appearance of being generated by a carbon mike consistent with the carbon mike wiring of the host telephone this signal includes a resistance whose average value is adjusted to give the appearance of the carbon mike r2 it represents the impedance that the telephone would expect to see from a carbon mike system q1 and r2 are modulated by signal passed through c3 the dc signal seen at r3 decouples audio component and filters the signal through c4 the dc signal is routed through r4 and d5 and is directed left when opposite direction of current is blocked by transistor q4 this signal powers the amplifier circuit and q3 to drive the speaker 60 the sound signal from the telephone fed from lines 51 and 52 is isolated by transformer t1 and routed to the amplifier circuit through q3 for driving the speaker 60 volume control is provided by a variable resistor vr1 returning to the positive signal at line 55 following the diode bridge a portion of signal passes through r6 d6 and through r9 to provide power to the electret mike 57 this power is in the form a high impedance low current signal which is modulated by operation of the electret mike to provide audio control the audio signal from the microphone is decoupled through capacitor c7 passes through resistor r7 and into the collector of q2 with its variable resistor r8 when switch s2 is closed between points 63 and 64 the collector at q2 is.