Offers a sonically pure, but fairly inefficient in terms of mains power usage and heat dissipation, method of operation. Perreaux preamplifiers and all driver stages of Perreaux amplifiers opearate in Class A mode.

The sonic purity and lack of distortion is realised through biasing the transistors ON all the time by applying high quiescent current. Effectively the transistors are ON at full power potential whether there is signal or not. This avoids crossover distortion, which is normally present in Class B design.

In Class B designs, there is very little quiescent current used so the transistors are not biased ON as per Class A. In fact at times they are actually OFF. During the full cycle of a sine wave, one transistor handles the positive half-cycle, the other deals with the negative half. Whilst one is working the other is switched OFF. The problem of crossover distortion occurs at the point where one transistor takes over from the other. Because transistors have to come up to speed when they are switched ON, the first portion of their operating curve is non-linear. This causes a "hump" at the mid-point of the sine wave, which is crossover distortion. The straight Class B design is not suitable for hi-fi, although it is used in other applications and has the advantage of being far more efficient in terms of power usage and heat dissipation than the Class A system.

To partially solve the problem of crossover distortion one can apply further amounts of quiescent current, which leaves whichever transistor is in the unused half cycle partially turned ON. This is called Class AB and provides a smoother transition between the half cycles, because the transistors have been given a head start by already being partially ON and are thus working more within their linear range. Unfortunately some crossover distortion is usually still apparent because of the trade off of quiescent current versus power usage and thermal efficiency. The more quiescent current, the greater the need for large expensive heat dissipation systems.

As mentioned before, all Perreaux preamplifiers and the driver stages of Perreaux power amplifiers are run in Class A, but efficiency is not a problem in these low power areas and the sonic benefits are vastly more important.

The output stages of power amplifiers do pose a problem. Even small Class A amplifiers require massive heat sinks and/or fan cooling and are generally very expensive. The owner tends to end up with substantial electricity bills as well.

The MOSFET output stages in Perreaux amplifiers run what is known as extended Class AB or A/AB. By balancing all the trade-offs; physical size, heat dissipation, power usage, and sonic quality, we have achieved what we consider to be the most beneficial result. By applying even more quiescent current, more than Class AB, but less than the requirement for pure Class A, we have biased the power MOSFETs to be ON at all times and are held just above their non-linear area, even during their OFF times.

Music is an ever-changing matrix of loud and soft. Even when listening to loud music with a 200 to 300 watts per channel amplifier, the average power output is usually in the vicinity of 15 to 30 watts. The extra power is used but only in momentary peaks.

By using class A/AB output stages, Perreaux amplifiers operate pure Class A up to approximately 10 watts per channel and then slide gently into Class AB from there up to their rated output. This means that the sonic benefits of Class A are retained for most of the music and because the power MOSFETs are biased above their non-linear area of operation, crossover distortion is virtually non-existent at all times.

In our opinion this provides, the most beneficial result in all areas. The sonic qualities are magnificent, the physical size is practical and the power usage is affordable.

Switch on, listen and enjoy.