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Micromoog trimpots replacement

PostPosted: Tue Jun 12, 2018 6:31 pm
by Roediger
Hi,
I'm refurbishing my old Micromoog, and I can't find any trimpots replacements. Those 4 pins pots seems very non-standard. Any ideas?

Thanks in advance.

/Roediger

Re: Micromoog trimpots replacement

PostPosted: Tue Jun 12, 2018 11:05 pm
by Mooger5
If you look at the schematics you´ll see that every trimpot has three terminals. I think the fourth terminal could be ignored and any vertical mount trimpot of suitable size could be used as replacement.
With the DMM check for example the VCA trimpot, r606. One terminal should read +15VDC, another -15, and the other, most probably in the middle of these two, should connect to resistor r605. That terminal is the wiper, or the center pin in any conventional trimpot.

Re: Micromoog trimpots replacement

PostPosted: Thu Jun 14, 2018 7:13 pm
by Roediger
Thanks for the answer.

I think I'll go with the old originals since it seems almost impossible to fit and solder any of the modern ones.

/Roediger

Re: Micromoog trimpots replacement

PostPosted: Thu Jun 14, 2018 9:38 pm
by Mooger5
If it´s not broken...
Trimmers are set-and-forget so there´s not much wear to the carbon tracks. Other than that the only reason I could see is to replace the originals with multi-turn pots. Those make the calibration of the kbd scaling and filter tracking a little more easier.

Re: Micromoog trimpots replacement

PostPosted: Sat Jun 16, 2018 12:45 am
by synthchaser
In general, I find that when a trimmer gets old, the carbon track gets damaged (indented, maybe?) where the wiper has been parked for years. Then you go to make a slight adjustment and you have erratic behavior close to the old parking spot of the wiper.

Re: Micromoog trimpots replacement

PostPosted: Sat Jun 16, 2018 11:05 am
by Mooger5
A good part of it is due to grime building up around the wiper contact point so a good clean sweep helps to minimize the "dent". Tuner cleaner does wonders but in such situation too much of it may turn the axis a bit loose. The force that rotates the trimpot must be higher than the force of the wiper towards the carbon track so the contact point stays in place even when slightly off the dent. A cotton swab filled with IPA is better.

Re: Micromoog trimpots replacement

PostPosted: Sat Jun 16, 2018 3:17 pm
by Mooger5
... and by the above slightly confusing statement I mean: as long as the resistance to rotation is higher than the wiper pressure...