Author Topic: Anyone care to overview how the DOD FX 91 Tone section works?  (Read 3176 times)

Earthscum

Here's the schem:

http://www.sugardas.lt/~igoramps/article16/fx91.gif

So, basically I'm wondering what is happening to the tone section. It looks to me like CCW, across the 22n, 1M+10k, gets a high pass of 7.2hZ, CW looks to me like it goes 47n , down the 100k, another 100k+1M+10k... that's about all I can figure out at the moment. I'm struggling to find the lowpass paths.

Heck, if someone gets bored and wants to model it and post a pic of the response, that would be awesome.

I own one of these, and quite frankly it sucks. First mod is going into the clipping section, probably fet or Ge clipping. It does NOT blend well with the dry signal as it is. The second thing that blows with this thing is the tone section. As it is, I have my drive about 1/4 up, blend usually about 75%, and the tone all the way down. Until I looked at the schem, I honestly thought that the tone section ONLY affected the driven signal side.

Basically, if I can get my head around the tone section, I may mod it instead of ripping it completely out and replacing with a BM tone section like I want to do every time I plug it in. I've also considered the Rat tone section, as well, since it's got a buffer after.
Give a man Fuzz, and he'll jam for a day... teach a man how to make a Fuzz and he'll never jam again!

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Earthscum

Re: Anyone care to overview how the DOD FX 91 Tone section works?
« Reply #1 on: June 04, 2011, 01:04:05 PM »
So, I figured out I can model this with a fender tonestack, using a "200k" pot, but only assuming full CCW to only half rotation.

Anyone have any ideas for good bass-friendly mods? Don't wanna add pots, no room.

*Edit to add: This is correct for the model? or do I have the mid knob the wrong way?

« Last Edit: June 04, 2011, 01:26:25 PM by Earthscum »
Give a man Fuzz, and he'll jam for a day... teach a man how to make a Fuzz and he'll never jam again!

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CynicalMan

Re: Anyone care to overview how the DOD FX 91 Tone section works?
« Reply #2 on: June 04, 2011, 01:48:15 PM »


Edit: Oops, I didn't see the little dot on C24. I had it as 47n. I've updated the image and, as you can see, it would be pretty useless for bass. The reason why it only seemed to work on the distorted signal is that there would be almost no harmonics from clean bass in the affected range.
« Last Edit: June 04, 2011, 01:57:01 PM by CynicalMan »

Earthscum

Re: Anyone care to overview how the DOD FX 91 Tone section works?
« Reply #3 on: June 04, 2011, 11:32:07 PM »
Yeah... I think I'm gonna "Zen" this thing. I'm working on a Zendrive based pedal (using 2n5457's, 1n60P Schottky's, and an OA85 Ge with a RC4558P). I'm just gonna rip the tone section out and Rat it. Should be a pretty sweet pedal after that... just wish I had room, I'd throw a "Voice" knob on it, but a PCB mount trimmer poking through may be do-able.
Give a man Fuzz, and he'll jam for a day... teach a man how to make a Fuzz and he'll never jam again!

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