Tone control for hearing aid - includes two transistors and potentiometer for controlling frequency determining resistors and voltage stabilisation

摘要

The tone control for a hearing aid allows the amplifier frequency response to be matched t characteristics of an individual's ear. A frequency response determining network is included in the input of one amplifier stage. Voltage stabilisation is provided for the transistor circuit which controls the frequency determining variable resistors. The control circuit includes two transistors (23, 24). The base of the first transistor (23) is connected over a resistor (32) to the upper of a potentiometer, one fixed contact of the potentiometer and to the voltage stabiliser. The base of the other transistor (24) is connected over a resistor (38) to a voltage divider (34, 35) connected between the other end of the potentiometer and the emitter of the second transistor (24).