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Positive Feedback ISSUE 51
september/october 2010


abbingdon music research

PH-77 Reference Class Phono Equalizer

as reviewed by Marshall Nack


ph77 front






Kharma Exquisite-Midi.

mbl 6010D preamplifier and Soulution 710 stereo amp. ASR Basis Exclusive phono preamp.

VYGER Baltic M turntable, Shelter Harmony cartridge, mbl 1521A transport, mbl 1511F DAC.

Interconnects are Tara Labs The 0.8, Kubala-Sosna Emotion, Audio Note Japan, and Kharma Enigma. Digital cables are Tara Labs The 0.8, Kubala-Sosna Emotion and Audio Note Japan. Speaker wires are TARA Labs The 0.8, Kubala-Sosna Emotion, and Kharma Enigma. AC power cords are Tara Labs The One and Kubala-Sosna Emotion.

TAOC Rack and TITE-35S component footers, Harmonix RFA-78i and Marigo VTS Room Tuning Discs, CORE Designs amp stands, Acoustic System Resonators, Argent Room Lenses, Echo Buster and Sonex acoustic panels, TARA Labs PM/2 and IDAT power conditioners, and Ensemble Mega PowerPoint outlet strips.


Most of the time, it's the same-old, same-old right? Nothing surprising there—isn't that the definition of "most of the time?" Speaking from the perspective of someone who's achieved middle age, while sporadic excitements are welcome, I do enjoy stability and routine. Personally, I'm glad to be done with the dramatic peaks and valleys of a youthful lifestyle.

Except when it comes to audio, of course, where that statement couldn't be further from the truth. We are always on the hunt for new titillations. And as a reviewer, the Holy Grail is discovering components that bring something that hasn't been reported on in other reviews. How refreshing when it happens!

I found that stimulating novelty in the AMR PH-77 Reference Class Phono Equalizer. In this case it did not constitute a grand paradigm shift. It was more the type that pushed up against aspects of reproduction that are already part of the conversation—and then nudged them.

More Music

What struck me while doing A/B comparisons with the PH-77 and my reference ASR Basis Exclusive was the unprecedented clarity of the view into the soundstage. Hold on, let me refine that: more precisely, it was the unprecedented clarity of the reproduced musical content.

Because it wasn't simply a matter of more information: the ASR betters it in this capacity. It wasn't a matter of noise level, either: the ASR has the edge there, too.

Something else was happening beyond detail retrieval and noise level. There are things that plague analog playback, like tics and pops and scraping noises engendered by the stylus tracking the groove and out-of-phase ghost sounds coming from impossible locations. These telltale artifacts are so ubiquitous we take them for granted. I've yet to meet the analog front-end that doesn't have large amounts of a musical stuff competing with the signal; you always have to work through them. By the way, among other things, this is exactly what analog upgrades address. Whether it's a better table or arm or cartridge, all reduce these signature distractions.

ph77 front

Well, we should add phono stages to the list, for these artifacts are just what were eliminated with the PH-77. It passes less of these mechanical sounding distractions than any phono stage I've met. The upshot is the ratio of music to distractions tips way over towards more music.

How does the PH-77 accomplish this? For one thing, it cleans up some of the little things in the area outside the image. This is where most of the distractions live. For another, the AMR phono stage has a way of encapsulating images in discrete parcels.

Sound-Stage Holography

The last piece of the puzzle is the way the PH-77 floats those images in space. You get discrete parcels of dense tone hanging in air all around the soundstage. The spatial illusion is startling and tangible, as if they have 3-D coordinates. Compared to other units, the PH-77's sound-staging is High-Def.

With less distractions and images packed into discrete parcels, the silences and the space between instruments seem to be emphasized. On recordings of small ensembles, this leaves lots of vacant real estate. On dense orchestral passages, the soundstage inflates proportionately. After the quietude of the first movement of Debussy's La Mer, with Reiner and the Chicago Symphony Orchestra (LSC 2462, Shaded Dog LP), the majesty and ecstatic crescendos of the second are panoramic.

