Integrated amplifiers — Soulution Audio 331 integrated amplifier

The 331 is the integrated amplifier of Soulution Audio's Series 3, the entry line of the brand below Series 5 and Series 7. It replaces the earlier 330, keeps that model's exterior and lowers the rated output per channel after an internal rework. Soulution describes it as a dedicated preamplifier, a dedicated power amplifier, a phono stage and a D/A converter sharing one chassis. The base US price is USD 32,975, with the DAC module at USD 4,275 and the MC phono module at USD 7,225, while UK pricing starts at GBP 25,000.

Key specs that matter

Output is 100 W into 8 ohm, 200 W into 4 ohm and 400 W into 2 ohm for under five seconds, with a maximum current of 30 A. Bandwidth runs from 0 Hz to 800 kHz at -3 dB, phase shift at 20 kHz stays within 3 degrees, THD is below 0.0005 percent, the damping factor exceeds 5,000 and channel separation is above 105 dB. Line gain ranges from -53 to +26 dB. Two XLR and two RCA pairs are standard, with input impedances of 5.8 kOhm and 4.9 kOhm. The case measures 430 x 490 x 142 mm and weighs about 18 kg. Consumption is under 0.5 W in standby and 110 W at idle, on 100 to 240 V mains.

Engineering and use context

Six switch-mode supplies are fitted, four of them new, giving 1,200 VA of continuous power and up to 4,200 VA peak for more than five seconds without reservoir capacitance. The output stage borrows three-stage current amplification from Series 5, each stage kept in a narrow, almost linear operating range, and a precision circuit manages the idle current. The power amplifiers are laid out dual mono and physically separated, with RF and DC input protection and short-circuit protection at the output. Volume uses relay-switched metal foil resistors in 80 steps of 1 dB, while an IC-based path carries the signal during each change so that steps remain silent. The optional DAC takes AES/EBU, S/PDIF, USB and network inputs, converts everything to DXD and uses one PCM1792 per channel with passive reconstruction filtering. The optional phono board is a two-stage active MC circuit with passive RIAA equalisation, 60 dB gain and termination adjustable from 20 to 1,260 ohm on a single RCA input.

Pairing

The high current capability and low-impedance rating allow difficult low-impedance loudspeakers, and two pairs of loudspeaker terminals are fitted. A balanced XLR pre-out can drive a further power amplifier. Buyers who skip the modules can add the Series 3 360 DAC or the 350 phono stage as outboard units.

Alternatives

The Soulution 530 is the Series 5 integrated amplifier, rated at 125 W into 8 ohm and 250 W into 4 ohm.