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Re: dc voltage at the output [message #22366 is a reply to message #22351]

Thu, 05 February 2015 11:10

stevem
Messages: 4772
Registered: June 2004
Location: NY

Senior Member

Since the volume control is right after the channels first gain stage if turning it down does not kill the hum then you are chasing down the wrong trail.
This does not mean that the jacks may not be wired wrong, but you have the other channel to compare that to!
Use your voltmeter to step back thru the signal chain from Q416 and look for dc voltage where there should be none.

Resistors are not a likely cause, more likely would be a leaky electrolytic coupling cap, or a leaky transistor, and also take note that all dc voltages are taken with all the controls full up and with no speaker load or test load on the amp as noted on the schematic!
Also just for kicks just check the two 8 volt preamp voltage readings as if they are not pretty close two each other then that can make for hum also!

[Updated on: Thu, 05 February 2015 11:15]

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[Message index]

		dc voltage at the output By: smackoj on Wed, 04 February 2015 10:35
		Re: dc voltage at the output By: chicagobill on Wed, 04 February 2015 12:42
		Re: dc voltage at the output By: smackoj on Wed, 04 February 2015 13:41
		Re: dc voltage at the output By: chicagobill on Wed, 04 February 2015 15:06
		Re: dc voltage at the output By: smackoj on Wed, 04 February 2015 16:18
		Re: dc voltage at the output By: chicagobill on Wed, 04 February 2015 16:39
		Re: dc voltage at the output By: smackoj on Wed, 04 February 2015 17:47
		Re: dc voltage at the output By: smackoj on Wed, 04 February 2015 19:40
		Re: dc voltage at the output By: smackoj on Thu, 05 February 2015 09:49
		Re: dc voltage at the output By: stevem on Thu, 05 February 2015 11:10
		Re: dc voltage at the output By: chicagobill on Thu, 05 February 2015 12:32
		Re: dc voltage at the output By: smackoj on Thu, 05 February 2015 17:24
		Re: dc voltage at the output By: chicagobill on Thu, 05 February 2015 17:35
		Re: dc voltage at the output By: smackoj on Thu, 05 February 2015 17:57
		Re: dc voltage at the output By: pleat on Fri, 06 February 2015 19:27
		Re: dc voltage at the output By: chicagobill on Thu, 05 February 2015 23:52
		Re: dc voltage at the output By: stevem on Fri, 06 February 2015 06:18
		Re: dc voltage at the output By: smackoj on Fri, 06 February 2015 08:47
		Re: dc voltage at the output By: smackoj on Fri, 06 February 2015 10:08
		Re: dc voltage at the output By: chicagobill on Fri, 06 February 2015 12:49
		Re: dc voltage at the output By: smackoj on Fri, 06 February 2015 17:42
		Re: dc voltage at the output By: chicagobill on Sat, 07 February 2015 00:39
		Re: dc voltage at the output By: smackoj on Sat, 07 February 2015 04:52
		Re: dc voltage at the output By: stevem on Sat, 07 February 2015 07:39
		Re: dc voltage at the output By: smackoj on Sat, 07 February 2015 10:28
		Re: dc voltage at the output By: chicagobill on Sat, 07 February 2015 11:56
		Re: dc voltage at the output By: smackoj on Sat, 07 February 2015 12:57

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