Flint's method for cleaning potentiometers

[Flint]

ATTENTION: Read the following posts in this thread before proceeding to use this method for cleaning a potentiometer. I will no longer be using it.

While my method is very common, I don't want to start a war about what method is most ideal, so this is the way I do it.

The electronics in my demo setup, the rig I use to show off speakers I've built, consists of a source (Turntable, CD Player, Echo Dot, or Portable Hi-Rez Player) and a good Parasound P3 analog stereo preamp. The preamp feeds any number of amplifiers connected to speakers to demo.

My current setup includes three Parasound HCA-Series amps actively driving my Rocketman speakers. To get the lowest noise and cleanest sound, I turned down the gain of the amplifiers so that they are about 12dB below the full gain, or about halfway down from maximum on the input controls. However, these amps are old and the tweeter amp was cutting out or, worse, getting fuzzy sounding. I could simply play with the gain control and make it work again, but then I was no longer calibrated.

So, I decided to clean all the pots on all of the amps.

After turning them off, removing the power cables and placing each one where it would be easy to work on with plenty of lighting, I took the top cover off and located the input gain potentiometers on the rear panel.

The electrical leads which come off the main body of the pot expose an opening to the inside of the pot. See the opening under the label "1" in the photo of a pot below:

I started by using some compressed air to blow out any dust or loose lint which may have collected inside the pot. I directed the straw from the can right
at the top edge of that opening I pointed out and pressed the nozzle for a couple of very short bursts.

Next I took a can of aerosol Caig DeoxIT D5 as seen below and similarly directed the end of the straw to the opening in the pot and pressed the nozzle for a single, very quick burst:

I then turned the control knob for the pot back and forth about 20 times, fairly aggressively. I then rotated the control to the opposite limit from the first spray and sprayed another fast burst into the pot. I repeated the turning of the knob about 50 times, very aggressively and after a certain point the resistance loosened and the pot turned fairly easily.

After I did that for one pot, I then repeated the process on the second input gain control pot.

Once I was done cleaning the pots, I then use a product called Caig PreservIT as a conditioner for the electrical surface of the pots. I don't believe they still make that specific product, but they do have a preservation & lubrication product which replaced PreservIT.

Just as with cleaning, I turned the knob fully in one direction, sprayed a fast spurt into the pot, then turned the knob back and forth dozens of times. Then I turned the control to the other extreme and repeated.

After putting the cover back on the amp, I was able to extremely accurately calibrate the gain of all the amps with ease and the issues I was having with fuzzy signals and cutouts was all gone.

Back in my recording studio days this was a regular cleaning process performed on all the gear in the studio on a scheduled basis, usually twice a year. Since I didn't allow smoking in the studio that was enough. If you smoke around electronics, the charged ions in the smoke are attracted to the conducting surfaces of the gear and build up and block the signal over time, so cleaning needs to be performed more often.

 

[MakeMineVinyl]

I don't really long onto this forum anymore, but this post is something I must take strong exception to; if you do follow this procedure, you will eventually ruin the potentiometers in your gear.

First, De-OxIT is expressly made for metal-to-metal contacts only. That fact is stated several times on the can, and is plainly visible in the picture - its right at the top of the can.

A potentiometer is not metal to metal. Only the wiper is metal. The resistive element which the metal wiper contacts is almost always a carbon compound. The pot in the picture is such a unit. The use of any cleaner which has ingredients other than solvent will cause the carbon to soften, which will make it wear from the metal slider moving over its surface. Your potentiometer may sound just fine for awhile, but you are absolutely doing more long term harm than good.

If you happen to have a high cost conductive plastic potentiometer, Caig Laboratories has a cleaner specifically made for these. Plastic does not absorb liquids like carbon does. Conductive plastic potentiometers and faders are used almost exclusively in analog mixing consoles and related professional gear. Some high end home gear might also use them, but they are generally too expensive for non-professional use.

