> Op-amps for mixers...
> But I would hasten to add why we really need to be 'hugely' accurate at
> DC for an external mixer. This only really applies for VCO pitch. The
> MOTM VCO has a 1V/oct input which are used for the pitch CV already.
> Presumably we need to mix other CV sources to our VCO through the two of
> the other potted inputs. The mixer performance that we need to control
> is therefore offset drift. I don't think absolute offset is that
> important unless you are feeding the mixer into a VCA then the VCO's
> pitch control. In most cases this could be nulled out anyhow. So for
> offset drift this will only be apparent if the op-amp does drift badly
> with temperature, and the VCO's input pot is set to its maximum
> senstivity. It is best then to use your mixer pots over their fullest
> ranges and set the VCO input to the lowest setting to get the sound you
> require.
This is exactly where I'll probably compromise. The modules that really are
looking for accurate DC
∗already∗ have a 3-in mixer. The question the begs itself: how many
instances do you ever need more than
3 simultameous control voltages into a VCO?
I am assuming that 99% of the time, a mixer module is for audio. But
certainly, you don't want to
introduce drift if you can avoid it just by better (read more $$$) op amp
selection.
I'll cruise data sheets this weekend and make my mind up.
Surprised no one has brought up lin versus log pots! <<duck>>
Paul S.