Replacement pots for 1987 Hohner B2A

[Doug Florence]

The pots on my trusty headless Hohner B2A have become unacceptably noisy. The serial number suggests it is from 1987 so that isn't surprising. I do find this bass useful for travelling or jam sessions where there is no space and it sounds good.
I am trying to replace the pots but have hit a few issues. The original pots have a 3/8" threaded shaft so the holes in the body are about 9.5mm diameter. They are long shaft mini pots e.g. total length about 27mm and body about 17mm diameter. 2 x A500ohm for volume  and one B500k ohm for tone. I have spent hours looking for the exact replacement pots and they just don't seem to exist.

 

Modern mini pots generally have a 7mm thread which is loose in the hole. There isn't room in the cutout for full size pots which do have a 3/8" threaded shaft. I can probably make a short bush to space the shaft out with some 3/8" brass tube 18SWG brass tube, but that will be a bit fiddly. Also the inside of the body cutout is not parallel with the outside so the pot doesn't sit flat. I might be able to get a chisel to it, but again rather fiddly. A drastic approach would be to take a fretsaw and remove the cutout entirely and replace it with a home made brass fascia plate which I can paint to match the black gloss guitar, but that is likely to look a bit of a botch.

[tauzero]

You could use M7 spring washers to space out a 7mm thread pot: https://www.ebay.co.uk/itm/363082401549

[Stub Mandrel]

The easy answer is to 3D print some sleeves for the pots, they can even have angled ends.

 

OR:

 

You could probably use two of these (audio taper on tone won't do any harm)

 

https://northwestguitars.co.uk/products/cts-500k-long-split-shaft-potentiometer-audio-taper

 

 

Edited Tuesday at 19:21 by Stub Mandrel

[Bassassin]

Have you tried a squish of Servisol lubricating switch cleaner in your original pots? I've revived many an ageing & crackly potentiometer with it.

[Sean]

Mods, would this post be better off in Repairs & Technical? 

 

I'll respond to the post tomorrow. I've rescued 6 of these so can add a bit of value. 

[Doug Florence]

Hmm, No easy solutions then. 
I will first try to make a brass bush from stock pipe and scrape away to flatten the back face of the cutout with a chisel. If that fails I will saw out the cutout all the way through and have my local engravers make me a Trafflyte fascia with holes for flush mount pots to cover the hole.

[kodiakblair]

On 03/02/2026 at 14:19, Doug Florence said:

They are long shaft mini pots e.g. total length about 27mm and body about 17mm diameter. 2 x A500ohm for volume  and one B500k ohm for tone.

https://www.banzaimusic.com/bourns-mini-kn-500k-log-xxl.html

 

€3.47 each + postage

 

Link to data sheet for a few other Bourns pots.

 

https://www.bourns.com/docs/product-datasheets/PDB181-GTR.pdf