soft-action muting switch

Posted on Mar 1, 2013

The circuit in Figure 1 adds a soft muting switch with power-up/power-down muting to a line-level audio circuit. R4, C1, and JFET Q1 quietly ground a signal in 100 to 200 msec when you close S1 or release it when you open S1. Potentiometer R2, set to twice Q1`s cutoff voltage, makes the on/off transition times roughly equal. R2 and D3 quickly discharge C1 and mute the signal during power-down.

For this process to work, the signal path should remain stable to below roughly one-third the normal supply voltagesbelow ±4V in this example. Q1 can then finish muting. Making Q1 a more tightly defined PN4392 can soften this requirement and

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