microphone amplifier with preset tone control

95 microphone amplifier with preset tone control The active parts of the circuit (ampli- fiers Al and A2) shown in figure 1 are contained inI Cl. Al operates as a non-inverting ampli- fier and the microphone input is applied to pin 1 via coupling capaci- tor Cl. The amplification factor of this stage is determined by the ratio of resistor R5 to the parallel combination of R 1 ... R4. With R1 switched in, the amplifi- cation factor is about 225, with R3 switched in about 60, and with Si in the centre position about 14. As the effective input sensitivity can be altered by Si, it can be matched to different input levels or microphones. The output of Al is applied to a tone control stage, A2. The ratio R13/R12 determines the amplifi- cation (about 18dB) of this stage. The effect of R11 and C6 is, in principle, the same as that of R2 and C2: a smaller value of C6 in- creases the lower cut-off frequency. The RC network between Al and A2 is the real tone control. Potentio- meter Pl sets ...