Soulution 711 Stereo Amplifier, 701 Monoblock Amplifier, and 725 Full-Function Preamplifier

Simply The Best

Equipment report
Solid-state power amplifiers,
Solid-state preamplifiers
Soulution 701,
Soulution 711,
Soulution 725
Soulution 711 Stereo Amplifier, 701 Monoblock Amplifier, and 725 Full-Function Preamplifier

Although I’d previously heard prototype 501 monoblock amplifiers and the 520 preamplifier at several shows around the country and the world, I was not fully prepared for the enormous change in sonic character that these fabulous new electronics brought to the table.

Everything that “as you like it” (or “musicality first”) listeners complained about in the original 7 Series electronics—the overly detailed presentation (that, for some, bordered on the analytical), the leaning out of tone color in the midbass and power range (that, for some, robbed the amp of natural warmth and weight), the “too-neutral-and-transparent” overall sound (that, for some, bordered on sterility)—was gone! In its place were a natural warmth and near-voluptuous beauty of timbre that I’ve seldom before heard in solid-state amplifiers, and a bass and lower midrange power, color, weight, and impact that I’d never heard before from any electronics of any kind.

What the hell happened?

If you read the sidebar interview with Soulution’s CEO, Cyrill Hammer, you will get a detailed answer to that question. But the short-form response is that the new power supplies in the 5 Series amplifiers and preamplifiers (and the consequent changes those PSUs allowed in circuit topology) made all the difference.

Unlike the original 7 Series amplifiers, the 5 Series used “switched-mode” power supplies (SMPS)—two of them, electrically isolated from each other (and from the audio circuit) by opto-couplers and transformers, “high-performance-filtered” for noise at the inputs and outputs, and high-speed voltage-regulated. Each of these switched-mode supplies was capable of delivering 600VA, and Soulution claimed that, together, they “delivered considerably more stable power than any conventional, transformer-based technology.” (Lest you be confused, the Soulution 501 was not a Class D amp. Though it used a switched-mode power supply, its gain stages ran in Class AB, heavily biased toward Class A. In addition to the switched-mode supplies, the 501 also used four linear power supplies for other functions.) 

The upside of SMPSes as I understood it (make that “as Robert Harley explained it to me”) is that they keep the power supply’s filter capacitors constantly and fully charged no matter what the signal-demands; they can also be power-factor-corrected (so that current and voltage are not slightly out of phase, as they are in conventional supplies).

As I said in my review of the 5 Series electronics, I was also aware there were switched-mode naysayers, who pointed out that, even if filtered and shielded, the strong noise (chiefly RF) of the digital switching signal could be radiated throughout the circuit. All I can tell you is that I didn’t and don’t hear this issue. (For measured confirmation, see the charts in my interview with Cyrill Hammer.) What I did and do hear is that when an amp has no droop in the supply at any level with any signal, the net effect seems to be equivalent to plugging your speakers directly into a wall socket.

When it comes to dynamic linearity the 501 was simply nonpareil. Every other amp I’d listened to, tube or solid-state, reached a point where it simply couldn’t get louder or more dynamic without also audibly changing its sonic character. Sometimes, this pivot point came relatively early on, as it did with the puny ARC Reference 210 monoblocks (less so with the stouter Reference 250s); sometimes it came relatively late, as it did with the Constellation Centaur. But came it did. And when it came, the music didn’t just get louder (if it did get louder); it also got more distorted. Typically, timbres began to lose their natural sweetness, becoming thinner, more skeletal; with the loss of tone color textural details seemed to be planed away, too, so that the resolution of instrumental body and performer articulations was greatly reduced; transients and big dynamic swings often acquired a sharp, unpleasant edge or, alternately, sounded flattened out, as if they were being compressed against an invisible loudness ceiling; the soundstage, in turn, congealed, as if it, too, were being pressed against a pane of glass. Understand that all of these effects set in well before actual clipping. Understand, as well, that the absence of this sense of strain or compression is one of the foremost differences (if not the foremost difference) between music performed live and music played back on a stereo.

