Adding Mids to a Dod FX69 Grunge pedal.

ianmgull · May 21, 2009, 02:33:03 PM

Hey all, long time no see.

I recently pulled my old fx69 off the shelf and just like I remember, it sounds terrible. I eventually put an eq after it and got some usable tones from it when I boost the mids heavily (think 300Hz-2k roughly). I was wondering if anyone knew enough about this to help me add more mids to the pedal. Actually you can tell there is an extreme mid scoop in the circuits design so undoing that shouldn't be too hard.

Obviously the first step is obtaining a schem. Anybody have one?

Thanks,

Ian

StereoKills · May 21, 2009, 02:59:45 PM

Schematic Heaven has it.
http://www.schematicheaven.com/effects/dodfx69b_grunge_dist.pdf

MikeH · May 21, 2009, 03:07:31 PM

It's so funny; when I was 16 or so, I thought that was the best sounding dirt box EVER. And now, yeah, I think it's pretty much the worst distortion ever conceived. Good luck!

Mark Hammer · May 21, 2009, 03:40:18 PM

The first and third op-amps have resonant boosts built into them; the first having one (based around that transistor) and the third op-amp section having two. Those three resonant boosts provide the specific coloration characteristic of the pedal. The first boost seems to be mid-oriented (going by the cap values) and boosts ahead of the clipping diodes. The second and third boosts emphasis what comes out of the clipping section, seemingly at lower and higher frequencies. The two tone controls available on the chassis are but two of many emphases provided by the circuit.

I couldn't tell you what the resonant frequencies are, but if you read the article on parametric EQ over at GEOFEX, I bet you could figure it out. Then, you could swap out a cap value here and there, and bend the beast to your will. Alternatively, try cutting the connection between the inverting pin in op-amp 3 and the 330n and 15n caps connecting to it. That will put the stage into unity-gain mode and eliminate the resonant boosts. The tone controls will still work.

space_ryerson · May 21, 2009, 06:14:51 PM

There was another thread on the Grunge pedal a while back, in which Mark gave some good advice. I tried the suggestions he listed, and it did make it into a much better distortion pedal. I suggest searching for that thread.

MoltenVoltage · May 21, 2009, 07:44:30 PM

Quote from: MikeH on May 21, 2009, 03:07:31 PM
It's so funny; when I was 16 or so, I thought that was the best sounding dirt box EVER. And now, yeah, I think it's pretty much the worst distortion ever conceived. Good luck!

I actually brought mine back to the store for a refund it sounded so f*ing awful (circa '92?)

Why would you start with something so lousy in the first place? Just gut it and use the enclosure. Cobain used a DS-1 anyway!
http://www.kurtsequipment.com/

Unless of course you are trying to sound like the Melvins...

WGTP · May 22, 2009, 11:24:31 AM

AMZ has a blog entry about Gyrators and a calculator to determine the values of boost. With some experimenting, you should be able to get an EQ you like.

deaconque · May 22, 2009, 01:12:58 PM

Quote from: MikeH on May 21, 2009, 03:07:31 PM
It's so funny; when I was 16 or so, I thought that was the best sounding dirt box EVER. And now, yeah, I think it's pretty much the worst distortion ever conceived. Good luck!

Ditto. 100%

80k · May 22, 2009, 02:06:19 PM

man, I loved that pedal when i was in jr high school! And then someone came over with a big green Russian Muff, and I think that was the last time I ever touched the FX69.

StereoKills · May 25, 2009, 12:31:41 AM

According to Brian Wampler, in his "How to modify effect pedals" book, you can remove C19 (15nF) to "add mids and body."

From the same source, you can replace C24 (8.2nF stock) with a 4.7nF value to "Make the high knob operate at a higher frequency range" tunes the highs instead of mid-highs.

I haven't performed those mods myself so I can't vouch for them, I just found the info.

djay · July 07, 2009, 04:06:42 PM

Hey

I have a DOD grunge and want it to make it trur bypass. The only problem is dat the wires ain't connected. I don't know whats fx in, fx out, 9V+,.... Can anyone help me with it or send a picture of the inside of the Grunge?

Greets

D.

fuzzo · July 07, 2009, 04:14:17 PM

look at the schema, there's all you need to do that.

But if you want to install a tru bypass, you've to drill the box to put the big blue switch . So, I don't know if that's really interesting

Fxin , where the signal from your guitar enter in the circuit
Fxout, where the signal leaves the circuit board to the switch (or buffer in dod pedal)
9V (or V) is the hole where the power comes into the circuit board.

dschwartz · July 07, 2009, 05:08:08 PM

the grunge pedal has input and output buffers..i seriously doubt that you have any tone losses....
Try bypassing those 10k/120Pf after the input, and the 100 ohm resistor to the input.

djay · July 07, 2009, 05:10:50 PM

I know that fx in is were the gitaar signal goes in but the pcb has 6 point were ik can connect a wire . and idon't know wich of the 6 is in, out, jack in , jack out, i only know that the second is the one that goes to the 9V jack.

I'm not that good in reading schematics. If anyone can take a picture of the connections i'll maybe can make it TB.

ddpawel · June 06, 2011, 02:01:55 PM

Here is my idea. Adding Metal Zone mid / frequency control.

http://img89.imageshack.us/img89/2637/dodgrungemetal.png

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Adding Mids to a Dod FX69 Grunge pedal.