Re: Guitar pickup output impedance

Oh WTF, it's Friday, hectic week at work, but I had a little time on my
hands, so I made a PDF of the response graphs I made corresponding to
the bleed circuit and uploaded them:

http://www.geocities.com/rpleavitt/Bleed_circuit_graphs.pdf

The first graph shows the responses with no bleed circuit at all. This
is a good indicator of why a lot of folks want one in the first place.
That resonance peak (just a little over 2 kHz in this case) is what
gives a guitar with passive pickups/circuit its "character" when the
tone control's wide open, but notice that even with the guitar at 3/4 of
full volume, the peak disappears.

Next graph shows what happens with just the capacitor. First the peak
moves to higher frequency (which is why a larger cap value is better if
you're not going to use resistors), but more importantly notice how
quickly the low frequencies fall off as you lower the volume.

Next shows the cap and series resistor. What the resistor essentially
does is keep the peak from moving so much as you turn down the volume
but you still have the issue with the bass frequencies.

Finally, cap + series resistor + parallel resistor. The "Q" of the peak
gets larger as you turn the volume down but the peak frequency pretty
much stays put, and more importantly, the bass frequencies are falling
off at roughly the same rate as the other frequencies with decreasing
volume.

So no the curves don't exactly retain the same shape but to the ears
it's doing the job I intended.


.

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