Circuit for a wha

[Gus]

http://www.aronnelson.com/gallery/main.php/v/gus/wha1.gif.html?g2_imageViewsIndex=1

Open it and look you might have fun with it.  Question only one person has posted they built this they also posted sound clips.  This was at a different forum. Is it because it is hand drawn?

You will need to adjust the sweep cap and input resistor to taste depending on the first stages gain setting.  It is a mix of a few fragments from whas with the added use of a bootstapped predictable bias EF stage.  Note no mixing/bias resistor from the first stage and the ablity to move the emitter bias to a predictable setting. 

This circuit is inspired from Wha posts, a lot from Paul M's posts about whas.  I thought about the posts and what was different about the whas and drew this circuit up note the input bias adjustments resistor marked * values are written next to Q1.

[aron]

Smaller and a little more clarity onscreen.

[B Tremblay]

Here's my response to Gus after I tried the wah circuit last summer:

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Gus, I can confirm that the circuit works as drawn.

For the user-specified parts, I used 18k for Q1's collector and 82k for the resistor marked with an asterisk. Your calculations for the pin voltages were very accurate:

Q1 MPSA18
C 4.27
B .600
E 0

Q2 MPSA18
C 9.07
B 5.25
E 4.71

I did add a 100k resistor in parallel with the inductor, which I previously mentioned was the 1k:8ohm Radio Shack transformer (part number 273-1380).

I'm using a Life pot (with the blue plastic base) and mounted it in an old DeArmond expression pedal.

The sound is terrific. Very full-range and clean. Interestingly, I did have to use a much smaller sweep cap (3n3). I may be able to record a clip. I'm curious to hear the circuit with a traditional inductor.

Well done, Gus, and thank you for sharing it. I hope others will try this great circuit.

----

And here are the clips:

http://runoffgroove.com/gswah1.mp3
http://runoffgroove.com/gswah2.mp3
http://runoffgroove.com/gswah3.mp3

The first two clips are Tele bridge pup - GS Wah - close-miked Ampeg Rocket II, then the third clip has my Sili-Face placed in front of the wah.

[PRR]

> because it is hand drawn?

The line-art is good.

The image is awful big on my monitor, I have to turn my head to read it, and the first thing I see (bottom left corner) is a bunch of cross-out text.

Many folks won't work from a schematic. (I think it is an essential skill, but I'm an old hacker and out of touch.) A suggested layout is tedious to draw, but many more folks may try it from a layout than a schematic.

There is a LOT of text on the image, too much to conveniently read.

To make it more obvious and "inviting", put most of the text in a post or text file. Start with an overview (What IS a "wha"? What song would I want it for? What will this cost?) then organize the details (construction, trims, use). Include some comments on how wonderful it sounds... nobody can "hear" a schematic. Clean, neaten, rotate, and resize the image; yeah, "we should be able to do that" but so many plans so little time. Schematic should have TITLE, author, part values, and in this case part-ID so your text can refer to "R2" and explain why it would be 10K or 22K. IMHO it should not be cluttered with notes.

http://i45.tinypic.com/30djdhu.jpg