenomenal power amp creative spree.
Cary Audio Design 805
This amp more than any other is responsible for the commercial success and revolution, if you will, wrought by single-ended triode designs in the early 90s.
This amp more than any other is responsible for the commercial success and revolution, if you will, wrought by single-ended triode designs in the early 90s.
EAR Yoshino 509
The major innovation is Tim de Paravicini’s balanced bridge mode output stage, in which the plate, screen grid, and cathode are assigned their own separate windings on a bifilar wound output transformer.
The major innovation is Tim de Paravicini’s balanced bridge mode output stage, in which the plate, screen grid, and cathode are assigned their own separate windings on a bifilar wound output transformer.
Paul Seydor
Dynaco ST-70
It matters not which David Hafler amplifier is chosen so long one Hafler is here. His best, IMO, was the Hafler DH‑200, but his most significant was the 70, which enabled of thousands of audiophiles to enjoy superb reproduction at budget prices in the early days of stereo and for a good while thereafter.
It matters not which David Hafler amplifier is chosen so long one Hafler is here. His best, IMO, was the Hafler DH‑200, but his most significant was the 70, which enabled of thousands of audiophiles to enjoy superb reproduction at budget prices in the early days of stereo and for a good while thereafter.
McIntosh
Tim de Paravicini has said that the only audio circuit apart from his own he wished he’d designed is McIntosh’s “Unity Coupled Circuit.” Of several obvious contenders, my choice is the MC275—introduced in 1961, designed by McIntosh co-founder Sidney Corderman—one of the first tube amps to sound truly neutral and offer high power (75 watts/channel, very high those days). Still in production today in its Mk IV version, this is an authentic classic.
Tim de Paravicini has said that the only audio circuit apart from his own he wished he’d designed is McIntosh’s “Unity Coupled Circuit.” Of several obvious contenders, my choice is the MC275—introduced in 1961, designed by McIntosh co-founder Sidney Corderman—one of the first tube amps to sound truly neutral and offer high power (75 watts/channel, very high those days). Still in production today in its Mk IV version, this is an authentic classic.
Marantz
As there must be a Marantz manufactured by Saul on this list, the Model 8 or 9 are the logical choices.
As there must be a Marantz manufactured by Saul on this list, the Model 8 or 9 are the logical choices.
Quad 303
Nice as Quad’s tube designs were, Peter Walker’s real breakthrough was the 303. Introduced in 1967, it is nearly the only early solid‑state amplifier that gave and still gives the lie to sweeping assertions about early transistor amps’ grain and harshness (thanks to Walker’s innovative use of “output triples,” which made the 303 unconditionally stable). Natural, nonfatiguing yet lifelike, it and it only is allowed to drive my 57s (and it’s also splendid on any number of other speakers, especially LS3/5as and their progeny).
Nice as Quad’s tube designs were, Peter Walker’s real breakthrough was the 303. Introduced in 1967, it is nearly the only early solid‑state amplifier that gave and still gives the lie to sweeping assertions about early transistor amps’ grain and harshness (thanks to Walker’s innovative use of “output triples,” which made the 303 unconditionally stable). Natural, nonfatiguing yet lifelike, it and it only is allowed to drive my 57s (and it’s also splendid on any number of other speakers, especially LS3/5as and their progeny).
Harman Kardon Citation 12
I will never forget the first time I laid eyes on the 12—it was the coolest and one of the most serious looking amplifiers I’d ever seen. I also remember that it was one of the rare electronic components that even “measurements tell everything” reviewers admitted sounded better than others measuring equally well. A real classic from 1972 (how I wish I had bought one!).
I will never forget the first time I laid eyes on the 12—it was the coolest and one of the most serious looking amplifiers I’d ever seen. I also remember that it was one of the rare electronic components that even “measurements tell everything” reviewers admitted sounded better than others measuring equally well. A real classic from 1972 (how I wish I had bought one!).
Audio Research
I’ve never been a hot enthusiast of this company’s products, but a William Johnson design must be represented. I leave to others choice of model (the D150, maybe?).
I’ve never been a hot enthusiast of this company’s products, but a William Johnson design must be represented. I leave to others choice of model (the D150, maybe?).
Phase Linear 400
Bob Carver’s 700 was higher powered and came first, but the 400, released in 1972, was the real beauty of the early super powered amplifiers with high output voltage swing. I used my 400 with great satisfaction for nearly five years on Dahlquist DQ‑10s.
Bob Carver’s 700 was higher powered and came first, but the 400, released in 1972, was the real beauty of the early super powered amplifiers with high output voltage swing. I used my 400 with great satisfaction for nearly five years on Dahlquist DQ‑10s.
NAD 3020
Since the criterion is “significant,” the highest‑selling integrated amplifier ever made—introducing NAD’s famous “soft‑clipping” circuit—must surely qualify. It was an ambassador to high-end audio for literally hundreds of thousands of impecunious audiophiles all over the world.
Since the criterion is “significant,” the highest‑selling integrated amplifier ever made—introducing NAD’s famous “soft‑clipping” circuit—must surely qualify. It was an ambassador to high-end audio for literally hundreds of thousands of impecunious audiophiles all over the world.
Mark Levinson
I have no experience with Levinson products, but surely a list like this must include one—the 25 watt Class A ML2 perhaps?
I have no experience with Levinson products, but surely a list like this must include one—the 25 watt Class A ML2 perhaps?
Krell
Dan d’Agostino’s pioneering work in Class A amplification must be recognized, though I’m uncertain which model—the KSA 100, perhaps? Whatever, contemporary amplifier design is inconceivable without him.
Dan d’Agostino’s pioneering work in Class A amplification must be recognized, though I’m uncertain which model—the KSA 100, perhaps? Whatever, contemporary amplifier design is inconceivable without him.
Jonathan Valin
Marantz Model 9 monoblocks
Along with its less-expensive, lower-power, stereo brother, the Model 8B, Saul Marantz’s legendary Model 9 was the best tube amp money could buy back in the 1960s. A 70W (40W in switchable triode mode) monoblock, it set the standard for liquidity and gorgeousness of timbre in its day—and to some diehards still does. Its many latterday descendants include the marvelous and still-very-much-with-us Air Tight ATM-3. Though dark and euphonious in tonal balance (the 8B was arguably more neutral), the Model 9 was and is so beautiful that many listeners forgive it its colorations.
Along with its less-expensive, lower-power, stereo brother, the Model 8B, Saul Marantz’s legendary Model 9 was the best tube amp money could buy back in the 1960s. A 70W (40W in switchable triode mode) monoblock, it set the standard for liquidity and gorgeousness of timbre in its day—and to some diehards still does. Its many latterday descendants include the marvelous and still-very-much-with-us Air Tight ATM-3. Though dark and euphonious in tonal balance (the 8B was arguably more neutral), the Model 9 was and is so beautiful that many listeners forgive it its colorations.
Dynaco ST-70
Sold as diy kits or factory-assembled, this very affordable, highly-tweakable, 35Wpc, EL34-based stereo tube amp from David Hafler is the best-selling audio component of all time with over 300,000 manufactured. The reasons for its popularity are obvious: This was (and still is) a simply lovely-sounding amp—sweet, bloomy, forgiving, and relatively neutral and transparent for its day (though it didn’t do the frequency extremes like today’s tube designs do). The ST-70 has too many descendants to list, including the early ARC amps and the late, great Luxman MB-3045. Perhaps the most prominent at the moment is the highly praised Van Alstine Ultrawave recently reviewed by Dick Olsher. (Dynaco also made several worthy solid-state amps, including the very popular 60Wpc Stereo 120 and the 200Wpc Stereo 400.)
