Repairing a broken pot on an amp

J

jndietz

The Way It Moves
'Morning everyone:

My vocalist was loading my amp into the truck and broke the volume knob for the overdrive channel clean off! All the way down to the pot.

I was wondering how I go about replacing this. What things do I need to consider when buying a new pot for this amp? How difficult is it to replace this?

Thanks in advance!

~Jared
 
Pots have several specs. Basic ones:
-value, in ohms
-type, log, lin or rev log (response curve through its range)
-shaft size, threaded part that'll be mounted to the amp faceplate
-shaft shape, 'D', round, split (prob. not on anamp)
-shaft length, how far out the front it extends so the knob will sit right and clear the faceplate.
post layout, when mounting to a PC board - straight out, right angle in a striaght line or not, etc.

If it's newer, it may have posts that connect directly to a PC board, so you'd have to find the right form-factor as well as value and type, etc.. Depending on the space in the amp, you may be able to install a standard pot with wires leading to the PC board if you can't find the right fit. I've done that with broken input jacks when I couldn't find the molded, enclosed plastic 1/4" jack.

Then there's your comfort soldering (and the tools). I buy guitar pots from Stewart MacDonald and the only amp pots I've bought in recent years are for a vintage Ampeg, so I went to a specific vendor who sells accurate replacements. Others can probably suggest favorite suppliers.

Been mostly buying Alpha-brand pots recently and had good experience with them, though I've seen opinions to the contrary around here.

I've been happy ordering components from Newark - caps and ICs.

Lastly, this all sounds worse than it is. I'm sure you can find a good replacement without too much pain.
 
Depending on the amp, some are a lot harder than others. Replacing the pot itself usually isn't that hard of a job but on some amps you have to do a lot of disassembly just to get to it, then a lot of reassembly putting it back together.
 
easiest thing to do is go to the manufacturer... sometimes they'll just send you one for the asking... (ok not often)... but you wont have to fuss over how well it will fit etc...
 
dementedchord said:
easiest thing to do is go to the manufacturer... sometimes they'll just send you one for the asking... (ok not often)... but you wont have to fuss over how well it will fit etc...
Click to expand...

Unless it's a Fender amp, they take forever to reply to any parts request or order.
 
B-52 hasn't even responded to my phone call that I left with them days ago. I'm going to end up e-mailing them and calling them simultaneously every five minutes until I get an answer :D
 
dementedchord said:
easiest thing to do is go to the manufacturer... sometimes they'll just send you one for the asking... (ok not often)... but you wont have to fuss over how well it will fit etc...
Click to expand...

Dunlop sent me a free toggle switch when the one on my Crybaby broke only a few weeks after getting it. Nice guys over there :)
 
just be careful with it and you'll be fine... be methodical about taking it apart... screws in a bowl and such so ya dont lose any that sorta thing... let the iron heat up before trying to desolder the old one... more damage has been done here than anywhere else... when your done the solder should look shiny... if it's dull then it's a cold solder joint and will eventually fail... get plenty of solder on it but avoid overdoing it...
 
dementedchord said:
just be careful with it and you'll be fine... be methodical about taking it apart... screws in a bowl and such so ya dont lose any that sorta thing... let the iron heat up before trying to desolder the old one... more damage has been done here than anywhere else... when your done the solder should look shiny... if it's dull then it's a cold solder joint and will eventually fail... get plenty of solder on it but avoid overdoing it...
Click to expand...

I recommend solder wick (braid) to remove the old solder. Put it next to the contact, heat up the contact, and watch the solder flow away from the pot. That way, there's minimal risk of lifting traces by doing something wrong (e.g. heating a lead while tugging, then accidentally pushing after it is halfway out). After the solder is removed with a braid, the part should pull out easily without heating or anything.
 
jndietz said:
B-52 is sending me a pot for $10.

Sounds all right to me. Hope it isn't too hard to put in... :)
Click to expand...

Seems a Little expensive to me...You can buy a carbon pot of pretty any value for about $1-$4...You will know what Value that is anyways when you go to replace the Pot....

I would simply open the amp Remove the broken Pot check it for its value which should be written on the Pot (If not you can measure it with a DMM)..One you know the Value you just go to an electroncs store with the pot and find one of the correct value and dimentions and replace it...should be able to do it in less than 1 hour....

:D
 
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