A high-performance single gain-stage preamplifier
There are many types of volume controls, from simple potentiometer to transformers (autotransformers) with switched taps, from light dependent resistors to multiplying digital to analog converters. However, in Dimitri’s views, the best volume control, for both technical and sound quality reasons, is a stepped very low impedance control. In his article he goes into the design, testing and system performance of a high quality single transconductance gain stage preamp, loaded with a low-impedance stepped audio attenuator. The preamplifier has balanced inputs and a single ended output. The circuit is the basic JFET differential pair with folded cascode and current mirror. Each FET of the input differential pair is enhanced with PNP bipolar transistors in the well-known Sziklai configuration to allow higher output current.