Four-Channel Stereo Switch

The circuit described here enables a choice to be made from four different stereo channels with only one switch. Internal switching is effected by CMOS devices to obviate crackling, bounce, and other annoyances associated with mechanical switches. The two D-type bistables in IC2 are con- nected as binary dividers by linking their Q output to the D input. The Q out- put of FF1 is also linked to the clock in- put of FF2, which results in a kind of four-bit counter. The push-button is connected to the clock input of FF1. The four OR gates, Ni to N4, decode the output states of the bistables, so that at all times only one gate has a high output. The outputs of the gates drive the CMOS switches in IC3 and IC4. The out- puts of the four electronic switches in these ICs are strapped together. The input of each switch incorporates a potential divider, ensuring that the switches operate in their linear regions. This arrangement ensures minimum dis- tortion of the audio signals: the negativ...