Capacitor to reduce switch off bang - diyAudio
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Old 17th March 2012, 03:56 PM   #1
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Default Capacitor to reduce switch off bang

hi

my cheap marshall guitar amp makes a really loud bang when I switch it off..

I've read that soldering a capacitor across the mains switch might reduce this noise
(presumably across live and neutral - UK mains 240v)

but what value and voltage and what capacitor type should I use?
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Old 17th March 2012, 04:14 PM   #2
DF96 is offline DF96  England
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Not across the switch, but across the mains transformer primary. Value 5-10nF. Voltage/type has to be one designed for safe use across mains: X or Y type.
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Old 17th March 2012, 04:17 PM   #3
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Which model? Doubt a cap on the mains will help.
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Old 17th March 2012, 05:05 PM   #4
Enzo is offline Enzo  United States
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I'd be inclined to agree. Try turning your volume/gain controls to zero. ANy difference?
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Old 17th March 2012, 07:01 PM   #5
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thanks for replies - it's an MG15 CDR
yes I turn volume to zero and turn reverb down but it still sounds like a gunshot
(overdrive is turned down too)

I've tried hitting the switch quickly and tried pushing it very gently.. no difference

ok i just realised it has a headphone jack so I could plug in a dummy jack but if I did that should I add some 8 ohm resistors across the output(s)?
(am not going to plug in my headphones, that bang will damage them)

Last edited by cretaceous; 17th March 2012 at 07:12 PM.
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Old 17th March 2012, 07:23 PM   #6
DF96 is offline DF96  England
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A sound like a gunshot could well be caused by the switch-off transient in the mains circuit getting induced into a signal circuit. The other switch-off sound is a dull thud when the caps discharge, usually a few seconds after switching.
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Old 17th March 2012, 07:58 PM   #7
pdul is offline pdul  Denmark
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Try to put 10nf across the switch to kill the rf spike and spark in the switch, still x or y type.
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Old 17th March 2012, 09:00 PM   #8
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http://www.amparchives.com/Amp%20Arc...%20MG15CDR.pdf

Can not see anything obvious. Try the chip amp guys.
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Old 17th March 2012, 09:06 PM   #9
pdul is offline pdul  Denmark
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I see great potential for soundshaping/ opamp rolling in that amp
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Old 17th March 2012, 10:14 PM   #10
DF96 is offline DF96  England
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The mains caps are on the wrong side of the switch for arc suppression. They will provide some crude filtering. Add a similar cap directly across the primary.
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