Impedance Question?

 Very informative thread. Thanks for asking the question sqitis. Maybe this was mentioned and I missed it but is there a simple mathematical relationship between the value of the coupling capacitors and the output impedance or other variables are in play?

Yes indeed! I've learned much from this thread.

Maybe this was mentioned and I missed it but is there a simple mathematical relationship between the value of the coupling capacitors and the output impedance or other variables are in play?

There is-  Zout+C, where C is the impedance of the cap at the specified frequency, and Zout is the output impedance of the circuit driving the cap.

At 1000Hz, typically the cap has no influence on the output impedance. But as the frequency is decreased, the output coupling cap begins to have a greater and greater influence as the cutoff (-3db point) frequency is approached, such that it is the major component of the output impedance rather than the circuit driving it.

Keep in mind that this is a bit oversimplified as there can be complicating aspects that do affect output impedance, such as the application of loop feedback which will reduce some of the effects of the output coupling cap.