Scratchy Sound in Pots - any cure?

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shockletit
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Scratchy Sound in Pots - any cure?

Post by shockletit » Sun Feb 09, 2020 2:23 pm

Sorry if this is covered elsewhere, but I have two modules that have developed scratchy sound in the pots: Sisters filer and Intellijel Quad VCA - only on one knob in each of the units. Is there an easy way to resolve this? The Sisters module is just a little over a year old. The VCA 2nd hand, so can't say. Thanks.

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wackelpeter
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Re: Scratchy Sound in Pots - any cure?

Post by wackelpeter » Sun Feb 09, 2020 2:33 pm

Is this scratching effect mostly when they're near the middle position? then obviously it's the pot... if it's also in their end position with some luck it's just a bad solder point...

had to replace a few of those cheap chinese 6mm pots which look like the Alpha pots... when i noticed that some of my VCO's or VCS' had some jumps in their pitch... noticed it was only when not turned to their end positions, so a bad solder point could be outruled and also no effect on slightly knocking on them...
btw. i had before re-soldered them already which was the first thing to do i had in mind...

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Re: Scratchy Sound in Pots - any cure?

Post by Dave Peck » Sun Feb 09, 2020 5:50 pm

Best stuff is a can of DeoxIT. Get some and watch a couple of videos for info on how to use it.

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Re: Scratchy Sound in Pots - any cure?

Post by KSS » Sun Feb 09, 2020 5:52 pm

shockletit wrote:
Sun Feb 09, 2020 2:23 pm
Sorry if this is covered elsewhere, but I have two modules that have developed scratchy sound in the pots: Sisters filer and Intellijel Quad VCA - only on one knob in each of the units. Is there an easy way to resolve this? The Sisters module is just a little over a year old. The VCA 2nd hand, so can't say. Thanks.
The answer will be different for different types of pots. But can say the answer is almost never the use of a spray-in-place solution like deoxit. So don't do that.

The rated life of panel pots can be as low as 5K turns, and as high as a million plus. Most typically used eurorack pots will be in the 10-15K turns life range. This does not mean they will all last this long. Years passed matter less than use levels. And as wankelpeter says, some do not fare as well as others. The advice to check the solder joints is good.

it's normal that heavily used pots can become worn and scratchy. Filter resonance and cutoff are typical heavily used pots in subtractive synthesis. Replacement is usually easy and inexpensive, but as before said, it depends on the pot. And the abilities of the person attempting the repair.

Scratchy pots can also be caused -or amplified- by the direction and type of current flow through them. It can also be a result of only using two rather than all three of the pins. This would ikely show up as a known issue in a particular mfr or certain modules of same. Since this is an engineering problem, there's not much a typical non-technical user could do in that case.

A photo of the pots in question would be helpful.

And as always, I recommend giving the mfr a chance to address any problem one has with a product. Even if they can't -or won't- fix it, it gives everybody directly involved additional useful knowledge. Please don't interpret this to mean a mfr "should" always fix every presented problem.

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Re: Scratchy Sound in Pots - any cure?

Post by KSS » Sun Feb 09, 2020 6:19 pm

Dave Peck wrote:
Sun Feb 09, 2020 5:50 pm
Best stuff is a can of DeoxIT. Get some and watch a couple of videos for info on how to use it.
Surprised to see this recommendation from you. At least without adding exactly which Deoxit *might* be useful, and with the caveat that there is a "religious" divide between even highly experienced and well-trusted synth techs on the issue. I was typing my warning as you were placing your suggestion.

Strongly suggest research of Caig's Deoxit range of products before use. And that means more than watching videos. You'll quickly find that there are two firmly unified camps; one for and one against. Pro synth techs are more often found in the 'against' camp. With some exceptions as one would expect.

The correct Caig product for a conductive plastic pot is different than the one they recommend for carbon tracks. You're not going to know this from most videos, and you're not going to see it in the shape or style of the pot. Details matter.

What goes under-reported about the Deoxit range of products is a result of the fact that they *do* often present an immediate improvement, but this improvement is short-term and often with devastating and long-lasting permanent destruction. To more than the pot(s) invoived. One such result is damage to PCB traces and components due to overspray. So a person tries it, sees good result, posts a happy video.

Then later, when there's problems, no follow-up video. Sometimes because the person doesn't even see the connection between the prior spray and the 'new' problem.

It's unfair to only mention Deoxit as another often seen recommendation is the use of WD-40. And other goops and sprays as well. Which is why my reply said to avoid "spray-in-place" solutions.

