Amplifier for use with telephone transmitter mounted in handheld telephone unit

Abstract From the Canadian patent

An amplifier for use with an electret, microphone utilized as a telephone transmitter in a hand held telephone unit or handset. Incorporated into the circuitry is a band pass filter which substantially inhibits feedback "singing" which occurs because of reflection when the handset or telephone unit is placed in a downward position on a hard surface or similar environment. The filter circuitry employs the source resistance of the telephone transmitter and the input resistance of a transistor amplifier stage as elements of the included filter circuitry.