Noisy volume pots - causes and cures

wizons

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Can someone shed light on the cause of this? A preamp I have crackles on the right channel when the volume pot is turned. The effect wears off to a certain extent after the amp has been on for some time, but it never clears.

Thanks

 

hearingisbelieving

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try Caig Deoxit - works a treat for me.

Remember to read the intructions carefully before use - ie. turn the equipment off an unplug it and make sure the cleaner has evaporated before you turn it back on.

 

RobHolt

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it's caused by a combination of dirt and grime on the pot tracks and/or oxidisation.

Often the latter can be the result of dc on the tracks and this will make pots and signal switches noisy over time, the result of tiny amounts of arcing. DC on pots is bad design but surprisingly common, and fixable with a 50p capacitor.

+1 for Deoxit - the best.

 

SergeAuckland

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The reason for the crackles is wear on the track that means that the wiper loses contact momentarily and so results in a crackle. The reason for the wear is usually two-fold. Mostly it's mechanical wear that wears away the track surface, but depending on the design of the amplifier and the condition ofd any coupling capacitors, DC on the track can cause micro-sparking, especially if the track is already mechanically worn, which erodes the track as well as causing crackling in its own right. Conductive plastics tracks are best for avoiding crackling from all causes, mechanical wear is very low, carbon tracks are the worse.<br>

<br>

S<br>Edit. Having just seen Rob's post, I agree that dirt is also a cause. I didn't think of it at first as all the pots I've used have been sealed so don't get dirty and unfortunately can't be sprayed with deoxit or any other contract cleaner.

 

wizons

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The reason for the crackles is wear on the track that means that the wiper loses contact momentarily and so results in a crackle. The reason for the wear is usually two-fold. Mostly it's mechanical wear that wears away the track surface, but depending on the design of the amplifier and the condition ofd any coupling capacitors, DC on the track can cause micro-sparking, especially if the track is already mechanically worn, which erodes the track as well as causing crackling in its own right. Conductive plastics tracks are best for avoiding crackling from all causes, mechanical wear is very low, carbon tracks are the worse.<br><br>

S<br>Edit. Having just seen Rob's post, I agree that dirt is also a cause. I didn't think of it at first as all the pots I've used have been sealed so don't get dirty and unfortunately can't be sprayed with deoxit or any other contract cleaner.
Very helpful replies. I suspect there's something more than dirt on the pot's tracks as the 'crackling/rustling' is more of a sharp cracking noise. Is it significant that the noise fades somewhat as the amp is left on? The pot is a sealed unit, so using deoxit is not possible.

A very strange thing happened when the system was powered up for the first time with this preamp: on turning on the monoblock power amps (having turned on the source and pre beforehand, then right and left monoblock) a thump sounded from the right hand speaker at the moment the left channel monoblock was switched on. Very odd...

Thanks for your replies.

 

felix

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A bit of an aside, but if you are into DIY and thinking of spending a goodly amount of cash on a pot, there's an architectural reason these problems develop in the first place you may want to consider: wiper current.

Reputable component manufacturers usually specify whether or not any current may be drawn through the wiper contact, or and if so, how much should be drawn. All this depends on the type of element and wiper material used. For Cermet elements and metal wipers' it's not unusuual to see a requirement of so many 10s of microamps.

Ignoring the advice for the component used is what leads to excess noise in use. It may be that a coupling cap should have been used after the wiper and was not (leaks current through the wiper into the parallel load) or that one was, and shouldn't have been! (not enough current drawn to 'wet' the wiper)

Carbon pots in low cost equipment will always go noisy eventually, though it may appear fixable. But if you are spending the necessary for a high-quality, really well-matched stereo fader in cermet or similar, do your research to make it perform at its best. The recommendations should be in the manufacturer's datasheets :)

 

SergeAuckland

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I would be very concerned using a pot that had DC going through it whatever the manufacturer says. If DC goes through a pot, it will always make noise whilst being turned. Perhaps the manufacturer takes the view that noise whilst being turned isn't important as long as the pot is quiet when static. That may be OK, but I always think of a pot as a fader and so must be silent whilst being turned. Considering that Penny and Giles make faders good for years of daily use moving back and forth with no noise whatsoever, there's no excuse for any manufacturer requiring wetting current to keep their pots quiet. Just smacks of poor engineering.

S

 
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felix

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Take a look at a few. Recomendations for wetting current through the wiper varies , quite a bit (i.e. from zero to a defined something)

Yes, I have a P&G unit in my preamp ;)

 

oldius

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It was recommended to me that, with the power off, I rotate the crackling pot through it's full rotation several times. I did that and I haven't had a further problem; it was was suggested to me by a very well respected audio engineer.

 

RobHolt

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It was recommended to me that, with the power off, I rotate the crackling pot through it's full rotation several times. I did that and I haven't had a further problem; it was was suggested to me by a very well respected audio engineer.
That's good advice and will usually help but is often a temporary fix.

Personally I'd give it a good squirt of Deoxit first.

 

tomart

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+1 for Deoxit

I have a 40 year old LUX amp which seemed almost dead.

Stripping it down and cleaning all the pots and switches with deoxit resurrected it

 

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