The Soulution preamp completes the whole virtual chart-topping Swiss audio system I have had pleasure to test at home over the last two years. It would include the 745 SACD player, the 710 power amplifier and the reviewed 720 preamplifier. Although the manufacturer does not give its products catchy names, it puts into them a lot of knowledge. The manufacturer is very much engineer-based, appealing to the best traditions of measurements, electronics and mechanical engineering. What sets it apart from other similar manufacturers is considerable capital behind it – it is a part of a large company manufacturing industrial engines, c/o Spemot AG.

As in their other products, so in the 720 preamplifier the manufacturer has implemented many of its proprietary solutions, based on earlier guidelines and design philosophy. The most important determinants are: minimum noise, negligible distortion, wide frequency response and ultra-short signal path. For example, let me mention that the 720 boasts a signal-to-noise ratio of 130 dB (yes!), THD distortion below 0.0006%, and frequency response span from DC to 1 MHz…
To achieve that, the Soulution engineers implemented minimal number of components in the circuit. Although the interior is incredibly crowded, the actual audio signal path is very simple. To keep the number of components down, the designers settled for unbalanced circuit topology (“As few components in the signal path as possible suggest an unbalanced circuit design.” The whole description can be read HERE).

It is a dual mono design with separate PCBs for the left and right channels. The inputs are switched by precise, hermetically sealed components, the best of its kind – reed relays. To minimize input cross talk, the input selector disconnects both the hot and ground paths. The signal from XLR inputs is converted to single-ended, and each input has three-step gain level adjustment – 3/6/9 dB. There are no capacitors in signal path. The input signal is continuously monitored for any DC voltage; to avoid damage to amplifier and/or speakers, a coupling capacitor is switched in and indicated on display whenever DC voltage greater than 15mV is present. As soon as the DC component decreases, the monitoring circuit automatically switches the capacitor out of the signal path after 15 seconds. The capacitor is also switched in for a while after powering on the device and while switching inputs – just for safety reasons. Volume control is by means of resistor stepped attenuator consisting of high precision metal resistors, switched by reed relays. However, since the use of resistor stepped attenuator may result in switching noise (bear in mind that there are no capacitors or DC offset compensation in signal path), the 720 is equipped with additional volume control based on PGA (Programmable Gain Amplifier), which is only active during actual volume control process. As soon as the new desired level value has been fixed, the unit simply returns to control via the precision resistors. The end result is similar to using a potentiometer or digital volume control; volume can be adjusted without clicking noises. The downside is a slight inertia of the system – the display shows new volume level some time before we can hear it the speakers. Output stage employs ultra-wideband transistors (2 MHz/-3 dB) linearized by an analogue computing network.
We reviewed the 720 model with a phono stage; also available is the 721, almost identical, with no phono stage. Unfortunately, due to time constraints the review is limited to line stage only. Let me remind you that the Soulution 710 stereo power amplifier has now been part of my reference system for almost two years.

SOUND

A selection of recordings used during auditions:

• Audio Accesory - T-TOC Records High Quality Data Master Comparison, TDVD-0002, DVD-R (2011), ripy 16/44,1, 24/96, 24/192 FLAC.
• Paganini for two, Gil Shaham, Göran Söllscher, Deutsche Grammophon/JVC, 480 246-5, XRCD24 (1993/2009).
• Stereo Sound Reference Record. Jazz&Vocal, Stereo Sound, SSRR4, SACD/CD (2010).
• Stereo Sound Reference Record. Nobu’s Popular Selection, Stereo Sound, SSRR5, SACD/CD (2010).
• André Previn, After Hours, Telarc/Lasting Impression Music, LIM UHD 051, CD (1989/2011).
• Assemblage 23, Bruise, Accession Records, A 128, Limited Edition, 2 x CD (2012).
• Beverly Kenney, Beverly Kenney sings for Johnny Smith, Roost Records/EMI Music Japan, TOCJ-9731, CD (1956/2012).
• Clan of Xymox, Subsequent Pleasures, Metropolis, Met 204, CD (1983/2001).
• Depeche Mode, Personal Jesus 2011, Sire/Reprise 21328-2, MS CD (2011).
• Dominic Miller & Neil Stancey, New Dawn, Naim, naimcd066, CD (2002).
• Dominic Miller, Fourth Wall, Q-rious Music, QRM 108-2, CD (2006).
• e.s.t. Esbjörn Svenson Trio, 301, ACT Music + Vision, ACT 9029-2, CD (2012).
• Handel, La Maga Abbandonata, Simone Kermes, Maite Baumont, Il Complesso Barocco, dyr. Alan Curtis, Deutsche Harmonia Mundi/Sony Music Entertainment, CD 88697846212, CD (2003/2011).
• McCoy Tyner, Nights of Ballads & Blues, Impulse!, IMP 12212, 20-bit Super Mapping, CD (1963/1997).
• Me Myself And I, Do Not Cover, Creative Music, 005, CD (2012).
• Pat Metheny Group, Offramp, ECM, ECM1216, CD (1982).
• Sara K., Don’t I Know You From Somewhere?, Stockfisch, SFR 357.6055.2, CD (2008).
• The Beatles, Rubber Soul, Parlophone/Apple/Toshiba-EMI, TOCP-51116, CD (1965/1998).

