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Old 4th July 2012, 09:36 AM   #1
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Default volume Pot noise

Hello, I replaced the cheap volume pot in my integrated tube amp with one of the Ebay Stepped attenuators but when change the volume there is an horrible "chak " noise out the speakers, Any idea how to solve this? Is this normal with this kind of attenuators?
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Old 4th July 2012, 09:41 AM   #2
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It sounds as if they built the attenuator with a break-before-make switch instead of a make-before-break switch. If that is the case, there's really nothing you can do about it other than replace the attenuator.
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Old 4th July 2012, 09:43 AM   #3
DF96 is offline DF96  England
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Are there couping caps on both sides of the attenuator? You need to keep DC well away, even the tiny input currents to an opamp or valve grid.
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Old 4th July 2012, 09:46 AM   #4
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Thanks for reply, Do you know any reasonable priced "noise free" stepped volume pot?
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Old 4th July 2012, 09:49 AM   #5
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Quote:
Originally Posted by DF96 View Post
Are there couping caps on both sides of the attenuator? You need to keep DC well away, even the tiny input currents to an opamp or valve grid.
No Caps, is installed with the instruction provided by the seller, maybe this is the problem, if I move the pot fast there is no noise but when slow souns like an electrostatic discharge
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Old 4th July 2012, 09:57 AM   #6
DF96 is offline DF96  England
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Quote:
No Caps
I think you have your answer. You can sometimes get away with omitting caps for a normal volume pot (although still not ideal) as the resistance variation is smooth. For a switched attenuator the variation is stepped so any DC turns into clicks.

One thing to try as a workaround is adding a high value resistor from output to ground. This may help if the problem is caused by the switch being break-before-make - or return it under warranty?
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Old 4th July 2012, 10:08 AM   #7
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I will try the resistor, thanks for your help
Kind Regards
Bernat
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Old 4th July 2012, 04:34 PM   #8
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Actually I believe they are supposed to be make before break switches, but in practice the wiper don't always have good contact. I have a few of those in my builds. It is annoying, but there are workaround:

- If they are new, or they haven't been used in a while, give them A LOT of exercise. You might find that there are some steps that are more problematic than the others, focus on them.

- If they are working well, try not to pull or push the shaft when rotating.

- The pop noise can be reduced by turning the knob very slowly (it becomes more like a scratchy noise than a really loud pop).

It is frustrating at first, but after a while you will be able to learn their temper.
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Old 4th July 2012, 07:32 PM   #9
DF96 is offline DF96  England
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Another option is just to use a pot, of whatever price you feel is necessary. What was wrong with the original pot? Have you swapped an imaginary problem for a real one?
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Old 4th July 2012, 08:59 PM   #10
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Originally Posted by DF96 View Post
Another option is just to use a pot, of whatever price you feel is necessary. What was wrong with the original pot? Have you swapped an imaginary problem for a real one?
this tube amp is a cheap chinese music angel Kt88, some parts are Ok, others like the wiring and pots are crap, Is my hobby and anti-stress therapy, I hard wired all the circuit, i Learned a lot but is a very dangerous work !! thanks God for read before some guidelines about working tube amps, one hand always in my pocket when working probably saved my life, I still have my ear bleeding when my screwdriver made a 450v short !! Now the amp sounds much better than before, there are a lot of parts changed like teflon wiring, capacitors and resistors, the pot is just a small part in the chain. I will attach some pictures of the work later. Thanks for read
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Last edited by bernat123; 4th July 2012 at 09:07 PM.
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