DoD FX-25 Mods

[HunkFunkPedals]

I've been looking around for a list of mods for the fx25. There are a bunch of really old threads that link to some guys website that he closed down so his schematics and mods are no longer visible.

One issue I'm having is that all the resistors are super tight to the board, so I have no idea what #s are what. one thread will say something like: "super easy bass mod....just swap out r11 and r21 with lower value and put a 100k pot on r7"......unless I remove everything from my board I cant seem to figure out where everything is and when they reference the schematic its no longer available.

Just wondering if anyone has any luck modding this pedal. I'm building this for my Dad, he wanted something with more options/range in line with a mutron, he loves jerry garcia.

Thanks in advance!

[11-90-an]

Hello and welcome to the forum... 

First of, here's the schematic of the pedal: (I think)


Could you probably post the links to all those other threads you mentioned? That would make it easier to see which components to swap...

Also, some pictures of the circuit board will also be useful... For tracing which component is which...

[Mark Hammer]

There's a bunch of things one can do to allow the circuit to dovetail nicely with whatever the song requires.

1) The filter design is essentially a state-variable filter, which means you can tap bandpass and lowpass outputs.  The stock design taps the bandpass output of the filter at pin 8.  If you tap the chip at pin 9, you get the lowpass filter.  Note that it will be a little louder, so maybe R22 should be a 100k log volume pot instead of a simple resistor.

2) The filter resonance/emphasis control which DOD calls "Range", has the effect of shifting the sweep to lower frequencies as you turn it up.  To keep the same degree of emphasis but cover more of the mids, capacitors C9 and C10 can be reduced in value.  The pop-free way to do this might be to have each of C9 and C10 be in series with a .012-.015uf cap, and use a DPDT toggle to bridge/unbridge that added cap to give a higher range.

3) Much like the "attack" controls in many compressors that use the tried-and-true rectifier circuit from the Dynacomp, R9 determines how quickly C7 "recovers"/charges up again.  Making R9's value lower will result in a faster decay. For starters, I'd suggest trying out a 2nd 1M resistor in parallel, and compare that to R9 on its own, just to see if you like it.

[mozz]

Maybe try those old links on the way back machine?

[HunkFunkPedals]

Here's what the board looks like...pretty sparse but those resistors are keeping thier secrets.....lol

[willienillie]

I had one, the only mod I did was swap the 1458 to a 4558, no change in sound but a noticeable reduction in distortion.  Are you wanting to mod it for bass?

[duck_arse]

try holding the board against a strong light, see if you can make out any board markings that way. two things I can see, probably of no import - the folded electro cap bottom right corner has a bad solder joint, looks like it's fatigued, and the ?51x? resistor next to it looks to have burnt from the discolouration around the third band.

and another welcome - belated.

[HunkFunkPedals]

Looking to give more options for guitar.

Its pretty pedestrian as is...so I just want to make it as much of a freak fest as possible.

[willienillie]

If you add a freak trimmer, you can dial it in to taste.

[HunkFunkPedals]

There's a bunch of things one can do to allow the circuit to dovetail nicely with whatever the song requires.

1) The filter design is essentially a state-variable filter, which means you can tap bandpass and lowpass outputs.  The stock design taps the bandpass output of the filter at pin 8.  If you tap the chip at pin 9, you get the lowpass filter.  Note that it will be a little louder, so maybe R22 should be a 100k log volume pot instead of a simple resistor.

2) The filter resonance/emphasis control which DOD calls "Range", has the effect of shifting the sweep to lower frequencies as you turn it up.  To keep the same degree of emphasis but cover more of the mids, capacitors C9 and C10 can be reduced in value.  The pop-free way to do this might be to have each of C9 and C10 be in series with a .012-.015uf cap, and use a DPDT toggle to bridge/unbridge that added cap to give a higher range.

3) Much like the "attack" controls in many compressors that use the tried-and-true rectifier circuit from the Dynacomp, R9 determines how quickly C7 "recovers"/charges up again.  Making R9's value lower will result in a faster decay. For starters, I'd suggest trying out a 2nd 1M resistor in parallel, and compare that to R9 on its own, just to see if you like it.

Which IC are we talking about? The LM13600N? or the FGC9716?

[Mark Hammer]

The LM13600.

[HunkFunkPedals]

 


I de-populated the resistors. I removed 2-3 that weren't the right ones according to the resistance and schematic idk whats going on but now I know the position of all the resistors.