The circuit is based on an inverting op amp using discrete transistors to overcome poor slew rate, fairly high distortion, and high noise problems. The output stage is driven by a constant current source, biased by a green LED to provide temperature compensation. With the controls flat, the unit provides unity gain so the stage can be switched in or out. The design is suitable for inputs between 100 mV and 1V and provides a good overload margin at low distortion for the accurate reproduction of transients
The usual screening precautions against hum should be carried out.