Sold as diy kits or factory-assembled, this very affordable, highly-tweakable, 35Wpc, EL34-based stereo tube amp from David Hafler is the best-selling audio component of all time with over 300,000 manufactured. The reasons for its popularity are obvious: This was (and still is) a simply lovely-sounding amp—sweet, bloomy, forgiving, and relatively neutral and transparent for its day (though it didn’t do the frequency extremes like today’s tube designs do). The ST-70 has too many descendants to list, including the early ARC amps and the late, great Luxman MB-3045. Perhaps the most prominent at the moment is the highly praised Van Alstine Ultrawave recently reviewed by Dick Olsher. (Dynaco also made several worthy solid-state amps, including the very popular 60Wpc Stereo 120 and the 200Wpc Stereo 400.)
Phase Linear 400
Introduced in 1972, this 200Wpc stereo amplifier from the redoubtable Bob Carver was perhaps the first big solid-state amps to offer high power without the usual price tag in grainness and odd-order harmonic roughness. Detailed, neutral, and transparent, the Phase 400 may not have generated all the wattage/voltage of its elder and bigger brother, the highly regarded Phase 700, but to some of us it sounded more lifelike in timbre and texture than the bigger PL. It was certainly a great buy at $500, setting a standard for affordable excellence in the 70s and 80s.
Introduced in 1972, this 200Wpc stereo amplifier from the redoubtable Bob Carver was perhaps the first big solid-state amps to offer high power without the usual price tag in grainness and odd-order harmonic roughness. Detailed, neutral, and transparent, the Phase 400 may not have generated all the wattage/voltage of its elder and bigger brother, the highly regarded Phase 700, but to some of us it sounded more lifelike in timbre and texture than the bigger PL. It was certainly a great buy at $500, setting a standard for affordable excellence in the 70s and 80s.
Audio Research Corporation D150
Preceded by the superior D75, D76, and D76A stereo amplifiers, this 150Wpc, 6550-based behemoth was the culmination of William Zane Johnson’s “first-generation” tube designs. An acknowledged classic from its debut in 1975, the D150 set the standard for high-power tube amplification in the 1970s and long after. The very model of neutrality, low distortion, substantial power delivery, and “high definition” (in the midband, not in the lowest bass or topmost treble), it is still highly prized by aficionados and led to the development of ever higher-powered, lower-distortion, higher-resolution, fuller-range designs from ARC, such as the Reference 600 and the current Reference 610T.
Preceded by the superior D75, D76, and D76A stereo amplifiers, this 150Wpc, 6550-based behemoth was the culmination of William Zane Johnson’s “first-generation” tube designs. An acknowledged classic from its debut in 1975, the D150 set the standard for high-power tube amplification in the 1970s and long after. The very model of neutrality, low distortion, substantial power delivery, and “high definition” (in the midband, not in the lowest bass or topmost treble), it is still highly prized by aficionados and led to the development of ever higher-powered, lower-distortion, higher-resolution, fuller-range designs from ARC, such as the Reference 600 and the current Reference 610T.
Mark Levinson ML-2 monoblocks
The little-known and underrated Hadley Laboratories 622C aside, this was the first solid-state amp I heard to put the transistor on an equal footing with the tube. Introduced in 1977, these 25W Class A monoblocks (50W into 4 ohms, 100W into 2 ohms) from Mark Levinson set a new standard of clarity, liquidity, timbral beauty, and three-dimensional imaging and soundstaging for solid-state. The polar opposite of the grainy, piercing, high-in-odd-order-harmonics sound that many of us then associated with solid-state designs, the ML-2 proved that the transistor could make music as readily as it could generate power.
The little-known and underrated Hadley Laboratories 622C aside, this was the first solid-state amp I heard to put the transistor on an equal footing with the tube. Introduced in 1977, these 25W Class A monoblocks (50W into 4 ohms, 100W into 2 ohms) from Mark Levinson set a new standard of clarity, liquidity, timbral beauty, and three-dimensional imaging and soundstaging for solid-state. The polar opposite of the grainy, piercing, high-in-odd-order-harmonics sound that many of us then associated with solid-state designs, the ML-2 proved that the transistor could make music as readily as it could generate power.
Krell KSA-50 monoblock
Dan D’Agostino’s dark, delicious, 50W Class A monoblock from the early 80s brought something to the table that we hadn’t gotten in quite the same way before: bass! Along with enough current to drive impossible loads like Apogee ribbons or Sound Lab ’stats. One of the truly great, pioneering solid-state designs, the KSA-50 was perhaps the first solid-state amp that could be justly called unflappable.
Dan D’Agostino’s dark, delicious, 50W Class A monoblock from the early 80s brought something to the table that we hadn’t gotten in quite the same way before: bass! Along with enough current to drive impossible loads like Apogee ribbons or Sound Lab ’stats. One of the truly great, pioneering solid-state designs, the KSA-50 was perhaps the first solid-state amp that could be justly called unflappable.
Conrad-Johnson Premier Four
It may seem capricious to bypass earlier c-j products, including its classic 55W MV60 stereo unit (which ushered the phrase “palpable presence” into the audiophile vocabulary) and the higher-powered and more highly regarded Premier One, for this relatively little-known 100-watter introduced in 1983, but I’m a sucker for EL34-based amps and this one was, IMO, the best of all time—astonishing soundstaging and imaging and an overall realism of tone color and texture that has rarely been equaled in a pentode tube amplifier. Anyway you slice it, a conrad-johnson Premier amp belongs on this list (or, at least, my list).
It may seem capricious to bypass earlier c-j products, including its classic 55W MV60 stereo unit (which ushered the phrase “palpable presence” into the audiophile vocabulary) and the higher-powered and more highly regarded Premier One, for this relatively little-known 100-watter introduced in 1983, but I’m a sucker for EL34-based amps and this one was, IMO, the best of all time—astonishing soundstaging and imaging and an overall realism of tone color and texture that has rarely been equaled in a pentode tube amplifier. Anyway you slice it, a conrad-johnson Premier amp belongs on this list (or, at least, my list).
Lamm Industries ML-2 monoblock
Throughout the SET craze of the mid-to-late 90s, I listened to a lot of single-ended-triode amps from Japan, Great Britain, and the U.S. None was (or is) as natural as Vladimir Lamm’s 17Wpc masterpiece, the ML-2. This was the first and virtually only SET amp I heard that didn’t sacrifice bandwidth or low distortion or a neutral tonal balance to achieve that sonic “directness” that only SETs then seemed capable of. Though it has recently been replaced by the ML-2.2, which judging by its showing at this year’s CES is even better, the ML-2 was for more than a decade not just the best SET but the best low-powered amp on the market.
Throughout the SET craze of the mid-to-late 90s, I listened to a lot of single-ended-triode amps from Japan, Great Britain, and the U.S. None was (or is) as natural as Vladimir Lamm’s 17Wpc masterpiece, the ML-2. This was the first and virtually only SET amp I heard that didn’t sacrifice bandwidth or low distortion or a neutral tonal balance to achieve that sonic “directness” that only SETs then seemed capable of. Though it has recently been replaced by the ML-2.2, which judging by its showing at this year’s CES is even better, the ML-2 was for more than a decade not just the best SET but the best low-powered amp on the market.