Finally, what a tech might do on tour to get an act through the gig -or to finish an expensive studio session- is not indicative of what might best be done when immediate -albeit temporary- results are not a factor. A good tech will follow-up and make a long-term repair after this kind of 'necessary' quick-fix.

The correct type of Deoxit, used in the appropriate place and manner, *can* be useful. But advice to "use Deoxit" is lacking important information.

FWIW I personally hold Dave Peck in high regard, and would generally trust his advice on synth matters without hesistation. As I said, Deoxit is one of a few 'religious' and polarizing issues. I'm sure he would agree that due diligence is appropriate here. In fact, that's probably what he was aiming for by mentioning the videos. MY experience of meany of those vids is explained above.

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Re: Scratchy Sound in Pots - any cure?

Post by Dave Peck » Sun Feb 09, 2020 7:55 pm

:tu: Yes, All of those caveats and disclaimers from KSS are valid, and it's correct that there are polarized opinions about the use of deoxIT and similar products. I was mostly just too lazy to offer a more thorough reply that included both viewpoints.

As KSS explains, Replacing the pot is probably the best way to address it with the most long-lasting results, but some people may just want a quick fix for now.

Try this - in many case, you can at least temporarily fix a scratchy pot just by working it back and forth several times. And this doesn't introduce any chemicals into the synth that may or may not have detrimental effects later.
:cloud:

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Re: Scratchy Sound in Pots - any cure?

Post by shockletit » Mon Feb 10, 2020 4:42 pm

Many thanks for the info guys. Won't use the spray (just yet) ;).

As the question was asked above - the scratch on the Sisters is in the Quality knob at about 9 o'clock, not at the bottom of the LH range but up from it a bit, so think I can rule out soldering? Expect it's dust or something. The VCA on the top linear/exponential stick knob all over the place (would expect that one just to be wear/age).

Again, thanks for the replies.

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Re: Scratchy Sound in Pots - any cure?

Post by umma gumma » Mon Feb 10, 2020 9:08 pm

I have heard that Faderlube works better than deoxit, as it doesn't flush out all the lubricant in the pot, and the pot doesn't become loose and lose it's "feel" afterwards

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Re: Scratchy Sound in Pots - any cure?

Post by bitflip » Mon Feb 10, 2020 9:20 pm

I recently used CRC QD Electronic Cleaner on a scratchy input pot - just put the straw into an opening and gave it a short blast. Pot's scratch-free from end to end now. :tu:

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Re: Scratchy Sound in Pots - any cure?

Post by KSS » Mon Feb 10, 2020 10:42 pm

umma gumma wrote:
Mon Feb 10, 2020 9:08 pm
I have heard that Faderlube works better than deoxit, as it doesn't flush out all the lubricant in the pot, and the pot doesn't become loose and lose it's "feel" afterwards
Faderlube is another category of goops where you need to be specific as to what you're using and where-how you're using it. Again there is a difference between what works for different types of resistive tracks in pots. The wrong type for the job is not a good thing.

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Re: Scratchy Sound in Pots - any cure?

Post by KSS » Mon Feb 10, 2020 11:34 pm

bitflip wrote:
Mon Feb 10, 2020 9:20 pm
I recently used CRC QD Electronic Cleaner on a scratchy input pot
Please promise to update us in a year.

If you read the applications for this, you don't see "pots" listed. You might choose to include them under "electronics" which *is* listed on the can and in the instructions. But keep in mind that most generally named 'electronic cleaners' are intended to clean switch contacts, and to degrease.

If you read the material safety data sheet -which is available on the CRC website- you see 4 ingredients listed.
The first is naptha AKA lighter fluid at 40-50%, and is often used to remove sticky crud from surfaces. Like the adhesive remains left after a longtime sticker is removed from a synth, window, wall, or other surface. If you've ever done this, you know it takes considerable active physical action. Inside a pot the only action you can apply is the force of the spray -watch out for overspray- and the movement of the wiper over the track. Typically a multi-fingered springy metal stamping tracing and re-tracing the same path over the track surface.

The second ingredient is 1,1-difluoroethane at 20-30%, AKA Refrigerant HFC-152a, here used as a propellant. It will also offer a cooling function to 'freeze' off particles.

The third listed is 2-methylpentane, also at 2030% is something you might want to look up before using. Nasty stuff.

Fourth is n-hexane at only 3-5%. Another nasty, It's likely used here as an oil solvent.

Knowing this, we can make an informed guess as to what happens when you squirt it into a pot. it's going to saturate a carbon track, and dissolve crud on the surface of both carbon and conductive plastic elements. The propellant will dissipate quickly, having brought the other ingredients to the surface and having cooled the surface through expansion as it evaporates. The effect of this cooling will depend upon how much is used.

