Introducing the 1970s USSR Made "Kvaker" Wah Pedal

[Paul Marossy]

Some of you wah nuts might find this one interesting.

I found this very interesting Soviet made wah pedal on ebay a couple of months ago. After watching the Curious Marc YouTube channel for a while and their reverse engineering of Apollo era space program elecronics and the Soviet Soyuz era "globus", Soyuz atomic space clock and similar things I have found old Soviet stuff interesting. So I was intrigued by this wah pedal made in 1976 because it's SO different looking and functioning than most wah pedals, and even more because of the circuit it uses. It does not use an inductor, is PNP positive ground and uses P416B germanium transistors. It also has a Range and Timbre control which makes it more interesting as well. I really like it! It has a nice growl to it with certain types of distortions.

While I was waiting six weeks for it to arrive from Ukraine (and wondering if I would actually ever recieve it), I tried to make a perfboard version of it and it didn't quite work... it would make a "wah" sound but then it would immediately fade back to the unaffected sound when not turning the wah pot. I figured maybe it had to do with the transistors and biasing, then I kinda stopped there. I think some people might like to build one, so hence the post here. I'm not sure if this a Twin-T type circuit, or exactly what it is. I did model it in LTSpice while I was waiting for it to arrive and the frequency response pretty much matched what it said it is in the owner's manual. I was able to round up a model for the P416B transistors too, but in the program it didn't differ that much from a 2N3906 for example. Still am perplexed as to why my clone doesn't work but maybe I messed something up and I just can't see where.

Here is my page on it - http://www.diyguitarist.net/DIYStompboxes/Kvaker%20Wah.htm
Here is the original manual in Russian (Google translate works to decode the cyrillic) - http://www.diyguitarist.net/PDF_Files/KVAKER%20Manual.pdf
And here is the factory PCB layout and shell drawings - http://www.diyguitarist.net/PDF_Files/Kvaker%20Wah%20PCB%20&%20Shell.pdf
There is also a link to the P416B transistors at the bottom of my Kvaker main page.