Audio Research Corporation Reference 610T monoblocks
The culmination of William Zane Johnson’s glorious career as an amplifier designer, the 600W+ 610T is the best ultra-high-powered pentode tube amplifier JV has yet heard—a paragon of neutrality, resolution, transparency, bloom, dimensionality, and seemingly limitless power from the bass to the treble. You can argue about the virtues of solid-state bass and treble vis-à-vis tube bass and treble, but what you can’t argue about is the overall realism of this amp’s sound. Since the 610T is also, in all probability, the last WZJ tube amp we will see, it makes a worthy final statement from one of high-end audio’s true greats—and final chapter to the high-end’s Golden Age.
The culmination of William Zane Johnson’s glorious career as an amplifier designer, the 600W+ 610T is the best ultra-high-powered pentode tube amplifier JV has yet heard—a paragon of neutrality, resolution, transparency, bloom, dimensionality, and seemingly limitless power from the bass to the treble. You can argue about the virtues of solid-state bass and treble vis-à-vis tube bass and treble, but what you can’t argue about is the overall realism of this amp’s sound. Since the 610T is also, in all probability, the last WZJ tube amp we will see, it makes a worthy final statement from one of high-end audio’s true greats—and final chapter to the high-end’s Golden Age.
Technical Brain TBP-Zero monoblock
Along with the Soulution 700, this 350W Japanese monoblock from designer Naoto Kurosawa is a poster-child for the New Age in high-resolution, low-distortion solid-state amplification that, for some of us, has wiped away any lingering prejudices we’ve had toward the transistor. Reviewed in this issue, the TBP-Zeros—which forgo the use of those banes of transitor amps, the emitter resistor—are simply the highest resolution, highest transparency-to-sources audio components I’ve yet auditioned, tube or solid-state. Though not all listeners will welcome this level of neutrality—which, while never punishingly analytical, does not do poor recordings the favors that more euphoniously colored tube and solid-state amps do—to me Technical Brain sets a new standard in high-fidelity reproduction that is currently challenged only by the slightly more gemültich Soulution 700 monos.
Along with the Soulution 700, this 350W Japanese monoblock from designer Naoto Kurosawa is a poster-child for the New Age in high-resolution, low-distortion solid-state amplification that, for some of us, has wiped away any lingering prejudices we’ve had toward the transistor. Reviewed in this issue, the TBP-Zeros—which forgo the use of those banes of transitor amps, the emitter resistor—are simply the highest resolution, highest transparency-to-sources audio components I’ve yet auditioned, tube or solid-state. Though not all listeners will welcome this level of neutrality—which, while never punishingly analytical, does not do poor recordings the favors that more euphoniously colored tube and solid-state amps do—to me Technical Brain sets a new standard in high-fidelity reproduction that is currently challenged only by the slightly more gemültich Soulution 700 monos.
Harry Pearson
McIntosh 275
This is a legendary amplifier, and from a legendary company, whose commitment to quality of construction and design has never wavered, not even during its long dark night of solid-state electronics. The earliest Mc’s were built around the transformer that Frank McIntosh and Gordon Gow designed (and patented), one that allowed them to move beyond the power limitations of Class A design and into the region of much higher outputs, without the audible and ugly “notch” distortion that had thwarted such efforts in the past. Historically important. The 275 has been restored as the company in the past several years has finally moved back into tubed amplification production, and with stunning results (I think its 300/300 watt 2301 unit is the purest sounding amplifier in my experience—to date.)
This is a legendary amplifier, and from a legendary company, whose commitment to quality of construction and design has never wavered, not even during its long dark night of solid-state electronics. The earliest Mc’s were built around the transformer that Frank McIntosh and Gordon Gow designed (and patented), one that allowed them to move beyond the power limitations of Class A design and into the region of much higher outputs, without the audible and ugly “notch” distortion that had thwarted such efforts in the past. Historically important. The 275 has been restored as the company in the past several years has finally moved back into tubed amplification production, and with stunning results (I think its 300/300 watt 2301 unit is the purest sounding amplifier in my experience—to date.)
Citation Two
I have chosen just one of Stewart Hegeman’s many amplifier designs. There are many worthies. The Two was a 60-watt mono tube amplifier that came out in the days of high-fidelity (as opposed to high-end) sound. It was designed by the man whose 550 pure-pentode design was the breakthrough and the basis for today’s best tubed designs. (The 550 got around the stranglehold McIntosh and Gow had on transformer designs—they patented their breakthroughs and used them to build their own amplifiers exclusively.) What Hegeman did, after studying the transformer issue, was devise an alternate way to eliminate notch distortion and build a different transformer winding, thus allowing higher power output. (It also happens that as a very young man I tried to build one of these from its kit version, to drive my acoustic-suspension speakers. Of course, I had to have help with the project, since then, as now, I was/am a technical klutz. The amplifier was, to me, an astonishment in the form of sound.) Hegeman was a freewheeling rover, who loved music and never made an amp (or anything else) that didn’t pay tribute to the real thing. He later, under the Citation rubric, designed the first serious solid-state design, the Citation B. Pioneering? Yes. A sonic breakthrough? No. But a class act.
I have chosen just one of Stewart Hegeman’s many amplifier designs. There are many worthies. The Two was a 60-watt mono tube amplifier that came out in the days of high-fidelity (as opposed to high-end) sound. It was designed by the man whose 550 pure-pentode design was the breakthrough and the basis for today’s best tubed designs. (The 550 got around the stranglehold McIntosh and Gow had on transformer designs—they patented their breakthroughs and used them to build their own amplifiers exclusively.) What Hegeman did, after studying the transformer issue, was devise an alternate way to eliminate notch distortion and build a different transformer winding, thus allowing higher power output. (It also happens that as a very young man I tried to build one of these from its kit version, to drive my acoustic-suspension speakers. Of course, I had to have help with the project, since then, as now, I was/am a technical klutz. The amplifier was, to me, an astonishment in the form of sound.) Hegeman was a freewheeling rover, who loved music and never made an amp (or anything else) that didn’t pay tribute to the real thing. He later, under the Citation rubric, designed the first serious solid-state design, the Citation B. Pioneering? Yes. A sonic breakthrough? No. But a class act.
Marantz Model 9
You might want to add in the 8B as well, since it and the 60-watt Model 9 are still considered classics, and bring in prices in excess of what they cost during the early days of high fidelity (as opposed to the more recent days of high end), especially in Japan where they go for insanely high prices. These were designed by Sid Smith (of Sea Cliff, no less) under the watchful eye of Saul Marantz, who was always in and ahead of the vanguard of state-of-the-art sound (from his marketing of the first straight-line-tracking arm/turntable—a commercial failure—to his early sponsorship of Jon Dahlquist and the DQ-10 speaker). The amps, to this day, sound amazingly good, powerful, and more than a tad romantic—they live on, though Smith and Marantz do not.