In the typical case, one would spin the pot a few times after application, to both "spread it around inside" and also after to test its effectiveness. The pot wiper will aid in this spreading, but it can have secondary effects too.

First is that the multi-fingers of the wiper will re-arrange the crud into 'walls' on either side of their tracing path. Essentially building little canals to later catch and retain new crud as it enter or is worn from the pots own miving parts. Making the problem worse than before.

If you've already got a scratchy pot, you might also have a scratched wiper. More likely with abrasive carbon tracks than conductive plastic, that's one reason why CP (conductive plastic) pots last longer. This scratched wiper means that as you rotate the pot with the cleaner in place, it is grinding the goop and crud into the track. If there are already scratches in the track, they may be filled with the crud. One might say, at least they're no longer on the surface making the wiper bounce. It's like cleaning a bedroon by hiding everything under the bed with a quick push.

As I wrote earlier , initial results with sprays can seem effective. But think about what's going to happen later.

You've not really removed any crud from the pot. Only pushed it around. But you have -potentially- removed some or all of the mfr applied lubrication. And you might have ground the crud into the wiper or track. Worst case, maybe an abrasive carbon bit is now sitting in one of the wiper's scratches. Or captured between two of its fingers. Where it's currently making excellent contact of carbon on carbon. Only over time it digs an even deeper groove into the track, or scratches the wiper more, or breaks down part of the 'canal walls' and potentially destroys the wiper as well if it should catch during rotation do to the added physical roughness due to all these factors.

And I didn't go into that naptha solvent saturated carbon track and those effects. But I'm sure that can be easily understood.

This is not meant to be a scare all, these same kinds of things are happening with any pot over its lifetime. But it is a goal in typing this to have one think carefully before applying a squirt-in-place, so-called 'solution' to a scratchy pot problem.

The only truly effective way to properly clean and lube a pot is disassembly, cleaning, perhaps polishing the wiper to remove scratches, adding lubrication, and re-assembly.

For many to most pots, this isn't worth the time and effort, when equal or better quality replacements are available. Replace is the best solution.
Expensive, higher quality pots are expected to be rebuilt over their life. But you're not likely to find these in a eurorack module.

Ultimately, it's in one's best interest to actually take an interest in what's happening with the choices you have before you. Consumer aimed quick solutions may not be the best -or even good- path forward.

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umma gumma
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Re: Scratchy Sound in Pots - any cure?

Post by umma gumma » Tue Feb 11, 2020 2:01 am

great post, thanks for taking the time to write all that up!

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Re: Scratchy Sound in Pots - any cure?

Post by Graham Hinton » Tue Feb 11, 2020 8:16 am

If a pot becomes scratchy it is because the track is damaged and the only solution is to replace it. If you can get a spray inside the pot it is a cheap open type and not worth repairing. All pot tracks are made by silk screen printing a carbon loaded ink onto a substrate--basically it's T-shirt technology, the same as an ident on a pcb. What varies is the quality of the carbon ink and the design of the wiper, but once a track is damaged there is no way back. Lower quality cheap carbon pots (which are used in most modules) have a rough surface as the ink dries and wears more easily and are usually rated about 10,000 turns. Better conductive plastic pots have finer grain ink and may be rated for 1 million turns. The very best quality Penny and Giles faders have a mirror finish track made by printing onto a polished mirror and then casting epoxy around it, but you won't find those in (m)any modules.

One thing that reduces the life of a pot is using a knob that is too large, as is sometimes done on modules for certain functions, e.g. filter frequency. The extra torque just gouges out the track and drastically reduces the lifetime. If you are going to do that it needs to be a better pot than the rest of the module and definitely not one with a plastic shaft and no bushing support.

I spent 15 years looking after an SSL console in constant use and I can tell you that even expensive sealed conductive plastic pots get worn out and need replacing. A good design makes it easy to replace pots when that happens. Cheap consumer mixers are disposable items because the labour to remove all the pots to get at the pcb is more than the item's value. The number of synthesizer modules with low quality pots is a time bomb waiting to go off and you won't want to be told it's a disposable item when that happens. Did you think to check pot quality when you bought it though? Did you think to obtain spares when they were available?

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Re: Scratchy Sound in Pots - any cure?

Post by Blairio » Tue Feb 11, 2020 2:20 pm

Graham Hinton wrote:
Tue Feb 11, 2020 8:16 am
The number of synthesizer modules with low quality pots is a time bomb waiting to go off and you won't want to be told it's a disposable item when that happens. Did you think to check pot quality when you bought it though? Did you think to obtain spares when they were available?
To be fair these are not part of your average eurorack hobbyist's requirements capture. Agreed that most of us hobbyists don't scrutinise MTBF stats, before we wonder why module 'x' is so affordable.

