Inductor-less wah wah [link]

[keko]

Check this out.

I can't say anything about it, 'cause I just came into it five minutes ago, but I think many of you will be interested...

http://www.iespana.es/electronred/Wha.htm

[Brian Marshall]

im not sure i understand what is going on on the inverting input of the 2nd opamp. or the 150 nf cap to ground for the + power suppy to it either.

looks like you need a dual ganged pot.

[Brian Marshall]

now i get it... i think, but looks like it wouldnt have a peak to it, it would just be a simple moving lpf.

[Boofhead]

It does have a moving peak.  The second stage is an inverting bandpass filter.  Not sure how it would sound.

There's a small error in that R1 and C2 should connect to +V (line A).

[Carlos Best]

Takin about inductor less wahs...
What do you think 'bout John Hollis Phantom Wah?

Has anyone built one?

[kroushl]

Check out RG's Technology of the Wah at http://www.geofex.com

He discusses different ways to make them, including gyrators (which simulate inductors using an opamp).

Brad

[Tim Escobedo]

It is a bandpass filter built around IC2. Interestingly, I've never see this type of filter using a dual ganged pot, which I guess helps solve one of the problems with this type  of filter. But it also adds a problem, since you now have to find a suitable dual pot and negates one of the main advantages of the design.  

Unfortunately, it seems the schem on the whole won't work, as R1, R2 and C2 look wrong.

[ExpAnonColin]

Mmm.. looks sort of like the anderton antiwah.

Here's a translation:
Function:
We know that a great variety of guitar pedals exist, one of the most popular is the "wha-wha".  We present to you all this circuit used with a double potentiometer, we use this system to make the use easier, instead of the "habitual" system of a photoelectric cell.

To use this circuit we should put a signal into the input and turn the potentiometer to test it.

This circuit consists of 2 parts that are quite different.  At first we find a IC, the 3140, that acts like a sperador of the signal strenth and the bandpass filter.  One should need to reduce the R3 until the value of 180W ().  Without incorperating the seperator circuit, the intput signal would practically be destroyed when it found such an enormous load.  IC1 aisla () the strength of the filtered signal to show the inpedence of the very elevated entrace, and an output impedence that's much lowered.  The gain of this part is equal to one plus the resistances of R1 and R2, ().  The bandpass filter consitutes for the inverse amplifier where the components C5, 6 P1 and P2 are incorperated in the network of regulation, those elements determine the central frequency.

To vary the central frequency we use the dual tandem pot.

-Colin

[EdJ]

Hopefully i will finally understand in the near future how to scan and up load things because i have the schematics for the tascam244 portastudio here.I used to make different wahs with the tonesection after recording.
It is based on dualganget pots but can be made with single .
Greetings,Ed

[keko]

One should need to reduce the R3 until the value of 180W ().  Without incorperating the seperator circuit, the intput signal would practically be destroyed when it found such an enormous load.  IC1 aisla () the strength of the filtered signal to show the inpedence of the very elevated entrace, and an output impedence that's much lowered.

-Colin

When he says 180W he means Ohms. I was reading the whole site, wich has some good electronics tutorials in spanish, and every time Ohms mentioned, they use the W instead of the Omega greek character. Maybe they didn't know how to generate such symbol, or there's something wrong with the Caracter Set in the html.

IC1 aisla means that IC 'isolates'.

hope this helps.

[Brian Marshall]

I STILL DONT GET C7  if it is a filter for power, seems like the cap could stand to be much bigger.

Brian

[Tim Escobedo]

Some electrolytics can have poor higher frequency response in this application, thus the use of smaller (typ. .1uF) usually non polarized caps in parallel with the bigger cap to compensate for the disparity.

Usually, though, in stompbox apps, you can go without.

[SiCKNeSs]

This schematic was released by Ricardo Alvarez Echaide for the spanish magazine Resistor (July/1984).

I build the wha for a friend some time ago. The schematic is bad, R1-C2 go to Vcc, but the pcb from the magazine is correct.

The sound is good, the only problem is the dual ganged pot and find a correct enclosure for use it.

keko, quieres saber algo mas?

keko, do you want know any more?

[keko]

keko, quieres saber algo mas?

Claro, si tienes el pcb a mano seria fantastico que me lo pudieras enviar por mail a s_majluf # tutopia.com.

Gracias.
De donde eres?