Some wah questions...

[GibsonGM]

Hey wah gurus,

Making my 1st wah, getting tired of distortions...I have the guts from an old Thomas Organ crybaby, and used that as the inductor in an original Dunlop Crybaby (Philpott 11-1997 version) circuit with 2N3904's.  Not sure of the inductance from the Thomas, tho! 

The ckt wahs, sounds good from 1/2way to treble,  but on the bass end I get a terrible (actually, it's rather musical) squeal.  Granted, the pot is 100KW taper and not audio.  Pretty much everything else is as it should be in the schema. 
Could this be because of too high a gain in the tranny stages, or because the pot is too close to the inductor? 
What's the relationship of pot to inductor - will increasing/decreasing either "change things"?  So if my inductor is too low a value, will a pot increase 'get me there'?

If I perf this thing up, I'd like it to be really nice.

Thanks,

MJP

[tcobretti]

If the value of the resistor on the emitter of Q1 is too low the pedal will oscillate, I guess because the gain of Q1 is too high.  It should be around 300-500R.

[GibsonGM]

One schem said to use 470K at the emitter of Q1, seems really high...Philpott's calls for 470R, which I used.  Maybe I'll try a 1K pot there and see what happens....

[tcobretti]

Yeah, 470k certainly sounds wrong.  A 1k trimpot is a good idea.  If you used a 470R, then I would check it so be sure it isn't mislabeled.  If it isn't, then I'd check for solder bridges that short the emitter to ground.  If you don't find anything, then the problem must be something else, but I don't know what.

[GibsonGM]

Thanks, T.  I'll try the pot. It's on breadboard, there could be a weird socket or something. Or maybe because the pot's not log taper.   Good project, tho. 

[tcobretti]

On a couple of different wahs, I subbed trimpots in for that resistor and for the 1k5 feedback resistor.  These pots allow you to tune the wah to your inductor.

[GibsonGM]

Thanks T, good call )

[petemoore]

  I had trouble [still do really] gettting the wah actually working 'perfect', I put regular pot just outside the wah, adjusted, tested under various conditions, tweeked, adjust, try toe down, index the potgear etc.
  Having that pot in a piece of cardboard taped to the bottom plate w/indicator knob made it easier for me to find a fixed R value to install.
  but I couldn't decide exactly so I built an 80% / 20% value from two series resistors, the '20%' R having a wire which can short across it..changing to the 80% value it just a quick iron touch and lift wire affair.
  ie for 1k / 820ohm swap,
  series 820ohm and 180ohm for 1k, short across the 180ohm for 820ohm.

[GibsonGM]

Hey, good idea, Pete.  I"m going to see if my Q1 emitter R is a wrong value...also will try the pot from my old wah (100kA, I believe) instead of my wrong taper one.  The 1/2 that works sounds really good - now to stop that squealing!  ;o)