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BillyF 31st August 2004 11:41 AM

Help on Preamp Mute Switch
I follow all the advise from this forum how to connect the mute swich to my preamp, output connect it to ground.
Yes it works. I used DPDT switch then connect 0.1F between the pins (input to output pins) and not the input to ground. But there was thump sound on both mute off and mute on...
Any advise how to deal with this????
Thanks a lot..

fdegrove 1st September 2004 10:22 AM

2 Attachment(s)

Not sure I understand how you hooked up the switch but I never had any trouble with this setup:

Cheers, ;)

BillyF 1st September 2004 02:22 PM

Thanks a lot... It works but still have a thump sound every time I mute on but @ off pretty quiet.

ray_moth 5th September 2004 09:26 AM

What you describe suggests that there could be DC on the mute switch. When the switch is activated, it causes the capacitor to discharge suddenly, giving a transient that you hear as a 'thump' in the speaker. When it is deactivated again, the capacitor charges again but slowly, through a high value resistor.

hacknet 5th September 2004 09:29 AM

do you have a large valued resistor after the cap?

BillyF 5th September 2004 11:54 PM

Thanks guys...
I have a 1Meg resistor connected to GND after the ouput cap of 0.47F/600V.
What value needed for this resistor to avoid the thump sound?

fdegrove 6th September 2004 12:05 AM



I have a 1Meg resistor connected to GND after the ouput cap of 0.47F/600V.
If I may say so: if you make a habit out of muting the preamp while it's warming up it's impossible for a DC voltage to develop at the output of the coupling cap.
It's shorted to ground so whatever the bleeder resistor's value, nothing can happen at that spot.

However, in case you measure a DC voltage after a period of warm up at the coupling cap and it doesn't go away, you have either DC coming in from the amp or a leaking coupling capacitor.
Either of which could be the cause of the turn-on/turn of thump you're hearing.


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