DOD FX69b Grunge - modifications [schematic]

[pinkjimiphoton]

this addiction really isn't any cheaper than any of my other ones, lol!!!!!

[skylark44]

Same goes for me...I'll have to pay RS a visit soon...I definately need more LED's to my electronic parts bin .

[TheShadowKnows]

I must thank pinkjimiphoton for the diode pattern idea. I didn't have the ones he suggested so I used the ones I had on hand at the time. I was frustraited with my Washburn Lyon Distortion i modded. I thought I had it dialed in but there was some edgyness to it and I don't know enough about circuitry to know what to change. So I started messing around with diode combo's and BINGO! I found... like Goldie Locks, just the right one.
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Believe it or not, I used the stock diode (yuck/barf/hurl) with a RS 276-1101 / 1N4001 Silicon micromini and BAM! That weird combo nailed it. Now that Lyon pedal sounds so sweet, I've got to buy another one. The way it 'now' works is with the distortion full OFF, through my tube Bugera Vintage 55HD, I swear to Gawd my Ibaned RG320 with humbuckers sounds like a Strat in the neck position.
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With the distortion full off, it sounds like a clean TubeScreamer, but if you lean into it you almost get that overdriven Hendrix / Stevie Ray Vaughan, clean mud, I guess is the best way to describe it. And that's full off. As you increase the gain it just gets better / more Hendrixy. But I'll post that in my Washburn Lyon mod review.
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Thanks PJP. You Duh MAN! If I knew how to use the 'thankyou' button I'd give you my vote.

[pinkjimiphoton]

well done mate!!!

glad it worked out for you...amazing how much simple diodes can do.

if you have to rely on radio shack, try some 1n914/1n4148's....they sell them in bags of 5 or 10, they sound ALOT like the pricier germanium 1n34a's.

they break up a little later, but sound close with less volume drop. the 1n4001's are a nice choice cuzz they give a lot of headroom before clipping, so you can get them nice neck tones.

try a combo of diodes 1-4 pointing one way, 1-4 pointing the other, mixed all up and you can nail a surprising number of tones.

[TheShadowKnows]

FYI, I discovered a great resource for general modding and diode clipping circuits specifically:

http://www.muzique.com/lab/warp.htm

Looking like this mad scientist is off the to lab again.

Good thing I keep my soldering iron on all the time.

[DrNomis]

I think I have some Red,Orange,Yellow and Green 3mm Leds floating around in my parts stash, they'll be ideal for trying out the mods you suggested pinkjimiphoton...cheers...


With my Dod FX58 pedal, there's an irritating buzzyness to it's sound, not the mains buzz but more like a "wasp-in-a-jar" kind of buzz, hopefully I can get rid of it and get the pedal sounding better, might post a clip or two soon so stay tuned...


The good thing about this electronics addiction as far as I can see is that there's no adverse effects to your health...

[pinkjimiphoton]

never thought i'd say this, but reefer is cheaper!!! lol

[TheShadowKnows]

Since I was cramped for space, I had to get creative with these diodes. Bend 'em 'n solder 'em here and there. The zener are really tiny but the silcon are pretty big. This was on the Washburn Lyon Distortion. Now I'm nearly in love with the tone and distortion range.

But this one combo of diodes on this pedal yields a transparent slightly clean mud distortion (Hendrix-ish) to all out raging over-saturated. And the chip is one of those weird oblong ones, unless it's being handles by the transistors? I don't know.

Now all I have to do is figure out how to get the gain down to zero. At full off / left It starts with a tad bit of distortion. I have no schematic to go buy at the moment. I guess I'll have to chase down a resister off the gain pot path. The joys of modding.
Any help with the gain pot problem would be greatly appreciated.

[skylark44]

FYI, I discovered a great resource for general modding and diode clipping circuits specifically:

http://www.muzique.com/lab/warp.htm

Looking like this mad scientist is off the to lab again.

Good thing I keep my soldering iron on all the time.

I just read the whole page, on those variable "Warp" mods...very, very cool & interesting ideas...thanx for the link .

[DrNomis]

That's a good webpage skylark44, lots of great ideas there....

