Wah range increase

[LiquidMetal]

Hello,

I am looking for ways to increase the range of a Crybaby Wah. I already checked the Geofex article (http://www.geofex.com/Article_Folders/wahpedl/wahped.htm) and Stinkfoot's web site (http://stinkfoot.se/archives/549), but only found advice of moving the effect range up or down. I am looking for clues for to extend the min/max frequency range while keeping everything else constant (Q factor, etc.). Any suggestions will be greatly appreciated.

Thanks!

[R.G.]

It is very difficult to do that. This is because the frequency of the resonance is proportionate to the square root of the change in the value of either the inductor or capacitor which set the resonance. The circuit changes only the capacitance, and therefore the range changes as the square root of the capacitance change.

That math jargon means that you have to (for instance) get four times the amount of capacitance change to double the change in frequency range; the inductor is fixed, and can't be changed. Diminishing returns set in very quickly.

The simplest thing to do for wide sweep range is to get another horse. The state variable style active filter can be set up to sweep the entire audio range if you work at it, so the wide range is less of a problem. But that's not as simple as changing a pot or capacitor value in the existing inductor-wah circuit.

[Mark Hammer]

Well, not to scoff at anyone who understands these things infinitely better than I do, but I will simply note that in building my own Cry Baby from scratch, I was unimpressed (well, sorely disappointed is more like it) with the range of sweep once I got it working.  Upon reading a bit more I found that tinkering with the emitter resistor of Q1 (more specifically, lowering its value to increase Q1 gain) solved my problems.

Now, I can't imagine that any manufacturer would fail to assure optimal sweep, and I don't even know what the actual range of sweep is on the OP's unit, compared to other wahs or other Cry Babies, or what sort of range the OP is imagining being able to achieve.  I will just say that if LiquidMetal wants to tinker, consider wiring up a 100k variable resistance in parallel with the emitter resistor of Q1, so as to be able to achieve emitter resistances that are slightly lower than stock.  That can simply be tacked on via the copper side of the board, without having to remove anything.  Maybe it will make a difference, maybe not.  If it doesn't, just unsolder the leads and reassemble.  No harm done.

[R.G.]

Well, not to scoff at anyone who understands these things infinitely better than I do, but I will simply note that in building my own Cry Baby from scratch, I was unimpressed (well, sorely disappointed is more like it) with the range of sweep once I got it working.  Upon reading a bit more I found that tinkering with the emitter resistor of Q1 (more specifically, lowering its value to increase Q1 gain) solved my problems.

Now, I can't imagine that any manufacturer would fail to assure optimal sweep, and I don't even know what the actual range of sweep is on the OP's unit, compared to other wahs or other Cry Babies, or what sort of range the OP is imagining being able to achieve.  I will just say that if LiquidMetal wants to tinker, consider wiring up a 100k variable resistance in parallel with the emitter resistor of Q1, so as to be able to achieve emitter resistances that are slightly lower than stock.  That can simply be tacked on via the copper side of the board, without having to remove anything.  Maybe it will make a difference, maybe not.  If it doesn't, just unsolder the leads and reassemble.  No harm done.

Sure. That makes sense, and fits entirely. The range of filter sweep is related to the gain available from the first transistor, as this is what is used to change the apparent size of the sweep cap. Making the gain larger does make the cap change range bigger. And if a small increase does it, great.

I was just noting that there is a math principle lurking down under there. Increasing the sweep range by a third or so can be done: doubling it would require quadrupling the raw gain, and if that's possible, the side effects of such an increase would get prominent too.

But you're absolutely correct - if twiddling the emitter resistor, or the collector resistor or both produces enough of a change, great.

[joegagan]

rg, , mark, great posts. thank you.

always open to new ideas, but so far, the non-inductor filters don't excite my ear as much as an inductor circuit.

playing around with the q cap on the 2nd in series of two crybabies yields a pretty massive range. i will do a clean sample later, but so far this is what it sounds like. not evident in the sample is the body-cavity-resonanting bass boost of this setup at full heeldown:

http://www.youtube.com/watch?v=hmHhGoF0Xfg

[joegagan]

That math jargon means that you have to (for instance) get four times the amount of capacitance change to double the change in frequency range; the inductor is fixed, and can't be changed. Diminishing returns set in very quickly.

funny, this is almost exactly the change that i made. your point about diminishing returns is exactly right; the loss of high end was severe. by adding a 2nd wah in front of it, i got it back.