However most Eurorack vendors make a decent fist of supporting their customers. I have experience of two such who have replaced noisy pots outside of warranty, for the cost of postage.

Perhaps the OP should contact the manufacturer - even if they are not the first purchaser of the module, and explore the costs of pot replacement?

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Re: Scratchy Sound in Pots - any cure?

Post by Pelsea » Tue Feb 11, 2020 2:36 pm

" The number of synthesizer modules with low quality pots is a time bomb waiting to go off and you won't want to be told it's a disposable item when that happens. "

In my experience, that time bomb is set for about 10 years of heavy use, at least for quality products with sealed pots. The other time bomb is the jacks. They will crud up (due to oxidation) in about 15 years, even if never used. (Subject to climate in your area.)
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Re: Scratchy Sound in Pots - any cure?

Post by Blairio » Tue Feb 11, 2020 10:02 pm

Pelsea wrote:
Tue Feb 11, 2020 2:36 pm
" The number of synthesizer modules with low quality pots is a time bomb waiting to go off and you won't want to be told it's a disposable item when that happens. "

In my experience, that time bomb is set for about 10 years of heavy use, at least for quality products with sealed pots. The other time bomb is the jacks. They will crud up (due to oxidation) in about 15 years, even if never used. (Subject to climate in your area.)
I have a DSI Mopho keyboard and DSI Tetr4. Last year I had to have all the midi sockets replaced on both, as they had corroded to the point that midi information was being scrambled. Both units are 8 years old. The two units are 'chained' together so that I have (1 + 4 ) 5 voices in total. The plugs on the midi cable used to connect the two were so corroded, it needed loose-oil to remove them from the sockets.

I mentioned this before on another thread and from memory the conclusion was some kind of galvanic reaction. Once the midi sockets were replaced (many thanks to DSI's customer service dept) I used only very high quality cables and every so often I pull then out and check the problem hasn't come back.

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Re: Scratchy Sound in Pots - any cure?

Post by twistedneck » Thu Feb 13, 2020 7:08 pm

I kept it simple, sprayed in contact cleaner through the open crevasse near the terminal of the pot, then air, then contact cleaner, then air.. then done. cured, no more scratch.. but now I probably am contaminated and my module will fall apart after a few years.

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Re: Scratchy Sound in Pots - any cure?

Post by Pelsea » Thu Feb 13, 2020 7:21 pm

twistedneck wrote:
Thu Feb 13, 2020 7:08 pm
I kept it simple, sprayed in contact cleaner through the open crevasse near the terminal of the pot, then air, then contact cleaner, then air.. then done. cured, no more scratch.. but now I probably am contaminated and my module will fall apart after a few years.
You may extend the life a bit by applying some Caig (De-oxit) F series lubricant.
https://caig.com/fader-f-series/
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Re: Scratchy Sound in Pots - any cure?

Post by KSS » Thu Feb 13, 2020 7:25 pm

twistedneck wrote:
Thu Feb 13, 2020 7:08 pm
I kept it simple, sprayed in contact cleaner through the open crevasse near the terminal of the pot, then air, then contact cleaner, then air.. then done. cured, no more scratch.. but now I probably am contaminated and my module will fall apart after a few years.
If you used contact cleaner it might be well less than a few years. Contact cleaner and pots/pcb traces are a bad mix.

If one absolutely feels the need to use some spray-in-place solution, get one of the pressurizable cans from Harbor Freight or similar distributor, and fill it with the purest alcohol you can find. Drug stores usually have 70% and 90%+ can be found without too much searching. This setup can be useful for other things a synth DIY person or Tech might need. I am NOT suggesting it as a good practice for cleaning scratchy pots. But it's much safer/better choice than contact cleaner, and will perform in place of many other proprietary sprays. A bicycle pump works to pressurize the can

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Re: Scratchy Sound in Pots - any cure?

Post by Severed head » Thu Feb 13, 2020 11:15 pm

Blairio wrote:
Tue Feb 11, 2020 2:20 pm
Perhaps the OP should contact the manufacturer - even if they are not the first purchaser of the module, and explore the costs of pot replacement?
I have had pgh modular, intellijel, & mutable
All repair 2nd or 3rd Hand modules for nothing more than round trip shipping.

And had numerous pedal manufacturers do the same.

It seems of the last couple years any company worth their salt is more concerned with the quality of their commodities than who or when the said commodity was purchased
WTB: modules, MA35 filter.
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