Phonostages — Soulution Audio 755

The Soulution Audio 755 is a phono preamplifier made by the Swiss high-end electronics company. Compared with Soulution's earlier 750 and 751 phono stages, it adds a precision volume control and the wideband output stage of the 725 preamplifier, so it can drive power amplifiers directly in a vinyl-only system or feed a line preamplifier.

Key specs that matter

The 755 offers a pair of MC inputs plus a single MM input, all on unbalanced RCA, with outputs on balanced XLR and unbalanced RCA. MC input impedance is adjustable from 10 ohms to 1 kOhm, and MM impedance from 47 ohms to 47 kOhm with capacitance from 0 to 750 pF. Maximum gain for MC is 78 dB balanced or 72 dB unbalanced, and for MM it is 66 dB balanced or 60 dB unbalanced. The frequency response extends from 0 Hz to 1 MHz (-3 dB), with THD+N under 0.002% across 20 Hz to 20 kHz and a 100 dB signal-to-noise figure. Volume runs from 0 to -79 dB in 1 dB steps, output impedance is 2 ohms and balanced output voltage reaches 16 V. Power consumption is 60 W in use and below 0.5 W in standby, and a 12 V LINK connection handles remote turn-on. The chassis measures 480 x 167 x 450 mm and weighs about 30 kg.

Engineering and use context

Soulution keeps the signal path unbalanced to minimise the number of components, but the two channels are separate dual-mono circuits to prevent crosstalk. Relays switch the inputs together with their ground connections, and input buffering presents a benign load to the cartridge. Gain and loading are set independently for each input. An IEC subsonic filter below 20 Hz removes rumble from warped records, and a mono mode is also provided. During a volume change a programmable gain amplifier briefly takes over, so level steps are smooth and free of clicks, before control returns to the resistor network. The output stage is identical to the 725's and uses special power transistors linearised by an analogue computing network, with a bandwidth of 40 MHz. The audio stages and the digital control circuits have separate power supplies, and the audio supply is built like an amplifier's, with large storage capacitance.

Pairing

Thanks to its volume control and low output impedance, the 755 can drive power amplifiers such as Soulution's own directly over long balanced cables, or feed any line preamplifier at a fixed level. Its three inputs serve more than one tonearm or turntable.

Alternatives

The Soulution Audio 750 predates the 755 and offers three MC inputs, lower maximum gain and only a simple 15 dB level trim.