Dodgy pot - Servisol not up to "scratch"

[Jono Bolton]

I picked up an old Peavey head recently, and it sounds amazing, but the volume pot clicks, pops and bangs whenever I turn it; not really  an issue at home, but I probably couldn't use it for gigging as it is. I've used Servisol on it a few times now, and it isn't getting any better. Is replacing the pot the only option or is there something more heavy duty than Servisol that I can use? The amp's probably 40 years old, and has cheap plastic shaft pots, although the others seem to have held up ok.

[Islander]

You could try a small drop of light oil but it'll probably just be a stopgap.  Replacement is the best option.

 

[rmorris]

Oil won't help if there's excessive track wear and after several decades there likely is.

Normally I'd suggest using a Daily DeOxit product. But in this case I'd say simply replace it with a new pot'.

[Islander]

Just now, rmorris said:

Oil won't help if there's excessive track wear and after several decades there likely is.

Normally I'd suggest using a Daily DeOxit product. But in this case I'd say simply replace it with a new pot'.

Yep, I suggested it as a stopgap while the OP arranges to replace the old pot.  It'll help settle and distribute excessive particulate buildup but if the carbon track is that badly worn then it'll have no effect.  

[Phil Starr]

Is the Servisol actually getting inside the pot casing onto the carbon track? A lot of people just spray in the general vicinity and it can't clean what it can't reach.

Having said that 'clicks, pops and bangs'? That sounds like more than the sort of crackly noise you ought to get if it is just a bit of dirt.

[Jono Bolton]

14 hours ago, Phil Starr said:

Is the Servisol actually getting inside the pot casing onto the carbon track? A lot of people just spray in the general vicinity and it can't clean what it can't reach.

Having said that 'clicks, pops and bangs'? That sounds like more than the sort of crackly noise you ought to get if it is just a bit of dirt.

I've been poking the straw on the can inside the wee hole in the pot to make sure the Servisol is getting everywhere. How much Servisol should I be using? I been giving it a fair few big sprays but I watched a video on YouTube where a guy was having the same problem with an old Yamaha and he was absolutely drenching the pots, so perhaps I'm not using enough. Here's said video; the noise from his amp isn't too dissimilar to mine:

 

[Islander]

I usually spray a good amount into the opening in the pot cover by the pcb contacts/wiring tags and work the spindle back and forth quickly a few times.   That's usually enough to clean the track and wiper.  If that's not working after a couple of applications then I'd replace the pot.  Volume pots are usually logarithmic (log) rather than linear (lin) so make sure you check the markings to ascertain this as well as the actual value before you source a replacement.

[Phil Starr]

That's about right from Islander. It isn't worth wasting time if you haven't cleared the problem after a couple of goes. I only asked about the spray because there's an increasing tendency for modern pots to have the two access points sealed.

I've had some problems in the past with decoupling capacitors going short circuit with age, or otherwise being troublesome. The effect is to cause DC to appear across the pot and cause sparking problems which create noise and even pitting. If your amp is really old I'd look for any signs of leaking capacitors. 

The other problem is that the spring on the wiper inside the pot just weakens making contact less secure, often combined with dirt ingress so just cleaning the track is often only a short term fix.

the biggest part of any fix is opening the amp up and removing the board. Once you get to that part replacing components is often just the quickest simplest fix.

good Luck

[Jono Bolton]

9 minutes ago, Phil Starr said:

That's about right from Islander. It isn't worth wasting time if you haven't cleared the problem after a couple of goes. I only asked about the spray because there's an increasing tendency for modern pots to have the two access points sealed.

I've had some problems in the past with decoupling capacitors going short circuit with age, or otherwise being troublesome. The effect is to cause DC to appear across the pot and cause sparking problems which create noise and even pitting. If your amp is really old I'd look for any signs of leaking capacitors. 

The other problem is that the spring on the wiper inside the pot just weakens making contact less secure, often combined with dirt ingress so just cleaning the track is often only a short term fix.

the biggest part of any fix is opening the amp up and removing the board. Once you get to that part replacing components is often just the quickest simplest fix.

good Luck

Luckily, with old Peavey stuff it's really easy to get inside; the head has separate front and back panels so just four screws need to be removed to get into it, and you can leave the back panel in place. I phoned my local amp tech to ask about having it replaced, and I was quoted about £25, which isn't too bad for a job that I wouldn't be comfortable doing myself. They also be better placed than me to identify if it is just the pot that needs changing, and not something else such as leaking caps.

[aitkenaudio]

you want to see if there is dc on the pot.

basically you don't need to put very much in but give it quite a few turns. if thats not working you can take the pot apart and clean the trsck. but usually at that point it's easier to replace the pot if its easy to find