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Re: Minimoog Model D Osc 3 Control switch defies expectation

Posted: Wed Apr 27, 2016 8:38 am
by megavoice
Stevie Ray wrote:Megavoice -- replacing ageing electrolytic caps in the power supply can only be a good thing. As others have noted above, replacing caps in the audio signal path can affect the the sound and character of the instrument so that's up to you. Personally, I replace ALL electrolytic caps and I've only ever noticed an improvement in audio quality and noise levels after doing this. Replacing the electrolytic caps in an ageing PSU is the first thing you should do in any restoration project IMO.


Thanks for the info.
I already know all this, and years ago when my Chroma didn`t work any more properly the first my former tech advised me was, to do a complete cap Job at first, and my very first question after was if there would be any risk of sound changing, but he denied immediately.
So I let him do the Job and the Chroma still sounded as "dusty" and "dirty" like before.

But once he told me as for the Minimoog, and I cannot reproduce what he told me as I`m no tech, people complained about the sound after having done the cap job on the PSU.
So he never did and with a great exception in comparison to all other vintage synths he still rejects doing any alterations on any Mini`s PSU, even NOT replacing it in total.

So that`s all I can tell about.

Re: Minimoog Model D Osc 3 Control switch defies expectation

Posted: Wed Apr 27, 2016 9:25 am
by MC
There's some truth in not re-capping a Minimoog.

Well into its production in the 1970s, they re-designed the power supply to make it cleaner and when it was installed it caused the VCOs to lock together. You NEVER want VCOs to lock together as this ruins the sweeping effect of multiple detuned VCOs. It turns out that the original power supply had just enough noise on the power rails that it prevented the VCOs from locking together. If you re-cap, you risk making the rails too clean and the VCOs will lock.

Imperfections can sometimes be a good thing. Turns out this is also true with the old Moog modulars. I almost did a re-cap on my RA Minimoog until I uncovered this "imperfection".

Minimoog is one of the rare exceptions though. In general a re-cap is a very good idea on any analog synth.

Re: Minimoog Model D Osc 3 Control switch defies expectation

Posted: Wed Apr 27, 2016 9:35 am
by megavoice
MC wrote:....Minimoog is one of the rare exceptions though. In general a re-cap is a very good idea on any analog synth.


YES.

Re: Minimoog Model D Osc 3 Control switch defies expectation

Posted: Wed Apr 27, 2016 9:54 am
by thealien666
MC wrote: If you re-cap, you risk making the rails too clean and the VCOs will lock.


Not really.

If you replace the original caps with the exact same values nothing should change, since the circuits were originally designed with caps of those values (imperfections and all).

BTW, unless your Mini was left/used in a harsh environment (very hot) those high quality japanese (Matsushita) electrolytics capacitors will probably be almost as good as the day they were made. I can confirm that they are on my own Minimoog D with ESR readings still well below nominal values even over 40 years later. So I agree with MC, but not for the same reasons, no recapping needed there.

Some caps that might need replacing are some Mylar ones (with color stripes) on which the external coating is cracking and delaminating. But even those still show correct values (both ESR and capacity), and the Mighty Mini is still working fine despite those.

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