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Thread: I'm building a Wah

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    Supporting Member John_H's Avatar
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    I'm building a Wah

    I spotted a good deal on a housing a while back, and couldn't pass it up. It took a while to arrive on what must have been a pretty slow boat from Shanghai, but it looks like a nice assembly that's complete with everything needed for all of the mechanical parts of the pedal. After it arrived, I started getting some of the other pieces together.

    Before I go any further I want to thank R.G. for his great article 'The Technology of Wah Pedals' at geofex.com . For anyone wanting to do this, it's absolutely the best place to start.

    I found a layout for building the circuit on terminal strips from diy MOD. It should be really easy to swap components. The PDF is the instructions for their wah kit. It uses the traditional schematic, and values except for the bias resistors on Q1. On the same schematic they use MPSA18 transistors. I have a few others that I can try, but I'll start with those, along with their bias resistor choices. I ordered the same capacitors that they use as well.

    I'll be using a dunlop fasel inductor https://www.amplifiedparts.com/produ...re-tone-yellow that is supposed to mimic the legendary tone. I don't know if there is any magic involved, but I measured it at 595mH, 14.6 ohm DCR, and 2.2uF. I've got a generic 100k wah pot for now. There are a lot of options, but I hope this will give me a good start, and a decent baseline.

    I would be doing it already if I had remembered to order a rotary switch, but I plan to do the adjustable center frequency mod that R. G. shows in his article. I'm hoping the balance of the parts show up this weekend. I'm excited to get started.
    wahtz_wah_schematic.pdf wahtz_wah_instructions_0.pdf

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  2. #2
    Bent Member Chuck H's Avatar
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    You might consider potting the inductor. My old wah has become pretty tender. I can't imagine new parts are much better. Call it a preventative measure.

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    Supporting Member mozz's Avatar
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    I did the same thing as the op. By the time i got the housing, parts and misc, i could have just bought one and modded it to whatever specs i wanted. That being said, you can often find non working ones for cheap, either repair it or tear it down and build to your specs. That being said, it is also a learning experience so that is good.

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    Supporting Member John_H's Avatar
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    The parts that I was waiting for showed up Friday afternoon. Building it on the terminal strips worked out fast and easy, and it will be easy to modify when the time comes. It was really helpful having a good layout to work with. The die cast housing is built like a truck.

    My first impression is that it works pretty good. I don't have anything here to compare it with right now, but sometime soon, I'll take to to my friends shop to compare it with some other wah pedals. He usually has some nice vintage stuff in the showcase, not to mention his large personal collection. I didn't have a problem getting full travel from the pot, but the alignment of the rack to the gear on the pot is off to one side. I'll modify the bracket that holds the rack to correct this.
    Quote Originally Posted by mozz View Post
    I did the same thing as the op. By the time i got the housing, parts and misc, i could have just bought one and modded it to whatever specs i wanted. That being said, you can often find non working ones for cheap, either repair it or tear it down and build to your specs. That being said, it is also a learning experience so that is good.
    This little project totaled around $75. About the price of a cheap Dunlop, or Vox from online dealers. I like making things, and thought it would be cool to add a wah to my collection of home built effects. While learning a lot about the wah circuit, and the ancient lore, I ended up with a nice home built pedal in a cool housing.

    Click image for larger version. 

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  5. #5
    Don't forget the joker g1's Avatar
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    Quote Originally Posted by John_H View Post
    but the alignment of the rack to the gear on the pot is off to one side. I'll modify the bracket that holds the rack to correct this.
    Maybe I'm misunderstanding, but it looks like playing with the spacers on the pot could correct for this?

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    Supporting Member John_H's Avatar
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    Quote Originally Posted by g1 View Post
    Maybe I'm misunderstanding, but it looks like playing with the spacers on the pot could correct for this?
    I can get a little by shimming it over further, but need more.

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    Don't forget the joker g1's Avatar
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    I guess the bracket for the rack is cast into the treadle?

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    Some '60s and early '70s wahs used a cam mechanism to rotate the pot; no gears involved

    I am currently trying to resurrect an old Korg Mr. Multi pedal which functions as a wah, but also doubles as a foot-controlled phaser. The unit has half the gear mechanism, attached to the foot treadle, but I need to order the part that sits on the pot shaft. Here's hoping the teeth spacing hasn't changed in the intervening decades!