Japanese versions are available from

The Soulution preamp integrated very naturally with my system. A special synergy with the 710 power amp was evident, and system link simplified the operation of the whole system. That is absolute high-end and I had no doubt about it from the beginning to the end of my review. I learned a lot on the way, corrected a few seemingly well-founded claims and saw my system from a slightly different perspective. Actually, I do not know where to begin; there are so many things to say and I wouldn’t want to get sidetracked. In order to show everything in right proportions, to cast some light on it, I’ll start from where my Ayon Audio Polaris III [Custom Version] was better. Not that there is much to say; some things were linked to my particular audio system and my listening preferences, but I found some bits nonetheless.

The Swiss preamp has slightly less saturated lower midrange against my Ayon. My preamp is unique in this respect, really exceptional and no other device surpassed it so far nor even came equal. It's not even so much the tone color, because, for example, the Audio Research Reference 5 SE, a great tube preamp, sounds lower and denser than the Ayon and the Soulution; however it does not have the same energy in that range and cannot differentiate it so well. The Soulution sounds a bit less focused, a little less dense than the Ayon. And while other sonic characteristics point to the 720 as a better device, I preferred Ayon’s lower midrange presentation.
It is related to what may be called my “comfort zone”; my private, personal area where I feel safe and comfortable; a place where I belong and which I like. A place where I sit down and drift away. And that is what I get with the Polaris. Listening to the Soulution 720 preamplifier, I finally managed to grasp what it’s exactly all about; to define, first of all for my own use, my expectations from the audio system. I will soon come back to that.
My Austrian Ayon also has a bit deeper bass. The point is not that it goes lower, for the “Swiss” is unbeatable in that game; I have never heard such well-defined, so well differentiated low end and only the TAD C-600 from Japan can do something similar (no coincidence in my opinion – both companies are run by engineers). The thing is that the Soulution sounds more transparent, shows less signal coloration. It better shows what’s in the recording. Only that – in my opinion – the Ayon somehow attempts to better show “real” instruments; not necessarily exactly as they are in the recording, but rather the way they sound in reality.
That is the basic dilemma faced by audio engineers. For on the one hand, the device should be so “transparent”, i.e. the signal coloration introduced by it should be so invisible, as to best show what precedes it in the audio system – in our case the source and the recording. However, on the other hand, there is a phenomenon for which we have yet no sensible explanation: some audio components can “jump over” certain source limitations and show material causing excitement associated with real event, not its reconstruction. In an ideal world they should be on and the same, but in reality we deal with recordings that are a completely different reality than a concert.
Anyway, the Ayon, probably due to extraordinary depth of sound, its resolution and fantastic harmonics (as they decide on sound fullness) creates in my audio system / listening room some sort of “bubble” into which I sink comfortably. I like deep midrange and I like it dense, even though I know it’s an artifact, distortion, departure from full correctness (at least in terms of “live event”; its re-creation at home is another story ...). The Soulution is more honest – without any rudeness and vulgarity – which provokes slightly different reactions and a different attitude.

I promised I’d write about some things the Ayon does better and I tried my best to describe them. I will, however, easily understand the readers who find the entire previous paragraph to be one great song of praise to the Swiss preamp!
For it is the most resolved, most transparent device of this type I’ve ever heard – not only in my system, but in general. I thought I heard a lot on my system and I had a wide open window on various recordings. However, it appears that maybe yes, but not necessarily and probably not always so. It turns out that music can be presented in an even more interesting, more diverse way. And I’m not saying that such presentation is limited to reference recorded and mastered albums. The Soulution does not butcher worse recorded albums, does not bring out their defects, but just as the best audio components it passes lightly over albums’ flaws, focusing on presentation, on music itself. I had that both with Rubber Soul by the Beatles and Metheny’s Offramp, as well as Do Not Cover by Me, Myself, only to mention some examples. I could hear how well the kick drum had been recorded on the Beatles album; how skillful a musician was the fourth, least respected Beatles. The album edition I used (Toshiba-EMI from 1998) is quite old and often accused of muddled sound, lack of resolution. The 720 proved that to be misunderstanding; that there are a lot of sounds, although recorded with low level and thus difficult to extract. The same was true with the Metheny’s album, sounding fairly light and bland on most systems – it turns out that most instruments are very deep and saturated; that they are simply well portrayed. Although the synthesizer “background” was more strongly emphasized by the Ayon which showed it even denser, the foreground instruments were deeper, more differentiated with the Soulution 720.

