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Pre-SRM Octave Cat PCB Trimmers?
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author Pre-SRM Octave Cat PCB Trimmers?
analoglsd
Has anyone here replaced the PCB trimmers, for scaling, tuning, ect..., on a pre-SRM Octave Cat? If so, would you mid sharing the part numbers of the trimmers you used? Thanks.
dksynth
I had to do that. they are a weird spacing. I mounted a standard top-adjustment trimmer on some stripboard and wired it up with solid core wire where the old trimmer had been. pretty solid, and it still lines up with the hole.
rampy
dksynth, would you happen to have a pic of this?
Jason Brock
Old thread, but I have the same problem and I'm hoping someone can help me find a replacement part.

I'm including a picture of the original trimmer, labeled 101C. My Cat is a Rev A. The schematics indicate that these trimmers are 100 Ohm.

Can anyone point me to a replacement part that would work, and still have the adjustment slot oriented upward (same as the original) so it can be access from the hole in the front panel with a screwdriver?
Thanks!

Modulart_JP
The Bourns 3386 series would be a good candidate.
https://www.mouser.jp/datasheet/2/54/386-776606.pdf
The model would depend on the footprint of the trimmer in your Cat.
Jason Brock
Modulart_JP wrote:
The Bourns 3386 series would be a good candidate.
https://www.mouser.jp/datasheet/2/54/386-776606.pdf
The model would depend on the footprint of the trimmer in your Cat.


Thanks. Someone else said the same thing in a PM.
Nothing will fit directly on the board so I'm going to try wiring it on a small piece of strip board first as dksynth suggested. If successful I'll post some pictures.
carygrace
I recently repaired an SRM, which uses the same trimmers. I replaced them with top adjust multi-turn trimmers that I had in stock, which I attached by bending the legs into position, and using extra bits of wire to extend them as needed. I insulated the legs and wires with sleeving, and I also painted over any exposed traces that the wires crossed with a solder mask repair pen.

Getting them lined up with the panel adjustment holes is tricky, but was possible. I put a big blob of silicone sealant around each trimmer to keep it in place and stop it from wobbling when adjusted.


Once I had replaced all the faulty trimmers, I discovered that all the resistor packages in the keyboard had degraded (probably from age, moisture, etc.) to a point where they were so far out of spec it was impossible to tune the keyboard. I made a new resistor chain for the keyboard using a piece of tag strip, and matched resistors, which I wired to the board and secured with a strip of adhesive rubber and tie wraps. It’s not the most beautiful thing in the world, but it works perfectly!





ETA: I should also mention that several of the IC sockets (at least on the unit I repaired) proved to be very unreliable. After all the above work, I was still having some intermittent tuning instability problems, and it turned out to be due to some of the IC sockets not making good contact. Once I replaced them, all was well. So that’s another thing that is worth checking, if you still have problems.
Jason Brock
carygrace - excellent info, thanks!
carygrace
Jason Brock wrote:
carygrace - excellent info, thanks!


No problem! Good luck in your repairs! Cthulhu
Jason Brock
Thanks again to everyone for the info.
I used a Bourns 3362P-1-101LF and a piece of strip board.
It lines up perfectly with the hole on the front panel, and everything is working again now. This is fun! w00t SlayerBadger!

delayed
Do you mind posting pictures of all the inside /pcbs? There are not many Octave images out there.
Jason Brock
delayed wrote:
Do you mind posting pictures of all the inside /pcbs? There are not many Octave images out there.


Sure, I took these a couple of years ago. I'll attach them here, and they're on this Imgur page:
https://imgur.com/gallery/O3aamjP

This is an early discrete model. CA3080 metal can OTAs in the filter, and CA3046 in the oscillators. A later revision used an SSM2040 for the filter, which would sound the same. I've also heard that toward the end of production (SRM II models) they switched to an SSM2044 filter, which would sound very different.
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