Fuzz Face - Impedance at Q2C Voltage Divider

[Jolly Jimmy]

Hello all,

Is it possible to estimate the impedance at the point of the voltage divider coming off Q2C (where the output cap would usually be)? For the purpose of more accurately modelling the frequency response of a BMP style tone stack in TSC.

Many thanks!

[antonis]

It's the value of upper splitted Collector resistor...
(470R if I recall it right..)

[iainpunk]

It's the value of upper splitted Collector resistor...
(470R if I recall it right..)

Im afraid this is not entirely correct, you should take in to account that the impedance is asymmetrical, due to how transistors work. But 470R is a good approximation.

[Jolly Jimmy]

Thanks for the input, guys.

I'm trying to read up on this. Would I be correct in thinking that the impedance is equal to the value of the collector resistor and the load resistor in parallel? So for example 8.2K and 470R, that would be 445R? Close enough to RL for those values at least then.

[antonis]

Right for Collector(*) & Load resistors in parallel but wrong for 8k2 one.. 

Collector-Base junction is reversed biased so there isn't any "path" for signal through 8k2 resistor..
(other than reverse leakage current..)

(*) We only deal with Collector resistor(s) when "seen" from Collector point of view - which  isn't true here..
(output cap isn't straight tied on Collector..)


<Im afraid this is not entirely correct, you should take in to account that the impedance is asymmetrical, due to how transistors work>
True & Correct but, for a Fuzz-Face, let it be..