Chicago Symphony Orchestra

First note that the climax is undistorted. Then note that instruments remain in the same place as in low-level passages. And at the zenith of the crescendo, soundstage quality and dimension do not deteriorate. Quite nice, that: Of those stages that manage to avoid breakup on peaks, few maintain instruments' positions. Even fewer maintain dimension—as signal strength increases, they tend to collapse the stage inwards into the center. Finally, note that the PH-77 plays big, much bigger than similarly priced phono stages. To put it crudely, this unit has balls. While it is not as dynamically fleet as some, it brings a substantial amount of brawn to bear and it renders crescendos marvelously. You have to look to more costly units for comparable performance.

ph77 circuit board

Taking Inventory

On to the checklist. The classic tube profile is unmistakable. High treble is a bit shelved. The low-end packs admirable thrust, but it is warm and a bit loose. Midrange dominates. (This will vary depending on where you set cartridge loading.) Tone is dense and full-bodied. Timbre is acoustic and lovely, without straying into over-ripe.

The ASR Basis Exclusive

Now let's turn our attention to my reference ASR Basis Exclusive. (Please note that mine is the 2008 version, not the current 2010 release.) When I first reviewed it in my Phono Stage Hoedown back in 2007, the battery-powered ASR literally blew away the competition. Soon after, I acquired it.


The thing I enthused over most was its extremely quiet presentation. For lack of a better analogy, I compared it to a vacuuming appliance in the way it removed extraneous sounds. I said, "It features not just the lowest noise floor I've ever heard with vinyl; it also purges all distracting, non-musical sounds that have been riding along unnoticed with, and masquerading as part of, the signal—stray mechanical noises that I didn't even know were there because they've always been present."

And now we have the PH-77, which does an even better job of "vacuuming." It's funny to find myself complaining about those very same analog artifacts in reference to the ASR. Everything is relative..

Other things I noted at the time were the ASR's dark tonal balance, good body and average timbre. The PH-77 out distances it in all these. It's been noted before that the ASR is a bit dark; the PH-77 is darker, and has much more body. The ASR's tone is whitish compared to the PH-77. In terms of bloom, there's really no comparison—the PH-77 is the other side of the coin.

The biggest difference has to be each unit's sonic footprint. The ASR gives you about as unedited a view into the recording as you're likely to come across, and imposes only the slightest imprint on the signal. The PH-77's tread is heavier.


Analog fans, the PH-77 has features and functionality you won't believe. How about remote-controlled gain and cartridge loading? Most exciting is a menu of 23 RIAA equalization filters. You can adjust all these on the fly from your listening seat while the record is playing using the remote control.

ph77 display

RIAA Filters

I wish life were easy and I could forget about RIAA curves. But to really hear Franz von Suppé Overtures (London CS 6146, original Blueback LP), you need the Decca/FFSS RIAA equalization curve. How do I know this? Because I had the PH-77 set to standard RIAA, and von Suppé was not making it.

Franz von Suppé Overtures

Likewise, a wideband, early Decca LP of the Beethoven Piano Concerto No. 3, with Wilhelm Backhaus (Decca SXL 2190) also benefited from the specialized equalization. By the way, this is an eye-opening performance. It caused me to riffle through my collection to place it in perspective. There are many good versions. Right now, this is the one I'd take to the desert island.

Beethoven Piano Concerto No. 3

Likewise, something like Slaughter On Tenth Avenue, a Shaded Dog from RCAs Golden Era (LSC 2294) wanted the Enhanced RIAA curve.

Slaughter On Tenth Avenue

One of the equalizations was developed for late LPs manufactured with the DMM process. Even though standard RIAA is indicated on the jacket covers these LPs tend to sound thin and bright. AMR speculates this is a byproduct of the DMM process and designed the DMM curve to compensate.

One complaint: Among all those equalizations they seem to have overlooked the needs of jazz aficionados—where's the Blue Note RIAA?

Features and Setup

The PH-77 comes in a big, impressive shipping box, the same as many other AMR Reference Class products. And it also sports a big, impressive chassis, the same as many other AMR Reference Class products. It is certainly the largest and heaviest phono stage I've encountered.

ph77 top front

Gain is adjustable from 30 to 72dB. There are 64 steps of resistive and capacitive loading. If you have multiple turntables, there is provision for three switchable inputs. Alternately, use the Direct Input for a single table. The Direct Input has the best sound.

ph77 rear

I normally load my Shelter Harmony MC cartridge at 100 ohms, but that sounded too tubey, so I used 250. The ASR gain is set to 56dB; that setting wasn't sufficient on the PH-77. I boosted it to 66dB.

