Power amplifiers stereo — Nagra AMP II-S

Nagra of Switzerland builds the AMP II-S as a transistor stereo power amplifier, one of the first models of its Series II range, presented to the public in October 2026. It shares the Series II styling with the PREAMP II-S valve preamplifier, for which it was conceived as the matching power stage. The recommended retail price in the UK is GBP 21,998 including VAT.

Key specs that matter

Output is 120 W RMS per channel into 8 ohm, with the opening 10 W handled in Class A and the remainder in Class AB. Nagra gives total harmonic distortion plus noise below 0.05% at full rated power. Frequency response runs from under 10 Hz to 75 kHz within +0/-3 dB, channel separation is better than 90 dB, and Nagra quotes a typical 110 dB A-weighted signal-to-noise figure. Input impedance exceeds 100 kohm, while the output impedance is 60 milliohm. The chassis measures 280 mm wide, 174 mm high and 461 mm deep, and the amplifier weighs 24.5 kg.

Engineering and use context

A new linear power supply is fed by a custom 800 VA potted transformer, mounted on a dedicated suspension that damps its mechanical vibration. Nagra states that this supply gives the amplifier more voltage headroom and larger energy reserves than before. Every channel has one MOSFET output pair, fixed to a large CNC-machined heatsink that keeps operating temperatures stable. The input board comes from the design used in the Nagra Reference AMP, with revised layouts and upgraded internal wiring, and the front-panel controls are optically isolated from the audio path. On the fascia sits the Modulometer, an analogue level meter modelled on that of the IV-S open-reel recorder. Signal arrives over XLR (balanced) or RCA (single-ended) sockets, and two remote jacks, marked in and out, link its switching to other units of a system.

Pairing

The intended partner is the PREAMP II-S, where a valve control unit drives this transistor power stage. Thanks to its high input impedance, other valve or transistor preamplifiers can drive it without strain, and with both socket types on the back most sources connect directly. Its low output impedance gives firm control over passive loudspeakers of moderate efficiency, and the trigger link allows switching on and off from the preamplifier.

Alternatives

The Nagra Classic AMP, the 2015 stereo model that the AMP II-S replaces, offers 100 W per channel into 8 ohm and relies on active power factor correction with a 300,000 uF capacitor bank.