Help Mod my crappy DOD pedal.

[shanter]

Hey,

Ive been reading about pedal mods and building for a few months now and i found a question too complicated for me to find out the answer alone.

i have a DOD FX86B Death Metal Distorion. I absolutely dont reccomend this pedal to anyone. I bought it when i was very young and loved it cause it was a crazy distortion, but now its jsut too much for me. I turn the High down all the way and its still outrageous.

my question was could anyone guide me in changing a few components in order to tone this pdeal down? I understand how to read schematics but i dont understand exactly which parts give the pedal the actual sound it produces. ie how differnt size capacitors change the tone or how different resistors change tone.

i was at the library yesterday for 4 hours reading up on electronics and none of the books i took out really spoke much on component influence on sound.

so heres the scematic of the pedal from FIS http://www.freeinfosociety.com/electronics/schemview.php?id=346

and heres a picture of the circuit board.

any help would be greatly appreciated

[Paul Marossy]

Here's what I personally would try:

1- Change the "guts", "pain" and "scream" pots to 50K
2- Remove the pair of 1N4148 clipping diodes
3- Increase C2 at the "scream" control to maybe 0.001 or 0.0022uF
4- Increase C20 to 0.068 or 0.1uF
5- Try lowering the feedback loop resistor values some at the first/second opamp stages and increasing the cap sizes, too

I would try these things one at a time and assess the results before going to the next one. I would probably try #5 first, then #2, then messin' with the caps. I would probably try changing the pots as a last ditch effort.

EDIT: Why don't you just get a different distortion pedal? Chances are you probably never will be happy with any mods to it. But there's only one way to find out...

EDIT #2: Actually, you could just solder in a 100K resistor in parallel with those pots instead of physically replacing them...

[shanter]

OH THANKS!

Well, i am getting news pedals, adnd i do have other distortions, i jsut wanna see if i could make this one better. even if the distortion isnt perfect it will probably give me an odd sound which might be pretty cool. Plus i wanna mess around with it so i can get better at this stuff.

when you say remove the silicon disodes do you mean jsut take em out? or shoudl i replace em with Ge ones?

[Paul Marossy]

when you say remove the silicon disodes do you mean jsut take em out? or shoudl i replace em with Ge ones?

No, I mean get rid of them. Those diodes clip everything coming from the first two opamps stages onwards. Take them out and you will (in theory) have less over the top distortion. This should also affect the harmonics generated and I think will lessen the high end harshness of the pedal. You may still have to mess with the cap values, of course. 

[cd]

If you're going to be experimenting with different cap values, I STRONGLY recommend either tack soldering in the different values until you find a value you like, or use sockets for the components.  Reason being, the DOD PCB is lousy at best, and you will likely have only 1 or 2 chances at most to unsolder/resolder before the traces start to disintegrate (yeah, speaking from experience here )  With caps, it's easy to stick another cap in parallel (caps in parallel add together for a larger value).

[Paul Marossy]

If you're going to be experimenting with different cap values, I STRONGLY recommend either tack soldering in the different values until you find a value you like, or use sockets for the components.

Good point. PCBs in these FX pedals are often kinda fragile...

[Stompin Tom]

I've actually been holding onto my old DOD metal maniac (very similar pedal and very crappy) in hopes of doing some modding experiments...  but I want to go in the opposite direction and make it crazier.  Maybe fuzz it out or, if possible, add some strange harmonics/octive down??  If anyone has any suggestions, I'd appreciate it!

[Fp-www.Tonepad.com]

I will never understand how they managed to screw it up (distortion), they had it right in the first place! (FF, BMP)

It must be ALL THOSE parts!

Fp

[moosapotamus]

...I want to go in the opposite direction and make it crazier.

Connect a pot between the input and the output. Experiment to find what pot value works best.

~ Charlie

[shanter]

yea id love to do something crazy like octaves, but the distortion is jsut tooo over the top. i get the worst possible hum there is with this pedal. i dont know if there's something wrong with the ground or what. at low volumes its meh...kinda buzzy then when i crank it, it buzzez like im playin a strat.

