Power amplifiers mono — Riviera Labs AFM70

The Riviera Audio Laboratories AFM70 is a mono power amplifier built as a pure Class A hybrid, combining a triode valve with bipolar-junction transistors and MOSFETs. Italian designer Luca Chiomenti and CEO Silvio Delfino developed it according to the company's three founding principles - no global feedback, hybrid circuitry and pure Class A operation - drawing on the work of Jean Hiraga. Riviera tunes its amplifiers by ear rather than purely for measured performance.

Key specs that matter

Rated output is 70W into 8 ohms in pure Class A, rising to 140W into 4 ohms. Gain is 22dB and input impedance is 47k ohms, which suits most preamplifiers. Inputs comprise one RCA line input and one transformer-balanced XLR input. The chassis measures 34 x 48.5 x 19.5cm and weighs 30kg. It comes in Gold or Dark Titanium finish, with 24kt mirror-gold or matte aluminium knobs respectively.

Engineering and use context

All voltage amplification is handled by a single-ended ECC82/12AU7 triode, while the output stage uses twelve semiconductor devices, each able to dissipate 150W. The split lets the valve stage handle the signal while the transistors supply current and stability. The power supply uses an oversized transformer rated above 400VA, followed by a pi-filter and distributed capacitance totalling more than 100,000 microfarads. No current-limiting circuitry is fitted, by design, so the amplifier stays stable into complex loudspeaker loads. The heavy construction is intended to limit vibration and electromagnetic pollution.

Pairing

With its high current capability the AFM70 can drive demanding loudspeakers, and as a monoblock it fits both a conventional stereo pair and multi-amplified systems with separate amplification for different drivers.

Alternatives

Riviera's AFM100 Special Edition monoblock offers more output for systems that need extra headroom.