please help me with this complicated Wah circuit

[oscar]

Hello,
I have a George Dennis Wah, and i am happy with it, however being a compulsive fiddler i want to try out some modifications. I have been reading the article on the technology of wah wahs at GEO, and i would like to try some of the suggested mods on my wah. However the schematics discussed on GEO are far simpler than my George Dennis pedal.
Here is the schematic for my pedal:
http://www.jga.u-net.com/wahswit1.jpg

If someone could help me understand which parts relate to this schematic on the GEO website:
http://www.geofex.com/Article_Folders/wahpedl/wah1.gif

I would be very grateful,
Thank you,

[oscar]

The George Dennis wah uses an LED rather than a pot to control the wah.

[R.G.]

If someone could help me understand which parts relate to this schematic

They don't relate at all. The schematic you show is a much more elaborate one, not particularly related to the Vox inductor style wah. I believe that it uses an active filter circuit similar to the multiple feedback opamp filter.

So sorry - I don't think you can do those things to that wah. They're too different.

[puretube]

sorry to be cynical: in- relates to in-,
out- to output.

to be serious: this one could be quite easily modded to
"envelope-followah"...

[Aharon]

I don't like mods personally.I much rather build from scratch and leave that one as is but then again that's me.
Aharon

[oscar]

I think in that case i will keep it as it is and try to find a vox wah case to build one from scratch. Does anyone know a place that specialises in cases or non working effects, in England?
Thanks,
Oscar

[Paul Perry (Frostwave)]

will keep it as it is and try to find a vox wah case to build one from scratch. Does anyone know a place that specialises in cases or non working effects, in England? Oscar

If you have a friendly music shop that lets people put up ads, maybe a 'broken wah wanted' would get something.. or a laundromat.. most musicians know someone with a broken wah & no money! Don't know if Excange&Mart is still going or would take this kind of asd.

[oscar]

yeah good idea, thanks.

[Nasse]

Just remembered some have built wahs in volume pedal cases

I once got nonworkin volume pedal for free. It was original JEN manufactured pedal, the case was very much like crybaby or vox, but no jacks there but bad quality fixed input and output cables. Dont remeber if I fixed it and gave back... he was a friend anyway.

Even a new volume pedal might be easy source for wah pedal case, if you do wah/wol combo - if you just can put two pots on one axle. I should try to build a wah, I never have owned a good one, or even near so, and I am getting old.

[thomas2]

hello nasse(setä). i own one of those jen volume pedals! it's exactly the same shape and size as crybaby.. i've been thinking of making a wah pedal of it, but i don't know where to get the inductor.. and it must be cheap.  :lol:

[StephenGiles]

Are we looking at a PWM controlled wah here?
Stephen

[Nasse]

Are we looking at a PWM controlled wah here?

Looks more like a filter controlled with fets to me, quess the logig circuitry is for switching

[Transmogrifox]

Actually this wah is a gyrator-based wah controlled by an LDR.  The LDR is controlled by D4, whose current is controlled by R23 (10k pot).  The thermistor is a type of feedback control device to keep the bias current in the current mirror stable.  That R23 just controls where the constant current from the mirror is directed.

Now look at the + terminal of IC1a.  There's where the photoresitor is.  
C9, R10, R11 and the photoresitor with IC1a compose the gyrator (active inductor simulator).

To complete the LC Resonant tank, look at C8.  If you ignore the JFETs and associated components, this doesn't look any different than a part of an active EQ from an HM-2 or DOD Death metal pedal.

So what are C6, C7, R7, R8 and the JFETs are just a range controll.  When the JFETs are open, the filter has a lower range (this is similar to the crybaby range mod), when they're off, the filter has a higher range, as it just switches C7 and C6 in parallel with C8 to lower the resonant frequency.  The rest of all that garbage with the logic gates and things are all related to the active bypass circuitry.

Mods:  
True bypass is very straightforward in here.
Range Mod (like crybaby):

Put in a rotary switch to vary the value of C6, C7, or C8.  C8 is probably the best one to mess with.

You can probably make it sweep further in frequency by changing R11 to 1Meg.

Play with C10 on the order of 10 nF to .1 uF to take off some of the highs so the filter looks more low-pass.

Make C11 larger to get more lows, smaller to make the filter more trebley.

Make R9 bigger to get more gain.

Replace R10 with a 100 ohm resitor in series with a 1k pot to adjust range/Resonance (it would be interactive with both).

Either way, the important parts of the circuit are in the components associated with IC1 (the NE5532).

...and yes, you can put an envelope follower in here and connect its output to R20 or something to use this as an envelope filter.

Does that help?

[gez]

Thanks for pointing out that this is a gyrator circuit T-fox, I'd have totally overlooked it otherwise (all that logic was a red herring!).