[sdiy] AC coupling caps on MS20 clone

[David G. Dixon]

> > Have you thought of this solution:
> > Use just one cap and one toggle switch.
> > Connect all inputs (after the level pots) to one side of a cap. Other
> > side of cap connects to summing point of op amp. Use the toggle switch
> > to short the cap when you don't want AC coupling. This solution saves
> > you two toggles and two caps.
> 
> (Would a blocking cap work in that location, between the input resistors
> and
> virtual ground, where the voltage is typically ~zero?)  I'm actually
> thinking of putting the cap-n-switch on the output of the mixer opamp.  It
> seems to me that it shouldn't matter whether the DC level is removed
> before
> or after the summer, which has a maximum gain of unity.


Well, I've just simulated it, and a blocking cap works just fine between the
input resistors and virtual ground.  In fact, a smaller capacitor does the
same job here than on the summer output.  I will rearrange my PCB layout
accordingly.  Thanks for the tip, megaohm!