[sdiy] Optimum Input Impedances

[harrybissell]

Hi Glen:

> On a different note, but somewhat related, how do you determine the amount
> of loading a circuit's output "likes" to have? For example if you had a
> microphone, or a Hammond tonewheel generator, or whatever, of known
> impedance--how do you determine the optimum load for your signal source?
> This question might be harder to answer, because I think there are so many
> different possible situations that it would probably be too hard to give
> any universal rule of thumb, but in case I'm wrong. let me know the
> universal rule of thumb.   :)

>

The universal rule of MY thumb (when it is not in unspeakable places) is to
have an input impedance of 10X the driving impedance.  So for a 10K
driving impedance, I'd go no lower than a 100K input impedance.

The only exceptions to this rule come when the input impedance would
become crazy (like 10M ohm)... in that case I'd probably cheat to try and
use lower values.

Also... it depends on what you want to do with the signal, did you need full
frequency response etc.  If you are driving a fuzzbox... you can afford to
load
the hell out a guitar pickup without problems... otoh you better 'disconnect'
that
load if you want to bypass the fuzz without the loading problem being really
obvious.

H^) harry