DOD FX69b Grunge - modifications  [schematic]

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Re: so, i broke a new dod pedal tonite..but found cool mod..

Postby skylark44 » 11 Mar 2013, 03:34

I just did the mods mentioned...but now there's no sound at first ...then it comes in, but doesn't sustain for long....what did I miss?
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Re: so, i broke a new dod pedal tonite..but found cool mod..

Postby pinkjimiphoton » 11 Mar 2013, 04:11

hey,
sounds to me like maybe a weak battery? solder bridge?
it does draw more current with the chips stacked up.
no idea why it would do what you describe tho. mine freakin' screams and sustains great.
can ya take a pic of it?
check the soldering... i gotta look back at the thread real quick to see what i did... was a while ago and i'm an old stoner..lol

just re-read the thread... specifically, which mods did you do?

we'll try and help ya sort it out. ;)
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Re: so, i broke a new dod pedal tonite..but found cool mod..

Postby skylark44 » 12 Mar 2013, 00:34

I did everything but piggyback the chip(op amp). There's no real sound, until you strum hard ...then it cuts out quickly.
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Re: so, i broke a new dod pedal tonite..but found cool mod..

Postby astrobass » 12 Mar 2013, 02:58

I'm no expert but that sounds a lot like the way misbiased transistors behave. Is yours a B model like the one here or a different revision?

This was my first pedal ever. I had the FX-69C, but I'm going to pull it open and see if it appears to be the same, and try some of the mods here, one at a time to see if any don't take.
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Re: so, i broke a new dod pedal tonite..but found cool mod..

Postby pinkjimiphoton » 12 Mar 2013, 03:31

does sound like a bias problem, but i still don't know which mods you did... mine, or the ones in the thread?
unless you're specific, gonna be really hard to figure out where it went bugger.

voltages, etc, may help.

but to me, it sounds suspiciously like cold solder. having to really whack it to get sound thru is almost always misbiasing, or bad solder.

i can only speak for my mods... the others i don't know about. you may want to undo them, testing at each stage, until it works again.. and then you should be able to proceed.
when modding pedals, ALWAYS do one thing, then test. doing a whole bunch of mods at once is a recipe for disaster, imho
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Re: so, i broke a new dod pedal tonite..but found cool mod..

Postby astrobass » 15 Mar 2013, 05:59

Here's some useful data. I figured out what R1, R2, and C2 are in the gyrator calculator here: http://www.muzique.com/lab/gyrator.htm on the DOD FX-69 circuit.

R1 is 47000 Ohms, R2 is 1000 Ohms, C2 is 0.001 uF.

If you swap C19 for a 1 uF cap, you get a 734.5 bump with a Q of 0.22. Very broad boost with a center point on the mids. Should result in a mild perceived mid boost.

If you swap C19 for a 0.1 uF cap and C20 for a 0.01 uF cap, you get a 734.5 Hz bump with a Q of 2.17. Just over a 2/3 octave filter. That's pretty useful.

C19 = 0.05 uF (2x 0.1 uF in series) and C20 = 0.01 uF = 734.5 Hz bump at Q 4.34. I'm guessing that's close to a tubescreamer style mid boost.
(C19 = 0.047 uF and C20 = 0.01 uF = 757.58 Hz @ Q = 4.47)

If you tweak those values further I'm sure you can dial in whatever you really want, I'm just giving the results of relatively common caps that most will have on hand. I'm going to try the 734.5 @ 0.22 mod first, then work from there.
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Re: so, i broke a new dod pedal tonite..but found cool mod..

Postby astrobass » 15 Mar 2013, 06:01

I should have been more specific that R2 is immediately below C19, and R1 is immediately to the right of Q7. C2 is C20 on the actual board.

Also, I don't have the FX69C, I have the FX69B. The components appear to all be the same, the board layout is slightly different but very, very close.
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Re: so, i broke a new dod pedal tonite..but found cool mod..

Postby astrobass » 15 Mar 2013, 07:48

What are people using for diodes in this thing? I replaced D2 with a 1N34A, but it's still way too distorted with the gain up. I've got a very wide selection of diodes on hand, thinking about removing D2 and using a 1N4001 in D3 to give it some more headroom. Any thoughts?

I've replaced the R16 with a 100 Ohm (yes, down from 10K to 1K to 100 Ohm) and now there's a lot more play in the gain dial before it goes to noise, but it's still too fizzy. Also I can't have the high all the way up with the gain all the way up or it feeds back on its own. If I drop either one just a bit that fixes it.

The one thing I haven't done is C24 to a 0.0047, as I don't have any on hand. It's a 0.0022 stock, if I'm not mistaken. Would going to 0.01 be a huge waste of time? Is that going to bring the range of the "high" knob too low?
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Re: so, i broke a new dod pedal tonite..but found cool mod..