You might want to add in the 8B as well, since it and the 60-watt Model 9 are still considered classics, and bring in prices in excess of what they cost during the early days of high fidelity (as opposed to the more recent days of high end), especially in Japan where they go for insanely high prices. These were designed by Sid Smith (of Sea Cliff, no less) under the watchful eye of Saul Marantz, who was always in and ahead of the vanguard of state-of-the-art sound (from his marketing of the first straight-line-tracking arm/turntable—a commercial failure—to his early sponsorship of Jon Dahlquist and the DQ-10 speaker). The amps, to this day, sound amazingly good, powerful, and more than a tad romantic—they live on, though Smith and Marantz do not.
Dynaco Stereo 70
If we want to talk about influence—and a long-lasting one—we’d start with this seventy-watt stereo unit, which, during its 20 year (or so) life span was studied and copied by many young designers. It was a diving board for some, like William Z. Johnson (of Audio Research) whose earliest tubed units were built around the Dynaco chassis and parts (highly modified, of course). The 70, and its descendants the Mk2 and 3 versions—came along just as stereo sound was being born. Fortuitously, its compact size, full-bodied sound (throughout most of the frequency range) put it in direct competition with the much more expensive Marantz and McIntosh units. David Hafler oversaw many amps later on, including the Stereo 120, which I thought the least transistory-sounding solid-state of its day. Then there was the 400 that came down the road later, and did at first sound transistory, thus it was subject to the golden touch of modifiers like Frank Van Alstine and became a formidable contender in the high powered solid-state amp sweepstakes. It wasn’t a Stereo 120 or a Phase Linear 700 though.
If we want to talk about influence—and a long-lasting one—we’d start with this seventy-watt stereo unit, which, during its 20 year (or so) life span was studied and copied by many young designers. It was a diving board for some, like William Z. Johnson (of Audio Research) whose earliest tubed units were built around the Dynaco chassis and parts (highly modified, of course). The 70, and its descendants the Mk2 and 3 versions—came along just as stereo sound was being born. Fortuitously, its compact size, full-bodied sound (throughout most of the frequency range) put it in direct competition with the much more expensive Marantz and McIntosh units. David Hafler oversaw many amps later on, including the Stereo 120, which I thought the least transistory-sounding solid-state of its day. Then there was the 400 that came down the road later, and did at first sound transistory, thus it was subject to the golden touch of modifiers like Frank Van Alstine and became a formidable contender in the high powered solid-state amp sweepstakes. It wasn’t a Stereo 120 or a Phase Linear 700 though.
Phase Linear 700
One of the first high-powered blockbuster amps of the modern (read: high-end) era. It was designed by Bobby Carver, one of the brightest and most innovative thinkers ever to grace audio. The 700 outpowered the Crown DC 300, the first high-powered transistor design, and was cleaner and less colored than the Crown, to boot. Carver wondered why his home-built big tubed amp of the day sounded much better than solid-state designs. He learned, through his measurements, that tube amps could swing 200 volts, while their solid-state counterparts only 35 or so. And he thought, at the time, that the high-voltage output was the decided advantage tube designs had. So he built into the 700 a very wide voltage swing. He engineered the unit’s power supply in a novel way—one too complex for me to discuss here (even if I did fully understand it). An accidental contribution to the 700’s excellent, low-distortion, and uncolored sound: Its biasing transistor sat very near to the unit’s massive heat sinks, so the longer you played it, the better the 700 sounded. Also, not incidentally in Carver’s mind, the 700 came along during the two-channel era when smaller and much, much less efficient speakers (especially the so-called “air-suspension” designs) were in vogue. These now could be driven to life-like levels, with greater control over the normally bloomy bass of such designs, The 700 also allowed reproduction of troublesome high frequencies with greater cleanness and lower distortion.
One of the first high-powered blockbuster amps of the modern (read: high-end) era. It was designed by Bobby Carver, one of the brightest and most innovative thinkers ever to grace audio. The 700 outpowered the Crown DC 300, the first high-powered transistor design, and was cleaner and less colored than the Crown, to boot. Carver wondered why his home-built big tubed amp of the day sounded much better than solid-state designs. He learned, through his measurements, that tube amps could swing 200 volts, while their solid-state counterparts only 35 or so. And he thought, at the time, that the high-voltage output was the decided advantage tube designs had. So he built into the 700 a very wide voltage swing. He engineered the unit’s power supply in a novel way—one too complex for me to discuss here (even if I did fully understand it). An accidental contribution to the 700’s excellent, low-distortion, and uncolored sound: Its biasing transistor sat very near to the unit’s massive heat sinks, so the longer you played it, the better the 700 sounded. Also, not incidentally in Carver’s mind, the 700 came along during the two-channel era when smaller and much, much less efficient speakers (especially the so-called “air-suspension” designs) were in vogue. These now could be driven to life-like levels, with greater control over the normally bloomy bass of such designs, The 700 also allowed reproduction of troublesome high frequencies with greater cleanness and lower distortion.
Audio Research D-150T
His huge stereo amplifier was, in its time, a breakthrough in tubed design, both in power output, and, in the more elusive aspects of reproducing a facsimile of a concert hall sound. Even the best solid-state designs could not then reproduce the three dimensions, the depth, of a real-world soundfield, much less its width, and reproduce these with something like the full range of dynamic contrasts. This amplifier could. Not only that, but throughout most of its range, the 150 captured the fundamentals and harmonics of the music, particularly the frequencies from the midrange on up. Thus, it had a hard-to-define (then) quality of naturalness, call it rightness, that made it unique. For experienced listeners, the 150 was such an overpowering (literally as well) experience by contrast, that its audible flaws were overlooked (highly colored bass, overly romantic midrange colorations, and a drooping top octave). Did I forget to mention the heat it generated and the number of tubes that failed? Yes, I did, but it had its teeth into the essential truth of music and it wouldn’t let go. In that regard, it was a singularity.
His huge stereo amplifier was, in its time, a breakthrough in tubed design, both in power output, and, in the more elusive aspects of reproducing a facsimile of a concert hall sound. Even the best solid-state designs could not then reproduce the three dimensions, the depth, of a real-world soundfield, much less its width, and reproduce these with something like the full range of dynamic contrasts. This amplifier could. Not only that, but throughout most of its range, the 150 captured the fundamentals and harmonics of the music, particularly the frequencies from the midrange on up. Thus, it had a hard-to-define (then) quality of naturalness, call it rightness, that made it unique. For experienced listeners, the 150 was such an overpowering (literally as well) experience by contrast, that its audible flaws were overlooked (highly colored bass, overly romantic midrange colorations, and a drooping top octave). Did I forget to mention the heat it generated and the number of tubes that failed? Yes, I did, but it had its teeth into the essential truth of music and it wouldn’t let go. In that regard, it was a singularity.
Mark Levinson ML-2
The ultimate in snob appeal for its sky-high cost (in the day), the quality of both parts and build, the momentous and cutting heat sinks, all designed to offset its Class A power output of less than 35 watts. Those watts were clean, clean, clean and analytic in a way other solid-states weren’t. At its best and in the areas in which it excelled, it gave new weight to the word “transparency.” (The ML-2 was created before Mark Levinson and its designer, Tom Colangelo, were absorbed into the innards of the Harman-Kardon octopus.)The ML-2 worked best as a mid-range amp, and its virtues show to fullest extent on an electrostatic (it was designed, it is said, for the Quads). I heard it at its best as the central speaker in Levinson’s massive HQD speaker system (H: Hartley, the woofer; Q: the midrange Quad electrostatic; and D: Decca ribbon tweeter), awesome in its day and an inspiration for the creation of the QRS-1D.
