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Old 4th March 2013, 03:11 PM   #1
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Default on/off switch pop when turned off

My amp I built pops quite loudly when I turn the power switch off. I've read to eliminate that put a cap across the switch. I did that, a 0.01uF 600v and no change.

Any suggestions?
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Old 4th March 2013, 07:11 PM   #2
Enzo is offline Enzo  United States
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How about turn the standby switch first.
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Old 4th March 2013, 09:40 PM   #3
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If that's the only alternative, but I would much rather not market this with that instruction, especially when it does not happen on all amps.
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Old 5th March 2013, 12:02 AM   #4
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Old 5th March 2013, 05:15 PM   #5
JMFahey is offline JMFahey  Argentina
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would much rather not market this with that instruction
Why not?
That's what standby switches are for.
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Old 7th March 2013, 11:07 AM   #6
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And as a power switch bypass, .01 uf @ 600 v is not enough voltage. Refrigerators and air conditioners can put 1000 v spikes on western power lines. Old TV's always had 1000 v rated caps, and that is what I installed in my ST70 and PAS2 tube amps. I got the idea from old Sam's photofacts schematics, decades before the internet. If you believe your supplier might lie on his cap voltage ratings, you might buy UL rated caps which are rated for the power supply they go on- typically 200 to 300 Vac for US market appliances. I believe they are described as x2 or y1 caps or something, although I am vague which rating you would use for a power off switch. The .01 uf @ 1000v cleaned up the turn off pop on my dynaco equipment, and the only failure in 35 years both vaporized the cap and arced over the turned off power switch, so I call that a lightning strike (particularly based on the weather that day).
Dynakit ST70, ST120, PAS2,Hammond H182(2 ea),H112,A100,10-82TC,Peavey CS800S,1.3K, SP2-XT's, T-300 HF Proj's, Steinway console, Herald RA88a mixer, Wurlitzer 4500, 4300

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Old 7th March 2013, 11:18 AM   #7
DF96 is offline DF96  England
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Caps across mains or mains switches should always be AC mains rated and fail-safe: X or Y. The DC rating can be ignored.
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Old 7th March 2013, 11:59 AM   #8
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Why don't try a MOV?
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Old 7th March 2013, 01:16 PM   #9
Tesla88 is offline Tesla88  Italy
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Most guitar tube amps make noise if switched of from main instead of stand by first !
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Old 7th March 2013, 01:23 PM   #10
DF96 is offline DF96  England
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Put a 10nF X rated cap across the mains transformer primary. If that doesn't work then you may have a grounding problem or inductive coupling between the power and signal circuits.
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