Replacing noisy pots.

[Canuke]

I've got a power supply unit that apparently uses the same sort of rotary potentiometers that get noisy with time. Remember when your stereo got old, you had to disconnect the speakers lest you blow them out when adjusting the volume? Yeah, those things. Well, they'll eventually blow out whatever I'm working on if I don't replace the pots.

What options are there for replacing these? Are modern pots better at staying clean? Do they sell higher grade units that are resistant to the dust/noise?

 

[VidPro]

digital :-( that has relaced a lot of pots nowdays.
if you can get up into the backside of them, you can put in "tuner cleaner" it will remove the carbon slopping around.
there are 2 types of tuner cleaner they used to sell, lubricated, and just cleaner with no lubrication. because i couldnt find it available again, i just used silicon spray (the prestone type stuff) its a lot of solvent, and very little silicon oils.
but if you cant get it INTO the backside on the carbon slider, it will do no good. on slide pots its much easier , because the face of them is open to the air.
spray it in, and while its still wet inside, move it around. umm dont do it with the power on obviously.

the solvent will also mess with thick greaces in the things too, so in the example of a slide pot, it can make the pot slide different because the greace is gone. it cleans it, but then the slide on it becomes stuttery . so use sparingly so you dont loosen or clean up the greace that is in them.

or of course the deoxit stuff might work the same way.

i hate when that happens, but it is "fixable".

there has to be higher grade pots, because high quality "10Turn" pots can be very accurate for ages longer, there are also curcuit tricks that are done on higher end stuff to keep pot slop from being crackley.

 

[louie]

Replacement is usually easy and recommended for bests results. You do need to replace with the same specs for power, resistance taper and so on. High quality pots are expensive. Take a look at Digikey for example. Deoxit spray is recommended for a quick fix, but in many cases is only temporary.

Note that there can be other reason for a noisy pot otheer than a bad pot, such as DC on the pot that isn't supposed to be there.

 

[Canuke]

Note that there can be other reason for a noisy pot otheer than a bad pot, such as DC on the pot that isn't supposed to be there.

These pots have the behaviour I've seen before, where if you twist them back and forth vigorously a number of times, the crackliness diminishes. Would that happen in the case of spurious DC?

 

[NA8]

I'd recommend spraying them and then wait and see if the fix is permanent.

 

[lctorana]

Pots get noisy if DC is allowed to flow through them.

Pots from Radio Shack and the like are OK, but I would advise you check for leakage in the coupling caps adjacent to the pots, and change those as well. Adhere strictly to the voltage ratings.

 

[mudman cj]

If it turns out to be the pots that are the problem, I recommend replacing them with a type other than wirewound. The wire tends to build a layer of oxidation that results in this sort of problem. Try a carbon or conductive plastic composition pot. These are available as well built (but expensive) units and not just as flimsy junk (though you can buy them that way too).

 

[richdsu]

Potentiometer having carbon elements are cheap and lousy, degrades over time, no point to clean it

Try to get Potentiometer made of Cermet elements ( modern material ), much more durable. Better current and temperature handling.

Sealed Trimmers is better choice because the elements are protected from dust and pollution.

Currently top brands for trimmer pots are Bourns and Vishay.


http://www.vishay.com/resistors-variable/potentiometers/industrial/

http://www.bourns.com/components.aspx?cmsphid=7631383|7163299|4003686

 

[MrAl]

Hi there,

In critical circuits that use pots sometimes a double pot is used. This is
a pot where there are actually two pots that both turn with the same shaft.
You can find them on old car radios and glue the two shafts together.
The two pots are then wired in parallel so that if one pot craps out with
its bad spots the other pot is still wired in place. Unfortunately the two
pots wired in parallel have to make the right value for your circuit and this
isnt easy to find.

Another idea is to wire two caps in parallel to the pot. One cap gets wired
from one end of the pot to the 'arm' of the pot and the other cap gets
wired from the other end of the pot to the 'arm' of the pot. This helps
a lot to get the signal to stay constant when a bad spot is hit.
You usually have to see how your circuit is wired, but if you want to try it
you can wire two 0.1uf caps in and see how well it works. Sometimes
only one cap works too so you could try that first, but you need to experiment
to find out which side to connect it to. If you connect it to one side the
output of your device might jump up suddenly to a high value when the
device is first switched on, but if you connect it to the other side it
ramps up smoothly. If this is a stereo system for example, on one side
the cap might cause a loud pop in the speaker whereas when it's wired
on the other side it would not bother anything.

I had an old stereo amp that had those 'slide' pots on it for the volume.
One out of the two pots (left and right channels) went bad and started
making very very loud static when i changed the volume. I sprayed it
and it would work for a month, then i'd have to spray it again. The spray
only seemed to work for a little while.

 

[louie]

These pots have the behaviour I've seen before, where if you twist them back and forth vigorously a number of times, the crackliness diminishes. Would that happen in the case of spurious DC?

With DC on an audio pot, the crackling during rotation is very loud. The vigorous turning cleans up the dirty/worn conductors and never lasts. It's just evidence that it is dirty and/or worn and needs at very least, a Deoxit treatment. Usually spraying doesn't last very long as most pots are cheap and are actually worn, not just dirty. Replacement is always best, then check electrolytic capacitors in the circuit for leakage. Old electrolytics are always suspect.

 

[altis]

Digi-pots would be noise free but are possibly a too-complicated solution:

http://www.maxim-ic.com/products/digi_pot/

 

[Canuke]

Thanks for the info guys!