[pinkjimiphoton]

Since I was cramped for space, I had to get creative with these diodes. Bend 'em 'n solder 'em here and there. The zener are really tiny but the silcon are pretty big. This was on the Washburn Lyon Distortion. Now I'm nearly in love with the tone and distortion range.

But this one combo of diodes on this pedal yields a transparent slightly clean mud distortion (Hendrix-ish) to all out raging over-saturated. And the chip is one of those weird oblong ones, unless it's being handles by the transistors? I don't know.

Now all I have to do is figure out how to get the gain down to zero. At full off / left It starts with a tad bit of distortion. I have no schematic to go buy at the moment. I guess I'll have to chase down a resister off the gain pot path. The joys of modding.
Any help with the gain pot problem would be greatly appreciated.

the chip sounds like an sip version of a dual opamp...they're used in boss distortions too, and are basically a 4558 in a sip (single inline package) rather than a dip (dual).

why do you want the gain pot to go to zero? that will effectively just turn the volume off. if you want to kill the distortion, leave the gain pot alone, and add a switch to lift the grounds of the diode clipper. not connected to ground, it becomes just a preamp...it may be able to have enough power to overdrive an amp, but i bet it becomes more of a clean boost, which seems to be what you're looking for. check out that amz page suggested, and make a warp control. fuck around with lifting the ground to the diodes, and connecting that to a pot to ground, maybe with some caps and tapering resistors.

i bet you'll figure it out...without disabling the gain pot completely.

[TheShadowKnows]

Yes, that's what I meant. I didn't want the gain to zero, just the distortion to zero.
Thanks for the info.
I"ll give your tips a go and see how it turns out.

[pinkjimiphoton]

well, lifting the ground of the diode clipper will render it unusable. that will definitely make the pedal a cleaner version. just add a switch from the free ends of the diode clipper to ground, and you're back in business. damn near any switch will work.

[TheShadowKnows]

unfortunately on this pedal, with the diodes to ground, it starts out at 8 and then goes into massive gain that's horrible. My new diode config really smooths it out. I'm wondering if I could get a layout of the inline IC I could find which pin the gain resistor is on and lower / raise that?
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Does anyone have a schmatic for a N5223AL chip? I've looking on the internet and no luck .
Or point me in the right direction and I"ll just solder myself to success.
Thanks.

[pinkjimiphoton]

the diode clipper you've modified is going to ground...or one side is. that's the side you want to lift.

i looked up the chip, or tried to...

it's chinese. again, most likely an sip dual opamp.

[KBN]

Great thread! So I pulled C19 and I think I kind of like it in there, but would like to split the difference if I could. Would changing the 3.3k resistor in the feedback path on that 3rd op-amp accomplish that? Any help would be appreciated.

The C24 change is great. I changed R16 to 5k and that was a great improvement as well.

[KBN]

Or would I want to look at the 1k coming off of Q4. Just taking stabs in the dark here...

[pinkjimiphoton]

beats me, mate...i'm a hack!!

[darthoverdrive]

I came across this post the other day and though this would be a worthwhile mod. The Grunge is my favorite DOD pedal but the distortion is a bit too much. I always play it with the gain set to minimum. I pulled a couple of them out to try the mods leaving one stock to compare to.

First I changed R16 to 1K. Now the pedal goes from a nice crunch to some usable distortion, much better. I changed R19 from 47K to 22K on one but I couldn't tell any difference between the two.

Then I removed C19 on one of them. Here you are removing a gyrator set to 5997Hz with a Q of 1.7 which gave the pedal a lot of highs. The mids do come out and the sound is noticeable darker. Cranking up the HIGH knob fixes that some.

I'll play around with the gyrator calculator over at muzique.com and try some different values for C19 and the other cap and boost some additional frequency.

I didn't try the C24 mod as I like the highs as they are plus I didn't want to remove the pots to unsolder the cap. I didn't try the LED mod either.

Also, the traces on these boards are super thin and easy to lift if your iron is too hot.

Thanks for posting this pinkjimiphoton!

[pinkjimiphoton]

you're quite welcome brother!
hope it turns into something useful for ya.

jimi