[sdiy] Moog minimoog osc board into module?

[WeAreAs1 at aol.com]

Brett,

You'll need to provide a regulated +/- 10 volt supply to power the VCO board. 
 Alternatively, you could modify the board to operate at +/- 15 volts by 
changing resistor values here and there, but I really don't recommend doing that, 
since we already know that board should operate properly with the 10 volt 
supplies.  Maybe there are 7810 and 7910 10 volt regulators available that you can 
just strap accross your 15 volt rails to make these supplies.  If not, there 
are tricks you can do with 9 volt regulators to make them act like 10 volt 
regulators (someone please step in and explain how this is done, please -- it's 
some kind of diode drop thing, I think).

As for the other mods you suggested, I don't think the thermal coupling would 
help much, since those transistor arrays are so far away from each other -- 
the heat aluminum sheet could still be at different temperatures at different 
locations on the sheet.  The same goes for the tempcos, although it might help 
to couple the tempcos onto the top of the transistor arrays with silicone goop.

I wouldn't change out the transistor arrays until you get the thing up and 
running.  You don't want to add any layers of complexity to your troubleshooting 
phase, and you probably aren't even sure if the board is currently operating 
properly, right?

Those Q81 tempcos are pretty much the holy grail of tempco resistors, so you 
might consider trying to find another one to match the two good ones.  They're 
hard to find, but they are out there.  On the other hand, you could probably 
drop a modern tempco into the missing spot and calibrate the VCO's tracking to 
identically match that of the other two, so it's not a big issue.  You might 
consider putting the two Q81's on VCO 1 and 2, and the new tempco on VCO 3, 
since it's the one that's likely to be used (at least sometimes) as an LFO.

The most dramatic improvement you can make on those old Minimoog VCO boards 
is to replace all those crappy wirewound trimpots with modern multiturn 
trimmers (10 to 20 turns).  Trust me, it is well worth the expense and effort.  You 
will thank yourself every time you go to calibrate the scaling of the VCO's, 
which will be fairly often.  Multiturn trimmers make this a painless, if not 
downright pleasurable experience.  Those old WWII-era wirewound trimmers are 
almost impossible to physically adjust to where you want them.  Can I get a 
witness on this?

You also might consider adding some proper initial pulse width pots to your 
control panel (instead of the original three-position pulse waveform selector). 
 You could also easily add voltage controlled pulse width modulation inputs 
to each VCO, and hard sync would also be useful.  Does anyone out there have 
any good Minimoog hard sync mod circuits that they can share? (for the old-style 
Mini VCO's)

Michael Bacich