1975 minimoog power supply issue

Tips and techniques for Minimoog Analog Synthesizers
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MHAUGHEY
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Joined: Mon Jan 06, 2020 1:17 pm

1975 minimoog power supply issue

Post by MHAUGHEY » Mon Jan 06, 2020 1:33 pm

I am attempting to adjust the +10 and -10v rails on the power supply.
I get the +10 v adjusted at 10.00 v , but I can only get the -10v rail to -9.86v before the -10v pot runs out of travel..
A couple of questions, where do the +10 and -10 v sense get their voltage from? How exactly does this work, I do have a set of schematics and it seems like these lines go to the oscillator board , which I currently have removed, should I put the board back before adjust? I also saw something about disabling the sense circuits.... I'm speculating that a resistance value has probably changed in the 30+ years that this mini has been sitting. The reference 909ohm resistors seem to be precision metal film, so should be o.k. … would replacing the 10ohm adjust pot with a 50ohm pot cause any harm ? It might buy me a little more range …..

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MC
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Re: 1975 minimoog power supply issue

Post by MC » Tue Jan 07, 2020 9:32 pm

The Minimoog power supply is a Kelvin system. Each rail has force/sense lines. They must be terminated for the supply to function. If' your oscillator board isn't plugged in, the power supply won't work because that's where the force/sense lines terminate.

The force line is an output source, the sense line is an input. It is a closed loop correction system to compensate for losses in the wires between the power supply and the end termination.

That's why your adjustment isn't working.

The same is true with Polymoog and Memorymoog power supplies.
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MHAUGHEY
Posts: 3
Joined: Mon Jan 06, 2020 1:17 pm

Re: 1975 minimoog power supply issue

Post by MHAUGHEY » Thu Jan 16, 2020 6:22 pm

I put the osc board back in and now the supply adjusts correctly.

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