Dr. Quack/Nurse Quacky question

[raulgrell]

On talking with my band about the guitar effects I will be making, I mentioned the Dr. Quack and the Nurse Quacky... They loved the idea and came up with an interesting point:

Is there a way to reverse the effect, such that it makes an "ow" sound instead of a "wah"?

Could lead to some funky sounds...

[Paul Perry (Frostwave)]

Any envelope follower can be reversed, by inverting the control voltage derived from the envelope.
The tricky thing is, to arrange things so that when you switch between modes, the "centre frequency" of the filter is the same (that is to say, the frequency of the filter with no signal going in).

[oldrocker]

Maybe you modify a Phuncgnosis to this well.  It already does this to a point but maybe it could be modified to be more pronounced with less high frequency filtering.  Maybe get faster response time too.

[raulgrell]

I was just checking out the Phuncgnosis schematic at Escobedo's site... what's the aux in for?

[grapefruit]

Yes, the mutron and some other circuits do this by inverting the signal and level shifting a dc bias at the same time. As Paul said it's a bit tricky to do with single supply, and possibly not wothwhile for the Dr Quack...

Stew.

[Mark Hammer]

Two, and maybe even three, ways ways to do this:

1) Invert the envelope voltage, as is done on the Mutron and the Phuncgnosis.

2) Use a different control element (P-junction vs N-junction JFET) such that the same envelope voltage produces the opposite result.

3) As in the Bass Balls, make the attack so quick that the decay is the most noticeable part of the sweep.

I have an old E-H Y-Triggered Filter that has a single sweep-width/direction pot.  At midpoint, there is no sweep.  Go in one direction from midpoint and you get stronger upward sweep.  Go the other direction and you get stronger (wider) downward sweep.  Unfortunately, the posted schematic (that has been up for over a decade, without any evidence of exploration) is really hard to follow.  I keep meaning to trace mine out along with the posted schem, but that task sits at the bottom of a very long list of projects and things to attend to.

[raulgrell]

If you post the gut-shots of your pedal, and a link to the existing schematic, I could try trace it...

Also, how would I invert the envelope voltage? and could the different control element be used with no parts changes?

[Mark Hammer]

Tim Escobedo's "Gargler" illustrates the part swap nicely: http://www.geocities.com/tpe123/folkurban/fuzz/gargler.gif

The filter section using Q1 sweeps upward, like the Dr Q.  The filter section using Q2 sweeps downward.  Q1 and Q2 are the two control elements in question.  Though the difference in trimpot values suggests they aren't directly interchangeable, they ARE fed by the same general envelope signal, with one element decreasing resistance while the other increases.

[oldrocker]

I was just checking out the Phuncgnosis schematic at Escobedo's site... what's the aux in for?

Good question.  I didn't add it when I built it.

[Mark Hammer]

It's for driving the envelope follower with an external source, the same way you might use an external source to key a noise gate.  For instance, you might want to adjust the filter in response to a drummer's kick drum, or with a singer's hand claps, etc.  Yo could use an external preprogrammed source too, like a rhythm machine, or for that matter a recording of your band doing that very song.

[raulgrell]

Could you use a signal coming from say a theremin to control the wah to produce a similar effect to that of a wah (eg crybaby) pedal?

Could lead to some very interesting applications...

EDIT: Forget the gut-shot I asked for... just took a look at the existing schem, and part list is too long for my liking :S

[raulgrell]

Sorry about the double post, by modify button seems to have disappeared =O

I had an idea with the theremin (assuming connecting it to the aux will produce the effect I want) - Placing the volume antennae on the guitar in such a way that the wah effect is controlled by your hand/elbow's distance to the guitar...

Viable?

[sfx1999]

IIRC, the Mu-Tron III can do this.

There are clips on this page (not in English): http://www.pisotones.com/MuTron-III/MuTronIII.htm

General Guitar Gadgets has a project for this: http://www.generalguitargadgets.com/index.php?option=content&task=view&id=135&Itemid=149

The board has space for an optional charge pump so you can run it from a 9V supply.