Modding the Weener Wah to a "Bow Wow Yoy Yoy"

[MarkL]

In looking at the schematic for the old Schaller "Bow Wow Yoy Yoy", it has a lot in common with the schematic for the Weener Wah.  Here is the schematic for the Schaller:



Some minor topology changes notwithstanding, it looks like the main differences are:

1.  The Schaller has a second inductor going to a .22 cap, going to a 1M resistor to GND...I am guessing that these additional components are what create the "yoy" sound (a switch bypasses the 1M to GND, is this what changes it back to more of a "wah" sound?). 

2.  The Schaller has a third transistor stage at the end (1M between B and C, 6.8K on C, 2.2K on E to GND), leading to a 10uF output cap, with the output taken between a 4.7K and a 6.8K (which I guess could just be replaced with a 10K "volume" pot).  Is this a boost stage?

I'd like to mod the Weener Wah to be able to capture the Schaller's "yoy effect.  I guess it wouldn't be too difficult to hack in the additional inductor and relates components...but how important is that third transistor stage? 

[stecykmi]

ya the extra inductor seems to be a 2nd pole to the filter, basically another cutoff frequency. an inductor and cap in parallel acts like a bandpass. the switch looks like it will change the Q and centre frequency. two poles are needed to create a vowel sound.

ya that output transistor is a gain stage, you can get a little more by lowering the 2k2. you could also try adding a 47uf of 10uf electro cap in parallel with the 2k2, but this might be too much gain. a pot on the output would work fine, or a trimmer. always best to ground the output with a 1meg resistor. wouldn't affect the feel of the pot much but ensures a reliable ground connection to the electro cap.

i would not say it's possible to easily build this on a weenerwah board (current or v2). you would be better off with stripboard or scoping out if someone has cloned it. might be possible with some tracecutting and trickery, but that's not too reliable.