[sdiy] AC coupling caps on MS20 clone

[Oren Leavitt]

David G. Dixon wrote:
> Hey Team,
> 
> When are AC coupling caps necessary on filters?  Should they be on the input
> and the output?  Should they be on all outputs of multimode filters?  Should
> they be switchable?  What's the best value and type?
> 
> I haven't used them on my lowpass filters, but I'm unsure how to handle this
> aspect of my 2164-based MS20 VCF clone design.  Any suggestions would be
> most appreciated!
> 

Hi David,
Cumulative DC offset in the signal path would be a reason for me to want 
optional AC coupling in an input.

Value/type?
Combined with input impedance, the coupling cap forms a high-pass filter.
The value depends on the lowest frequency you want to pass.
For example, a 0.1 uF cap coupled to a typical 100K input impedance will 
cut-off frequencies at 16Hz and lower.
Most any non-polar type ought to work.

- Oren