strange wah behaviour at closed pedal

[Fuzzy-Train]

Success... finally.

Thanks to my brother I finally got my clip working. Damn cubase is a bitch to figure out.

He forgot to get my mic cable from his bandmates place, so I can't upload new clips of the different transistors... I'll get those when I get the cable back... but this one was the original clip I made back in Sept '06. This was on the original dunlop board I had... but the problem is still the same.

http://tch.dmusic.com/

The notes that ring out are much louder in real life than in the recording, the pedal was also never moved from the heel position... still think it's normal??

[rockgardenlove]

Yep, totally normal!  That's what a wah does.

[Paul Marossy]

In the traditional wah pedal, the resonant peak is variable and is dependent on the setting of the pot. It is perfectly normal for a certain frequency range to be accentuated while the others are lessened. That's the whole idea behind a wah pedal! 

[tcobretti]

I set up a wah where I could switch back and forth between inductors, and my Vox v847 inductor was doing that while my Yellow Fasel wasn't.  However, I could tune it away by changing the value of the resistor at the emitter of Q1, which is why I recommended you play with that value earlier in this thread. 

Just pull that resistor, solder in a 1k trimpot, and adjust to taste.

[Paul Perry (Frostwave)]

that is an interesting observation, tcobretti.
Looking at the Geofec Wah notes, you can see that as the frequency peak changes, so does the resonance.
If one inductor is OK and the other isn't, then either they have different inductors & one is going at the end into a frequency zone that you don't want, or else one has a higher Q and the resonant peak is too sharp.
You can decrease the resonant peak either by adjusting feedback - I presume the emitter resistor is tweaking this - or by adding resistance in series with the inductor in order to decrease Q.
It is quite possible - the analysis is beyond me - that the two tweaks (emitter resistr and coil series resistance) give somewhat different results. That's what makes DIY so entertaining!

[tcobretti]

The trimpot I used is kind of cheap, so when I adjust it, there is some friction.  So, if I plug in the pedal, turn it on, rock it all the way back, and overcome that friction you can hear the frequency of the resonant peak change.

Here's a sound clip of me turning the pot on Q1's emitter.
http://aronnelson.com/gallery/albums/album72/wah_trim_pot.mp3

That loud "dong" sound is me hitting the end of the pot's travel.  I believe with higher hfe transistors it'll oscillate at the lowest range of resistance (I've got 500 hfe 5089s in there now).

I wonder if you could do the same thing with the emitter resistor for Q2, but this time tweak the high end of the circuit?  Probly the most interesting experiments I have done have been subbing trimpots in for resistors and hearing how it affects the sound.