    I made myself a wah a decade or so back, using a suitable inductor I found cheap at a local surplus electronics place, since closed down. It has the desirable ferrite core that Fasel and similar share, but measured 900mh, with a tap around 800mh. I adjusted a few component values, and I'm really pleased with it. More throaty than quacky.

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  9. #9
    Supporting Member John_H's Avatar
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    Quote Originally Posted by g1 View Post
    I guess the bracket for the rack is cast into the treadle?
    The 'stand' that the bracket attaches to is cast in the treadle. The bracket itself is made from bent sheet metal. I'll try shimming the pot over as far as possible, and elongating the holes in the bracket. If that isn't adequate, it wouldn't be too hard to fabricate another with a bit of offset.

    I am currently trying to resurrect an old Korg Mr. Multi pedal..
    Nice! It's cool to see old gear brought back to life.
    ...but I need to order the part that sits on the pot shaft.
    I have one here that came with the pedal. It's just a gear that slips on to a pot shaft.

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    Quote Originally Posted by John_H View Post
    I have one here that came with the pedal. It's just a gear that slips on to a pot shaft.
    I found one in my bin of old pots last night...but I think I may have crazy-glued it to the shaft of the pot it's on, so I may still need to get one from Small Bear.

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    I didn't have a problem getting full travel from the pot, but the alignment of the rack to the gear on the pot is off to one side.
    As far as I can tell from your picture, the alignment of the mechanical parts is not worse than with my Vox/CryBaby originals. For a nice feel, some sticky grease on the teeth and the rear side of the toothed rack helps a lot.

    I recommend to cover the window in the pot housing with tape to avoid dust getting inside.

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    Last edited by Helmholtz; 11-26-2018 at 06:08 PM.
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  12. #12
    Don't forget the joker g1's Avatar
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    And remember to count when you're wah-wah-ing, as the hot potz are only rated for a million cycles.

    Who wants to design a counter with a display for these things?

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    And remember to count when you're wah-wah-ing, as the hot potz are only rated for a million cycles.
    Hardly any other standard pot gets as much (ab)use as a wah pot. The action of the wiper scrapes off carbon from the track, causing increased track resistance and a changed taper after extended use. I once replaced a scratchy original pot in a 60s Vox wah, which had "drifted" from the initial 100k (as stamped on the housing) to around 300k!

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    Last edited by Helmholtz; 11-26-2018 at 11:01 PM.
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    Supporting Member John_H's Avatar
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    Quote Originally Posted by Helmholtz View Post
    As far as I can tell from your picture, the alignment of the mechanical parts is not worse than with my Vox/CryBaby originals. For a nice feel, some sticky grease on the teeth and the rear side of the toothed rack helps a lot.

    I recommend to cover the window in the pot housing with tape to avoid dust getting inside.
    All good advice. Thanks!

    Quote Originally Posted by g1 View Post
    And remember to count when you're wah-wah-ing, as the hot potz are only rated for a million cycles.

    Who wants to design a counter with a display for these things?
    You mean I have to count wah-wahs and chicka-chickas at the same time? Crap!

    Quote Originally Posted by Helmholtz View Post
    Hardly any other standard pot gets as much (ab)use as a wah pot. The action of the wiper scrapes off carbon from the track, causing increased track resistance and a changed taper after extended use. I once replaced a scratchy original pot in a 60s Vox wah, which had "drifted" from the initial 100k (as stamped on the housing) to around 300k!
    That one might have exceeded a million cycles.

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    OEM pots from the Cream/Hendrix era were simple italian made (Icar) 100k linear types. When analyzed in later years, the changed tapers (by wear) gave rise to a lot of speculation about the magic "original taper" and resistance value.

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    Last edited by Helmholtz; 11-27-2018 at 12:13 AM.
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    "Thermionic Apocalypse" -JT nickb's Avatar
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    Quote Originally Posted by John_H View Post
    I spotted a good deal on a housing a while back,
    Out of curiosity what was the bottom line, delivered price of the enclosure?

    Reason for asking was that I've seen them advertised and wondered how accurate (or misleading) the headline price was.

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    Supporting Member John_H's Avatar
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    Quote Originally Posted by nickb View Post
    Out of curiosity what was the bottom line, delivered price of the enclosure?

    Reason for asking was that I've seen them advertised and wondered how accurate (or misleading) the headline price was.
    The price was $40 US with free shipping. It took several weeks to arrive.









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