I've got a guitar effect pedal here that has a little plastic preamp gain trim pot accessible from the floor of the unit, through a little hole. And I think it might be knackered. Basically:

At "minimum", my bass overdrives the crap out of it. I have to turn my bass down below 1 to stop the distortion.

As I turn the pot up, it only reaches around 1 O'Clock before the signal cuts out completely. The rest of the range of the pot is silent.

So, people who know about electronics: Does this sound like a broken pot? Like, maybe, the "max" setting has ended up near where "min" ought to be, and for the rest of the rotation I'm just turning it across plastic? It's strangely silent up there though - I'd expect some crackling or something at least if it was mechanically knackered.

I'm waiting to hear from the manufacturers, but I thought I'd ask for opinions here since some of you seem to be quite clever.

Quote from thisnameistaken :

some of you seem to be quite clever.

True .

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Have you actually opened it and checked that the wires are properly attached et all? It might be very simple defect and possibly easy to fix.

I assume you've tried playing without the pedal in the loop? Because that description sounds just like when I blew my first amp

Also, is it a regular guitar pedal or specifically for bass effects? Because if it's a guitar pedal it's possible you've just blown it up with the massive low frequencies that regular guitars would never produce.

Quote from Hyperactive :

Have you actually opened it and checked that the wires are properly attached et all? It might be very simple defect and possibly easy to fix.

I haven't had a proper look. There are two boards wired to eachother and to the jacks/switches on the casing, and the pot I need to look at is inbetween them so I can't take a good look without disconnecting wires. The solder joints to the board look OK though.

I just heard back from the manufacturer, who has offered to "look at it", but that would mean shipping it to the USA which I don't want to do if it's just a duff pot that I could fix myself.

Quote from Dajmin :

I assume you've tried playing without the pedal in the loop? Because that description sounds just like when I blew my first amp

It's only when this unit is in the chain - the preamp is boosting the signal hugely.

Quote from Dajmin :

Also, is it a regular guitar pedal or specifically for bass effects?

It's an EHX Bass Micro Synth, intended for bass guitar. Although the only difference between this and the guitar model is the frequency response of the filter - I'm sure I could run through the guitar one just fine, it just wouldn't work very well in the low register.

FTR: (With the input gain at a sensible level) It's a really cool bit of kit. It'll do nasty analogue synth lead sounds, dirty sub-bass, quacking filtered funk, percussive effects, bowed sounds with the attack delay, all sorts of stuff, and it sounds warm and musical and useful all the time. Would be nice to have the cutoff frequency wired to an expression pedal though... I might have to see about doing that.

Sounds to me like you have yourself one of those Logitech Amps, Kev. Contact them, maybe you can get them to send you the Revision B amp

Quote from thisnameistaken :

Does this sound like a broken pot? Like, maybe, the "max" setting has ended up near where "min" ought to be, and for the rest of the rotation I'm just turning it across plastic? It's strangely silent up there though - I'd expect some crackling or something at least if it was mechanically knackered.

There's no way for the max to end up near the min in a potentiometer unless there's a short-circuit which causes it to be by-passed or the potentiometer was faulty to start with (it would exhibit this trait from the very first day). In the first case it might have grit in it which you might or might not get cleaned out with some contact spray.

Quote from xaotik :

There's no way for the max to end up near the min in a potentiometer unless there's a short-circuit which causes it to be by-passed or the potentiometer was faulty to start with (it would exhibit this trait from the very first day). In the first case it might have grit in it which you might or might not get cleaned out with some contact spray.

Hmm. Well like I said it's accessible through a hole in the floor of the unit, so foreign crap getting lodged in there isn't impossible. It's only a few months old though and in pretty good nick, I don't think it's been gigged.

I wondered if maybe it had been rotated past the "end" at some point, and so it had got... un-calibrated or something. It's quite odd how it goes silent when I start turning it up. It almost certainly can't have "worn out" from normal use - it's the sort of thing you adjust once and then leave it, unless you're swapping instruments with wildly different output levels.

I might have to take the soldering iron to it, but I don't really want it lying around in bits when I could be making Bernie Worrell noises with it...

Ooh, it's working!

Must've just been dirty - I tried dialling it in again just now and it worked fine. Damn thing sucks a lot of tone out of my bass when it's off though, have to stick it in its own loop so I can bypass it when I'm not using it.

Can't wait to take this to rehearsals and scare the crap out of everybody with it.

Thanks Xaotik!

Glad you can make some noise now.

Quote from thispotisbroken :

I wondered if maybe it had been rotated past the "end" at some point, and so it had got... un-calibrated or something. It's quite odd how it goes silent when I start turning it up.

That can't actually happen (lose calibration) - as you can tell by seeing what it looks like in there. At most if your rotate it past the end if it has a stopper it'll break the stopper. The going silent bit is odd indeed, it could indicate that one of it's points of contact loses contact - at best the wiper from dirt or at worst the external connectors due to a bad soldering job.