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An ideal for FX pedal.


 
12/18/1998 12:41 PM
BHarrison
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An ideal for FX pedal.
Here's an idea  
 
A multiple wah wah pedal built around the Tube screamer. Multiple wah meaining, two maybe three wah circuits controlled by the same rocker. Have all of that mixed down into a tube screamer circuit. I had thought of this earlier but it wasn't until I saw the review on harmony central for the seek wah that got me thinking again.  
 
I wonder what this would sound like? Crap? or Worse! SO a wah wah is just a notch filter that you move back in forth. Would there be any advantages in have mutliple notches?  
 
Anyway, just trying to think/create something new and different to play around with.  
 
So what do you think? Anybody interested in working on this together/ group effort or whatever, or is this just a bad idea.  
 
 
Brian H.
 
12/18/1998 12:56 PM
Jack Orman
Website

Actually a wah is usually a pedal variable bandpass filter. Years ago Anderton designed a dual wah that had 2 filters that could be swept at the same time. As you add more filters you thicken the sound and it will probably begin to sound more and more like phasing (which is equivalent to 2 NOTCH filters being cycled).  
 
regards, Jack
 
 
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12/18/1998 4:32 PM
erin
So if you made an auto wah with multiple filters youd have a phasor, right? sounds easier than buying a bunch of jfets and hoping they match!
 
12/18/1998 5:49 PM
R.G.
Website
email

Well, maybe, maybe not. As always, the devil is in the details.  
 
What Jack said was:  
quote:
"As you add more filters you thicken the sound and it will probably begin to sound more and more like phasing (which is equivalent to 2 NOTCH filters being cycled)."
 
That statement contains a lot of references and commentary in an apparently simple statement.  
 
As you add more bandpass filters, you get a peakier response curve, more peaks and valleys. Phasers sound the way they do because they have notches, literally places where the response goes to almost zero. If you have a bunch of bandpasses, the places between the bandpasses begin to sound relatively like notches, so there is some "phasiness" that would happen, but it's not going to be a solid -20 to 40db notch. The key there is "more and more like phasing". Also, phasers may have one, two, three or more notches, depending on the number of phase shift stages.  
 
But your conclusion is almost correct. (The standard phase shift stage is an "all-pass" filter itself, by the way.) If you use voltage or current tunable notch filters, you can indeed wiggle the notches around and it gets the same phaser response as the phase shift implementation. I've seen at least one of these built from multi-VCA modules, and one from OTA modules. The EH Small Stone is another variation that is done with OTA modules, not matched JFETs.  
 
The problem with this approach is that you have to move the response of the notch filters around, too, and that leaves you with either VCA/CCA chips to get or resistors to vary, which is what the JFETs are doing. By the time you get done, the circuit is either complicated or uses special purpose chips. The Small Stone is the only notable exception to this that I know.  
 
There is a trick you can use with CMOS CD4049 and 4069 hex inverter chips that make them into effectively six matched mosfets. The old EH Bad Stone did this, some other commercial effects did too.  
 
I once collected a batch of ways to do phasers and posted them somewhere - maybe the synthesizer list I subscribe to. Lemme see:  
 
Stock all pass stages with  
- variable resistors by  
jfet Rds  
mosfet Rds  
bipolar diode junction Rac  
bipolar transistor collector resistance Rce  
LDR  
OTA faking a resistor  
voltage variable resistor (varistor)- old Magnatone amps did this  
mechanically rotated multipot  
Duty-cycle switched variable resistor  
switched capacitor variable resistor implementations  
- variable cap by  
mechanically variable cap  
voltage variable junction capacitance (never seen one...)  
Switched capacitor and duty cycled capacitors  
 
OTA implementations like the Small Stone and Maestro stage phaser  
 
Variable notch filters with VCA and CCA modules  
Variable Twin T notch filters swept by one of the variable  
resistance techniques  
Variable (other notch filters...) swept by the variable resistor/cap  
methods.  
 
What am I missing, guys?
 
12/18/1998 8:03 PM
erin
Oh well, if it were all as simple as the innocent, naive musings of a newbie techie. I'm just giong to have to put this on my list of "How the World would be different if i were God"  
Maybe you covered this in your post, (i'm going to have to go to my books to look up a little) but if the auto wah has a bandpass filter to wah the couldnt you change the filter to a notch filter , and get closer to it?  
Ah, problably not, looks like ive got to woodshed with my 'So you want to start electronics' books. I need to any way!  
 
Thanks, erin
 
12/19/1998 5:12 AM
Jack Orman
Website
email

...and to throw in another apparently simple statement: as you create additional notches in a phaser, the circuit begins to sound more and more like flanging.  
 
Some phasers have a feedback control, which I've also seen labeled as color (or is that colour :) As the control is advanced a peakiness is introduced into the filter response which gives the output more of a multiple bandpass taste.  
 
Using a single notch can give a phasing type of sound if the notch width is fairly broad. But it is not as 'rich' sounding since the notch is probably not as deep as true phase delay notches.  
 
There was a circuit in an old issue of Polyphony that used a cmos hex inverter package to create 6 VCAs. I'll dig it out and see how it could be applied.  
 
regards, Jack
 
12/18/1998 6:00 PM
BHarrison
email

Yeah I guess your right, it does start sounding like a phasor. I started playing around with my "vintage" GSp 2101 with the notch filters and discovered the phasing effect.  
 
What can I do to thicken up a wah-wah pedal. I would love to get the wah sound like on Stevie Ray Vaughn's cover of Voodoo Child (slight return). It just sounds so thick! Maybe that doesn't describe it very well. Anybody know what he used there or is it the tube amp cranked thats giving that thick sound, since Stevie always played real LOUD.  
 
I've got this MorLey wah pedal that's dying to get reborn. Any suggestions for a wah circuit?  
 
I think the (one)Wah pedal + Tube screamer would still be a neat project, call it Wah-Screamer.  
 
Anyway,  
Thanks
 
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