Here's a different thought - why not just make it simple and use a relay? It would have less impact on signal quality than any active muting circuit.

Here's an interesting article I just found on a variety of audio muting circuits:

http://sound.whsites.net/articles/muting.html#s11

Back when I was building a lot of audio stuff, I used several of AMB's designs - he's kind of a big name in the DIY DAC and headphone amplifier community. He has a relay-based muting circuit with a dual purpose, first, a brief delay before passing the signal when your equipment turns on (to eliminate power-on pop) and second, to mute the signal if DC offset is detected (which can damage headphones or speakers).

The need for detecting DC offset is because high-end amplifiers rarely use coupling capacitors to eliminate DC offset because of perceived audio quality issues, but eliminating them requires using other approaches to eliminate DC offset which are not always totally reliable.

quote:

Originally posted by maladat:
Here's a different thought - why not just make it simple and use a relay? It would have less impact on signal quality than any active muting circuit.

I was thinking that but am wondering if a physical switch will make a noise in the audio line. The transistor can be ramped with a capacitor. It's definitely on the list of things to try though.

Just realized I didn't include the AMB link!

https://www.amb.org/audio/epsilon12/

If you use a good relay, there should be either no noise on switching or a barely detectable click.

Relays also give you some easy options for circuit behavior - you can use a latching relay, where it stays where you switch it until you hit it with "switch" voltage again, or you can use a normally-closed or normally-open momentary relay that needs to have voltage constantly applied to maintain the other position.

A normally-closed relay, given a failure in the muting device, would fail to acting like a wire. A normally-open relay, given a failure in the muting device, would fail to being disconnected. Either behavior might be desirable depending on the exact usage scenario for the muting device.

I believe the relays specified for AMB's muting circuit are the normally-open type.

I have a handful of relays here. I'm going to have to try it.

One other note - be thoughtful about how you set up the "off" position of the circuit, in relation to the equipment you're using it with. Shorting the muting device's input directly to ground may damage audio equipment, and just disconnecting it completely can also (with solid-state equipment, this is usually fine, but it can damage tube equipment).

You can switch it to ground via a resistor, but then you need to make sure the resistor has a sufficient power rating for the signal the muting device is likely to see. For line level, this isn't a big issue, but for an amplifier, it can be.

quote:

Originally posted by maladat:
One other note - be thoughtful about how you set up the "off" position of the circuit, in relation to the equipment you're using it with. Shorting the muting device's input directly to ground may damage audio equipment, and just disconnecting it completely can also (with solid-state equipment, this is usually fine, but it can damage tube equipment).

You can switch it to ground via a resistor, but then you need to make sure the resistor has a sufficient power rating for the signal the muting device is likely to see. For line level, this isn't a big issue, but for an amplifier, it can be.

It's being designed to go between the preamp and the power amp so line level is correct.

Maybe a turbo encabulator would work?

quote:

Originally posted by jhe888:
Maybe a turbo encabulator would work?

You can't short those to ground without issues.