I have a question. the Muting pin of the LM3886 has a 100UF capacitor on it to the ground point in most designs that i see.
some questions:
Is the capacitor required? if so why? What is the point of this cap?
is the value of this capacitor critical?
what is the typical voltage rating of the capacitors and would a 100uf at 35V work? (all i have on hand. +/-35v rails).
some questions:
Is the capacitor required? if so why? What is the point of this cap?
is the value of this capacitor critical?
what is the typical voltage rating of the capacitors and would a 100uf at 35V work? (all i have on hand. +/-35v rails).
The resistor un-mutes by pulling a small amount of current from the mute pin when connected to the -ve rail. I think that's right. I just woke up, but it certainly involves a small amount of current either way 
A capacitor will very briefly act as a short while it is uncharged, so when powering on it will tie the mute pin to ground for a short period of time while it charges (through the resistor to the -ve rail), and thus the chip will be muted briefly upon power up, and will mute upon power down as the cap discharges.
This can be used to help remove any power up / down thumps or strange noises.
It's not strictly required. Just the resistor will un-mute the chip, but for the extra couple of pence this capacitor will likely cost, you might as-well have it there really. If you leave it out and experience thumps and such when turning on / off the amp it might annoy you. Though saying that, in the past I have left out the cap and it was fine.
I believe it will see the voltage of the rails, so a 50v cap would be a safer option.
A capacitor will very briefly act as a short while it is uncharged, so when powering on it will tie the mute pin to ground for a short period of time while it charges (through the resistor to the -ve rail), and thus the chip will be muted briefly upon power up, and will mute upon power down as the cap discharges.
This can be used to help remove any power up / down thumps or strange noises.
It's not strictly required. Just the resistor will un-mute the chip, but for the extra couple of pence this capacitor will likely cost, you might as-well have it there really. If you leave it out and experience thumps and such when turning on / off the amp it might annoy you. Though saying that, in the past I have left out the cap and it was fine.
I believe it will see the voltage of the rails, so a 50v cap would be a safer option.
1 No but it is very nice to have an absolutely pop free amp!mbates14 said:
2 The value sets the time.
3 35 V is OK since it's a low duty location, nothing much is required in terms of performance.
I have chosen (C13)100 uF + (R10)33 k. Check the datasheet for determine the resistor value. You have it in a diagram.
Schematic here
Here you can see how the pop free action looks like.
http://www.keld.eu/gainclone/test.htm
FWIW I've never used the muting cap - 3886, 4780 or 4766, and never have I had to suffer switch-on or switch-off pops. A very slight click at switch-off is the worst I've encountered, and that cap doesn't prevent that in any case.
There is no chance of the amp failing at switch on due to absence of that cap, IMO. The built in pop protection of the chips (under-voltage protection) ensures that the on and off thumps are minimal.
There is no chance of the amp failing at switch on due to absence of that cap, IMO. The built in pop protection of the chips (under-voltage protection) ensures that the on and off thumps are minimal.
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