If a potentiometer is "noisy", it might not even be from dirt or airborne films accumulating on the carbon track. The metal slider usually wipes foreign material from the track anyway. In those instance where there is some kind of material on the track which cannot be dislodged by simply moving the pot back and forth rapidly, either use a solvent-only cleaner, or one which is expressly intended to not harm carbon tracks (if you can find such a product). Radio Shack used to make a solvent-only cleaner. These cleaners contain no ingredients which remain after the solvent evaporates; all they do is dissolve and flush away any foreign material on the track.

Sometimes, the problem is not from a polluted track, but because there is DC voltage present because of a leaky electrolytic capacitor somewhere upstream. A good way to tell, is that if the pot makes noise in the absence of audio signal, then its probably DC leakage. If it makes noise only with audio present, then the pot is probably actually dirty.

Potentiometers absolutely hate passing audio in the presence of DC. If this is what is making the noise, the only solution is a repair shop.

I know, I know there are zillions of people who probably will swear that using products like De-oxIT on carbon based pots is just fine. It is...for awhile. Sorry, they are wrong. They either don't or can't read the simple language on the can. Anybody who actually services the gear in a recording studio would be fired if they used that stuff on anything but switches, metal jacks etc.

 

[Flint]

Well, hell.

Thanks for posting. I learned this decades ago watching studio technicians in Nashville, NY, and Los Angeles using DeoxIT. Then when I opened my studio I attended a trade show and a Caig rep showed me this method as well.

I wish I had known more back then.

Do you think I've ruined every carbon potentiometer I've cleaned?

 

[MakeMineVinyl]

Yes, at the least you've softened the carbon track, shortening the life of the pots.

I know people who use DeOXit on these pot too. The misconception is common; hell, I've even done it on gear I don't care that much about, just to get rid of the noise for a week or so (the noise always comes back). I've owned an 8 track studio, and worked in probably a half dozen big studios (Sound City, Ike Turner's Bolic Sound, Record Plant among others not to mention JBL, Altec, and currently ATI), and I've seen DeOXit D5 mis-used several times. However the majority of the time CaiLube is used for conductive plastic pots and faders (Penney and Giles etc), but even this is not great on carbon because carbon absorbs the residue and this causes the carbon to soften.

By the way, pots never need to be "lubricated". They don't come from the factory that way, and they don't need it later. If the wiper is scoring or otherwise damaging the track, something is terribly wrong and the pot needs to be replaced. Also, added lubrication just attracts debris.

By far the best way to clean a carbon pot is to open it up by bending the tabs and cleaning the track with a Q-tip moistened with alcohol or some other solvent. I used to use 1-1-1 Trichlorothane or Freon before they became impossible to get. Many studio grade carbon pots are sealed and don't ever get dirty. The Allen-Bradley or PEC pots fall into this category.

As for the Caig rep saying that using De-OXit on carbon pots is OK? I don't know what to say other than I have witnessed company reps say inaccurate things right in front of me at companies I've worked at. Sometimes they're just as unaware as anybody else, and just say things they haven't really researched cuz it takes time to do research.

I could probably find dozens of "experts" who would say I'm full of shit. Whatever.

 

[Flint]

Well, heck.

Never mind.

 

[team_tsp]

If a potentiometer is "noisy", it might not even be from dirt or airborne films accumulating on the carbon track. The metal slider usually wipes foreign material from the track anyway. In those instance where there is some kind of material on the track which cannot be dislodged by simply moving the pot back and forth rapidly, either use a solvent-only cleaner, or one which is expressly intended to not harm carbon tracks (if you can find such a product). Radio Shack used to make a solvent-only cleaner. These cleaners contain no ingredients which remain after the solvent evaporates; all they do is dissolve and flush away any foreign material on the track.

Sometimes, the problem is not from a polluted track, but because there is DC voltage present because of a leaky electrolytic capacitor somewhere upstream. A good way to tell, is that if the pot makes noise in the absence of audio signal, then its probably DC leakage. If it makes noise only with audio present, then the pot is probably actually dirty.

