Contributors include: Peter Breuninger, Neil Gader, Robert E. Greene, Robert Harley, Dick Olsher, Harry Pearson, Paul Seydor, and Jonathan Valin.
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.
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.
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).
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.
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).
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!
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).
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 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.
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.”
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.
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.
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.
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.
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.
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.
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.
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.
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.
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’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.
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.
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!
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.
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 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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
As there must be a Marantz manufactured by Saul on this list, the Model 8 or 9 are the logical choices.
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’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.
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.
I have no experience with Levinson products, but surely a list like this must include one—the 25 watt Class A ML2 perhaps?
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.
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.
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.
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.
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.
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.
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).
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.
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.
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.
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.)
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.
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.
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.
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.
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.
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.)
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.
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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