Stepped Volume Control

EE JULY/AUGUST 1988 The circuit consists of three distinct sec- tions. The first consists of a straightfor- ward amplifier, ICI. and IClb. The sec- ond is a digital counter, 1C3, which con- verts a binary code into a resistance value via 1C2. That value is used to con- trol the degree of amplification. Finally, there is a pulse shaper, IC4, which enables IC3 to count up or down. Amplifier IC lb has a switch-controlled gain of 0 dB or 24 dB. The control switch, S3, is an electronic type driven from output Qd of 1C3. The gain of IC la can be set between 0 dB and 21 dB in steps of 3 dB. The total gain of the two amplifiers can thus be set between 0 dB and 45 dB. The bandwidth of the amplifier extends from 10 Hz to 40 kHz. The peak value of the amplified signal should not rise above 8Vpp with a supply voltage of 5 V. The pulse shaper, formed by bistable Ni-N2 and network Cs-R16, indicates to 1C3 whether it should count up or down. The RC networks suppress spurious pulses. The delay in...