V G wrote:
> Since the frequency of an RC filter is =3D 1/(2piRC), and is affected
> by the value of R:
>
> 1. Wouldn't the frequency response of the filter change based on the
> signal source impedance? (Since R would be in series with the source
> signal)

Yes, which is why you need to control the impedance to get predictable
filter characteristics.  Since the amp output impedance is quite low, you
use a much larger resistance in the filter so that this resistance
dominates.

Since your desired time constant is so long, you need a fairly high
impedance to avoid excessively large capacitance.  As I said in a earlier
post, a 10uF ceramic cap from the amp output followed by 100kOhms to ground
should about do it.  That signal now has up to 100kOhms impedance, but
that's no big deal for the next stage to handle as long as you take that
into account.  The next stage can easily have multiple MOhm input impedance=
,
which won't load the filter output.


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