I can certainly vouch for this upgrade as I use a Net Audio modified Quad 405-2 whose upgrade is very similar. If any current owners of the Quad 606 Power Amplifier are interested, Fidele Audio offer an upgrade service which improves the original sound by replacing the class A circuits op amp (Texas Instruments TLC271) with a much a higher quality one - a Burr Brown OPA627AP and upgrading some capacitors with Black Gate (just about the best you can buy - if you can find someone who stocks them). The Quad 606 Power Amplifier was discontinued in 1997 to make way for the Quad 707 power amplifier which was another current dumping design that improved slightly on the Quad 606 and was one of Hi-Fi World's recommended amplifiers at that time. The Quad 606 Power Amplifier was also very popular with professional audio people as well as audiophiles possibly because of the sheer power of this amplifier coupled with Quad's reputation for producing solid well built amplifiers. The Quad 606 Power Amplifier was originally launched in 1987 and essentially was a new improved version of Quad's 405 amplifier with extra oomph and a whopping 140 watts per channel into 8 ohms whose sonic improvement compared to original Quad 405-2 was significant. Essentially a current dumping circuit like the Quad 606 Power Amplifier consists of a very high quality low power class A amplifier feeding a high power low quality amplifier which is used when required.

The Quad 606 Power Amplifier is another classic amplifier design from Quad utilising their patented current dumping technology.

Power amplifier reviews