DOD FX25 Volume mod
Disclaimer
Making this mod and even taking screws of bottom will invalidate warranty.
Background
I am not particularly into Funk, but I liked the sound of this pedal in a Digitech model so I thought I would buy the real thing (I know the original FX25 is preferred my many).
However I noticed a distinct volume change when switching in effect, while some of this may be a result of losing signal due to filter effect, there seems to be a broadband loss in volume too.
After looking at schematic, I noticed that effects path gain could be doubled by changing a voltage follower opamp stage to have a gain of two by inserting a pair of equal value resistors and a large cap for unity DC gain.
Summary of Mod
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Open up unit to get at board; unscrew 4 bottom screws, unscrew pots, but jacks can be left in place
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On underside of board cut board copper track between pins 6 and 7 of U4B (check with a DVM that track is really cut)
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Add resistor 6k8 between pins 6 and 7 on underside
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Solder another 6k8 resistor direct to pin 6 on topside, solder this to capacitor (plus end) and solder cap negative end to GND - a convenient GND is on switch SW1 pin
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Re-assemble, adjust Blend knob for best effect/volume continuity
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I just happened to use 6k8 resistors and 33uF capacitor because its what I had lying around; 10K and 10uF should do exactly same job
Some details with photos
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Photos below are hopefully self-explanatory
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Schematic says U4 is a TL072, but in my case a JRC4560D was fitted
Topside of board with series soldered RC from pin 6 to GND
Resistor on bottom side between pins 6 and 7, with cut track visible.
Schematic with two added resistors, one added capacitor.
