YAMAHA M-80 (1984) | AUTO CLASS A

The M-80 power amplifier was designed by Yamaha as a flagship high-end amplifier for listeners demanding both purity and serious power. With 250 watts per channel and technologies such as Auto Class A and Zero Distortion Rule (ZDR), the M-80 combines refined amplification with enormous dynamic reserves.

M-80 Main Specifications

Continuous sine-wave power, per channel:

250 W at 8 ohms, 20–20,000 Hz, 0.003% THD

290 W at 6 ohms, 20–20,000 Hz, 0.007% THD

340 W at 4 ohms, 20–20,000 Hz, 0.02% THD

Peak power: 380 / 480 / 640 / 850 W per channel at 8 / 6 / 4 / 2 ohms

Power bandwidth: 10–100,000 Hz at half rated power, 8 ohms

Frequency response: 20–20,000 Hz, +0 / −0.1 dB

Signal-to-noise ratio: 127 dB / 119 dB, IHF A

Total harmonic distortion: 0.002% at half rated power, 8 ohms

Dimensions: 435 × 165 × 425 mm

Weight: 23 kg

The technology: Auto Class A and ZDR Technology. Auto Class A circuitry is at the heart of the M-80's approach to amplification. At normal music levels, the amplifier operates in Class A, where low-level signals benefit from exceptionally low distortion and clean amplification. The design is based on the observation that around 95% of typical music power requirements fall within this operating range. When a musical peak suddenly demands substantially more power, the M-80 automatically switches to Class AB operation. This provides the additional output capability needed for demanding passages without requiring the amplifier to remain in high-power Class AB operation continuously. Zero Distortion Rule. The ZDR circuit addresses one of the traditional weaknesses associated with Class AB amplification: switching and crossover distortion. Integrated into the M-80's power-amplifier circuitry, ZDR is designed to suppress distortion introduced during the transition between output devices. It also counteracts distortion associated with the non-linear operation of the power transistors. The result is an amplification system intended to preserve the original music signal with the purity associated with Class A operation, while retaining the high-power capability of Class AB amplification. Massive Power Reserves for Difficult Loads. High-capacity capacitors and high-performance circuitry give the M-80 substantial reserves for sudden musical peaks. The amplifier is designed to remain reliable even when driving low-impedance loudspeakers. The specified peak output reaches an impressive 850 watts per channel into 2 ohms. For demanding speaker systems, that reserve can be particularly important when music contains rapid and substantial changes in level. 20-LED Peak Power Display. Twenty precision LEDs provide a visual indication of speaker load and amplifier output activity. An impedance control allows the display to be adjusted for 2-, 4-, and 8-ohm speakers. Peak memory is also provided, while the display sensitivity can be switched to a 10× range. Beyond its practical function, the large LED display gives the M-80 the unmistakable visual character expected from a serious vintage power amplifier. Three Speaker Pairs and Flexible Switching. Three speaker groups—A, B and C—can be selected using the amplifier's connection and switching system. The speakers can be operated independently, simultaneously, or in combined configurations. This gives the M-80 considerable flexibility for systems using multiple pairs of loudspeakers. The amplifier is also designed to handle low-impedance loads without distortion or unnecessarily triggering its protection circuitry. The specification for operation down to 2 ohms underlines just how seriously the M-80 was engineered for demanding loads. Heavy-Duty Speaker Connections. The speaker terminals accommodate different cable diameters, allowing both large-gauge speaker cables and conventional cables to be connected without soldering, crimping, or other special preparation. It is a small but significant detail that reflects the M-80's practical, high-power design philosophy. Protection and Additional Circuitry. An overload protection circuit monitors potentially dangerous operating conditions. If excessive power levels or a short circuit occurs, the protection system automatically shuts down the amplifier to help prevent damage to the M-80 and connected loudspeakers. Additional circuitry includes: DC gain configuration, DC protection circuit, Independent left/right level controls, A/B/C speaker-group selector. Original sale price in Germany: 2300 DM.

Looking for more? Head to 1001hifi.com for more.

Like Our Work? Support 1001 Hi-Fi