Dallas Arbiter Fuzz-Wah Face
I pulled the circuit board out of my old wah pedal and traced it so that I could add the schematic to the DMZ archives. I bought this foot pedal in early 1973, so it was probably made a few months earlier, in 1972 in Italy. The bypass switching has been eliminated from the diagrams for clarity.
The circuit consists of two parts; the fuzz unit and the wah-wah filter. Since I had long ago removed the selector switch from the side of the unit, I not entirely positive but I think that the fuzz circuit came first in the signal chain, followed by the wah circuit. The switch allowed you to bypass the fuzz and just use the wah-wah.
If you are familiar with the Fuzz Face circuit, you'll notice that the distortion part of this unit is very similar to the NPN Fuzz Face, except a few component values have been changed and there is no drive control. The input transistor was unmarked but it is a small "top hat" package NPN transistor. The other transistor is a BC170B.
The wah-wah circuit is very similar to the Dunlop Cry Baby and Vox Wah units. As I recall, the Electro-Harmonix Wah was similar as well. The two capacitors that I show as 3900pf were unmarked except for 4 color bands (black-orange-white-red), and that's the value that I calculated from them. Both transistors are marked BC170B. The inductor is small metal can about 5/8" diameter and 3/4" tall and clearly marked on top. The circuit uses a mixture of carbon film and composition resistors. The larger caps appear to be film types and the 4.7 and 10uf are aluminum electrolytics. The two 0.22uf caps are rectangular plastic block types.
If you want to build either of the sections of this pedal, I would suggest that you try the common 2N3904 transistor all the way around and see how it performs. Download the schematics and get a look at how this classic unit was designed.
Copr. 1997 by AMZ
Back to the Analog Music Zone