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 Post subject: Wah mods for bass
PostPosted: Sun Apr 04, 2010 12:50 pm 
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Joined: Tue Nov 18, 2008 11:18 pm
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Location: Harrisburg, IL - USA
I modded my Thomas Organ (TDK) wah this morning. I did the following mods:

"Vocal Mod"
Replace the 33K resistor in parallel with the inductor with a 68K. This gives a more vocal quality to the wah. Some Vox Clyde McCoy wahs had 100K resistors here. I really like this one

Gain and Bass Response
Replace the 470 ohm resistor (some have 390 or 510) at the emitter of Q1 with a lower value. This increases gain, which is useful if you've converted to true bypass. The bass response is also increased. Too low a value here may introduce some distortion and make the wah sound muddy. Try 270 - 330 ohms to start with. This seemed to help tame down the highs when using a fuzz in front of the wah

Midrange
Replace the 1K5 resistor between the base of Q1 and the inductor with a larger value. This increases the midrange and helps if your wah sounds dull and muted when you rock the pedal back. Try 1K8 to 2K7. Higher values than stock also smooth out the bass-treble transition. Most people refer to the 33K as the "Q" resistor, but this resistor also affects the Q. I'll probably play around with this one a bit more, if not go back to stock. It does smooth out the transition, but really washes out the wah effect.

Sweep Range
Change the sweep by swapping the 0.01µF cap between the emitter of Q2 and the inductor. A smaller value will make the wah sweep more trebly and vice-versa. If you're converting to or from a bass wah, this is the one to change. Try 0.068µF for a bass wah. This had the greatest impact, I only had a .05µF to put in there.


I also added 10pF capacitors between the collector and base of each transistor to try and cut out the country radio station I was picking up... but it didn't work. Any suggestions on this?

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 Post subject: Re: Wah mods for bass
PostPosted: Sun Apr 04, 2010 5:35 pm 
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Location: Zanesville, OH
Hmmm. Shouldn't need to install caps between collector and base. And I don't see how that would help. It's caused by the inductor picking up a strong radio signal nearby. I've had a wah do it before but was just for a second. Read this: http://www.jimdunlop.com/index.php?page=support/faq_gcb_radio

With the mid-range mod you could try a 1.8K or so. I've modded a wah with a .068uf value on a rotary but never had a bass guitar & amp to test it. I just added it to fill an empty position on the switch.

How did the .05uf work out for you? Strong wah effect from heel to toe or kinda weak? Being that the list of mods are geared towards electric guitar they may not interact as well with bass.


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 Post subject: Re: Wah mods for bass
PostPosted: Sun Apr 04, 2010 7:58 pm 
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Joined: Tue Nov 18, 2008 11:18 pm
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Location: Harrisburg, IL - USA
Interesting read... thank you.

I just stuck the caps on the tranny's cause I've did that on a fuzz pedal before. I've read a few other tips, including the cap at the input. The .05 definitely helps move the sweep. I put a 2.2k in for the midrange, think I"ll go back to stock on that one.

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