Pot Cleaning (please help)

[Dave]

Hi everyone. Before you ask I did attempt a search on this topic and didn't find anything directly relevant to my query. Basically I have a couple of old Marshall bass amps with scratchy/crackly (actual words?) pots and I want to get this sorted. After searching this site I did find out about a product called Servisol, and someone else mentioned getting some Maplin Switch Cleaner to spray on the pots, but I'd still like a little more info. If I purchase one of these products do I simply spray them on the outside of the volume/EQ knobs (should I try to remove the plastic knobs first before using) or do I actually need to do something internally to get rid of the problem?

I also read how the dust/dirt can build up from lack of use (I have a feeling these amps were stored unused for long periods of time), and some people have simply twisted the knobs frequently to get rid of the crackling sound. Does this really work? I'd be happy to remove the knobs if this would allow better access and lead to improved results, though I'm not sure if I should simply try to pull them off or not (I'm somewhat worried about damaging them)? Any suggestions as to how I can make my playing/adjusting less crackle-y would be (as ever) GREATLY appreciated! If you think I need to seek a professional to sort out this problem, then any recommendations would also be appreciated (I'm based in the Midlands/Birmingham area). Cheers!

[Musky]

You need to apply the switch cleaner from the back of the pots, which will mean opening up your amp. The pots will probably have a small access hole in the rear, though some are completely sealed. Use the small tube supplied with the switch cleaner to get it in there, and turn the knobs to dislodge any dirt.

This might have to be repeated from time to time to keep them crackle-free, but if it doesn't sort out the problem the pots will need replacing. It's not a big job, and you can do it yourself if you can handle a soldering iron (though if it's a valve amp be wary of the voltages of even an unplugged amp). As far as I remember Marshall used knobs that were held on by a screw on their older amps (not sure about the newer stuff) and it's simple enough to remove them without causing any damage, should you need to do so.

Edited October 30, 2008 by Musky

[Dave]

Cheers for the info, Musky! I also copied this thread to the technical section and received a number of useful responses there. With regards knob removal, I assume if I don't see a visible screw holding the knob onto the stem (from the outside) then it is likely I can simply pull the knob straight off? I'm never sure if they glue these things on or how they are attached, which is why I don't want to use any excessive force for fear of breaking something (and then having one wonky knob or having to replace them all to match). I can't believe I just typed wonky knob!

I must also admit I'm somewhat curious about the whole pot cleaning idea. After cleaning it to remove the crackling, where does the dirt actually go??? Seems almost mystical.

[Musky]

Yeah, I noticed the other thread after I posted here.

The knobs should pull straight off (ooo-er!) without much difficulty and shouldn't be glued, though you never know what strange things a previous owner might have been up to. They use a split shaft on the pots, which someone might have opened up slightly to grip the knob a bit tighter, but either way the knobs should just require a little force. I have heard of someone managing to pull the whole shaft out of a pot, but realistically this is a pretty unlikely scenario. In any case, you don't have to remove the knobs unless you actually want to remove the pot, which isn't necessary to clean them.

Incidentally, any dirt in the pot will probably stay in there, but using switch cleaner and turning the knob will clear the dirt from the track.

[Dave]

Thanks ever so much for your suggestions/help, Musky, I really appreciate it! So much conflicting info on the net, I guess I shouldn't really be surprised. Some suggest WD40 is OK, others say it definitely should NOT be used. Some say you can clean the pot by simply spraying cleaner down the stem/shaft to get to the inner workings, while others say you definitely have to take it apart. Use compressed air, contact cleaner, oil/grease-free lubricant, the options/opinions are endless. Think I'll try to use common sense, try a few obvious things first, and delve deeper as required.

[SS73]

With most pots there is an opening near the solder contacts that gives access straight to the pots track.

Servisol is a good product that will sort a mildly scratchy Pot. For real stubborn ones you can try Isopropl alcohol, (its very pure so there should be no ill effects hoho ) Servisol will lubricate to a certain degree and Isopropl will not. But, both will dissolve any grease that lubricates the pot shaft and if there was a lot of grease to start with, it will thin this and spread this around the pot track, which is the last place you want it, so if a little dosen't work then its time to replace the pot. WD won't help.

Sean.


[quote name='Dave' post='318370' date='Oct 30 2008, 02:07 PM']Thanks ever so much for your suggestions/help, Musky, I really appreciate it! So much conflicting info on the net, I guess I shouldn't really be surprised. Some suggest WD40 is OK, others say it definitely should NOT be used. Some say you can clean the pot by simply spraying cleaner down the stem/shaft to get to the inner workings, while others say you definitely have to take it apart. Use compressed air, contact cleaner, oil/grease-free lubricant, the options/opinions are endless. Think I'll try to use common sense, try a few obvious things first, and delve deeper as required.[/quote]

[thinman]

As mentioned above, some pots contain a grease that helps give them a damped "quality" feel. Servisol can wash that out and your knobs won't feel quite the same afterwards.

[Mottlefeeder]

If you haven't picked it up already, the WD in WD40 stands for water repellant or something similar. It isn't a cleaner and it isn't a lubricant.

You need to get a can of something that says it is an electrical switch or contact cleaner.

[Dave]

[quote name='Mottlefeeder' post='320542' date='Nov 2 2008, 10:27 PM']If you haven't picked it up already, the WD in WD40 stands for water repellant or something similar. It isn't a cleaner and it isn't a lubricant.

You need to get a can of something that says it is an electrical switch or contact cleaner.[/quote]

Yeah, I assume WD stands for Water Displacement, or something along that ilk. The Servisol I bought is labelled as contact/switch cleaner, so I assume that's the stuff I need. I have seen some more expensive products on ebay (Deoxit, which a lot of the Yanks seem to prefer) but figure I'll give this stuff a try first, since a lot of the people over here seem to use it to clean out their pots with some success.

As for the lack of lubricant, Thinman, I have read about that problem as well, but must admit my Marshall knobs don't feel particularly smooth even now, so if I clean out the pots and notice a detectable difference, I guess I'll need to address that problem next!

Cheers!