I have a very early Minimoog here for a future consignment sale.
Serial number 1401 (engraved s/n) Williamsville, NY era.
The 400th Minimoog ever made.
All metal panel, clear wheels, etc.
The oscillators are the common temp compensated types, not the very early or very later types and are stock at this serial number.
Built in March 1972.
A later repair sticker inside is dated 1974, along with the letters “ASP”, which I believe are the initials of ex-Moog engineer Alan Pearce, known for his later Polyfusion line.
Immaculate condition all over except for spots on the wood from case foam damage.
But… opposite of how most Minis arrive here for service, this one suffers from horribly bad pots all around, yet the switches appear to be faultless.
The keyboard needs the usual work and there’s no buffer board present, which was stock for later Minis.
(A “buffer board” aids in tuning accuracy when octaves are switched.)
So while I will do some work on the unit, how far is too far?
Is replacing the wood case, a sin in this case?
The power cord?
Adding a buffer board?
Should I use only NOS original pots which are much more expensive?
I want it to be as stock as possible, but also want it to play well.
Doing both will likely cost a lot of money, so I’m interested to know what collectors or Mini fans think.
I normally never ask something like this and also have instructions from the owner what he’d prefer.
But this particular Mini (out of 400+ I’ve serviced) must win the age vs condition contest of all I’ve seen and making it play well is going to be a huge job.
I’m wondering if stock wins over playability, I guess.
Hi Kevin.
My opinion, for what it’s worth, is playability over everything else. It’s a musical instrument and should function as such for as long as possible (I have two old Minimoogs, one stock except for added buffer board, one heavily modified).
Replacing the case? Not unless it is no longer functional. The scars are part of this instruments history.
Replace power cord? I would if the old one is questionable.
Buffer board? Definitely add.
NOS pots? Use whichever is the best quality. Since the originals are bad, NOS pots are still replacements, not repaired originals. Use what will prolong the playability.
Thanks for continuing to post here Kevin. Always interesting.
Don’t get hung up on “stock as possible”. I’d vote for playability. Get it musical first - buffer board, new pots. Case is just eye candy. Some people like “road karma”.
The only place I would use exact replacement pots is the mixer, filter emphasis, anyplace that passes audio. For EGs and control voltage pots, the element type is not significant (as long as the taper is maintained).
You’re already aware of the heavy mods I did on my RA. When I first received the RA it was not musically useable as the drift was really really really bad. It was begging for improvement so I modded it to stay in tune. I later added a Lintronics MIDI kit to it. Now it is a valid instrument ready for the modern MIDI sequencer.
The only modifications that would be a problem are anything with no documentation - IE RMS.
Thanks for the input.
Some people consider drilling any mini this old a sin, even if for a buffer board.
MC, I’m curious of your concern with pots used for audio purposes.
I generally use Clarostats as replacements for the original A/B’s.
They’ve worked well in all locations that doesn’t need some special taper or spec (such as mod pots.)
I think they’re conductive plastic, which is obviously different than the original carbon types.
While I’ve gone over your notes and schemos for the changes you made to yours, I don’t necessarily agree with them all. No slam though.
To each their own and you’re an owner/engineer.
Some changes I’ve found that are very important are matching all the vco summing resistors, cross-wiring octave switches, improving grounds and obviously cap replacements.
With the work on the pots added in, this alone should keep me busy.
Btw, here’s a good question.
On old Minis, they used two 500uf caps for the power supply.
Later ones used two 1000uf and a 470uf or even three 1000ufs.
More filtering was added later on.
Since this could change the sound, does one update these to the later spec?
500uf caps new aren’t as easy to find and going the other direction to two 470uf caps would mean even less filtering.
I agree that playability is more important than stock. They’re all meant o be played not put under glass . I think unless the case is falling apart I would keep the original and do what ever touch up work is needed to make it more presentable. With the buffer board I think I would add it, didn’t a lot of early ones have it added at some point. Where is it mounted ? I’ll have to open my early 1973 one up and see if it’s there . With the power cord are you talking about replacing with a non removable or putting a socket in ? While having a removable power cord would have some benefits, I think I would stick with a non removable one. If the newer pots are of the same quality and will perform as good as or very close with hardly any difference, I’d go for the newer ones if the cost saving is significant, say $15 to $20 per pot, if only a few dollars more and if the amount needed are readily available got for the NOS ones . Withthe caps, I think I would try and stay witht the 500’s if you could find them, if not how much of a difference will the 1000 make ?
My bad, I thought the A/B pots were wirewound, they are not. Disregard my comment about pots in the audio path.
I don’t think there is going to be much difference between 500uf and 470uf caps. It is well known that the minimoog power regulator has some dirt on the rails that keeps the VCOs from locking up. The only thing to be concerned with the slightly smaller caps is current load. On a totally stock mini with zero modification or accessories plugged into the power ports, should not be a big deal.
Brian, no need to take yours apart.
A stock buffer board installation requires two small holes drilled on the top for screws.
So if you have two small screws located on the top panel directly in back of the vco section, you probably already have one.
MC, Moog may have upped the caps on the later ones after people used the standalone sample and hold module with their early minis.
The clock can bleed back in a bit.
I’m not sure I’ve ever seen mini vcos lock before, even when I’ve subbed in a very clean lab supply.
But hard to say.
I’ve read the Jim Scott info, but think there’s probably as much noise present on the grounds as the rails.
The right side of a mini being where “true” ground is established, the VCOs on the other side, with a combo of star distribution and daisy chaining in between.
Not a great recipe for clean signals.
If you ever take a thick wire and jumper it from the ground on the rectifier board to the VCO board, you’ll can observe what I mean.
The pitch will change and it’ll get a bit cleaner with less mod bleedthru.
Well, I have much work ahead of me.
I’ll likely be retaining the original wood and will install the buffer board.
Thank you very much for your input.
I appreciate it.
There’s always a ground difference between rectifier ground and ground at the VCO board. The power regulator has a Kelvin force/sense power rail system exclusively for the VCO board, and ground has its own F/S lines. This is supposed to keep the rails tight at the VCO board (compensates for connector contact oxidation), thus better tuning. They neglected other elements affecting the tuning though - because tuning pots and pitch wheel are at separate rails, they’re a source of drift especially at the tail end of daisy chain wiring. My hot-rod corrected that.
There’s always a ground difference between rectifier ground and ground at the VCO board.
On yours maybe- you hooked back up the sensing on the power supply.
Moog disabled this to provide lower mod bleedthru.
I agree with this change too, but from a practical, not engineering standpoint.
Taken from the point of view of an engineer, it’s a good idea to have sensing.
But in the real world, all the additional sensing pins make for a synth that proves more unreliable in the real world.
Oxidation can affect these sensing pins as well and only makes for more connections to fail.
Afterall, how can some pins compensate for connector oxidizing when they themselves are located in the same connectors and likely to see the same oxidation?
Moog realized that sensing wasn’t very necessary since the Mini had fairly constant current draw and disabled it early on.
I prefer it this way also.
Thanks Kevin, It’s been awhile since I’ve had the cover off, didn’t recall seeing one
[quote=“Kevin Lightner”]Brian, no need to take yours apart.
A stock buffer board installation requires two small holes drilled on the top for screws.
So if you have two small screws located on the top panel directly in back of the vco section, you probably already have one.
. I think unless the case is falling apart I would keep the original and do what ever touch up work is needed to make it more presentable. With the buffer board I think I would add it, didn’t a lot of early ones have it added at some point. Where is it mounted ? I’ll have to open my early 1973 one up and see if it’s there 
