Power amplifiers mono — Perreaux 750

The 750 is the monoblock power amplifier of the Prisma series from Perreaux, a company based in New Zealand that has been building audio products since 1974. One unit is needed per speaker, meaning stereo playback takes two, and UK pricing for such a pair is GBP 15,390. The design combines a true balanced circuit, power MOSFET output devices and a custom toroidal supply in a convection-cooled case with exposed heat sinks.

Key specs that matter

Continuous output is 750 W RMS into 8 ohm across 20 Hz to 20 kHz at under 0.04% THD, and 1,300 W RMS into 4 ohm at under 0.07%. Typical THD+N at 1 kHz is 0.008%. Response runs from 20 Hz to 25 kHz within 0.25 dB. Voltage gain is 34.3 dB, voltage swing is 322 V peak to peak, and maximum current output is 160 A. The damping factor is above 700 at 1 kHz into 8 ohm, and the unweighted signal-to-noise ratio at rated output is 100 dB. Full output needs 1.5 V on the RCA input or 0.77 V per leg on the XLR input, which present 22 kohm and 3.3 kohm. The unit is 430 mm wide, 186 mm high and 497 mm deep and weighs 31 kg.

Engineering and use context

Bipolar transistors in the driver stage run in Class A, while the output stage uses sixteen high-current Toshiba MOSFETs that stay in the equivalent of Class A up to about 10 W before moving into Class AB. Perreaux points out that MOSFETs have a negative temperature coefficient, which protects them from thermal runaway. The massive toroidal transformer is wound with heavy gauge wire and carries an electrostatic shield against mains-borne interference, and filter capacitors totalling 60,000 uF feed the output stages. A soft-start circuit limits inrush current so the charging capacitors do not trip household breakers, and opto-coupled protection circuits guard the amplifier. A rear toggle selects the balanced or unbalanced input, an earth lift switch separates signal ground from mains earth, and 3.5 mm trigger jacks accept 5 to 12 V to wake the unit and pass 12 V on to other gear. Idle draw is 65 W, rising to 1,400 W at full output into the lower impedance. The heat sinks can get very hot, so the maker asks for 80 to 100 mm of free air on every side, no carpet underneath and no stacking.

Pairing

Any preamplifier with a balanced output suits the XLR input, and its lower sensitivity leaves ample volume range. Two pairs of binding posts per chassis allow bi-wiring, and Perreaux notes that the amplifier rating should equal or exceed the power rating of the loudspeaker, which makes the 750 a candidate for large, low-impedance speakers that need high current.

Alternatives

Perreaux makes no other mono power amplifier besides the 750, so the brand offers no same-category alternative.