VOXAC15c1 loose treble knob help!

[zamyloo]

Hey guys just looking for some advice before I contact KORG for further assistance. So, Ive got a VOXAC15c1 and for a while now the treble knob was always a little loose and it didn't bother me since it didn't make any crackling or anything and was still pretty sturdy. Well fast-forward to yesterday and the treble was directly effecting the sound of the amp in that the sound would only cut through when the treble was in a certain position or i pulled up on the loose knob. I was able to get the knob off and try to insert it back into the slot to see if I can get it to work but now it won't go in all the way. I've made sure to check the pot inside the amp and there does not seem to be any damage whatsoever. It is very confusing because if i get the knob into the slot it is very loose and if i pull up on it, it holds and the sound cuts through but once i release the knob there is little to no sound. All tubes seem to be on and working so I have ruled that out (unless them on doesn't neccesarily mean they are working). Any sort of advice would help, thanks.

[g1]

Do you have a picture? Normally the shaft that the knob mounts on is part of the pot. So saying there is no damage to the pot is confusing. It sounds like the shaft has pulled out of the pot?
Or maybe the pots solder joints have broke loose?

[Justin Thomas]

Or the pot was never tightly (properly) mounted to the chassis/board, and now the connections have come loose. Fraid you'll prolly have to open it up. If you haven't seen this yet, it's well worth the visit:

New Page 1

Check the upper left corner and click on "Tube Amp Debug Page." Read safety info first, then take your time. If you feel unsure, get help (the tech kind! ). No doubt you can do it yourself, though... Good luck!

Justin

[zamyloo]

Thanks for the reply , Ive done a quick fix for now and just put cardboard under the loose knob haha....As far as the shaft..... it could have broken off but there is also a moving part that slides up and down the shaft of the knob so not sure if it is like this or broken off. Here are some pics of the possibly broken shaft and the piece that is sliding up and down with it, its got a pretty snug fit so i can't tell if that's supposed to be there or not haha. Thanks again guys.

[g1]

Yep, that's half the pot stuck in that knob there. You need a new pot.
There should be a set screw in that knob to release it from the (broken) pot shaft.
Or, if it's not a set-screw type knob, it's just real tight or has been glued on.
The plastic should separate from the metal.

[Justin Thomas]

I'm pretty sure the threaded mount isn't supposed to pop off the pot like that... >:O
I think you need a new pot... Can you remove the knob from the part of the shaft it mounts to? That would confirm.

Justin

Edit: simulpost... if there's room, try & put in something a little better...

[Jazz P Bass]

What you have in your hand is the potentiometer shaft.

Inside the assembly, that shaft is press fit to a rotating , plastic disc, which has all of the contacts attached to it.

I have repaired such damage in the past .
You will have to disassemble the pot & remount the disc.

A little heat from a solder iron should hold the disc to the shaft.

OR, buy a new control.

Edit: here are some 'gut shots' of a control.

[zamyloo]

Yep, its broken just wasn't sure....Jazz P I see what you're saying about the plastic. Will try to get my head around to trying that sort of fix...if not I will buy a new control. Could any control be used or is it a specific type I should go out and look for?

[Jazz P Bass]

You have to use what was in there.

The overall resistance & the taper (Log (A) or Linear (B) also matters.

Plus the size, the way it mounts.......

I hate sourcing pots.

Maybe you will be able to find the correct item.

Look around.

[J M Fahey]

1) can you solder properly?

2) can you un-solder properly?
It's easy to damage the PCB while removing some part, even more with a pot (3 legs while you can only heat 1 at a time) but it can be done.

3) either you learn or get a Tech to do it

4) I suspect it's an easy to find and inexpensive pot (post a couple pictures) so I'd just get a new one.
Value is usually printed somewhere, or stamped on the metal body or has a small sticker.
Worst case get the schematic and tell us which one it is , so we look there.

5) *where* are you?
That determines suggestions on where to buy.
No need to deal with Korg, I bet it's a regular inexpensive pot, but we'll await pictures for suggestions.

[g1]

I don't think that pot can be repaired as it appears the threaded bushing is broken.

[Jazz P Bass]

The schematic indicates a 1M Audio control.

AC15C1 Schematics (Rev 2).pdf

[Jazz P Bass]

Yeah, for sure it's busted.

(I only looked at the first pic.)