The VCAs you can make from a 13600/13700 in pairs. They're just OTAs
with an expo pair attached and no I/V converter. In fact, the expo pair
is not needed for linear modulation level controls like this. The expo
control input is just used for the DC offset trim. This is what I've
done on my M board design that uses no IG chips at all. I have not made
a discrete equivalent circuit for the 150 yet, but it is a "VCO-II" with
a sine shaper and will be a lot simpler than the VCO-III was to make
with standard parts.
Nice mods, all the same.
Crow
/∗∗/
kent spong wrote:
>Hi Erik,
>
>Yes that's right. The 16 IG00150 VCO's are for the VCO, VCF and VCA of the
>LFO section and are also controlled by the after touch too. The only down
>side to this mod is the 64 IG00151 VCA IC's it uses. The whole thing is
>switched in and out on the LFO EXT point on the waveshape slider and also
>swiches out on the EXT Modulation socket on the back. So there is no change
>to the front panel of the 80 at all. However, I am working on a totally
>faithfull replacment front panel for the 80 to restore one's that have seen
>to much damage over the years. I want to keep these fantastic machines going
>for as long as I can.
>
>
>