Lowering input gain on wah to avoid clipping

[mcasey1]

I havent seen this particular topic addressed before.  I've got a Boomerang wah and for clean playing I'd like to avoid the clipping that occurs when feeding the wah a relatively high gain input like a PAF bridge humbucker.  When playing in the lower-output neck position through a clean amp, clipping is barely noticeable.  Switching to the bridge pickup requires me to lower the volume control on the guitar to avoid the clipping sound that occurs.  I have an output buffer installed with a trimpot that allows the control of the ouput volume.  My question is, could I raise the input resistor from 68k to something higher to bring down the front-end gain and just compensate for the volume difference through the output buffer gain adjustment?  I suppose to be more specific, I should ask if there is anything that could be lost by raising the value of the input resistor.  I know going too low could cause some RF interference, but are there any adverse effects to raising the input resistance and lowering the gain on the front end of a wah?  Thanks!

Matt

[MrStab]

Do you use Invader pickups or something along those lines, by any chance? I have a coupla those in a guitar and the bridge pickup seems way hotter than the neck.

one solution would be to sandwich a voltage divider or volume [trim]pot between two buffers before the wah input (...unless the pickups clip those, too!). you probably wouldn't need both buffers, but it would prevent unwanted interactions. then you'd have to worry about emulating the original impedance of the wah, though, if that's a concern. if you have low-output-impedance pedals before that which are on when the wah's on, then it doesn't matter anyway.

[mcasey1]

I use fairly low-gain alnico II pro pickups by Seymour Duncan.  I think the bridge only has a DC resistance of aroun 8.5K or so.  Definitely low output compared to something like an Invader.  I would imagine with low output single coils I'd get even less of this type of clipping, as it does seem to be dependent on the volume of the source. 

[Transmogrifox]

Another mod would be to replace the 48k resistor with a resistor "T" network in which the Thevenin equivalent impedance looking into either end looks like 48k, but the center tap resistor to ground provides the attenuation.

For example, to make it easy with all 3 resistors equal value, then
R = (2/3)*48k = 32k

Replace this:

Code Select Expand


        48k        
IN--- \/\/\/\--->BJT BASE


With this:

Code Select Expand


Since 33k is more common than 32k, then here is a recommended network:
        33k          33k
IN--- \/\/\/\----\/\/\/\--->BJT BASE
             |
             |     33k
              --- \/\/\/\--->GROUND


This neglects the reactive portion of the input impedance (frequency response between guitar pickups and pedal position) but generally this isn't desirable anyway.  An input buffer would be a nice feature to add to that circuit.

[R.G.]

Changing the transistor gain will also affect the overall peakiness of the resonant circuit plus transistor.

It might be better to pad down the input signal, although that gives away some signal to noise.

[joegagan]

 i sell a faux boomer, based on a dunlop gcb95 PCB with all of the components stripped exc. for 4 resistors.

for the first few dozen units sold, i had minor issues with getting the tone nice & fat while not blowing away the bypassed volume ( my kit has no volume pedal function), i played around for a couple months with output buffers, output pots ( really messes with the curve ), and all other gain modifiers, even trying a lot of it out in LT spice before trying for real.

the solution i finally found was so dumb i only tried it out of desperation.

there is a 100k trim in place of the input resistor, but when a i put a 250k voltage divider ahead of THAT, all the problems were solved. the gain/ lows/ wallop are variable by messing with the bias trim first, 100k 2nd, then the input 250k lets you set volume without  much noticeable change in the freq curve, which none of the other solutions provided.

i know your problem was trying to find a way to reduce gain, and this works equally well in both directions.

[plexi12000]

hey guys,  just wondering.....what exactly does clipping sound like when its going through a clean amp?  like a mild "distortion" or something?  obviously i guess it's not pleasing to the ears.