Vox/Crybaby Wah Transfer Function

[Rob Strand]

no buffers, nothing ... pure

Probably shouldn't overlook stuff like that contributing to the tone.

[Rob Strand]

My original goal was to have the uber classic (Zappa/Hendrix/Clapton) WAH response,
... but without any headroom issues // absolutely nothing else altered

I was poking around my stuff and I notice something interesting:

1) The very early wahs seem to have no resistor across the inductor.
   The inductor details are unknown to me.  They are bolted to the PCB and don't use a base with PCB pins.
   The construction is in a strip.

2) The script Clyde McCoys (at least the earlier ones, Italy 1967/1968) use the "small hole" halo inductor
  These have a 100k across the inductor.   The DC resistance of this inductor is high like 80ohms.
  You can identify the small-hole by sight because the ferrite ring inside the halo has a width a bit
   larger than the diameter of the hole.  Sometimes you can see text on the top ".../11".

3) After that the inductors have lower DC resistances (say 15 to 56ohms) and the resistance across the
inductor is 33k.
  Of these the earlier ones use a "large hole" halo inductor.   You can identify these by sight because
  the ferrite ring inside the halo has a width about the same as the *radius* of the hole.   The resistance
  of these is about 56 ohms.   The text on the top is always chopped off.


The inductor DC resistance and the parallel resistors change the character of the response:

In (2) the high inductor DC resistance decreases the peaks in the LF region and the larger parallel resistance increase the peaks in the HF region.  As a consequence these will emphasize the high-end.

I have no info on the very early inductors but having no resistor across the inductor would exaggerate this further.

In case (3)  the LF peaks are higher than (2) and the peaks stay relatively even at the hf-end.


Here's a schematic and pic of the small-hole halo inductor + 100k resistor:
http://fuzzcentral.ssguitar.com/mccoy.php

The large-hole halo + 33k is like this,
https://i.pinimg.com/736x/09/4f/33/094f33f81201fbe84aa00086e89ced0b.jpg
https://gbmedia.azureedge.net/usercontent/gear/5730118/p3_uljrdlbln_ss.jpg?maxwidth=500

[Transmogrifox]

It's true though, simplified closed form expressions let you see into the problem.  Once you make them to generalized they can can get out of hand.  They get to the point where you can no longer visualize how changing a parameter affects the response.  ...

Well anyway, hopefully my rendering helps somebody who is starting to explore this circuit.  It looks simple enough, but it is deceptively non-trivial.