The ultimate in snob appeal for its sky-high cost (in the day), the quality of both parts and build, the momentous and cutting heat sinks, all designed to offset its Class A power output of less than 35 watts. Those watts were clean, clean, clean and analytic in a way other solid-states weren’t. At its best and in the areas in which it excelled, it gave new weight to the word “transparency.” (The ML-2 was created before Mark Levinson and its designer, Tom Colangelo, were absorbed into the innards of the Harman-Kardon octopus.)The ML-2 worked best as a mid-range amp, and its virtues show to fullest extent on an electrostatic (it was designed, it is said, for the Quads). I heard it at its best as the central speaker in Levinson’s massive HQD speaker system (H: Hartley, the woofer; Q: the midrange Quad electrostatic; and D: Decca ribbon tweeter), awesome in its day and an inspiration for the creation of the QRS-1D.
Electro Research A-75
This unit was designed by John Iverson, one of the high-end’s most memorable characters, around whom many a story, even legend hath sprung up. The solid-state A-75 was built for the military, perhaps for a radar installation. It was thus built to military specs (and overbuilt for audio listening purposes). So, it was said only a few units were left over for Iverson to sell to the general public. When they worked without breaking down, they were unlike, in sound, anything else on the market. The thing I remember best about them was their incredible purity, both at the tightly defined and taut bass frequencies on up into the, like their designer, ethereal ionospheric regions. Iverson was also legendary for developing a “force-field” speaker that, it is said, the military had its evil eye upon for some dark purposes. (Legend: It could make solid-objects disappear into a nowhere dimension.) There were other designs that did not quite materialize either, including a strain-gauge cartridge/preamp. No one, to my knowledge, ever heard one of those gizmodos. Later on, Iverson simply disappeared, after one or more runs in with the law, or, perhaps, to his alternate business base in Singapore. Many have tried to find him but no one has, so complete is the mystery. (Legend: He was assassinated. Maybe not. Maybe he simply fed himself into his force-field speaker.)
This unit was designed by John Iverson, one of the high-end’s most memorable characters, around whom many a story, even legend hath sprung up. The solid-state A-75 was built for the military, perhaps for a radar installation. It was thus built to military specs (and overbuilt for audio listening purposes). So, it was said only a few units were left over for Iverson to sell to the general public. When they worked without breaking down, they were unlike, in sound, anything else on the market. The thing I remember best about them was their incredible purity, both at the tightly defined and taut bass frequencies on up into the, like their designer, ethereal ionospheric regions. Iverson was also legendary for developing a “force-field” speaker that, it is said, the military had its evil eye upon for some dark purposes. (Legend: It could make solid-objects disappear into a nowhere dimension.) There were other designs that did not quite materialize either, including a strain-gauge cartridge/preamp. No one, to my knowledge, ever heard one of those gizmodos. Later on, Iverson simply disappeared, after one or more runs in with the law, or, perhaps, to his alternate business base in Singapore. Many have tried to find him but no one has, so complete is the mystery. (Legend: He was assassinated. Maybe not. Maybe he simply fed himself into his force-field speaker.)
Conrad-Johnson Premier One
This was the first high-powered tube amplifier designed by Lewis Johnson and it had a quality I had not encountered in a tubed unit before: authority. It spoke with a kind of dynamic truth that was undeniable. I’ve been re-reading the review I wrote, wondering whence that authority. Perhaps the quality of “authority” here that was distinctive and that so impressed me lay in the basics. That is, Johnson had got the midbass right, which, to this point, no tubed amplifier had done. The critical range of the midbass (say 40 to 80 Hertz) is where the fundamentals of music lie, and this is exactly the region in which other tubed designs sounded either bloated and bloomy, or anemic and antiseptic. The Premier One, however, got these basic frequencies right and more importantly, their resulting harmonics. And, simultaneously it also got the dynamics right—yes, the other units could play midbass notes at the loud end of the ffff spectrum, but not fully at both ends, including the softest. Dynamics contrasts, those going from microsoft (not MSNBC) to very loud, are the defining characteristic of the real thing. So when you heard the Premier One play music, you believed it. Conrad-johnson has never produced an amplifier, even its solid-state ones, that sounds less than believable. Thus its gear you can almost buy blind-folded, knowing you’ll get something true.
This was the first high-powered tube amplifier designed by Lewis Johnson and it had a quality I had not encountered in a tubed unit before: authority. It spoke with a kind of dynamic truth that was undeniable. I’ve been re-reading the review I wrote, wondering whence that authority. Perhaps the quality of “authority” here that was distinctive and that so impressed me lay in the basics. That is, Johnson had got the midbass right, which, to this point, no tubed amplifier had done. The critical range of the midbass (say 40 to 80 Hertz) is where the fundamentals of music lie, and this is exactly the region in which other tubed designs sounded either bloated and bloomy, or anemic and antiseptic. The Premier One, however, got these basic frequencies right and more importantly, their resulting harmonics. And, simultaneously it also got the dynamics right—yes, the other units could play midbass notes at the loud end of the ffff spectrum, but not fully at both ends, including the softest. Dynamics contrasts, those going from microsoft (not MSNBC) to very loud, are the defining characteristic of the real thing. So when you heard the Premier One play music, you believed it. Conrad-johnson has never produced an amplifier, even its solid-state ones, that sounds less than believable. Thus its gear you can almost buy blind-folded, knowing you’ll get something true.
Threshold 400a
The follow-up to the Threshold 800, a not-easy-to-find big amp that introduced Nelson Pass as a coming star in the field of audio. What made it an interesting product, aside from its unusually smooth sonics, was the fact that it was called a Class A (high-powered) unit. About which there was some controversy, particularly from other designers, who thought Pass had pulled a sleight of hand. The trick here lay in the biasing of the unit—one then unconventional in the extreme. The use of shifting bias allowed the unit to stay in Class A as the demands on its power output shifted. The 400 would go into Class AB if the sonic demands exceeded its capabilities (said to be a rarity). What interested me then was just how closely it sounded like Class A, but with considerable power up to a quite loud point, it had most of the advantages of Class A sound, with few flaws (the unconvincing bass, lack of sparkle in the upper midrange) as well as a tendency to oscillate and blow fuses.
The follow-up to the Threshold 800, a not-easy-to-find big amp that introduced Nelson Pass as a coming star in the field of audio. What made it an interesting product, aside from its unusually smooth sonics, was the fact that it was called a Class A (high-powered) unit. About which there was some controversy, particularly from other designers, who thought Pass had pulled a sleight of hand. The trick here lay in the biasing of the unit—one then unconventional in the extreme. The use of shifting bias allowed the unit to stay in Class A as the demands on its power output shifted. The 400 would go into Class AB if the sonic demands exceeded its capabilities (said to be a rarity). What interested me then was just how closely it sounded like Class A, but with considerable power up to a quite loud point, it had most of the advantages of Class A sound, with few flaws (the unconvincing bass, lack of sparkle in the upper midrange) as well as a tendency to oscillate and blow fuses.
