The first BC109C transistor acts as a buffer. It provides the circuit with an input impedance of around 250 000 has a voltage gain of slightly less than unity. As Baxendall tone control circuit is a passive design, all audio frequencies are attenuated. The position of the controls and the ballast capacitor alters the audio response. The last trans
istor provides a slight increase of about 3 times. The output is designed to feed an amplifier with an input impedance of 10k to 250k. Both tone controls should be linear potentiometers type.