[sdiy] AC coupling caps on MS20 clone

[David G. Dixon]

> I think you just want R1 in your first sentence?

I guess I didn't make myself very clear, but I was talking about the
impedance at the virtual ground itself, not on the other side of the input
resistor.  Does that make sense?  (I hope so, because I'm drawing my
inspiration directly from the analysis in Horowitz and Hill!)

> > I believe that the impedance at the inverting input of an inverting
> > opamp is
> > R1 || R2 (where R1 is the input resistor and R2 is the feedback
> > resistor).