Soulution 755 Phono Preamplifier

Crème de la Crème

Equipment report
Soulution 755
Soulution 755 Phono Preamplifier

I’m not going to reprint the charts (from John Eargle’s great book Music, Sound, and Technology) that I used in my review of the VAC Statement gear in Issue 263, but the point I made there remains the same: In life and on disc, instruments do not image in a single flat plane; they have volume, body, directionality, and dimensionality that changes with changes in register, timbre, and dynamic. The addition of this third dimension, combined with its near-solid-state like speed and resolution, and richer and more saturated tonal palette, brings the VAC Statement Phono even closer to the absolute sound without any sacrifice in fidelity to sources (indeed, in my view, with an increase in fidelity to sources).

Yet again, the VAC is not perfect. It falls a bit short in the power range and the low bass, where (because of inherent limitations in current delivery) it simply can’t supply all the transient speed and dynamic impact of something like the Constellation Perseus, or the dense color and astonishing grip of the Soulution 755.

Speaking of which.

Like the Constellation Perseus (which was designed by John Curl and Peter Madnick) and the Swiss-made Audio Consulting Silver Rock, the Soulution 755 is a solid-state phono preamp. And there, folks, the similarities—technical and sonic—end.

Like all Soulution electronics (see my interview with Soulution’s Managing Director Cyrill Hammer, who also happens to have designed the 755), the 755 uses very high speed, very high bandwidth (into the megahertz range) circuitry. (Speed and bandwidth are the same thing in this context.) Soulution doesn’t do this because it expects its components to be called on to reproduce a 2MHz tone; it does it because it wants to make negative feedback work as it should.

As you all know, negative feedback has a bad rep. Some amps (tube and solid-state) dispense with it entirely (at a substantial cost in THD). Cyrill Hammer and the other engineers of Soulution have taken a different approach. It is their view that NFB has gotten a bad rep because it has been improperly applied. To make feedback, which compares the output signal to the input signal in order to correct errors, work properly, it must occur instantaneously. Otherwise, the input signal will have changed with the passage of time, and you will be comparing an apple at the output stage to an orange at the input. Very high bandwidth (which, as noted, translates to very high speed) allows Soulution to compare apples to apples. All Soulution components reduce propagation delay (the time it takes to make corrections) from the typical-for-solid-state 1–5 microseconds to 1–2 nanoseconds (one thousand times faster). The result is standard-settingly low distortion levels in preamps and amps that, unlike some, don’t give up the ghost and go into runaway distortion precisely when you hit their rated power limits.

Thanks to Soulution’s circuitry, the 755 is, in fact, a marvel of low distortion, with a noise floor of -140dB (quite phenomenal in a phonostage). Of course, the 755 isn’t just a phonostage. Unlike every other preamp considered in this review, the 755 is a stand-alone phono-preamp. Like those dedicated preamps with built-in DACs that are so popular today (one of which, the 760, Soulution also makes), the 755 is a phonostage and a linestage. Its large chassis houses a highly linear phono equalizer circuit (with a gain of 78dB) and the exact same output circuitry, highly sophisticated PGA (programmable gain amplifier) volume control, and power supply (with more than 500,000 microFarads of capacitance!) found in Soulution’s 725 linestage preamplifier.

The long and the short of this is simple: If you listen to LPs exclusively, the 755, which is able to accommodate up to three phono sources at the same time (two moving coil and one moving magnet), allows you to play back your vinyl with complete control of level and balance. At $72,000, the unit is quite expensive, yes. But you can go directly from it to your power amp (or, since it has two analog outputs, to your power amp and your subwoofer) without degrading the signal by connecting to a separate linestage through a pricey pair of interconnects. (I can tell you from experience that going directly to amplifiers from the 755 is a big sonic step up compared to going from phonostage to linestage to amplifiers, though the 755 can also be used as a traditional phonostage in a system that includes digital sources.)

As for the way it sounds, well, if you take the extraordinary midband resolution of the Audio Consulting Silver Rock, the top-to-bottom transient speed, detail, and soundstaging prowess of the Constellation Perseus, and the bloom, color, and dimensionality of the VAC Statement Phono, then add the most solid power range and powerful low bass you’ve heard from a phonostage preamplifier, you’ve got something like the 755.