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Posted on August 31, 2013 at 01:02:59 | |
Michael Samra Dealer Posts: 36109 Location: saginaw michigan Joined: January 30, 2005 | First of all this is my last weekend to horse around before I go back to my real job on Tuesday.Oh how I love getting summers off but teaching is very rewarding as long as you have cooperative students.I have been fortunate for the most part but I won't jinx myself until I see what I'm handed upon my return. Anyway,I promised myself and others that I would take measurements on the Mac Iron.On the Mc60s,the OPT transformers measure 595 ohms which we might as well call a 600 ohm primary impedance.The Mc275 is also reading that same primary impedance on the 16 ohm tap.It takes exactly 6.1vac in to get 1vac out on the 16 ohm which 6.1 divided by 1 equals 6.1 and then squaring the 6.1vac gives you 37.21vac times the 16ohm tap and that gives 595.32. The Mac circuit is very different in the sense that no voltage amplification is done in the output stage.All the voltage amplification is done in the prior stages to where there is 325vac on the grids of the KT88s.Now,some think there is a two to one voltage gain going on in the output stage and I assure you there is not.This is a unity coupled transformer and unity gain circuit and what it does is swing the voltage in the output stage from the driver,but it doesn't amplify it in any way,shape or form.I had a long talk with Doc Hoyer and he verified what I already found out from measurements.Now,the output stage does increase current with respect to idle current in the PS,and with the voltage it swings thru the low impedance output stage,that is how it develops its power,IxV=P.You can actually remove the output tubes in a Mac amp and you will hear your speakers but they won't have much bass.I just verified tonight about low impedance primary.This is one of the most remarkable circuits of all time as was the Deuce.I guess we could say that Frank McIntosh and Stu Hegeman were no idiots. We always hear of amp builders striving for lower impedance in their driver and output stages but,to have a 600 ohm impedance loading two high power tetrodes,that is remarkable. 'For every complex problem there is an answer that is clear, simple, and wrong' H. L. Mencken |
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RE: The McIntosh Unity coupled circuit., posted on August 31, 2013 at 06:10:07 | |
Posts: 1472 Joined: March 6, 2004 Contributor Since: December 24, 2004 | Wow, that is incredible. I am not an in depth tinkerer in electronic circuitry like you; however, I appreciate excellent design topologies. When I first read about the Autoformer technology from Mcintosh, I was really interested in their use of the concept. Ultimately, after about 30 years in the audio hobby, I have been able to afford a pair of MC2301 tube amps, and can't be happier. Thanks for the detailed analysis. Ciao, Audioquest4life |
The load presented to the finals isn't as low as your meas seem to indicate.., posted on August 31, 2013 at 07:39:20 | |
Posts: 9700 Location: SE MI Joined: September 6, 2001 | ..In this case there is ~ 600 ohms loading both the anode and the cathode but if you refer the cathode load to the anode as if this were a more conventional output stage, the equivalent impedance is ~2,400 ohms P-P. 2,400 ohms while seemingly low is probably on the mark for class B 6550s. |
RE: The McIntosh Unity coupled circuit., posted on August 31, 2013 at 09:26:37 | |
Posts: 654 Location: Guber Ohio Joined: December 30, 2005 Contributor Since: May 22, 2009 | Mike, Took a look at the schematic..looks curiously similar a cathode follower OP along with similar characteristics like unity gain and low OP impedance. Yet the plates are loaded. Are the inductors on the cathodes part of the OPT primary? Looks like these guys figured out how get best of both worlds. Very nice Stuben |
RE: The McIntosh Unity coupled circuit., posted on August 31, 2013 at 09:45:33 | |
Posts: 14343 Location: So. Cal. Joined: February 9, 2002 | 'Are the inductors on the cathodes part of the OPT primary?' Yes and no. They are a second, separate primary winding. Tre' Have Fun and Enjoy the Music 'Still Working the Problem' Aug 23, 2020 FabFilter Total Bundle v2020.6.11 Crack & License Key (Win/Mac) FabFilter Torrent is designed to help you achieve your sound in the quickest way possible. Via the large interactive EQ display, you can create bands where you need them and select and edit multiple bands at once. Fabfilter bundle crack torrent. Feb 22, 2018 DOWNLOAD FabFilter Total Bundle v2018.02.22 Incl Patched and Keygen WIN Mac OSX 36.3MB The Total Bundle is a set of all FabFilter plug-ins. With this bundle, you get our professional EQ, reverb, compressor, multiband dynamics, limiter, de-esser and gate/expander, creative multiband distortion, delay, filter and synthesizer plug-ins. |
RE: The McIntosh Unity coupled circuit., posted on August 31, 2013 at 11:05:40 | |
Posts: 10313 Location: Monroe Township, NJ Joined: March 31, 2000 | IIRC, the windings in 'Mac' O/P 'iron' use a bifilar technique. Eli D. |
RE: The McIntosh Unity coupled circuit., posted on August 31, 2013 at 11:23:20 | |
Posts: 9700 Location: SE MI Joined: September 6, 2001 | Most Mac unity coupled OPTs used bifilar windings in the primary (anode of final 'A' against the cathode of final 'B'). They were double insulated due to high DC potential difference betw the two 'filaments'. The MC 75/275 OPT used a trifilar primary to accommodate the voltage limitations of the bootstrapped 12AZ7 drivers. IIRC, the MC3500/MI350 used a quadfilar primary winding. |
Tre.You are right, posted on August 31, 2013 at 11:56:15 | |
Posts: 36109 Location: saginaw michigan Joined: January 30, 2005 | But it also reads the exact same 600 ohms when I apply the AC to the cathodes where its 6.1vac to get 1Vac out which I thought was unusual being the cathode winding looks like it wouldn't inductively couple to the secondary with the plate primary in front of it. 'For every complex problem there is an answer that is clear, simple, and wrong' H. L. Mencken |
RE: The load presented to the finals isn't as low as your meas seem to indicate.., posted on August 31, 2013 at 12:02:21 | |
Posts: 6984 Location: Seattle, WA Joined: April 23, 2001 | Actually it's 2400 plate to cathode, for each tube. That would be 9600 ohms plate to plate if it were in class A, but it's a class B amp basically so the per-tube impedance is where the tube is operating. |
RE: The load presented to the finals isn't as low as your meas seem to indicate.., posted on August 31, 2013 at 12:47:57 | |
Posts: 14343 Location: So. Cal. Joined: February 9, 2002 | That's what I thought. But I looked and the windings are not in series, per se. It's 2 separate windings. One center tapped for the plates with the center tap feed by the B+ and a second center tapped for the cathodes with the center tap grounded. Does that put them in parallel? Or are they in series with the tube as part of the chain? What does that do to the load seen by the tube? No answers, just questions. Tre' Have Fun and Enjoy the Music 'Still Working the Problem' |
RE: The McIntosh Unity coupled circuit., posted on August 31, 2013 at 13:30:54 | |
Posts: 36109 Location: saginaw michigan Joined: January 30, 2005 | Stu I was able to inject the AC voltage at the cathodes and get identical readings which I thought was odd. 'For every complex problem there is an answer that is clear, simple, and wrong' H. L. Mencken |
Hmmmmm.., posted on August 31, 2013 at 14:15:35 | |
