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Wah pedal circuits

8/26/1998 3:16 AM
Wah pedal circuits
Does anyone have a circuit for a wah pedal  
that does not involve a 500mH inductor?  
I have managed to find about five that  
do involve this part, which I can source  
but it would take two weeks and cost me  
a total of $US20 to have it delivered to  
New Zealand.  
I built one circuit using a design from a book  
which sounded lame (filter parameters all wrong). If anyone has a halfway  
decent schematic for a wah pedal based on  
an active filter instead of an inductor,  
I'd be very grateful. My email address is:  
8/26/1998 6:26 AM
Preben Hansen
Hi Hamish.  
Try Stellans site. He has a section for his home build rack. In this rack is a VCF.  
As Stellan says "you can wah your brains out". There is a schematic and a sound sample too. Nice sound I think.  
Regards, and happy building.  
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8/27/1998 5:45 AM
paul perry

Hamish, seeing you are in NZ, the latest copy of Silicon Chip mag (sept 98) has a wah as its lead (no pun intended) article. Uses a 4046 as a voltage controlled oscillator, which goes to a MF5CN switched capacitor filter. Nary an inductor to be seen. A good feature is that the Q of the filter can be tweaked by the ratio of 2 resistors.  
The only unfortunate thing is their plans for a pedal assembly, with a metal plate scraping around and forcing a linear pot back and foward. Yeah, right, OK for an hour maybe.  
Use a linear hall efect device & a magnet.  
The UGN3503 is easy to get, it's used in the gear change indicator elsewhere in this issue.
8/27/1998 5:58 AM
paul perry

Another approach is that in one of Penfold's books of guitar effects, "Advanced Projects for Electric Guitar"ISBN 0.85934.380.4 where a hall effect device UGN3503U (Ungar) changes the apparent resistance of a fet.
8/27/1998 4:17 PM

Thanks - it's ironic, that the magazine is  
on the newsstands while I am searching the  
internet for a circuit. Anyway, I build the  
wah out of the first Penfold guitar FX books  
and it sounds horrible. FWIW I am using an  
old Vox volume pedal as the mechanism.  
A hall effect sensor would be better, but  
I am halfway through building the wah from  
Stallan's (sp?) site. Thanks for the leads  
though, I have another wah to build for  
someone else and I might try one of those  
8/28/1998 6:20 AM
paul perry

Thanks for telling us the Penfold wah sounds shitful. Mr Penfold has done some terrible things, notably his book on building your own analog synth, almost every ckt has a fatal error just for starters! Be sure to let us know how Stellan's one goes ;-)
8/31/1998 4:46 AM

I may have to reserve that opinion against  
the Penfold wah. When I was dismantling it  
for parts to make Stellan's wah I discovered  
I had not soldered a joint on one of the  
resistors that is used to bias the input  
signal to one of the opamp stages, since  
the circuit does not have a -ve. Also,  
I found the cct you mentioned that uses the  
hall effect device. (Almost finished the  
new Wah, has the disadvantage of running  
two 9V batteries, my design expertise does  
not extend to changing that).  
I have an original Vox volume pedal. I'm  
thinking of using it as a template and  
casting some copies in aluminium, to use  
as volume/wah/whatever. That might  
be a few months from now, if anyone is  
interested feel free to email me.
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