[sdiy] AC coupling caps on MS20 clone

[Oscar Salas]

David,

If you want switch in front panel, this solution implies connect a cable in a high impedance part -the inverting opamp input- when ideal design pcb wants short traces at that points.
I don't see the need.

It would be better place the capacitor on the input or between two stages. So I would say between the sum inverting amplifier and the 30K input ssm2164 resistor. (I'm supposing the schematic)
--- On Sat, 8/7/10, David G. Dixon <dixon at interchange.ubc.ca> wrote:

> From: David G. Dixon <dixon at interchange.ubc.ca>
> Subject: Re: [sdiy] AC coupling caps on MS20 clone
> To: "'megaohm'" <megaohm1 at gmail.com>
> Cc: "'Synth DIY'" <synth-diy at dropmix.xs4all.nl>
> Date: Saturday, August 7, 2010, 9:48 PM
> > > 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!
> 
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