[MartyMart]

Sounds to me like Stompin tom and shantar should just "swop" pedals !! 

Marty. 

[Paul Marossy]

i get the worst possible hum there is with this pedal.

Really high gain distortion pedals will amplify the heck out of any hum that finds its way into the signal path. What kind of guitar are you using with it, and is it well shielded?

[Stompin Tom]

I think all those crap dod distortions are almost completely identical.  The board on mine actually has 'American Metal' (a different pedal) printed on it and crossed out in sharpie! Shanter's descriptions of his own pedal apply to mine, too. 

If no one knows how to fuzz it up, does anyone have any other ideas (I'll investigate Paul Marossy's this weekend)?  I'd rather not just throw it away, and it's certainly useless as is.  Thanks.

By the way, I highly recommend DOD's old analog delay (FX90).  Can get some nice self-oscillation.

[Paul Marossy]

If no one knows how to fuzz it up, does anyone have any other ideas (I'll investigate Paul Marossy's this weekend)?  I'd rather not just throw it away, and it's certainly useless as is.

If you don't care that much about it, it's a perfect testbed for modding it/experimenting with it to your heart's content. I'm thinking that you might get something of a fuzz sound if you just bypass those tone controls - I bet the waveform before those tone controls is a massively clipped sinewave, so much so that it almost looks like a square wave. The tone controls allow you to manipulate the waveforms a little bit after they are annihilated in the preceding circuitry. A Fuzz Face creates some square-waveish stuff, you know. Ge clipping diodes may also be worth a try in the quest for "fuzzing up" your circuit there.

Might be worth a try...

EDIT: Also, try adding a 10K pot in series w/ the positive lead of the battery for some weird noises.

[Stompin Tom]

Thanks Paul!

Although I enjoy modding my pedals, I'm pretty much a moron when it comes to electronics...  could you explain the idea behind putting a pot on the battery lead?  Some sort of variable voltage thing?

[Paul Marossy]

could you explain the idea behind putting a pot on the battery lead?  Some sort of variable voltage thing?

I'm not sure if this wokrs on every distortion circuit, but in theory, it changes the impedance of the battery and can cause the circuit to go into strange sounding oscillations. It's worth a try at least. Who know, you might end up with something that sounds a little like a Fuzz Factory! 

[shanter]

ok so i tried out the few mods you suggested paul and here are the results.

crap.

after i removed the clipping diodes the sound was the same. then i upped the two caps, the it sounded a bit more like a overdrive/fuzz but when i played high notes it sounded like i was sticking the soldering iron in my ear. so then i thought  ef it  so i went ahead and swapped out random things in hopes of finding a cool sound but no luck. im jsut salvaginf some of these parts in hopes of putting together my own overdrive.

the IC's are (1) ' MC14007UBCP'  and  (2) '4560D JRC 8009D'

i only found a datasheet on the MC14, i cant find anything on the other two.

any ideas?

[Paul Marossy]

Interesting. That tells me that the signal is already really clipped before it reaches those "clipping diodes". You could try lowering the values of the resistors in the feedback loops to decrease the gain of the first two opamp stages and also increasing the cap sizes in those same feedback loops to roll of more of the high frequencies as well. Did you try bypassing those tone controls at all? I think that would really change the way it sounds if you bypassed those entirely.

Then again, this may be one of those cases where there may not be much you can do to make it better or much different. (Or, question if it is even worth it)

[James V]

Here's the datasheet for the 4560. It's just an opamp.

http://www.ampslab.com/PDF/njm4560.pdf


Unless I'm suffering from a huge brain fart, that schematic doesn't seem to correspond to the circuit that you've photographed though. There's more stuff on the sircuit that there is in the schematic.

[shanter]

you are very correct on that comment James, i looked around for certain components on thcircuit borad and was unable to find them. im thinkin the problem would be because my pedal is FX86B and the one listed is FX86. but a mhile ago i did some research and found out that the only difference was that one was jsut made in a different country and that the cicuitry is the same.

so i assume this opamp is simple interchangeable with most any other op amp in other pedals?