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Soulution Audio 325 preamplifier and 311 stereo power amplifier

Soulution Audio 325 preamplifier and 311 stereo power amplifier

Much as there is lots to like about the products from the Swiss electronics firm Soulution Audio, there is a commonly held concern about the company’s bigger models: they are ‘bigger’! The top 701 mono power amplifier is more than half a metre wide and deep and weighs in at a fruity 75kg per channel. A complete 7-Series system also costs as much as a very well-specified 7-Series of the four-wheeled variety, and while Soulution’s 5-Series is smaller, lighter, and cheaper than its flagship siblings, there are still hernia-inducing cases in the range. However…

Meet the 3-Series, the three-strong range of integrated amplifier, preamplifier, and stereo power amplifier. They distil much of what makes Soulution Audio such a force to be reckoned with in top-end audio, but in boxes you can lift and that stay just inside the zone of ‘attainable’ pricing. Launched in 2017, the trio of 330 integrated amplifier, 325 preamplifier, and 311 stereo power amplifier are Soulution’s ‘entry level’ pre-power system, although any pre/power package that works out at more than £20k before you add optional DACs and/or phono stages pushes the boundaries of the term ‘entry level’. On the other hand, the price of the 325/311 is roughly the same as a 20% down-payment on Soulution’s top 725 preamp with 701 mono power amps. And, if we are doing this, the 325 preamp is roughly half the weight of the 725, while the 311 power amp is almost one-fifth the weight of a pair of those big 701 powerhouses. 

These figures are not just there for brute comparison purposes. The simple way for a company like Soulution Audio to make more attainably priced amplifiers would be to make hobbled versions of those that skirt the stratosphere. Sometimes this strategy pays off, and you just get a scaled down version of the flagships. Other times, you lose much of the identity of that flagship in the scaling-down process. By way of contrast, Soulution has taken the more laudable route of looking at the 300 series in and of itself; making a product that coheres to the company’s fundamental ethos, but that does so in its own right. These are new designs, calling down technologies and concepts developed in the 500 and 700 series, but making them wholly and uniquely from the 300 series.

Starting with the 325 preamplifier, the circuit is a single-ended (although there are balanced XLR inputs and outputs) stereo chassis, as opposed to the dual mono, balanced designs of the more up-scale preamps. Also, where the power supply for the big 725 preamp is essentially an amplifier in its own right, the 325 uses a switch-mode power supply, albeit one with audiophile DC‑DC converters and a linear regulator. This is physically separated and shielded from the analogue audio circuit boards. 

Soulution does not throw the baby out with the bathwater, however. The 325 retains the high-precision, low-noise metal foil resistors used to set volume and balance found on the 725. Also like its bigger brother, the 325 uses a second volume control with a PGA (Programmable Gain Amplifier) to block switching peaks during volume changes. Active only during the volume control process, it is similar to a potentiometer and enables the volume to be adjusted in smooth, click-free steps. As soon as the new desired level value has been selected, the unit returns control to the precision resistors.

Although we tested the 325 in pure line-preamp mode, it can be supplied with optional MC phono stage and/or a network and USB-equipped DAC.


The 140W per channel 311 stereo power amp does follow many of the ideas developed for the 511 stereo amplifier, but not in a slavish or discounted way. It uses a three-stage current amplification system, with each stage operating in a narrow, almost linear, range. In essence, however, this is a high-Class A design with more than 160,000µF of storage capacitance and careful idle-current management (so a Class AB design can deliver mostly Class A power to the loudspeakers, without creating an amplifier that could pass muster as a heater in the process). This management acts independently to music signal and requires no warm-up time, so the amp sounds good from power-up. That being said, leaving both preamp and power amp constantly powered up is sonically beneficial, and as they don’t draw enormous amounts of power, no polar bears were drowned in the making of this sentence. Additionally, control circuits that protect against RF or DC signals are present at the input, and there is additional short-circuit protection.

The 311 also sports a total of six power supplies, with four switched-mode power supplies delivering 1,200 VA to the signal path circuitry. These power supplies feature high performance filtering at the input and output, and use Soulution’s own high-speed voltage regulators, which are claimed to deliver more stable power than traditional, transformer-based technology.