Despite such fantastic resolution and transparency, the Swiss preamplifier sounds differently than a direct-coupled CD player and power amp; also differently than passive preamps such as Music First Audio (see HERE), or other transparent preamps. The 720'sounds more like a tube amp, at least when it comes to color and sound attack; it does not harden, highlight or isolate anything and is not hyper-correct. Neither does it take anything away from the sound, as almost always happens in the system once I disconnect a preamplifier; on the one hand it remains transparent while on the other it so “conditions” the signal that we get a better sound with it than without it.
Of course it is not absolute transparency; a comparison with the TAD C-600, even more transparent (although more “technical” at the same time and a little withdrawn), or with my Ayon shows that the Soulution actually has its own character, that it shapes the sound in a certain way, and not in other ways.

And perhaps it is through a combination of that “disappearance” and what the 720 adds to the system, an inconceivable but – as you can see – possible paradox (“I disappear yet I can be seen”), that the preamp is so unique.

If I were to somehow describe its tone color, I would say that it is nearer to the TAD C-600 or direct coupling of the source and the power amp, than to the Audio Research REF5 SE, the Luxman C-1000f, the Accuphase C-3810 or the ModWright LS 36.5. The tonal balance is very well balanced; there is no impression of extra lightness or excessive weight. As I said, I personally prefer a bit fleshier midrange and slightly closer first planes, but only my Ayon showed it better than the Soulution.
The Swiss preamplifier has another amazing property – it invites to crank up the volume every now and then in order to better hear that or other detail in music, and we can reach very high sound pressures without any weariness, without headaches or irritation. It’s such smooth sound, so natural in its “essence” that it doesn’t bother us; we don’t need to turn down the volume knob to get away from it.
What helps in it is the dynamics, which seems to be totally unrestricted, uncompressed. Everything sounds so natural that you can be cheated from time to time that now you hear a real kick drum, a double bass, etc. There is no “haze” in front of speakers that’s present with almost all other preamplifiers. Obviously, some credit has to go to my Soulution 710 power amp and Harbeth M40.1 speakers, as I am captivated by them more and more, but the 720 perfectly matched my system.
And then that air… I’ve only once heard so defined events in the 3D space, so well described instruments’ bodies – on my friend Janusz’s ultra-purist system, which consists of power monoblocks on 300B tubes from Takatsuki and a CD player integrated with an extremely purist preamp (Janusz says that there is no preamp in his system). What I mean is a sense of instruments’ detachment from other events, but not from context. They were not “cut out” from the background; instead there was natural differentiation of what is nearer us to what is further, above and below. Similarly, in the context of a particular instrument – it was a saturated and “heavy” body, shown against some background, in a particular acoustic environment. My Ayon, although excellent in this respect, showed everything with a little more “grease”, as if the edges slightly stuck to each other. In comparison with other preamplifiers my preamp is simply stunning, better differentiates the dimensions, but the Soulution 720 proved that it can be done even better.

Summary
It's easy to say that the (almost) most expensive preamp in the group is the best. No need to think, simply translate price to quality. Well, it’s not always that easy! On the other hand, it is equally true that good gear is expensive, and the best usually cost the most. To say that the same can be done at home for half the price is misleading (I’ll say more – it’s bull…) – a DIY prototype is not a commercial product, backed by years of research and heaps of money. And, in fact, DIY products are usually not as good as top notch equipment available on the market. There are exceptions to that rule, but they are very damned rare.
The Soulution 720 proves that to speak of the absolute top high-end you need to pay for it and pay a lot. I went through it two years ago searching for my next power amp and ended up with the Soulution 710, costing 140,000 PLN. And I really wanted to spend much less.
The 720 preamp is exceptionally transparent and resolving without sacrificing texture and fullness. Its tonal balance is, to me, perfect, though it might seem to sound slightly tubey. That’s due to natural edges of attack, lack of hardening. Bass is very low and splendidly differentiated in time and color, although my Ayon sounds a bit more “fat”, a little more “from the gut”, which I happen to like. The unit’s design is outstanding, with unique engineering behind it. That is definitely not a “garage” device and it does not pretend to be. It’s a hi-tech product with looks to boot, although it’s also “human”, not detached from life; one where technology serves us, not the other way around. The 720 shows that at the top end various technologies get sonically close to each other and the goal, which is a faithful rendition of what has been recorded.

