GM 20

About the GM 20

The Graaf GM 20 is a high-end Italian-made OTL tube power amplifier delivering 20 watts per channel RMS into 8 to 16 ohms. It uses four massive Russian 6C33c tubes per channel operating in pure Class-A without output transformers, which avoids transformer-related limitations and contributes to its highly refined, natural sound. The amplifier features a Circlotron-style floating output design and requires careful bias adjustment and burn-in of the 6C33 tubes for reliable performance and longevity. It has an input sensitivity of 600 mV and input impedance of 50 kOhms. The GM 20 is praised for its wide and high soundstage, quiet operation, clear and beautiful midrange, and spectacular female vocals. It is often used with high-impedance speakers and can be converted to mono operation by paralleling channels with a special wiring kit. The build quality is excellent, with high-quality valve sockets and robust construction. Although rated at only 20 watts per channel, it delivers dynamic and detailed sound, especially with electrostatic speakers like vintage Quad ESLs. The amplifier is no longer in production but remains highly regarded among audiophiles for its sound quality and engineering.