[sdiy] AC coupling caps on MS20 clone

[David G. Dixon]

> >>  3) level pot with pull-switch, to select AC or DC coupling.
> >
> > Too complicated/expensive for my tastes (which are simple and cheap).
> 
> It's no more complicated than a pot and a toggle switch. If you use
> quality toggles (NKK for example) then a P/P pot is less expensive
> than a pot and toggle.

I don't.  I use Taiway switches from Small Bear (love 'em -- never a
problem) and an SPDT On-On runs about $1.50 for 50 or more.  I'm trying to
avoid having to stock too many kinds of panel hardware.
 
> 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.