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semi-OT: another cry for help from the electronics experts!


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I posted in the lowdown forum about trying to replace a pot in my Ibanez bass. Little did I know what I was getting into. It seemed like a no-brainer. Maybe it is â as in me having no brain!

 

In February I thought I ordered the correct part from Mouser but because stock was zero (huge shipping delay), and there was a pandemic (delay made huge-er), and I was semi-isolated in Maine for 5 months, I didn"t open the package until last night! It doesn't fit. After some investigating it seems I ordered a pot with M7 size bushing. The Ibanez pot appears to use an M8. I might have been able to use this M7 guy, but the bushing is shorter than the one on the Ibanez pot and doesn't reach through the front of the bass where I can attach the nut. The splined section is longer so the total length of the bushing and spline is the same as the Ibanez part. I only paid attention to that measurement, which had me thinking I was in good shape - nope.

 

both.jpg

 

This website was very helpful - that's what turned the light bulb on for me. The pot I'm looking for is this one, shown at the bottom on the left of that web page. A 9.5mm long bushing with an M8 thread:

 

what-I-need-small.jpg

 

I've searched Mouser and unless I screwed up, all they seem to have are the M7 or the imperial (3/8") pots. I also looked at Ebay. Ibanez? They're a joke, they only show two pots, neither of them right and $24 each!

 

The bass is no longer made but it's less than 10 years old. The pot is a 17mm 100K linear taper with a center detent (I can work with no detent too). I had no idea this kind of a part would be so hard to source! Any tips are appreciated. THANKS!

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Did you contact Ibanez?

 

I've gone down the replacement pot rabbit hole myself. Details are paramount. I had an HHB Radius 40 channel strip and the pots got scratchy. No practical way to clean them, short leads to the PC board with the access hole for cleaning tight up to the board. One pot died a horrible death, self destruction via "simple removal of the knob" (I had to go in to see what I could do).

 

Eventually I decided that I didn't really like the unit that much anyway so I searched for a pot online, thinking I'd fix the thing and sell it. I found a pot that had the correct spacing for the connections to the PC board and ordered it.

Shaft was too short, the original pots had longer shafts for the knobs. I put the pot in, put it back together - working except still scratchy pots - and flipped it for dimes on the dollar just to make it go away.

 

Ugh. Good luck!!!!!!

It took a chunk of my life to get here and I am still not sure where "here" is.
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No I did not contact Ibanez - I went on their web site which has a "parts store" and when you click on the link to see the potentiometers there are exactly two of them to choose from. They have no picture or description other than the bass they're supposed to go on and the function. Even if either of them was the correct part, I'd rather go without than spend $24 on it.

 

http://shop.ibanez.com/shop/parts/for-el-bass/potentiometer

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Ah - the mighty pot search. See if you think this one will work:

 

100k Pot

 

It's got the right length bushing but a smaller diameter, (6.35mm per that link above) that you might be able to make work with the right washers.

The longer shaft can be trimmed with a Dremmel.

 

Here's the actual spec although they don't seem to show the bushing diameter in this one.

 

Spec

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Looks like we cross-posted there! I have no clue how you got to the page you linked to, but thanks for pointing me to it. Unfortunately it doesn't look like the pot I need is stocked. I was able to find this on what I assume is their Japanese site - which is a page for my exact model. It looks like I can buy the entire preamp which, according to the pic, comes with the pots. I'll pass on that option.

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Ah - the mighty pot search. See if you think this one will work:

 

100k Pot

 

It's got the right length bushing but a smaller diameter, (6.35mm per that link above) that you might be able to make work with the right washers.

The longer shaft can be trimmed with a Dremmel.

 

Here's the actual spec although they don't seem to show the bushing diameter in this one.

 

Spec

 

Thanks Mark. That pot might be a long shot. Looks like the bushing is 3/8" - is that not an imperial measurement? I'd have to drill out my bass a little. Also the pot body's diameter is shown as 1.120 which I assume is inches. My pot is smaller (17mm) and things are a very tight fit inside the bass.

 

I'm considering a different option: since the pot itself works, and it's only that one of the split halves of the shaft is about to break off, I was thinking of superglueing the halves together (with some kind of spacing material in the split). I'm wondering if there's a chance I can get this right enough so the original knob fits snugly? Maybe I'll just have to hope I get lucky. Thanks again for looking!

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Maybe HERE ?

 

I cannot do the search for you because I´m always searching for parts for myself and it needs ages ...

 

But maybe, it helps.

I remember I had to replace almost all of the pots in my Rocktron devices and that "bushing" issue drived me nuts.

At the end of the day, we drilled larger holes in the frontpanels of the devices to get new pots in which electronically matched.

Today, it´s a nitemare to find negative logarithmic audio taper and tandem pots originally being used in late 70s designs.

All that analog guitar (amp/ fx) type stuff became rare.

 

:)

 

A.C.

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Couple options not mentioned:

 

- 3D print a sleeve type adapter. Or get a service which does this to do so. (Female to female through hole adapters are a thing, but I doubt there is any standard part in this threading and length.)