Posts: 9700 Location: SE MI Joined: September 6, 2001 | .. My understanding of the Macintosh unity coupled output circuit is derived from the Radiotron Designers Handbook volume four. The Macintosh circuit is discussed (and somewhat dismissed) in some detail on pages 594 through 596. On page 595 it seems to be fairly clearly stated that the overall equivalent plate to plate impedance seen by the output tubes is four times that of either the individual plate to plate or cathode to cathode windings. I can verify that Mike's raw measurements are essentially correct for the 75/275 @ 600 ohms/overall cathode or plate winding, thus my 2,400 ohm equivalent overall plate to plate figure. Have I misinterpreted the RDH4 discussion or did they get it wrong? |
RE: The McIntosh Unity coupled circuit., posted on August 31, 2013 at 14:30:17 | |
Posts: 36109 Location: saginaw michigan Joined: January 30, 2005 | Steve you are exactly right.All three windings have the same number of turns and that's why the 600 ohm impedance no matter where it's measured.Imagine winding the quadfilar.According to Doc,the Mc60 and Mc275 are essentially the same transformer only the Mc60s have C cores and they are bifilar as you stated. 'For every complex problem there is an answer that is clear, simple, and wrong' H. L. Mencken |
Doc implies the 75/275s aren't double C-cores? (nt), posted on August 31, 2013 at 14:39:58 | |
Posts: 9700 Location: SE MI Joined: September 6, 2001 |
RE: Doc implies the 75/275s aren't double C-cores? (nt), posted on August 31, 2013 at 14:44:50 | |
Posts: 36109 Location: saginaw michigan Joined: January 30, 2005 | They aren't according to him.The 30s and the 60s are but didn't make sense to me either.The 275 is trifilar the 60s are bifilar.How did you guys come with 2400 ohm P to P.I know the tube conducts from cathode to plate so in reality,I would have measure the plate to cathode windings some how.If I measure 600 ohms plate to plate and 600 ohms cathode to cathode,wouldn't we just sum the two and get 1200 ohms? 'For every complex problem there is an answer that is clear, simple, and wrong' H. L. Mencken |
RE: The load presented to the finals isn't as low as your meas seem to indicate.., posted on August 31, 2013 at 15:03:08 | |
Posts: 36109 Location: saginaw michigan Joined: January 30, 2005 | Paul How did you measure from plate to cathode to come up with 2400 ohms? The cathode winding is inductively coupled to the secondary as is the plate but are both primary windings.How could we effectively measure,a summation of cathode and plate windings at the same time.When I measured plate to plate and cathode to cathode,it was 600 ohms total for the plate and 600 ohms total the cathode.Are you working in the FB winding also? 'For every complex problem there is an answer that is clear, simple, and wrong' H. L. Mencken |
RE: The load presented to the finals isn't as low as your meas seem to indicate.., posted on August 31, 2013 at 15:32:36 | |
Posts: 36109 Location: saginaw michigan Joined: January 30, 2005 | I understand that part but,wouldn't we add the cathode impedance to plate impedance to get the total load impedance the output tubes would see? 'For every complex problem there is an answer that is clear, simple, and wrong' H. L. Mencken |
RE: The load presented to the finals isn't as low as your meas seem to indicate.., posted on August 31, 2013 at 17:08:13 | |
Posts: 14343 Location: So. Cal. Joined: February 9, 2002 | If we look at the 600 ohm winding in the plate circuit as being in series with the 600 ohm winding in the cathode circuit, windings in series don't add that way. 1/2 of a winding is 1/4 the total impedance so 600 + 600 = 2400 Now I'm not saying that those 2 two 600 ohm windings are in series, because there is a tube in the meddle, but if they are then it's 2400 ohms. Let me put it this way. If the center tapped cathode winding was 2 separate windings and we took one of them and wired it in series with one half of the plate winding (and did the same for the other side) and then built a normal PP amplifier with the cathodes grounded, the load for each Class B tube would be 2400 ohms and the P to P impedance would be 9600 ohms. (the Class A load for each tube would be 4800 ohms) I have a pair of Freed output transformer from Krone-Hite LDS-102R amplifiers and the cathode windings are separate and are the same impedance as the separate plate windings and can be used the way I described and the impedance will be as I have described. The same goes for the 2 identical secondary windings. This transformers are great because you can wire the windings any way you want. Right now I have all the primary windings in parallel and both secondary windings in series and a 13 ohm load on the secondary reflects 325 ohms for my circlotron output stage. 4 6as7gs give about 20 watts Class A. Not BS Class A, but real Class A. Tre' Have Fun and Enjoy the Music 'Still Working the Problem' |
Can you elaborate on how you arrive at the 9,600 ohm figure?., posted on August 31, 2013 at 19:12:00 | |
Steve O Audiophile Posts: 9700 Location: SE MI Joined: September 6, 2001 | ..It seems clear to me that the equivalent P-P load for the stated conditions is ~ 2400 ohms. My logic: We know that the cathode and anode windings have a 1:1 turns ratio compared to each other and by measurement, a 6.1:1 turns ratio referenced to the 16 ohm secondary. If the two primary windings are placed in series, the turns ratio pri:sec is now 12.2:1 and the equivalent primary impedance reflected from the 16 ohm tap = (12.2)^2*16ohms = 148.8*16 = 2,380 ohms. This analysis appears to be in full agreement with that given in RDH4. Since both you and Paul come up with 9,600 ohms under the same conditions, I must be missing something really fundamental here. |
RE: Can you elaborate on how you arrive at the 9,600 ohm figure?., posted on August 31, 2013 at 19:25:17 | |
Posts: 14343 Location: So. Cal. Joined: February 9, 2002 | ' If the two primary windings are placed in series, the turns ratio pri:sec is now 12.2:1 and the equivalent primary impedance reflected from the 16 ohm tap = (12.2)^2*16ohms = 148.8*16 = 2,380 ohms.' And if those two primary winding are placed in series with the other two primary windings we get 12.2 + 12.2 or 24.4:1 24.2 squared is 595.36 * 16 = 9525.76 ohms across the whole primary. P.S. I should re-read Mike's post but I understood him to say that each half of each winding (plate and cathode) measured 600 ohms impedance. If I'm wrong and each whole winding measures 600 ohms then that would be 2400 ohms for the whole thing (the whole plate winding and the whole cathode winding) in series. Edit, I re-read Mike's posts and found this 'When I measured plate to plate and cathode to cathode,it was 600 ohms total for the plate and 600 ohms total the cathode' That means it's 2400 ohms for the whole thing and only 600 ohms for each tube. I'm not sure how that works, a 6550 in Class B loaded at 600 ohms? That doesn't sound right to me but I don't spend much time with anything but true triodes without feedback. Tre' Have Fun and Enjoy the Music 'Still Working the Problem' |
The McIntosh Unity coupled circuit. is the only creation Tim de Pavaricini says he wished he had invented~nT, posted on August 31, 2013 at 19:33:39 | |
Posts: 7074 Location: Kentucky Joined: June 30, 2005 | ~! The Mind has No Firewall~ U.S. Army War College. |
I see the point of confusion.., posted on August 31, 2013 at 20:21:43 | |