Testing methodology
The Soulution 720 was compared against my reference preamp, the Ayon Audio Polaris III [Custom Version], as well as other linestages reviewed for this issue of “High Fidelity”: the ModWright LS 36.5, the Audio Research Ref5 SE, the Avantgarde Acoustic PRE, the Octave Jubilee, and direct coupling of my Ancient Audio Lektor Air V-edition CD player and my Soulution 710 power amp. The 720 drove two power amps – the above mentioned Soulution 710 and the Leben CS-1000P. It was connected to the AC mains by the Harmonix X-DC350M2R Improved-Version power cord and sat on its own feet on the Base IV [Custom Version] rack.
The testing had a character of A-B comparison with A and B known. Music samples were two minutes long. I also auditioned whole albums. Coupling was via RCA unbalanced cables – both on the source and the power amp sides. Despite the fact that the preamp has XLR balanced inputs the audio circuit has – according to description – unbalanced topology. Coupled via RCA cables it sounded better than via XLR cables.
It’s important to properly warm up the device before auditions – an hour should be enough to stabilize the temperature and the parameters of active amplification and power supply components.

DESIGN

Front and rear panel
The Soulution 720 is a linear preamplifier with a phono stage. Its modern design is characteristic for this manufacturer and is often compared with cubist works, or possibly with designs from Kelvin Klein. It is a very large and heavy device, with straight, aluminum planes and a large window on the front panel. The window is largely decorative, since a red dot matrix display and three LEDs behind it only take up some of its space.
Next to the display there are three buttons: Power (from standby), Mute, and Prog, which changes device mode – either normal (Operating-Mode), or Programing-Mode, in which we make individual settings. We can choose the active input after powering on, choose which input is the monitor loop, set the power-on volume level, display brightness, maximum volume, channel balance, input names, frequency range (e.g. if we have a SACD Player ), each input’s individual gain, as well as phono stage settings. It is a modern, highly versatile device.
On the right side we have two rotary knobs – input selector and volume control. They also work as buttons to confirm our selections. Volume can be controlled within 80 dB range in 1 dB increments.
The 720 is an unbalanced preamplifier, hence the most important are the RCA connectors, not the two XLRs. In addition to the two XLRs there are four pairs of high quality unbalanced RCA input connectors. One of them is a phono input. There is also a linestage version of the preamp, the 721, costing 15,000 PLN less, with all line inputs. The phone input connectors in the 720 are shorted by special RCA plugs to reduce input noise. Above each phone connector there is a pluggable component with a handle – a phono input load module that may be changed. And there’s the ground terminal. We also have three pairs of outputs – an RCA monitor loop and two pairs of controllable outputs – one RCA and one XLR. Next to the XLRs are ground lift switches.
And on the far left side we have the IEC mains socket with a mechanical power switch and high-quality RJ45 (Ethernet) ports from Neutrik. That’s a system link between Soulution components. We also have a multi-pin (remember a DB-25 parallel printer port?) DC-out power connector for an outboard phono stage from Soulution.

Interior
The enclosure is made of very thick, rigid aluminum plates with no connecting bolts to be seen. These are all located on the bottom plate.
That is not a preamp with some NOS components. It’s an ultra-complicated design, however based on the same philosophy as the 710 power amplifier – a hyper-short signal path and several gain stages. The rest of components are power supply, parallel and control circuits.
The circuits are spread on several PCBs, with the largest housing gain circuits. Each input sports a buffer on the Burr Brown OPA627. Then the signal is sent to a stepped attenuator on ultra-precision Dale resistors switched by reed relays, much better than relay switches. Reed relays are used e.g. by McIntosh and… Linear Audio Research from Poland. Next step is individual gain stage for each input, also on a resistor ladder, and finally we come to the output gain stage. Its input is based on the OPA627 and the AD817, the latter from Analog Devices. The output is driven by pairs of 2SA1606+2SC4159 transistors from Sanyo, mounted on a common heat sink. They are bipolar transistors called “Epitaxial Planar Silicon Transistors.”
Power supply looks absolutely brilliant. These are actually four separate power supplies, with many secondary windings. The largest power supply powers the main PCB. It sports a large toroid transformer that does not, however, serve to reduce the voltage to the usual dozen or so volts, but powers a very large switching power supply, coupled with thick copper stranded wires to the main PCB. The stranded wires are soldered to thick copper rails, running along the whole PCB and distributing power. There is also a separate power supply, with two smaller transformers, and another small switching power supply for auxiliary systems. Everything looks very impressive. Perhaps that’s what stands behind such impressive dynamics and low noise – the 720 boasts a staggering 130 dB signal to noise ratio! All power supplies are fully shielded; the toroid transformer has its own shield and the switching power supply is mounted on a thick aluminum plate.
And finally, a few words about the phono stage. It occupies a separate, small PCB. Gain stage is based on several OPA627 chips, two of which sport small heat sinks. RIAA equalization circuit is built on high-quality BC foil capacitors. In general, there are no “ordinary” components – all are very expensive Dale resistors, Wima capacitors, etc.

Remote control
Remote control is the same as for the Soulution SACD player – a small, plastic but very handy