Vox847 clone + mods, odd results in spice simulation

[DiscoVlad]

I'm just about to make a new board for my wah pedal, the general concept is a tweakable Vox847 with input and output buffers, so I started off by drawing out the wah portion in LTSpice to see the effect of various Vox847/Crybaby mods.

As it stands the component values for everything but the transistors are the same as a Vox847 wah.
Schematic

Explanation of the {x} component values (for those unfamiliar with spice):
R11, and R12 are the potentiometer. The equation for the value in conjunction with ".step param wip..." is used to change the value of these resistors (and hence, the position of the pot's rotation).

R2: this is usually changed in the "mid-range boost" mod, which is done to lessen/stop the volume drop when the pedal is rocked all the way back. the .step param mid... in blue is commented out (typical resistor values for this mod)
param mid=1.5 sets the value to 1.5k (standard)

C3: changing this capacitor alters the sweep range of the wah, standard value = 0.01uF. altered by changing the value of the swp parameter (e.g. 0.68uF will make it a bass wah)

R7: the vocal mod... In theory, this directly affects the sharpness (Q) of the resonant peak producing a  more/less "vocal" wah sound...
In simulation, changing this appears to have an effect somewhere in the range "none", to "very little".


Frequency response plot

Explanation of the Traces:
The three separate lines are the result of changing the R11/R12 potentiometer  red is at one end of the sweep, blue in the centre, green at the other end.
The brown/purple/yellow fuzziness around these three traces is the result of changing R7 from 33k, to 68k, to 100k.

Does anyone know what's going on here? I'm expecting there to be 3 peaks (corresponding to each part of the wah sweep), with narrower frequency bands within each peak.

this isn't the case so I'm left with 3 possibilities:
1) I've made a mistake somewhere.
2) Spice is wrong.
3) This mod doesn't do anything.

[tehfunk]

I'm interested to see how this comes out, but first I must say hahahahah, i love your "possible conclusions". Theyre just classic.

[Arno van der Heijden]

I can't spot a mistake in your spice schematic. However, I think one thing that may misled you is the fact that we're not dealing with a linear pot taper. With the chosen values of 0.1, 0.5, 0.9 the peaks shouldn't be evenly distributed over the freqency range anyway.

Moreover, I think you should better try to get the simulation running correctly without the mods first. Do some simulations without the mods and with different (more) values of wip and see if that looks correct. If that seems to work, try the mods.

[DiscoVlad]

Yeah, I'm aware of that, and also that the pot won't travel through a full rotation due to the rack/pinion.

Just looked at the schematic again...I was right on one of my conclusions, I _have_ made a mistake  R10 (10k) is supposed to be connected to ground, not the feedback/resonant circuit.

more to come...