Minimoog "Model D"

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Minimoog Model D ... a dream comes true

 

The story of this Minmoog ...

This one was built in 1974 ! it's older than 40 years now and has this unbelievable early oscillator board inside. But it came to me in a non-working condition with a lot of electronic problems. Nevertheless it was one of my synthesizer dream-machines, since i get my hands on one of these synths in the early eighties :o)

 

The pre-owner, a very succesful dance musician in the seventies, bought it and play it several times on stage in addition to his electric piano. But he was unsatisfied with it's monophonic design. Then he gave it to his brother-in-law, but in the end ... in 2015 they both decided to give it away. And I was lucky enough to be there ... right time, right place. Thanks to Michael and his brother-in law. It was the right decision !

 

The restoration ...

After an excessive Restoration including cleaning, changing defective potentiometers, repairing oscillators, the modulation mixer, changing the keyboard bushings, a first calibration and a little wood-working, it was time to enjoy these outstanding sonic quality.

restoration impressions ...

Minimoog in the kitchen

The optimization ...

But after some weeks of playing these wonderful instrument, i decided to stabilize these old oscillator boards. I started with the power supply, it needs new caps and new trimmers to provide a stable and clean DC-Power to all stages. Then I changed the internal trimmer-pots of the oscillator boards against new temperature stabilized trimmers on small piggy-boards. So they can be mounted exactly like the originals and tuning is still possible with a closed cabinet.

 

The old electrolytic-capacitors are changed against new parts with a greater temperature range. All unshielded cables in the main audio path are changed against shielded variants. At the first look this seems to be necessary because I've detected a bleed-through of disabled oscillator signals in the audio-output. But I wouldn't do it a second time ... it only give you a slightly cleaner signal. The "Bleeding" signal problematic is often solved by a good cleaning of the gold contacts of all boards (use a rubber/eraser for this job) and a proper adjustement, or better matched transistors, in the vca stages.  

 

The last optimization was a temperature housing for the two VCA-stages. This provides a mostly equal ambient temperature to both transistors and reduce audible noise.

 

Now it's enough for the moment :o) ... look at these pictures ... see that undescribable built-quality ! It's a joy for each engineer, repair-man and musician.

 

Update 06/2016 :

Replace the ladder-filter cap's against a precisely matched quartett of Red Wine Super Dip's. These Goldfoil Capacitors are matched, and have 0.1% capacitance difference against each other ! Yes ... its true 0.1% difference. That's really a little bit more as nothing !

 

These caps improve the audio capabilities in the middle and higher frequency ranges

dramatically. This is a result of the precise matching and the very low losses of these parts.

A "must have" for any sonic nerd and Mini-Enthusiast :o)

 

optimization and upgrade ...