Some Mods for the DOD FX-17 Wah/Volume Pedal
By Paul Marossy
Last Updated 09/25/05
There are some mods that can be done to the FX-17 which are fairly simple
to implement. The easiest one of all requires no modifications to the circuit, all that
is required is a small screw driver - there are two holes in the rear cover which enable adjustment of the two internal trimpots. The one on the right controls the minimum/maximum
volume level and the one the left adjusts the wah sweep response.
The easiest one to do that requires modificatons to the PCB is to change the 0.01uF "sweep caps" to give the wah
a little different sound. Increasing the size of the caps will shift the wah range down.
Decreasing the size of the caps will shift it up, but I do not recommend it unless you
want a really nasally sounding wah. Changing the caps is very simple, just remove the caps
labeled "C7" and "C9" from the PCB and replace them with new ones. For use with a bass guitar, something like 0.022uF might be a good choice. See the picture below for a quick view of where these caps are on the PCB.
Another mod you can do to get a slightly different sound is to tap the low pass output
from Pin 8 at the LM13600 IC chip. A resonance control could be added by changing the 100K
resistor from Pin 9 to 13 to a 10K resistor with a 100K pot. I haven't tried this idea, but it
sounds interesting enough to experiment with.
It may also be possible to convert the pedal into a foot-controlled phaser by changing
a connection for those 0.01uf caps on Pins 5 & 12 of the 13600 IC chip. Some work still
has to be done to determine if this really is possible, and if there are enough stages to
achieve a good phaser effect. I will probably try this at some point in time after I have determined what has to be done, if it appears to be worthwhile.