We used the Soulution Audio 311/325 combination in a suitably price and performance-matched system, with a dCS Rossini CD and Clock upstream, and a pair of Wilson Audio Sabrinas downstream. Cables in this context were from Transparent Audio (for the signal path) and Shunyata Research (for the power, with a Denali 6000/T power conditioner feeding the whole system extremely well. Music was a combination of 16-bit CD, streamed music from Tidal’s online service, and a selection of music ripped and downloaded to hard disc via the network. Both standard and high-resolution files were played.

It’s quickly clear that the word ‘clear’ features prominently in any summation of the Soulution 325/311. They are resolutely neutral, honest, balanced, level-headed, accurate, clear, correct, and all those other adjectives that describe an amplifier system that neither disrupts nor tweaks the sound of a system. While those who set their watch to 1970s time might contend ‘isn’t that what amps are supposed to do?’, the rest of us armed with a working pair of ears will admit that many are called, but few are chosen to the true path of neutrality… and Soulution is one of the chosen. 

Far from sounding boring and listless, however, true neutrality is an energising, exciting listening experience, and one that is instantly recognisable as such. Sounds rise from a completely silent background and have no artifice about them. Depending on where your priorities lay, this will manifest in one of several ways at first, with the other aspects joining the fray soon after. For me, it was high-frequency definition. It didn’t take much… a few bars of ‘Love In Vain’ from the Rolling Stones StrippedCD [Virgin] was all it took. The treble was almost muted by comparison to most amplifiers, and yet there was more going on; the chime of Keef’s acoustic playing, the resonance of Jagger’s voice, the dimensionality of the studio, all presented perfectly. 

In short order after that, I became aware of some world-class stereo imaging, pushing excellent depth and even some height out of those Wilsons. This was followed by an almost electronics-free coherence and dynamic range, a sense of effortless – rather than forced − rhythm, and the kind of dynamic shading that makes people who talk ‘microdynamics’ grow a broad smile. Musical examples followed in the style of the Glimmer Twins, revealing musical expression and finesse that is typically locked away behind the amplifier electronics and unveiled here. While there will always be those who like their music filtered, tuned, or emphasised in some way, the 325/311 sing true.  


The limits to this system are fairly small. Granted the 311 is not the 600W powerhouse of the 701, but I’d trade that power for being able to lift an amplifier and still have a working spinal column afterward. I’m not entirely convinced by the red LED readouts on the amps – they look a bit 1980s retro – and the wibbly-wobbly remote that is favoured by Soulution (and Nagra… perhaps it’s a Swiss thing) does nothing for me.

The first minutes with the Soulution 311/325 are key. It’s the lean in or lean back moment; if you lean in and are captivated by that sound, nothing else will do. If you lean back and think ‘no soul in the Soulution’, then everything the brand does will leave you wanting more. Personally, I think eight out of ten people will lean in. That famous Harry Lime speech from ‘The Third Man’ is wrong. There’s more to Swiss neutrality than the cuckoo clock, after all. There’s the Soulution Audio 311 and 325.


325 preamplifier

Type: solid-state line preamplifier with optional MC phono and DAC boards

Inputs: 2 ×balanced (XLR) pair, 
2 ×unbalanced (RCA) pair, optional 1 ×Phono MC (RCA) pair

Digital inputs: 1 ×AES/EBU, 1 ×SPDIF, 
1 × USB, 1 ×Network

Outputs: 1 ×balanced (XLR) pair, 
1 ×unbalanced (RCA) pair

Gain: -79dB to +10dB

Frequency response: 0–800kHz (-3dB)

THD+N: < 0.0001%

Signal-to-noise ratio: >120dB

Channel separation: >120dB

Peak output current: > 0.2A

Dimensions (W×H×D): 430 ×350 ×142 mm

Weight: 15kg

Price: from £8,000 (line only)

311 power amplifier

Type: Solid-state stereo power amplifier

Analogue inputs: 1×balanced (XLR) pair, 3.5mm jack (×2) remote LINK power

Outputs: 2 pair loudspeaker binding posts

Power output: 120 W @ 8 Ω, 240 W @ 4 Ω, 480 W @ 2 Ω (dynamic)

Gain: +26dB

Frequency response: 0–800kHz (-3dB)

THD+N: < 0.001%

Signal-to-noise ratio: >120dB

Channel separation: >110dB

Damping factor: >2,000

Dimensions (W×H×D): 430 x 490 ×142 mm

Weight: 30kg

Price: £12,500

Manufactured by: Soulution Audio


Distributed by: Select Audio


Tel: +44(0) 1900 601954


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