sugden a28b

Sjaak · 29th November 2008, 07:07 PM

Hello DIY'ers,

Can someone tell me what could be wrong with my sugden A28B?
There is noise in the left channel when the volume control is operated. I replaced the potentiometer (ALPS) but the problem is still there. I have no schematic so it is difficult to find the problem.
Thank you for any advice!
Sjaak

Rikard Nilsson · 29th November 2008, 08:59 PM

Noise from a potentiometer can origin from DC voltage across it. That in turn may be the result of a shorted electrolytic cap, or an DC operating point way off.

But a schematic would help a lot.

Sjaak · 30th November 2008, 12:11 PM

Thank you Rikard,
So if DC is over the potentiometer I have to search for a short capacitor in the pre amp stage only?

Rikard Nilsson · 30th November 2008, 01:58 PM

I think so, or something else that might cause a stage to operate at the wrong DC level. I can´t imagine there should be any DC voltage across the pot. You could always measure the working channel to see if there is any DC.

If there are tantal caps these are the ones to check. They are known to short.

29th November 2008, 07:07 PM	#1
Sjaak diyAudio Member Join Date: Nov 2008	sugden a28b Hello DIY'ers, Can someone tell me what could be wrong with my sugden A28B? There is noise in the left channel when the volume control is operated. I replaced the potentiometer (ALPS) but the problem is still there. I have no schematic so it is difficult to find the problem. Thank you for any advice! Sjaak

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29th November 2008, 08:59 PM	#2
Rikard Nilsson diyAudio Member Join Date: Aug 2008	Noise from a potentiometer can origin from DC voltage across it. That in turn may be the result of a shorted electrolytic cap, or an DC operating point way off. But a schematic would help a lot.

30th November 2008, 12:11 PM	#3
Sjaak diyAudio Member Join Date: Nov 2008	Thank you Rikard, So if DC is over the potentiometer I have to search for a short capacitor in the pre amp stage only?

30th November 2008, 01:58 PM	#4
Rikard Nilsson diyAudio Member Join Date: Aug 2008	I think so, or something else that might cause a stage to operate at the wrong DC level. I can´t imagine there should be any DC voltage across the pot. You could always measure the working channel to see if there is any DC. If there are tantal caps these are the ones to check. They are known to short.

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