[sdiy] summing amp v/oct trim

[Scott Bernardi]

Happy Harry wrote:

>
> >In the ASM-1 vco there's a trim pot in series with the feedback resistor of
> >the summing amp. This is tweaked to get 18mV/V to the base of the first
> >expo
> >tranny.
>
> You can do it this way... Remember in this case that the control voltages
> are going to be inverted by the summing amplifier. In some cases this may
> mean you need an additional inverting amp after the
> summing amp... with extra components, errors, etc.
>

If you use the typical two transistor exponential converter, you can invert just
by changing which transistor base you drive with the summing amp, and which one
you ground. An extra opamp inverter is not needed.


--
Scott Bernardi
sbernardi at home.net