It needs about an hour to warm up and then gets slightly warm. At the end of the night, after maybe four hours, it's generating a fair amount of heat. Give it breathing space above.

ph77 top

When shutting down, put it in Stand By. This turns off power to the tubes, but leaves the solid-state circuits active.

I almost forgot to mention, there's an on-board 24 bit/96kHz Analog-to-Digital Converter, in case temporary insanity sets in and you feel the urge to digitize your LPs.

To Power Condition or Not

Here's a tip: don't use your power conditioner with the PH-77—go straight into the wall. For one, the unit's power supply draws considerable wattage, almost as much as an amplifier, and is likely to challenge the capacity of most active conditioners. For another, the unit has Opti-Mains.

All Reference Class AMR components feature Opti-Mains, a built-in, full-strength conditioner. Here's the web description: "Instead of traditional (power supply) regulators, the PH-77 employs a far more elaborate set of 4 virtual battery supplies, which are characterized by zero negative feedback and lowest possible noise. These are followed by a further 28 stages of passive power supply filtering, 8 of them utilizing very costly large value film capacitors…"

ph77 circuit board power supply

The PH-77 sounds better right from the wall. Yes, control loosens up, but dirt and grunge didn't become an issue. When used with my TARA Labs IDAT conditioner, focus and transients were sharper, but the sound had a slick surface and was too clean.

Engineering Aspects

The PH-77 is a pure single-ended, direct-coupled, Class A, zero negative feedback design. It incorporates six tubes arrayed symmetrically, three to a side. The tubes are all NOS Mullard ECC81/12AT7, Philips 5687WB, and EZ80. Everything is dual mono, even the grounding.

ph77 circuit board tube

Special attention was given to achieving exceptionally low noise levels. I can vouch for their success here—the PH-77s noise level rivals that from solid-state phono stages.

It is nearly as quiet as my battery-powered ASR Basis Exclusive.

How did they achieve this? Parts quality is one obvious factor. I'm not a techie, but I recognize all the currently respected brands and parts in the unit's inventory, like film and tin foil coupling capacitors. Elsewhere, you'll find silver leaf capacitors in the RIAA EQ section.

The same care is evidenced in the circuit board layout. Shortest signal paths are used. Capacitors are selected with much higher values than is required. The explanation for the latter is interesting: "In order to ensure that any remaining dielectric effects in the capacitors are minimized, all capacitors carry bias voltages many times that of the signal voltage applied. This unusual approach operates the capacitors in a mode that is similar to single-ended Class A operation for amplifiers…" It is implied that the under-utilized caps sound better because they are un-stressed.

ph77 circuit board

ph77 circuit board

Another precaution: three layers of magnetic shielding stand between the transformers magnetic fields and the input signal. And, of course, there's the Opti-Mains conditioning, definitely a big factor in reducing noise.

Beyond all this, the real story behind the uniqueness of the PH-77 is the résumé of AMRs resident designer, Mr. Thorsten Loesch. None of the commonly used audio circuits met his ambitious goals, so he went exploring far a field in areas he knew from his involvement in scientific research. He found what he was looking for in an adaptation of something called "Advanced GAmma Tracking Array" (AGATA), a preamplifier design used in nuclear and quantum physics research labs.


If music is your pleasure, you will find the new tube hybrid AMR PH-77 Reference Class Phono Equalizer an excellent communicator. Its strongest suit is clarity. Not the clarity of a component designed as a pass-through, with neutrality and resolution as the prime objectives. The PH-77 has exceeding clarity of musical content. It tips the ratio of music to artifacts and distractions towards the former. With the PH-77, you get more music.

Secondary strengths are its beautiful tone in the classic valve model, very satisfying weight and ability to scale. Crescendos are rendered with admirable heft and no change in quality. Symphonic fortes were outstanding.

The PH-77 is loaded with cutting edge features and functionality that are on everybody's wish list. How about remote controlled gain and cartridge loading? Best of all is a menu of 23 RIAA equalization filters that you can adjust on the fly from your listening seat while the record is playing.

The PH-77 was a joy to listen to. Indeed, it melted away my concerns as it brought my analog front-end up to speed with the rest of my system. I was strongly tempted to hang on to it. Marshall Nack

AMR PH-77 Phono Equalizer
Retail: $11,995

Abbingdon Music Research
web address:

Distributor Information
Avatar Acoustics
Fayetteville, Georgia 30215
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