Soulution Audio 325 preamplifier and 311 stereo power amplifier

Solid-state power amplifiers,
Solid-state preamplifiers
Soulution 311,
Soulution 325
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.

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