Audio Research Reference 75 power amplifier

After I read Brian Damkroger's rave review of the Audio Research Corporation's Reference 5 SE line stage in the November 2012 Stereophile, I was excited about getting the review sample into my system so that I could do a Follow-Up (February 2013). However, the sample had already been returned to the factory, so I called ARC to see if it could be rerouted eastward to me. Chief Listener Warren Gehl answered the phone.

"Sure, you can listen to the Ref 5 SE, but I'd assumed you were calling about the Reference 75 amplifier."

"Reference 75? What's that?"

"It's our newest amplifier—a half-power version of the Reference 150."

Hmmm. Erick Lichte had reviewed the Reference 150 in July 2012 and in December, Stereophile had named it Product of the Year for 2012. The Ref 150 had replaced the Ref 110 in ARC's lineup; I'd reviewed the Ref 110 in August 2007, then bought one for my reference system. It would be interesting to compare the References 75 and 110 . . .

"Would you like to review it?"

Design
The Reference 75 ($9000) is similar to the Ref 110 and Ref 150 in that all three use input circuits using direct-coupled JFETs and a 6H30 tube. However, the Ref 75 has only four Tungsol KT120 output tubes (in ARC's ultralinear "partially cathode coupled" topology), compared with eight in the Ref 150, and eight 6550Cs in the Ref 110. Warren Gehl told me that, compared with the 6550C, the KT120—apparently the first output tube specifically designed for audio applications—is more robust and powerful, with greater dynamics, lower distortion, better tonal balance, a larger soundstage, and a greater sense of presence. The Ref 75 shares the same oversize power supply (520 joules of energy storage) as the Ref 110, but has improved interstage coupling capacitors, and more damping material on its capacitors and heatsinks.

I asked Gehl what makes the Ref 75 special.

"Its simplicity."

The circuit design is straightforward, and careful attention was paid to ensure that signal paths would be as short as possible. Removing the cover and looking inside confirmed the simplicity and elegance of the circuit layout. In fact, with only one pair of output tubes per channel, there's no need for a cooling fan. Weighing only 47 lbs, the Ref 75 is the lightest tubed stereo power amp I've had in my system.

One aspect of the Ref 75's design particularly intrigued me. Some audiophiles hold that a single pair of push-pull output tubes is capable of greater sonic purity than multiple pairs of tubes, which, when ganged, can create a subtle smearing; because tubes are never precisely identical, they can't work in perfect concert. This effect can worsen as the tubes age, each deteriorating at a different rate. The advent of the more powerful KT120 provides the opportunity for avoiding this potential problem because two KT120s can replace four 6550s or EL34s in push-pull topologies.

The Ref 75 also sports a pair of VU meters, which give the amp a bit of the vibe of ARC's classic D79 amplifier, from the 1970s. These double as adjustment meters for biasing each of the four tubes individually. Setting bias was a snap (a bias adjustment tool is provided), and the settings remained very stable throughout my listening. ARC claims that the tube biases should need to be adjusted only when the amp is moved from one house to another (the voltages fed the different houses may vary), or when output tubes are replaced. The meters are illuminated, and their lights can be turned off; I noticed no difference in sound with lights on vs off. The Ref 75 comes with a burly, detachable, power cord fitted with a 20-amp plug. It has 4 and 8 ohm output taps, as well as 12V triggers for input and output. My review sample was in ARC's standard silver finish; black is available.

Listening
It was difficult to get a handle on the Reference 75's sound—after many weeks of listening to a broad range of recordings, I'd heard no shortcomings whatsoever. I never noticed a single coloration, or any deficiencies in dynamics, transient articulation, soundstaging, or retrieval of detail and ambience. I decided it would be most revealing to use specific reference recordings to focus on those areas in which the Ref 75 exceeded the performance of every amplifier I've heard in my reference system.

I first noticed the articulate manner in which the Ref 75 delineated the dynamic envelopes of all instruments. In all tracks of Bill Evans's At Shelly's Manne-Hole, Hollywood, California (CD, JVC JVCXR-0036-2), the unique personality of his technique was perfectly captured—every low-level nuance of the pianist's phrasing shone through across the instrument's entire register. Transient articulation was crystal-clear and lightning-fast with all recordings, and those with significant percussion textures were stunning. Drummer Paul Motian's Selected Recordings (CD, :rarumECM 8016) includes several tracks featuring solos by him. Through the Ref 75, every subtle drum and cymbal texture of the late master was clearly delineated with a wide dynamic envelope; it was easy to visualize just where Motian's sticks were striking each instrument.

I listened to the 2009 remastering of the Beatles' Abbey Road (CD, Apple 3 82468-2) in its entirety, and marveled at how dynamic Ringo's drums sounded, from his crash cymbals in "Come Together" to his floor toms in "Maxwell's Silver Hammer." The ARC's transient articulation combined with its superb dynamic capabilities to make many recordings sound more dramatic than I'd ever heard them. I've described before the Ellen Test: With components capable of reproducing a broad dynamic range, I put on a recording at a normal volume level and wait for the music to hit a fortissimo passage—and for my wife to say, "Turn that down!" I expect a great component to pass the Ellen Test when I put on a big orchestral work, or even a great electronic jazz or rock recording, but I didn't expect to hear those three words during Ringo's drumming in "Octopus's Garden," as I did with the Ref 75.

COMPANY INFO
Audio Research Corporation
3900 Annapolis Lane N.
Plymouth, MN 55447-5447
(763) 577-9700
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COMMENTS
volvic's picture

I have gone to a lot of shows and heard a lot of equipment costing hundreds of thousands but the one system that still sticks in my mind was an all Audio Research back end complete with CD player and Verity Audio speakers at the Montreal Hi-Fi show several years back.  The 3-D effect, seperation of instruments, transients, etc, etc wasn't matched by any other equipment including the venerable MBL's.  Reading Mr. Reina's excellent review last month confirmed my experience but also brought me back to that day in Montreal.   

lambrostuff's picture

An "Ultra-linear" Ciruit using KT120 beam power pentodes --  AKA, a Williamson Circuit design, these amps have the screen grids fed from a primary tap on the output transformers as opposed to fixed screen grid voltage.  The biggest enemy in these AB biased amps is Crossover Distortion and heat.   

Interestly many years ago, there had been listening challenges comparing the sound of the Harmon Kardon Citation II against the highly efficient Class B Unity Coupled circuit McIntosh MC-275.  The even-order harmonic distortion of  the ultra-linear Citation II was so pleasing to the ear, it presented a more lively musical experience than the low distortion MC-275.  Most listeners may have loved what they were hearing, but a graphic test sweeping the 20 to 20 khz audio spectrum at full output power showed the Citation's Ultra-Linear circuit to be a "Train Wreck" compared to the clean, cool running Mac Unity Coupled circuit.  Judge for yourself!

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