I want to learn about the mute circuit. Is there any easy documents or reference for it?

[psychepool]

Recently, as I made an amplifier with two or more channels that can switch channels while playing with a footswitch, pop noise when switching channels has become a little worrisome.
It is said that using an optocoupler has an advantage in reduce pop noise because the switching speed is slow.
But reliable products are expensive and hard to find so I am trying to make my own and use it, I think that it will have a negative for sound such as tone loss, so I prefer a relay.

But I realized that using a relay couldn't avoid pop noise.

I know that many amplifiers have a mute circuit to prevent this.
I know this is a method of removing pop noise by temporarily muting the preamp the moment the channel is switched with the switch.

It seems that the basic operation is to send a signal to the ground by temporarily sending a pulse at the moment of switching by attaching a FET or TR between the signal at the end of the preamplifier and the ground.
I looked at the switching circuits of Mesaboogie amps, but I wasn't majoring in electronics, so it wasn't easy to understand them by looking at the completed circuits.

So, if you have any pages that you can get to know from a very basic level, I would like to ask you to share them.
In particular, I can't understand the switch that is connected to supply power to the relay is continuously connected, but the signal sent for muting is temporarily applied.

Actually, this pop noise feels loud when I hear this sound separately but when I use it at home, I use PPIMV, so I can hardly hear it.
And when used at a large volume in a practice room or similar, it is significantly smaller than the guitar output signal.
So I am not feeling very uncomfortable while using it,
But I wanted to make an amp with a little more completeness, so I asked a question because it is a part I want to learn.

[sluckey]

A Vactrol VTL5C1 optocoupler is perfect for a mute circuit. This optocoupler consists of a LED and a LDR in the small housing. The LDR (light dependent resistor) normally has a very high resistance, but when you turn on the LED, the LDR resistance becomes very low.

Look at the data sheet for more info... https://www.tubesandmore.com/products/o ... -switching

Here's a simple mute circuit. Just use a drop of silicone adhesive to stick the optocoupler to the back of the volume pot.

[xtian]

Usually, you can silence the "pop" switching noise by installing resistors across the switch. Dumble uses 22M resistors, other designs 1M.

[R.G.]

Pops and clicks happen two ways. Generally, a minor <tic> comes from accidental capacitive coupling of the on/off signal from the mute circuit into the signal path. For instance, a manual switch can't do this at all. But a relay has many volts suddenly go across the relay coil, and that coil voltage can be coupled in by through-the--air capacitance.

The bigger clicks and things that really pop are generally caused by the switch contacts suddenly forcing the audio signal line to be at a different voltage. The sudden jump in voltage is heard as a loud pop. So the trick is to arrange your circuits so that the DC voltage on the muted signal is identical whether muted or not.

Most tube circuits use series capacitors to couple signal from one plate to the next grid. If you put a switch in series with the capacitor, the switch will indeed cause the signal to be muted when it's open. It will almost invariable click or pop when you reconnect it. That's because there is a DC voltage across it when it's conducting signal. After all it's there specifically to block that DC. When one end of the cap is open, the cap internally leaks down a little, so it holds less DC voltage than it did with the switch closed. When the switch closes again, the amount of leaked-down voltage appears as a pop until the grid and plate circuits charge the capacitor up again. You can make this kind of mute switching silent by two methods. One is to make the change between open and closed so slow that the capacitor leakage charges at a below-audio speed. So the "pop" is still there, it's just too low a frequency for it to get through the circuit, and too low for your ears to hear. This is the origin of the "just make it open and close slowly" advice. The other way is to use a high-value resistor on the side that is being opened. This resistor pulls the cap to the right voltage while it's open, so no pop/click can happen when it's closed.

Shunt muting is generally much less prone to clicks, but only if the shunt to ground is on a circuit point that is already held at DC ground anyway. If you try to shunt-mute a plate voltage to ground, the pop will be monstrous.

There's one more original for clicks. If you suddenly clamp/unclamp any signal to ground, the edge is heard as a <click>. To defeat this, you either only switch near a zero crossing, or use the go-slow fade trick.