- See if you can pull the upper mechanical couplings off the pots and exchange them.

 

-Z-

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Everybody - I really appreciate the help but I'm looking to find either an exact replacement or something close enough to work without major surgery. It's become obvious through reading the replies here that sourcing this piece will either be a major PITA or just impossible. As I said, my pot works fine â it's just that one half of the split shaft is about to break off (you can kind of see it in the picture I posted in my first message of this thread). I think I'll just put a piece of plastic in-between the split shaft and superglue it together. Let's put this thread out of its misery! Thanks again everybody.
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search for Bourns potentiometers

 

Will a 250K work?

 

Ha - just as I was throwing in the towel you post. If this was a 100K with a center detent I think it would be a drop-in replacement. I can live without the detent but have no idea whether the 250K will work - the original is 100K. Thanks though!

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Perhaps I missed something, but I didn't see any information as to what's actually wrong with the pot.

 

From the picture it appears that the shaft is bent. If that's all it is, a gentle pry with a screwdriver will generally set things right.

 

As to whether a 250k can be substituted for a 100k, the answer is...it depends. Lacking a schematic of the circuit, I can't say...and I'll bet the schematic will be unobtanium.

 

Me? I'd ream out the hole and put in a standard pot. As long as you can get the knob to fit and look right and it does the job electronically, it won't matter. Or wouldn't to me, anyway. You may feel differently. Long-shaft pots can be a pain to find sometimes so there's a limit as to how much PIA I'll put up with in a situation like this.

 

Or maybe more information was given and I just missed it. That happens when I'm short on sleep (which is pretty much all the time).

 

Grey

I'm not interested in someone's ability to program. I'm interested in their ability to compose and play.

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You said the split shaft is about to break and that it was visible in the picture. I don't see it, but whatever. It just looks bent.

 

Superglue won't work. It doesn't stick to most plastics. In fact, I use cut-up pieces of milk jugs (polyethylene) in my shop to keep super glue leakage/squeeze outs from getting all over things. I knew someone who attempted to glue the plastic handle of a shower faucet back together. It lasted about a day. In addition, the fumes from the glue made a hazy mess on the surface of the plastic. Claims that super glue will stick to anything are hopelessly optimistic. It works best on things with a slightly rough surface (e.g. ceramics); smooth surfaces aren't good. Superglue doesn't do all that well on metals, either. If you do decide to use super glue, make sure the metal is scrupulously clean. I'd use a paper towel to rub lacquer thinner across the inner surfaces. Lacquer thinner will clean most anything off of anything. At the very minimum, use isopropyl alcohol. Note also that super glue is not very good at space filling, meaning that it doesn't fill gaps.

 

If you're going to glue it, I'd suggest epoxy with a wooden insert. If nothing else is available, cut a toothpick in half with a sharp knife and epoxy the two halves into the gap. Note that epoxy is only so-so at sticking to metal, but it's better than super glue.

 

If the shaft was brass, you could solder one or more pieces of copper wire into place, but from the picture it appears to be aluminum, so soldering is out.

 

If, by chance, you can bend it back into place, it would be a good idea to shim it, regardless, whether it's broken or not.

 

I'm not a big fan of T-18 shafts, but you find them everywhere. You just have to live with it sometimes. Good luck.

 

Grey

I'm not interested in someone's ability to program. I'm interested in their ability to compose and play.

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The shaft hasn't actually broken yet, but in bending the "bent-in half" back to a straighter position, you can feel a looseness that tells me the metal is about to snap! So forget about sticking a knob on there. Thanks Grey, I didn't realise supergluing was a poor option. JB Weld sounds like a good idea, thanks Moe. If I can find any small piece of metal (maybe a small clevis or tension pin) to put in the "split" space to work as a shim, then JB Weld it, I might be good to go. Once again the KC electronics squad answers the call! :)
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Nothing at Mouser or Digikey. Mouser is where I first ordered from. Frys? They have very little selection, nothing even close to what I need.

 

I am declaring myself gone from this thread - thanks to all who've made helpful suggestions, but I really feel like we're beating a very dead horse now. I had assumed that the part would be easy to find and that I just didn't know where to look. That might still be the case, but given the time and energy expended I would rather now fix the exiting pot's shaft as I detailed above and hope for the best.

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Stewart MacDonald has long shank pots. Luthier's Mercantile. Allparts. Think luthier supply houses. Also Antique Electronic.

 

As far as standard parts houses, I don't remember anyone mentioning Allied, but luthier places are more likely to have an array of long shank pots.

 

Don't count on a center detent--that's likely an OEM item that Ibanez had made to spec at the time. If you're clever, you can use two pots (on the same shaft) to construct your own, but it's bulky and inelegant.

 

Depending on how well-stocked your junk box is, you might be able to steal the shaft out of another pot and install it in your ailing pot. Note that this is a fairly invasive procedure, but I've done far crazier things in the fifty-odd years that I've been doing electronics (and gotten away with more than my fair share of them).

 

Grey

I'm not interested in someone's ability to program. I'm interested in their ability to compose and play.

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