on/off switch popping

[dscottguitars]

I have read to eliminate the pop from turning off an amp, put a cap across the switch.  I put a 0.01uF cap across mine and that did not make a difference. 

What can I do?

[FranciscoPerez]

Never tried it myself, but I heard some people adding a resistor across the power switch when the capacitor did not solve the problem.
Don't remember the exact value, but I think it was about 220k and rated 5W (maybe less power rating would be just fine).
Doing that, the amp will draw some current even when it's powered off, but maybe that's ok for you.

Perhaps someone else has tried this and can tell us if it's worth it.

Regards,
Fran

[dscottguitars]

That does not sound like a good option, but thanks.  I don't like the idea of current going through the amp when plugged in and not on...

[Willabe]

Switch 5 on your drawing is wrong. Switch to a and the bias is shorted to ground, switch and the cathode R is shorted.


               Brad     

[dscottguitars]

No Brad, it is correct.  Switch to 'a' and I bypass the cathode RC circuit so all the current goes to ground from the cathodes.  Switch to 'b' and I ground the fixed bias circuit, then all the current from the cathodes goes through the RC circuit.

[Willabe]

Yes, I see now. It seems I was only looking at the switch and not where it was going to.


              Brad   

[catnine]

Does it only pop when powering sw1 off? Have you tired powering  off with the other switchs in a different position? Sounds like a cap is draining or being charged when the off switch in switched off.

[dscottguitars]

Yes, but I have not tried in any other modes like tube rectifier, low power or cathode bias.  But, I want to be able to switch it off without having to do the standby first.

If it is possible... 

I've had a few others with the same circuit that didn't pop like this does.  But this amp has  a more powerful transformer, about 50 to 75 volts more on the B+.

[catnine]

the Ho /low sw3 is before the standby sw4 . I would try to power down in other modes just to see which switch makes a difference then at least you can isolate it.

[dscottguitars]

I want to sell this when I finish it.  If I'm going to be required to have special instructions for powering down, I'll do the standard, standby off first then power.

[dscottguitars]

I just replaced the 0.01uF/600v orange drop to a 1000v ceramic disk cap and that made a good difference.  It's not near as loud and threatening sounding.  And, I noticed if my guitar is plugged in there is no pop turning off the amp...

[jojokeo]

...some people adding a resistor across the power switch

This is to placed across the "standby" switch not the "power" switch - that would be unwise. Across the standby switch it allows a small current & lesser than full voltage to slowly charge up the resevoir and other caps in the power supply safely. When hitting the standby switch, the full voltage and current only then is "released" but the caps are all ready to go and do their job. When the caps are not charged, hitting the standby to "on" there is a brief short-circuit to which the tube rectifier takes the brunt of this condition. In electrical terms this is a long time. The resistor helps to eliminate the cause unnecessary wear and possible catastrophic damage to the recitifier - which according to Murphy's Law will occur on stage and not at rehearsal or in your room getting ready to practice.

Applied to the standby switch this does not allow any current "to continue to flow" (except in discharging the caps) when the amp is off and is perfectly safe.