Power amplifiers mono — Soulnote M-3X

The Soulnote M-3X is a monoblock from the Japanese brand's Series 3, a revised high-current version of the M-3 monoblock. Where the M-3 uses a single push-pull output stage, the M-3X adopts a parallel push-pull architecture for much greater current delivery. It is sold in silver and black finishes at about EUR 41,800 per pair, with a 2 year warranty that extends to 3 years after registration.

Key specs that matter

Output is 80 W into 8 ohm and 160 W into 4 ohm, with a maximum of 240 W into 2.7 ohm. Total harmonic distortion is 0.1% at 1 W, and the frequency characteristic extends from 2 Hz to 200 kHz within 1 dB. Input sensitivity is 2 V at an impedance of 25 kohm, and gain is 22 dB. Power consumption is 156 W in operation and 38 W with no signal. Each unit is 340 mm wide, 257 mm high and 512 mm deep and weighs 31 kg.

Engineering and use context

The voltage amplification stage uses Soulnote non-NFB differential circuits, described as the new Type-R design, and amplification is single-stage without feedback. Four Darlington construction stages drive TO3 output transistors that are matched with a newly developed pairing method. The power supply is also a high-speed non-NFB design, fed by an ultra low loss 1600 VA toroidal transformer that is not filled with epoxy resin, SiC rectifier diodes and 470 uF foil filter capacitors. Soulnote states that the transformer provides twice the current of the M-3, and the extra TO-3 transistors of the parallel stage sit on the combined power and heat sink rail. Construction is kept extremely simple, with a single function and no selectors, attenuators or microcontrollers. The amplifier section sits in an enclosure fully separate from the main body, and each part rests on three spikes, giving six spike points in total. An isolated internal support frame is suspended by four safety bolts, and a lightweight wooden base with openings lets air circulate.

Pairing

The only signal connection is a single set of XLR input terminals, so the source or preamplifier must have balanced outputs, and a stereo system needs two units. Given the input sensitivity, a source delivering at least that level is needed for full power. The rise in power toward the lowest rated load shows the design is intended to handle speakers with impedance dips far under their rated value.

Alternatives

The Soulnote M-3 is the original monoblock of Series 3, using a single push-pull output stage.