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Buchla 291r "Q" knob plastic knurled shaft pot? Wh
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author Buchla 291r "Q" knob plastic knurled shaft pot? Wh
sanders
Anyone happen to know a supplier or maybe have a few extra of these pots used for "Q" control on the 291 and "fine tune" on the 258?

I had a link years ago for a Mouser or Digikey part number, but I can't seem to find them now.

Please help me kind people
diophantine
I typically use one of these:
http://www.smallbear-electronics.mybigcommerce.com/alpha-single-gang-9 mm-right-angle-pc-mount-w-knurled-plastic-shaft/

Tayda carries them, too. Just can't readily find it on my phone...
guitarfool
Mouser part number is 652-PTV09A-4030UB203
Manufacturer (Bourns) part number is PTV09A-4030U-B203
This is the 20k version as used in the 281r and 258r, listed in Roman's BOMs.
snaper
Actually, I'm interested in these the older things, you know, which looks like a trimmer or something :

https://www.modulargrid.net/u/buchla-model-291
guitarfool
Yes, that is like the Bourns I mentioned. Black plastic shaft...

There was an old version long ago that had a small screwdriver slot in the end - I don't know who made it, and I believe they were used mostly in TV tuner circuits and such. You might find one eventually on Ebay.
sanders
thank you for all the replies; these are apparently going to be harder to source than I anticipated.

@guitarfool-- I should have looked closer at the BOM, thanks. Unfortunately, this is not the pot I'd like to use. I would much prefer to find pots closer to those used in the original modules. I'm pretty sure Verbos sourced a similar styled pot when he issued his 258v around 2008. I just assumed they were currently available at that time. I'm guessing this is the best bet, to find out what he used (the info may be somewhere on his Buchla Tech blog).

@snaper-- yes, this is what I'm looking for as well. The original pots were made by Allen and Bradley; They are "Type W"; In the photo below, you can just make out the following part number: "WA2G0..." I believe that the black knurled plastic "grip" (for lack of a better word) may have been an add-on dressing for these pots. When I see them listed for sale, I only see them with 1/8" metal shaft. Even if they were available, they don't look like they'd fit very well on the Roman PCB. I'm hoping the ones Verbos used might work however.

If I find a something close to the original knurled plastic shaft pot, I'll post a link here. If anyone else has this info, I'm still looking.

sanders
hmm, looking again at the 258v, it looks as if it uses a similar pot as those on Roman's 258r BOM.

well, forget that
tobb
What you need is the CTS 296 Trimpot looks closer to the original then the Alpha trimmers:

https://www.digikey.co.uk/product-detail/en/cts-electrocomponents/296U D104B1N/CT2268-ND/203847


Picture file
tarandfeathers
sanders wrote:
thank you for all the replies; these are apparently going to be harder to source than I anticipated.

@guitarfool-- I should have looked closer at the BOM, thanks. Unfortunately, this is not the pot I'd like to use. I would much prefer to find pots closer to those used in the original modules. I'm pretty sure Verbos sourced a similar styled pot when he issued his 258v around 2008. I just assumed they were currently available at that time. I'm guessing this is the best bet, to find out what he used (the info may be somewhere on his Buchla Tech blog).

@snaper-- yes, this is what I'm looking for as well. The original pots were made by Allen and Bradley; They are "Type W"; In the photo below, you can just make out the following part number: "WA2G0..." I believe that the black knurled plastic "grip" (for lack of a better word) may have been an add-on dressing for these pots. When I see them listed for sale, I only see them with 1/8" metal shaft. Even if they were available, they don't look like they'd fit very well on the Roman PCB. I'm hoping the ones Verbos used might work however.

If I find a something close to the original knurled plastic shaft pot, I'll post a link here. If anyone else has this info, I'm still looking.



Yep, these are ~1/4" knobs fixed onto the 1/8" pot shaft, the metallic part at the bottom of the knob has a threaded hole that a grub screw goes into to secure the knob to the shaft. In the above photo of the 258 you can see that this grub screw is missing from the fine frequency control on the square oscillator revealing the metal shaft of the pot.

I don't know of anyone making a similar product now. It wouldn't be hard to machine if you have a lathe or friend with a lathe and could then be powder coated or anodized black. 3D printing might work, but threading 3D printed plastic is not especially easy/reliable in my experience.

The good news is, if you decide to go for pots with 1/8" shafts there are some excellent high quality choices available, my favourites are the Clarostat 308 series which I use a lot. In my opinion they are cheap, but virtually no one on this forum agrees. You won't find anything that fits the PCB footprint without custom ordering I don't think, but the original pots are panel mount anyway so wiring to the PCB on flying leads is even more "original" and will surely make the module sound extra vintage. Hmmm...
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