Potentiometers absolutely hate passing audio in the presence of DC. If this is what is making the noise, the only solution is a repair shop.

Something I've noticed with the volume knob (potentiometer) on my Parasound 2100 preamp, is that it will occasionally make crackling sounds when I turn it, whether manually or via the remote control, and whether music is playing or not. I find that if I turn the knob a couple times, it goes back to being quiet for another month or so, before I need to repeat the process. Is this an example of some dirt getting on the carbon track?

I wasn't sure about the next paragraph you typed, since you mentioned noise in the absence of an audio signal, and noise only with audio present, can indicate different things. But in my case it can make crackly sounds either way. Just trying to understand what I'm experiencing with my preamp, thanks!

 

[MakeMineVinyl]

Since you hear it without signal, the first thing I would suspect is DC leakage. You can check it out by measuring across the two outside terminals with a DC voltmeter. If you measure any DC at all, it needs to be repaired at a shop. Its not something you can do yourself. If there is no DC, the pot is probably shot. Contact cleaner won't fix it any better than just spinning it like you are already doing.

 

[team_tsp]

Since you hear it without signal, the first thing I would suspect is DC leakage. You can check it out by measuring across the two outside terminals with a DC voltmeter. If you measure any DC at all, it needs to be repaired at a shop. Its not something you can do yourself. If there is no DC, the pot is probably shot. Contact cleaner won't fix it any better than just spinning it like you are already doing.

Thanks for the ideas! The preamp is just a little over a year old, so I hope the pot isn't shot already, but I know there are always manufacturing issues, etc.

Also just curious, if it was DC leakage, would the crackling stop after turning the potentiometer a few times?

 

[MakeMineVinyl]

Thanks for the ideas! The preamp is just a little over a year old, so I hope the pot isn't shot already, but I know there are always manufacturing issues, etc.

Also just curious, if it was DC leakage, would the crackling stop after turning the potentiometer a few times?

If the problem is DC leakage, then nothing you do to the pot will eliminate the problem. The leaky capacitor must be replaced. By rotating the pot, you are "burninshing" the track somewhat which might temporarily cover up the problem, but that is just a band-aid, not a fix. If the problem is actually a defective pot, then it has to be replaced. No potentiometer lasts forever, although they should easily last a decade or more depending on how much use they get.

Frankly, I'm amazed that this is happening to a preamp which is just over a year old. That most certainly should *NOT* happen, manufacturing issues or not.

 

[malsackj]

I used the Trichlor cleaning agent also and still have a small amount. I have used the 98 percent alcohol also. The De-ox lube I was told was for the slide rails. I clean and lube the rails but not the surface of the resistor.

 

[MakeMineVinyl]

The thing is, Caig Laboratories has always been cagey about where to use their products. They never say where you cannot use something, which I think is a bit self-serving to not turn away any potential sales.

Their knowledge base sheet (https://system.na3.netsuite.com/cor...&c=ACCT113328&h=eae6764a200575e713ca&_xt=.pdf) says that carbon pots with metal wipers "respond best" to D100-S2 DeOxit. I don't know what the hell "respond best" exactly means; to me its more important that the chemical does not degrade the pot after the passage of time.

As I stated before, the safest method is a solvent only spray, or opening the pot up and cleaning the carbon track with a Q-tip and solvent like alcohol. Caig does not make a solvent only spray.

Whatever chemical you might spray into a potentiometer, there is going to be one side effect which is hard to avoid. The lubrication which surrounds the rotating shaft will likely be flushed away, and the pot will turn more freely. How you look at this is up to you. Manufacturers intentionally inject thick lubrication around the shaft and bushing to give the pot a "luxury" feel. The lubrication damps out roughness which might be felt without the lube. Cleaning the carbon track manually by opening up the pot avoids this.

Whatever.......