Minimoog old style VCO

[Terry Michaels]

Message text written by Rotwang the Mad Inventor
>Recently, I bought a Mini-Moog cheap. Very cheap. The catch; it need
service and the VCOs are of the old, less stable kind. Anyone of you
Synth-DIY:ers have a pre-#10175 (or whatever that magic number
was) Mini-Moog?

I have dismantled my Mini, and found that the VCOs are of a traditional
relaxation-oscillator type, with those notorious tempcos in the CV summer
feedback. My Mini was drifting wildly, and I found out that someone had
replaced two of three tempcos with ordinary 1k resistors! :(
Then I noticed the poor construction/layout of these early boards; the
tempcos and the exponentiator transistor-pair (CA3046) are not thermally
coupled, and they are not even close to each other on the board! No wonder
these VCOs had temperature stability problems! (shame on you, Bob! ;) Now,
my idea is to get myself new tempcos, and rearrange things a
little; placing the tempcos in direct contact with the 3046 capsules with
some silicon paste and epoxy glue. This would greatly improve at least the
thermal stability of the VCOs, don't you think? A good thing about having
these old VCO boards is that there is no need for worry about those 726
heated expo pairs breaking down! 

Any more experiences with old-style Mini-Moog VCOs? Comments? Ideas?
When I get back from christmas vacations I'll fire up the soldering iron
and get things going... 8-)

        Moog Christmas!

        /Patrik above arctic circle (need temperature compensation!!! :)<

Hi Patrik:

I moved the tempcos on my Minimoog many years ago, it is definately a good
idea.  Just glue them to the CA3046's and extend the leads with insulated
wires back to where they originally went.  Another improvement is to
replace the 741 op amp used in the VCO control voltage adders with OP07's.

Terry Michaels