Core Design Philosophies for Parasound Amplifiers

by John Curl

1. Balanced Complementary Topology

Solid state amplifier designs have a certain amount of distortion generated by each active part. If the parts can be used in push-pull or in differential mode, then much of the inherent distortion can be canceled as it is being generated.

2. FET's Where Possible

FET's are inherently more linear than bipolar transistors. FET's have a voltage gain that is proportional to the square root of the current in the FET. Bipolar transistors have a voltage gain that is directly proportional to the current in the transistor. FET's are more linear over a greater current range.

3. No Signal Capacitors

Removing any need for input, output, or feedback capacitors, removes a potential distortion source, and can lower cost as well.

4. Class A When Possible

All else being equal, Class A is better. It has lower overall distortion, and the higher harmonics are reduced significantly.

5. Quality Parts

We have researched the potential problems with passive parts. Most passive parts have some measurable distortion. Some distortion mechanisms are subtle and are difficult to measure, but are detected in listening tests.

6. Regulated Driver Stages

The output stage can demand a great deal from a power supply. It is impractical to make a virtually perfect power supply in a cost effective product. We regulate the driver supplies to remove any potential distortion in the drivers, when the output stage makes a strong demand on the power supply.