Posts: 9700 Location: SE MI Joined: September 6, 2001 | ..while the bifilar wound unity coupled scheme utilizes four separate physical primary windings, schematically Mac draws them as two center tapped primary windings: cathode to cathode and anode to anode. IOW there are two 600 ohm composite windings, each built up from two physical windings of 150 ohms each. What Mike measured @ 600 ohms was the value of two physical windings in series: From cathode to cathode Mike measured ~ 600 ohms and from anode to anode he also measured ~ 600 ohms. So .. There are either 4 x 150 ohm primary windings or 2 x 600 primary windings depending on how you choose to look at the situation. Mike measured from the 2 x 600 ohm perspective and I'm in agreement with his numbers. From this I arrive at the 2,400 ohm figure for the equivalent, single end to end primary impedance. Note that the cathode to cathode winding 'center tap' is grounded and anode to anode winding 'center tap' is fed from B+. Edit: see schematic of similar MC240. Mike measured from 'yel to yel/wht' and from 'blu to blu/wht'. |
It's ingenious at multiple levels.., posted on August 31, 2013 at 20:28:25 | |
Steve O Audiophile Posts: 9700 Location: SE MI Joined: September 6, 2001 | ..but real world implementation is complex which is off putting to many. |
Got it. Thanks for sticking with it and straightening me out. (nt), posted on August 31, 2013 at 21:14:56 | |
Posts: 14343 Location: So. Cal. Joined: February 9, 2002 | . Have Fun and Enjoy the Music 'Still Working the Problem' |
RE: It's ingenious at multiple levels.., posted on August 31, 2013 at 21:51:41 | |
Posts: 36109 Location: saginaw michigan Joined: January 30, 2005 | but real world implementation is complex which is off putting to many. It is a brilliant piece of engineering but very few know how that output circuit works in actuality.It is like nothing else out there and we have limited access to any technical data that could even vaguely explain it.We know the principle of what happens but as far as what goes on inside that transformer,it would take Frank Mcintosh,Sidney Corderman,or Stu Hegeman to explain it.Doc Hoyer explained quite a bit but I would love to see the inner workings of the unity coupled output transformer in action. 'For every complex problem there is an answer that is clear, simple, and wrong' H. L. Mencken |
RE: It's ingenious at multiple levels.., posted on September 1, 2013 at 03:56:55 | |
Posts: 70 Location: Europe Joined: January 16, 2012 | From the horse´s mouth.. |
Thanks Jaz, posted on September 1, 2013 at 16:24:08 | |
Posts: 36109 Location: saginaw michigan Joined: January 30, 2005 | I have the hard copy of this magazine and I never knew the rest of the article was in it. 'For every complex problem there is an answer that is clear, simple, and wrong' H. L. Mencken |
My mistake!, posted on September 1, 2013 at 17:45:23 | |
Posts: 6984 Location: Seattle, WA Joined: April 23, 2001 | Sorry all; I thought the 600 ohms was from one end of a winding to the centertap of that winding. I understand now, it's from one end to the far end. As for the windings in series, I simplified by assuming class B operation, so when one side is conducting the other isn't doing anything. The power supply has essentially zero impedance at audio frequencies, so B+ is the same as ground - at audio frequencies. Then the signal current loop ia B+ to half the plate winding to the plate through the tube to the cathode to half the cathode winding to ground which is B+. So the two half-windings are in series. |
RE: My mistake!, posted on September 2, 2013 at 07:22:27 | |
Posts: 14343 Location: So. Cal. Joined: February 9, 2002 | 'So the two half-windings are in series.' Yes and, the way I understand it now, those two half windings are 150 ohms each so each output tube is loaded with only 600 ohms assuming Class B operation. Tre' Have Fun and Enjoy the Music 'Still Working the Problem' |
RE: The McIntosh Unity coupled circuit., posted on September 2, 2013 at 08:00:57 | |
Posts: 10313 Location: Monroe Township, NJ Joined: March 31, 2000 | Vintage 'Mac' amps should be refurbished. They exist to play music, not occupy space on a shelf. OTOH, parting a 'Mac' out in order to obtain 'iron' for experimentation is (IMO) an act of vandalism. There is an option for the DIYer who wants to 'play' with unity coupled O/P stages, Plitron's PAT-1070-UC toroidal transformer. Warning, this is expensive 'iron'. Eli D. |
errr..No, posted on September 4, 2013 at 05:07:49 | |
Posts: 11737 Joined: May 14, 2002 | roughly speaking the voltage gain is 2:1. input signal at the grid is followed by the final's cathode, and that same current also moves the plate in the opposite direction. Very much like a split-load PI circuit..:) And of course the 600R of plate is combined with 600R int he cathode, so a 2k4 Ohm load is what the final's actually see. Can't help thinking that if Doc Hoyer actually thinks what you report him to that he should re-examine the circuit. cheers, Douglas Friend, I would not hurt thee for the world..but thou art standing where I am about to shoot. |
THERE IS NO VOLTAGE GAIN WHAT SO EVER IN THE OUTPUT STAGE., posted on September 5, 2013 at 03:16:50 | |
Posts: 36109 Location: saginaw michigan Joined: January 30, 2005 | DOUG If you don't believe this you need to talk to Doc Hoyer who knows the circuit better than anyone in the country now,including those at Mcintosh. 'For every complex problem there is an answer that is clear, simple, and wrong' H. L. Mencken |
Why not just make a few measurements and settle the matter?.., posted on September 5, 2013 at 05:00:43 | |
Posts: 9700 Location: SE MI Joined: September 6, 2001 | ..if you do, be sure to report your results here. |
Someone has already done it.., posted on September 7, 2013 at 02:10:01 | |
Posts: 70 Location: Europe Joined: January 16, 2012 | Doug's calculation is closer (in fact his 2:1 estimate was merely a shorthand I believe), the gain of each tube's gain is determined by its bias, but typically less than 1, in Jan's example shown on the link below, it turned out to be 0.85, so for the whole output stage 0.85x2=1.7. The McIntosh Unity Couple moniker is more for marketing rather than a description of its electrical property.. From the original article by McIntosh & Gow (see link above) - [i]'..almost the entire gain in this final stage is lost by virtue of the feedback resulting from this method of loading..'[/i] Note it did not say that the final stage has unity gain. Also the unity output design is patented by McIntosh and NOT taken from RDH4. |
Mcintosh Unity Coupled Transformer 2
The suggestion to have Mike make the measurements.., posted on September 7, 2013 at 07:57:44 | |
Posts: 9700 Location: SE MI Joined: September 6, 2001 | ..was primarily intended as a means of enhancing understanding of the output stage operation. i.e. 'Trust but verify'. My own personal discussions with 'Doc' Hoyer indicate he does indeed understand the operation of the unity coupled output stage quite well and this. understanding is essentially consistent with what Doug stated (my understanding also). I think Mike may have misinterpreted what he believes the Doc to have stated. For the record, RDH4 presents a relatively clear and concise if abbreviated analysis and critique of the unity coupled output circuit. The discussion fully attributes the circuit to Gow and McIntosh/McIntosh labs and in no way claims any creative involvement with its development and realization. |
RE: The suggestion to have Mike make the measurements.., posted on September 7, 2013 at 08:14:48 | |
Posts: 70 Location: Europe Joined: January 16, 2012 | Glad it is all sorted out ;-) |
It is indeed simple..:), posted on September 9, 2013 at 04:32:56 | |
Posts: 11737 Joined: May 14, 2002 | The stage has ~2:1 votlage gain, and with more detailed numbers it is indeed likely to turn out somewhere between 1.5 and 1.8:1 depending on which tube you stick in there. The lesson ought to be, examine it yourself and see what is going on instead of trusting a statement. cheers, Douglas Friend, I would not hurt thee for the world..but thou art standing where I am about to shoot. |
Mcintosh Unity Coupled Transformer 4
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