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Vintage threads from the first ten years

Re: You rang, sir?

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8/26/1999 5:57 PM
GFR	Re: You rang, sir? What about using a RF oscilator where the osc frequency is varied by the capacitance from an "antenna" (a metal plate) and "ground" (the guitar player body). Then you get a control voltage proportional to this frequency and you can control the wah with the proximity of your body or hand, somewhat like a theremin. No manual contact!

8/26/1999 12:08 AM

Updated Wah Technology article

I've just posted a fairly major update to the Technology" target="_blank">http://www.geofex.com/wahped.htm">Technology of Wah Pedals article at GEO." target="_blank">http://www.geofex.com">GEO.

The update includes a number of reference schematics, how to implement the classic wah circuit with opamps, and some discussion of what each part does, preparatory to adding a fairly in-depth discussion of mods to the basic pedal.

Have fun!

8/26/1999 6:17 PM

Good Article RG. Reading through it I wanted to probe your mind about the Inductor Magic portion of the article. Where you theorize that one of the poles saturates earlier than the other. Could it be possible that a poorly wound bobbin could cause this premature saturation of on eof the poles? Also, the type of core material plays a role in Q factor and ultimately the saturation point of the core. Were you ever able to determine what type of core material was used in the Fasel inductor?

CJ Landry

8/27/1999 11:25 AM

Wha-Volume on the Boomerang and Mr. Cry Baby

Now it's clear how the wha/volume switching works. You lift the grounded end of the 4.7u cap and you've got AC feedback - now the first transistor is an inverting amplifier with the base being the low impedance point for summing currents. Now use a big capacitor in series with an appropriate mixing resistor from the emitter of Q2 to have variable full-range feedback - instead of a variable capacitor it's now a variable resistor. The pot is now a gain control!

8/27/1999 2:29 PM
R.G.	Yeah, pretty slick. The Boomerang designers at least understood how this thing worked. This has a lot of the things I like - subtle use of components in a fairly elegant circuit, and lost for lack of understanding. Kind of like circuit archeology.

8/27/1999 2:07 PM
Carsten Hütter	Re: Updated Wah Technology article Hello R.G.! Thanks a lot for your article, it is very instructive. There's one thing I'd like to see in there and that's optoisolators replacing scratchy pots. I remember you once sent me an e-mail about, but I still do not dare to do the job without further information. Regards Carsten

8/27/1999 2:32 PM
R.G.	I'll try to get that added in the near future. It's pretty clear how that works now - a fixed resistor and an LDR replace the pot, and the real pot controls current in an LED. Anything that acts as a volume control on signals into the emitter follower will vary the wah setting.

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