Replacement volume knob issue.

mattyfez

mattyfez

mattyfez

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Joined
12 Apr 2007
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Hey all,

Not sure if this would be better in the HiFi forum, but I guess it's more of a general electronics question.

Basically I have an old guitar effects unit, which is a rack-mount pre-amp for all intents and purposes. Its out of production and well out of warranty.

It works 100% fine apart from the volume knob, which takes a lot of fiddling to get any sound at all, or crackly sound. if its in just the right position it works fine with a clean sound. I've tried giving it a good spray with some iso alcohol to maybe clean it a bit but its made little difference.

So I figure I need to rip the volume pot off, and solder in a new one.
It looks to have 6 pins soldered onto a little PCB, whos only purpose is seemingly to feed into a 6 wire ribbon cable.

I know nothing about this sort of stuff but it looks like an easy job..

My question is, what's commercially available that's good quality? maybe somewhere like maplins? or something more audio specific?

I cant see any markings on the volume unit, so not sure if there are different types/resistance etc.

Some pics below, thanks for any tips...

20130623_190032_zps6dcae730.jpg



20130623_185957_zpsbbcd79db.jpg


20130623_185930_zps87804d83.jpg
 
It'll just be a stereo log scale potentiometer I would have thought.

You'll have to have a look at it to see which resistance it is. It could be 10k, 100k or something else more exotic. They also call them audio taper sometimes rather than log but it's the same thing. The rating should be stamped on the side. If not you can measure using a multimeter across the two outside pins of either channel.

It doesn't look like anything special but you will have to get something physically similar otherwise it won't match the holes in the PCB.
 
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Ok thanks that's some food for thought, I might drop the manufacturer an email and see if they can suggest something, as like you say I'm not sure if it has to be a particular resistance.

It doesn't look like a special part, I just want to get the bleeding thing working properly again! hah.

Thanks
 
neodude said:
It wouldn't really need to match the PCB. That's why god invented wires ;)
Click to expand...

well yes, the pcb doesn't seem to be there for any reason, so if I can just source the correct type of knob, I can get it soldered onto the PCB or straight onto the ribbon cable without much hassle.
 
Could just be lack of use/dirt - get some contact cleaner and spray it into the pot then work the knob back and forth through its full rotation for 5 min - you really need to work the dial a couple of hundred times, not just wiggle it a little bit.. Cheap fix from a guitar tech/repair guy on youtube (davey4557).
 
mattyfez said:
looking at it more closely, the volume knob has six pins but the cable only has 5... hmm and only 4 of them seem to be 'wired up'
Click to expand...

The top two contacts in the last image are routed to ground, which is a common connection. Ground will be a whole ground plane within the multilayer PCB. It works well like this and PCB often have several ground planes. The middle two contact are connected top the wiper of the potentiometer. The bottom contacts are where the inputs are connected.
 
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jumpy said:
Could just be lack of use/dirt - get some contact cleaner and spray it into the pot then work the knob back and forth through its full rotation for 5 min - you really need to work the dial a couple of hundred times, not just wiggle it a little bit.. Cheap fix from a guitar tech/repair guy on youtube (davey4557).
Click to expand...

That's exactly what it is I think, lack of use, it's basically been sat in the cupboard for about 10 years but its quite an expensive bit of kit so I want to get t fixed.

I have used some pure alcohol/contact cleaner although I've not wiggled it a hundred times, maybe I just need to work the knob more :o, but the 'volume unit' doesn't have many holes in it so I wasn't sure if it was worth messing with.

But I'll attack it a second time with some more pure alcohol. I've also sent the manufacturer an email so I'll see if they can recommend anything.

Thanks for the advice so far :)
 
if you're replacing the volume knob anyway then it could be worth considering a new one which goes up to 11... then you can be 1 louder :D

 
Tealc said:
The top two contacts in the last image are routed to ground, which is a common connection. Ground will be a whole ground plane within the multilayer PCB. It works well like this and PCB often have several ground planes. The middle two contact are connected top the wiper of the potentiometer. The bottom contacts are where the inputs are connected.
Click to expand...

Ahh thanks for that, so the top two aren't there just for show! I didn't think the PCB would be multi layered, but then I'm not well up on these things! Cheers :)
 
scrlk said:
There's only one sane thing to do, and that is to buy this replacement knob:

SWb58l4.png
Click to expand...


That is quite bizarre as whenever I see or hear Audiophiles mentioned, I always think: Knobs.

Most of them have their heads so far up their own arses it's a ****ing miracle they can hear anything.
 
doofer said:
That is quite bizarre as whenever I see or hear Audiophiles mentioned, I always think: Knobs.

Most of them have their heads so far up their own arses it's a ****ing miracle they can hear anything.
Click to expand...

They're a bit like alternative medicine or spiritual types... they have a set of beliefs that they like to stick to or want to fee special about and there are suppliers out there ready to pander to them

expensive speaker cables/interconnects are one area people get conned - though in some ways I can see why otherwise sensible people might get suckered into that... though when you then see digital cables and kettle leads getting the gold plated/magic pixie dust treatment and people claiming that their superior ears definitely can tell the difference (of course this isn't something they've actually tested under a double blind test) then there isn't much point in arguing with them

worst part is that the reviews in hi fi publications aren't generally objective and help spread the myths... people claiming all sorts of things about expensive HDMI cables when in reality the best they could do in theory is have less errors (which any properly made hdmi cable should have very few of anyway) - not improve the contrast etc...
 
We are kinda going off topic here, we are talking about a broken volume pot, not how to improve the transient vibrations of molecules through the medium of thought and prayer. ;)
 
I've actually found a direct brand new replacement on the bay, for 14 bucks, plus shipping it from the USA will end up quite expensive. it's listed as "Digitech Output Potentiometer volume pot for many units GSP2101 2112 2120"

Seems a lot for a basic knob though, and it doesn't list any tech specs, which is annoying as I cant just spec up a similar thing locally.
 
It's worth checking if it is actually a logarithmic pot, it might be linear.
Most are log10K, some are log1M

Alps is a good make, used on many amps, try eBay.
That doesn't actually look like an expensive pot to me, so don't spend more than a few quid.
 
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Good news! Jumpy was bang on the money...

Got a reply from the manufacturer: "In the USA, call 801-566-8800 and ask for Digitech parts to order pot # 40-2011. You may also try spraying your 2101 output pot with DeOxIt, available at most electronic stores."

I interpreted this as 'drench it in solvent' and 'give it some welly'

I've given it a good clean with some surgical spirit, soaked into a bit of towel to try and squeeze it into the openings in the vol pot (and lot's of knob twisting) without actually removing or de-soldering anything.

It's a million times better, there's still a little bit of crackle when adjusting the knob, but when the knob is stationary, it sounds clean as a whistle, it works almost perfectly! I think another treatment or two and it will be spot on :D
 
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