Input/output impedance

[comfortably_numb]

I've been reading up on the virtues of buffers, how they relate to true bypass, and how each effect in the chain drives the next.  Apparently the ideal stompbox should have a high input impedance and a low output impedance. 

From what I've been able to deduce (which feels very uneducated) the first resistor to ground, usually the pulldown resistor in a stompbox, will set the input impedance.  2.2M is pretty high right?  So we're okay there.  In reading about the Dallas Rangemaster, I learned that the 10k audio pot that controls gain sets the output impedence - 10k at the max.  This is apparently sufficiently low for good results. 

My questions are:

Is 100k, the most common output pot value, a sufficiently low impedance in compliance with our wishes?

Is there something else that is determining impedance that I'm just not understanding?

Thanks!

[Peter Snowberg]

The input to ground resistor is only part of the input impedance. If the input goes to a basic (non-bootstrapped) bipolar transistor, the transistor may present an impedance of less than 20K. A JFET opamp on the other hand may have an input impedance of 10,000,000,000K. In both cases the impedance of the source of the bias voltage will also be presented in parallel with the input. Most boxes seem to shoot for an input impedance of about 500K, but there isn't any standardization other than trying to make the output impedance 1/10th the input impedance of the next box, or there abouts. Boosters are a special case with an extremely wide input impedance range.

For an output pot, 50K is a better choice, but a wide range will work. Sometimes a larger value (like 100K) is used because the circuit in question doesn't have that much output current capability.

As usual, GEO has got more details.

[comfortably_numb]

Thanks Peter, I'll check GEO to see what I can come up with.