Input impedance questions

[AM]

Hi people,
I' ve been doing some reading (R.G.'s articles) about calculating input/output impedance. I think I'm starting to understand a bit but I have a couple of questions.
First I would like to couple what I read with a practical example of calculating the impedance of a simple circuit. Let's take something like the Red Llama for example.This is a simple circuit that practically everybody has built here. (I've built at least three for friends).
http://www.aronnelson.com/gallery/main.php/v/MarkMs-Gallery/album15/album76/Red_Llama_LAYOUT.gif.html
What would be the input/output impedance of that circuit?

My second question is regarding a buffered wah pedal I own with input impedance of 470 Kohm and output impedance < 1 Kohm.
If this is the first pedal in my chain. Is there any danger of loading my guitar's humbucker pickups which I believe they are rated at 500 K ? By practical experimentation I haven't notice any tone sucking so far. The only drawback is a slight volume drop (measured at 0.8 dB) but no tone alteration. I don't know if it's even worth tinkering with the pedal to correct that slight volume drop since I'm more than happy with the overall sound.

[R.G.]

Looking at the schemo at gaussmarkov: the input impedance is close to 100K. This is because the input is driven from the output by negative feedback, and the input goes to the inverting (and only!) input through a 100K resistor. Negative feedback to an inverting input drives the input node to be approximately at AC ground with a low impedance. So the 100K is the only thing standing between the input signal and "ground" except for the cap, which is negligibly smaller than the 100K at all frequencies where it is not also restricting signal current. So 100K, approximately.

If you are experiencing no noticeable tone sucking, it's fine. The only problems with guitar loading are tone sucking and volume loss. The volume loss in this case is the loss inside the wah itself. If you hear no sucking, you're good to go. It's not work tinkering with it if you are happy with the sound.

[AM]

Looking at the schemo at gaussmarkov: the input impedance is close to 100K.

Thank you so much for replying. I guess that with this impedance value  there is some high frequency signal loss initially but restored at a later point in the circuit. Is this a correct assumption?

If you are experiencing no noticeable tone sucking, it's fine. The only problems with guitar loading are tone sucking and volume loss.

I think that the bypass signal is really acceptable. That was a bit of a surprise because I though that an 1M input impedance was the best compromise. (quoting from another post of yours:  "the deciding factor is that guitars sound like we expect them to when they drive the 1M the guys used in the "golden age". That value was set then because of cable and capacitive requirements in tube amps in general, not just guitar amp. It carried over." )

Is there something special in the design of the buffer of the pedal that prevents the signal loss or a 470k input impedance is still high enough?
Schemo link:
http://cid-90562a4f99e2b9cc.spaces.live.com/photos/cns!90562A4F99E2B9CC!110/?ViewType=4

[R.G.]

Frankly the difference between 1M and 100K is not huge. Some people ignore it. Some people like it. Some people think any loss is intolerable. Some people would rather be in Las Vegas.

The answer is always inside your own personal ears.