[sdiy] schematic for Moog 901 VCO

[Dave Leith]

Hi Terry  and thanks for the response

hmmm..wish I had that module to look at :-)

just got pictures and schematics and old catalogs..

however it seems the 901A has:
the switched (semitones) and 0 to 2 variable voltage for tuning
901B has
switched Lo to 2 foot plus a frequency vernier of 0 to 10.
When they are put together as a 901 there are only the 3 controls not
4 (which makes sense) of  switched  (semitones), switched Lo to 2
foot, and 0 to 2 variable voltage for fine tuning. The additional
frequency vernier of 0 - 10 (dual 10K pot) is missing as the
oscillator is no longer part of a bank and would not need to be offset
from another VCOs within the bank.
So it is the circuitry for the 901B frequency vernier that seems to be
missing and small changes are made to accommodate this - well that's
how it looks on the remakes on the site link above. The schematics for
the 901A/B do not indicate how the dual 10K pot is omitted.  Maybe the
original 901's were wired different and just left the extra parts on
the board? Not quite sure how they would bypass the function of the
dual 10K - that's what I'm looking for.

Dave


On 3/21/09, TJ <daytona at verizon.net> wrote:
>
> > I'm looking for the schematic for the Moog 901 VCO - not the 901 A, B
> > or C - I have these already in an old service manual. The 901 combines
> > them ( A B and C) and removes some of the redundant circuitry. Seems a
> > bit rare.......
> >
> > Anyone able to help? I saw a remake of these here
> > http://www.moogmodular.com/9501/
> >
> >
>  Hey Dave,
>   It is difficult to see from those photos, but I have an old 1969 901 here.
> It is simply just a 901A on the one side mounted upside down, so you can
> adjust the trimmers from the left. And a 901B on the other side, and there
> is no 901C involved. I'm not aware of any circuit differences, other than
> the front panel attenuators for the four waveforms? Perhaps you are thinking
> the 921 oscillator that has additional circuitry for the auxilary output
> section?
>  Terry
>