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Craig Anderton Wah-Antiwah

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2/13/2003 4:38 AM

Constantin Necrasov

Craig Anderton Wah-Antiwah

My question is about the Anderton Wah-Antiwah Schematic.
This one here - http://www.muzique.com/schem/wah2.gif
What is the op amp there? I tried TL072, and the potentiometer worked as a volume control without any change to the Q. All the connections look alright, little chance to mistake in such a simple circuit. Maybe it's the mysterious BIPOLAR power supply? Or any specific chip?
Has anyone tried it? Did it work?
Write to me, cuz I want to build that one. Need help, yours truly.

2/13/2003 3:53 PM

It quite possibly *is* the bipolar power supply if you call it "mysterious". Most of Craig Anderton's projects require two batteries, one hooked up the normal way as +9 volts to pin 8 of a dual opamp, the other hooked up as -9 volts to pin 4.

I seem to recall making the same mistake when I built a wah from a schematic I found on the net (can't remember just which one). It didn't specify a bipolar supply but after trying for hours to get it to work, in desparation I tried using two batteries. Bingo!

2/13/2003 8:25 PM
Constantin Necrasov	So basically it will be a 18V (9+9 series connection) powered circuit then? Where will the other ends of the battery connections go? I can't send both remaining +9V & -9V to the ground.

2/13/2003 11:49 PM
Bernt	Yes, that is exactly what you're supposed to do! Call back if it's unclear! Kindest regards, Bernt.

2/14/2003 5:35 AM

Constantin Necrasov

Me again.
By saying that that's exactly what I'm supposed to do you meant the 9+9 in series? Or sending unused terminals of the two batteries to ground?
Cause I figured that since the pin 4 of the op amp should be grounded and ground receives both the +9V from source "A"(feeding pin4) and -9V from source "B"(feeding pin8), and we ground the pin 4 and are supposed to supply it with the negative charge from source "A", we are shorting the "A" battery.
That's my reasoning, I didn't try either of the ways yet, and wont until next week probably.
So there's time for me to wait for your answers.
Thanx to the two previous posts, yours tuly.

2/14/2003 11:33 AM
griff	nope, pin 4 just goes to the -9V, doesnt go to ground as well. You want the signal voltage to be in the middle of the supply voltage range for the opamp. Look up opamp biasing if you want to know why. BTW i havent done effects for a while, i could be wrong. griff

2/14/2003 4:16 PM
RickL	You are right. Pin 8 gets +9v, pin 4 gets -9v. Ground is the black wire of the +9v battery, the red wire of the -9v battery and wherever ground is indicated on the schematic. Even projects that use only one 9 volt battery and have pin 4 hooked to ground esentially use a bipolar supply. The 9 volts is turned into +4.5v and -4.5v.

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