JHS Vintage active bass pot replacement.

[caitlin]

I have what I believe to be terminal crackle.

A solid blast of switch cleaner in the back of the pot and some wiggling clears it up for a time but the death rattle returns in hours.

The balance pot is a wee bit crunchy

This bass has what I believe is a PJ arrangement, split neck size pups and a bar pup near the bridge.

It doesn't work without a battery so I surmise it's 100% active.

Inside the back looks like this:

and pulling off the knobs reveals some nuts:

 

So I think if I get those undone and the jack out of the way the board should come out.

The volume pot is labelled A100K

The balance (I believe ) is labelled B100K and is center notched.

The bass and treble pots are also center notched (I guess because that's to mark when it's neither boosting or cutting) but the labels are mostly worn I think one says B100K and the other one *probably* says 100K but there's no trace of an A or a B.

I'm more than confident soldering, I've build point to point and strip board tube amplifiers which actually work and haven't cause a fire, but I've not got a lot of confidence identifying these pots.

I have a multimeter so I guess I could pull them and measure the range and rate (I don't know if they're linear or log) but I wonder if anyone might know what this arrangement looks like.

Any advice would be greatly appreciated, I'm just learning what these knobs DO and now when I turn them I get sad.

[BassBunny]

You're spot on with what you have said so far. The bass and treble in the centre "notched" position is flat, no boost or cut. Similarly the balance in the centre position has both pickups equally blended. 

If it is the blend pot that's faulty, you've already identified it as a 100K linear and they are easy to get hold of. The pre-amp looks identical to one from a bass I have. I'll have a look and report back if you need the values of the bass/treble pots.

[itu]

http://www.resistorguide.com/potentiometer/#Taper

[caitlin]

20 minutes ago, BassBunny said:

You're spot on with what you have said so far. The bass and treble in the centre "notched" position is flat, no boost or cut. Similarly the balance in the centre position has both pickups equally blended. 

If it is the blend pot that's faulty, you've already identified it as a 100K linear and they are easy to get hold of. The pre-amp looks identical to one from a bass I have. I'll have a look and report back if you need the values of the bass/treble pots.

If you could, that would be reassuring! Thanks.

Thanks for the link, itu. I didn't realise the A and B were the log/lin designation. Smells like they're all 100K and just the taper varies. It's irritating that the screen printing on them is so weak.

It would be nicer to have replacement pots inhand before taking the bass to bits so it's a fast changeover.

[itu]

As you can see, the manufacturing country might help a bit. The markings are a mess: A equals Audio/log except it is not that everywhere.

Another thing is to check other preamps. The solutions are very similar, so you may get an educated guess, whether the pots are log or linear. And as the parts are pretty cheap, the trials are not that expensive.

[BassBunny]

So the pre-amp is not exactly the same but certainly similar to one I had in one of my basses and the Blend/Bass/Treble are all B100K.

[caitlin]

Cool, I'll see what I can scare up from the internet then.

I've got a bit further in than I intended and won't be playing for a few days, oops. The wiring is a mess, unsure whether to leave well alone or to try and make it a bit nicer.

[caitlin]

Ew, I realise suddenly that the pots are mounted *through* the pcb and so have the pins pointing in the opposite direction to every single pot I can so far find on the planet.

Is this a *thing* and I lack search foo? I can see no evidence on the pots of the pins having been bent this way, but just possibly they were straight pins at some time that were mangled into place. I just can't find any 'the same'.

Such learning, so inability

[itu]

There's another issue: those pots have long shafts. May take some time to find similar.

[caitlin]

1 minute ago, itu said:

There's another issue: those pots have long shafts. May take some time to find similar.

Yep, I've basically given up, I'm buying a 5 string on Friday (unless someone else gets to it first; I won't settle for a red one.)

I'll resurrect this one if I stumble into any pots that will work, or possibly rework the cavity to use remote pots.

[itu]

Please try to clean and oil the pots. It usually works, so plenty of cleaner - and I mean plenty, let dry a bit and then oil the track. Use spray, not 10W-40...

[caitlin]

I've SMASHED the pots with switch cleaner and wiped them like a maniac and the fixing is only temporary

When you say spray oil do you mean like WD40, I do have some quite posh transmission oil for 90s japanese engines, but that's getting a bit towards 10W-30

I'm not sure any amount of cleaning will save the one that feels crunchy, I fear the track is delaminating in there. I will try anything you suggest though, having nothing to lose.

Also, SHUT UP, I'M MAKING UP REASONS TO GET THE 5 STRING, why are you stopping me?! 🙂

[caitlin]

Actually would blowing them out with compressed air possibly have any effect?

[caitlin]

I'm replying to myself a LOT here, but https://www.ebay.co.uk/itm/MINI-POTENTIOMETER-B100K-100K-16MM-LONG-SHAFT-WITH-CENTER-DETENT-ACTIVE-PICKUP/273651439128

looks roughly right, the pins are the wrong type, but if i cut the old ones off leaving the pins in the board i could trim these to fit and solder the stumps to the in place pins perhaps? the shaft lengths look within the ballpark anyway.

Whatcha think?

[lemmywinks]

My default solution to preamp problems on any cheapo bass is to just whack a cheap Artec in it, the 2 band 4 knob version is under £27 delivered. Saves messing about trying to resurrect the (likely inferior) stock one, unless you like mucking about with bass guts of course!

 

Have one in my spare bass and it sounds reet, nicer than some preamps on more expensive basses in fact.

EDIT: Last one apparently:
https://www.ebay.co.uk/itm/ARTEC-SE2-Bass-and-Guitar-electronics-board/352530556899?hash=item52147567e3:g:sfkAAOSwTapV6Che

Edited October 8, 2019 by lemmywinks

[caitlin]

My best friend nagged me to put it back together because I was whining about not having a bass to practise on.

I've just been out to the garage, wafted a couple of bar past the holes in the cans, but not actually forced that pressure straight through them, I think that would lift metal out. I've washed a BUNCH of wd-40 through the pots and honestly, I can't remember which one felt gritty any more.

The EQ responses seem heightened, but what's psychosomatic at this point? The treble one certainly gets a bit hissy at full up and I don't recall that from before.

All the pots now travel full range without any scratchy sounds, so I'll leave it to sit for a while and find out if that's a fix that's going to hold or fade.

Thanks for the shout about the oil, I didn't realise that was safe to shove in there.

Now I have no justification for that 5, worst forum ever.