Up until it could give no more and its protection circuits simply shut it down to silence, the 501 was the only amp I’d heard that didn’t do any of this. It just kept getting louder without any change in sonic character—so far beyond what you might expect from its nominal 125 watts that its actual output was difficult to gauge. And because it kept getting louder without strain or outright distortion magical things happened in the bass and power range on big dynamic moments. Tymps, bass drums, gongs, doublebasses, trombones, sarrusophones, tubas, trumpets, bassoons and contrabassoons, bass clarinets, saxophones, pianos, organs acquired the acoustical power that they have in life on big orchestral tuttis—that sense of effortless, seemingly limitless power focused by the hall and projected toward you with enough physical force to be felt like an onrushing wave. With the 501s, bass-range instruments gained sweetness, texture, solidity, and energy as they got louder, as if the amp were continuously kicking itself into higher gears—as if there were no end to the gears it could engage. (The question of how an amplifier performs when it is stressed by musical dynamics, particularly in the bass, and by volume levels is the main reason why I feel that the old saw about the seminal importance of “the first watt” is, at best, misleading. In many—if not most—real-world systems, it is the hundredth watt that counts, and as I just got done saying the hundredth watt rarely sounds anything like the first one.)

When you combined this incredibly lifelike delivery of power, top to bottom, with the 5 Series’ newfound warmth and density of tone color, you got a solid-state amp and preamp the likes of which I’d never before heard. No, I don’t suppose the 501/520 sounded quite as incredibly detailed as Soulution’s 700/720 (or Constellation’s Performance Series products), but, as I said in my review of the Odyssey Stratos monoblocks in our last issue, it is hard to know whether this was an inherent shortcoming (and if it were a shortcoming, it sure wasn’t much of one), or whether the addition of so much more power, color, and weight in the bass and midrange was simply making the upper midrange and treble (where a goodly number of transients live) sound less “exposed.” In any event, a lack of detail was the last thing you’d complain about in a 5 Series product.

True, the tonal balance of the 5 Series amps was now inherently dark, warm, and beauteous—what Michael Børresen of Raidho calls a “bottom-up” sound, far removed from the brook-clear neutrality and colorlessness of the 7 Series offerings. But having spent most of my life listening to warmish tube amplifiers, that didn’t faze me. In fact, after living with the 501 monoblocks and the 520 preamplifier (driving Raidho D-5s and D-1s) for the better part of a year, I would’ve been hard put to imagine electronics that were better, which is to say, more beautiful, more exciting, and more lifelike on everything from violin sonatas to Lou Reed in his glam period. I truly loved the Soulution 5 Series electronics and wouldn’t have traded them for anything else. Indeed, I would still feel that way were it not for the damnable arrival of Soulution’s second-generation 7 Series amp and preamp under review.

As I said at the start of this tome, saying something is “the best” is meaningless if you don’t define the term. So…let me define it now. No, it does not come down to detail or dynamics or imaging or soundstaging or timbre or texture, although all these things play key parts. And, no, it does not come down to the absolute sound, either, although, on well-recorded acoustic music the fool-you semblance of real instruments playing in a real space is essential. At this point in my long, grey career in audio reviewing, I think a thing can only be called “the best” a reviewer has heard if, and only if, he honestly believes that it is likely to fully satisfy every kind of listener on every kind of music in just about any kind of system.

Let’s face it (as I’ve tried to do in review after review), most gear appeals primarily to a certain kind of listener—be he a “fidelity-to-source” or “absolute sound” or “musicality first” one. This doesn’t make such equipment unworthy—far from it—it simply means (if one is honest and objective, rather than biased and absurdly dogmatic about our hobby) that what is perfect for a given listener with a specific taste in sound and music and a certain kind of hi-fi system isn’t necessarily going to be as perfect (or close to as perfect) for another listener with a different taste in sound and music and a different system. This, friends, is the way the world works, ignoring such variables and telling readers what they should prefer (because the reviewer himself prefers such things) is, IMO, propaganda.

Don’t get me wrong: A reviewer must have his own preferences, but he should not let them stand in the way of objectively describing and/or recommending equipment that, while it may not fully meet his own needs, will clearly meet those of someone with a different approach to sound and a different taste in music. I’m not advocating the abandonment of standards (personal or professional), and I’m certainly not saying that there aren’t appreciable differences among audio components, nor am I advocating the kind of test-based absolutism or blind (in more than one sense of the word) listening that results in absurd positions such as: “All amplifiers sound the same,” or “Outside of the way they load sources, cable and interconnects make no sonic difference,” or “The LP is a low-resolution medium.” I’m simply saying that reviewers could do worse than to become a bit more catholic in their approach to what they’re reviewing. I’m also saying that for me, calling something the “best” of its kind means that I can’t imagine a listener who wouldn’t consider the component in question ideally suited to his sonic preferences and musical taste and hi-fi system, no matter what those things happen to be.