NU-WA - inductorless vintage wah  [schematic]

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NU-WA - inductorless vintage wah  [schematic]

Postby Freppo » 03 Sep 2014, 21:25

Hi folks

A friend brought me an old wah that he wanted me to repair (which I have done)
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It's a inductorless wah with only two transistors and very few components.
Image
Image

It sounds pretty decent, so I decided to trace it, and this is the result so far...
Image

I have put it up on the breadboard with general-purpose transistors matching the HFE of the originals, but it's not quite working 100%
The output is very low and the pot/filter works but it doesn't sounds very resonant/wah-ish like the original, more like a regular highpass filter.
I'm pretty sure I got the layout/topology(?) right and all the values are confirmed by measurement and by the screening on the components/colorbands.
But I'm unsure about the second transistor.. the first one is marked F 19398 and from what I could find it's a NPN silicon transistor.
The second transistor is unmarked.. but by guessing the pinout (based on the surrounding components) I could get a reading in NPN mode on my meter.
transistor 1: 302 HFE, transistor 2: 360 HFE. I used a 2N3904 for Q1 and 2N2088 for Q2 on the breadboard.
Maybe it's the specific transistors use, or something is wrong. Maybe the second transistor is a PNP after all..
I don't know. What do you people think? Anyone seen a similar wah circuit that could work as a reference?

I have not included any switching in the schematic, but maybe I will in the final version.
The bypass switch basically connects the input directly to the output (while still being connected to the circuitboard),
disconnects signal ground from the circuit and it puts a 10uF cap from the in/out to battery negative in bypass (to prevent popping?)
The battery negative is kept separate from signal ground and there is also a switch for the battery.

Image
Image

I don't know anything about it, except what says on the top "NU-WA" There is absolutley nothing else on it - nothing written or stamped.
It comes from a recording studio "studio by the pond" in hendersonville USA that was run by Lee Hazen. He recorded some classic stuff, Dr Hook ect. :)

Anyone recognize this wah pedal and happen to have any info on it?

/ Fredrik
Check out my building blog at http://www.parasitstudio.se

For this message the author Freppo has received thanks: 9
Blitz Krieg (04 Sep 2014, 04:05), Fredenando (05 Sep 2014, 20:40), Intripped (03 Sep 2014, 23:45), jrod (04 Sep 2014, 04:40), Manfred (03 Sep 2014, 23:09), modman (03 Sep 2014, 21:53), Nocentelli (04 Sep 2014, 06:30), rs (04 Sep 2014, 01:07), toneman (05 Sep 2014, 00:52)
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Re: NU-WA - inductorless vintage wah

Postby jreeves47 » 04 Sep 2014, 13:25

Probably by Rosac/Sierra
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Re: NU-WA - inductorless vintage wah

Postby Freppo » 05 Sep 2014, 14:28

I made a soundclip and put it up here: parasitstudio.se :)
It's not the best sounding wah.. sounds lo-fi, a bit harsch and has a limited sweep, but it's not terrible.
I was kinda rushed to do the soundclip. Leaving for tour tomorrow..

Oh, and today I found a tiiiny text on the bottom plate that I had missed before.
It says MFG.co / Rosac Electronics. Can't believe it missed that after looking many times..
Maybe it's time to get new glasses :lol:

Anyone know about which years this one could have been made?

/ Freppo
Check out my building blog at http://www.parasitstudio.se

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Blitz Krieg (06 Sep 2014, 07:40)
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