Postby astrobass » 15 Mar 2013, 15:08

skylark44 wrote:I just did the mods mentioned...but now there's no sound at first ...then it comes in, but doesn't sustain for long....what did I miss?

Post a close up of your soldering on R16. I made a mistake last night messing about with R16 that had a VERY similar effect, and if you've done the same I bet I can tell you what you need to do to fix that. I'm not at home right now so I can't describe the fix because I don't remember how things are labelled around there and I don't want to give bad instructions, but I think this is a really easy mistake to make with R16.
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Re: so, i broke a new dod pedal tonite..but found cool mod..

Postby skylark44 » 15 Mar 2013, 15:26

I think it could be R16 too...I swapped everything back to stock, except for the. 0047 cap (C24)...and now, I don't get any sound when the pedal's engaged. I orig removed C19 completely ...and that helped. The only thing I did different, was use 2 3mm orange/clear LEDs for D2 &D3. :mrgreen:
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Re: so, i broke a new dod pedal tonite..but found cool mod..

Postby astrobass » 16 Mar 2013, 00:10

Okay, so when I use this with my bass, as soon as I engage the pedal the bottom drops out. Doesn't matter if I have the bass knob all the way up and the treble all the way down, gain up or down, level up or down. Can't figure out where the filter is taking place. Any suggestions?

Edit:
Like, there are a few spots with 47K resistors to ground from the base of a transistor and a cap, but are those acting as RC filters? Is that in the signal path?

Should I just take a 1uF cap and touch it's leads to those of every small cap on the board while looping audio through the pedal into a bass amp until I find the magic cap? That seems like it'd be tedious but effective.
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Re: so, i broke a new dod pedal tonite..but found cool mod..

Postby sacredplague » 01 Apr 2013, 23:51

Does anyone have a picture of how the circuit board attaches to the inputs and LEDs?

I had an old DOD FX 58 Metal Maniac that I was trying to put into a new enclosure and some of the wire connections broke free from the circuit board solder and my guesses at reconnecting them were wrong.

I'm now getting the LED to light up, but no signal to the output.

I should've taken a picture on my own, but this is the second pedal I've trouble shot so of course hind-sight...

Thanks!
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Re: so, i broke a new dod pedal tonite..but found cool mod..

Postby astrobass » 12 Apr 2013, 00:24

astrobass wrote:Here's some useful data. I figured out what R1, R2, and C2 are in the gyrator calculator here: http://www.muzique.com/lab/gyrator.htm on the DOD FX-69 circuit.

R1 is 47000 Ohms, R2 is 1000 Ohms, C2 is 0.001 uF.

If you swap C19 for a 1 uF cap, you get a 734.5 bump with a Q of 0.22. Very broad boost with a center point on the mids. Should result in a mild perceived mid boost.

If you swap C19 for a 0.1 uF cap and C20 for a 0.01 uF cap, you get a 734.5 Hz bump with a Q of 2.17. Just over a 2/3 octave filter. That's pretty useful.

C19 = 0.05 uF (2x 0.1 uF in series) and C20 = 0.01 uF = 734.5 Hz bump at Q 4.34. I'm guessing that's close to a tubescreamer style mid boost.
(C19 = 0.047 uF and C20 = 0.01 uF = 757.58 Hz @ Q = 4.47)

If you tweak those values further I'm sure you can dial in whatever you really want, I'm just giving the results of relatively common caps that most will have on hand. I'm going to try the 734.5 @ 0.22 mod first, then work from there.


I don't know what I was thinking when I posted this, I had my values for C20 wrong. If you want 734.5 Hz at Q 4.34 you need C19 = 0.05 uF and C20 at 0.02 uF. ANYHOW:
I had the stock C20 and C19 = 0.47 uF, gave a 1071.38 Hz bump at Q = 0.32. It was decent, but I just got a new order of components and had to fiddle.

I put in C19 = 0.047 uF and C20 = 0.022 uF, giving 722.32 Hz at Q = 4.69. REALLY like it now. Awesome for adding filth to lead parts, and with the distortion turned down it works well enough for chords.
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Re: so, i broke a new dod pedal tonite..but found cool mod..

Postby astrobass » 12 Apr 2013, 02:30

Just changed C6 from 0.027 uF to 1 uF per Wampler's book. With that mid hump I added? It is the most incredible swarm of angry bees fuzz pedal. This is a must do mod. If you don't own one but do like fuzz pedals, get one used for $20 and do it.
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Re: so, i broke a new dod pedal tonite..but found cool mod..

Postby P3pp3r » 12 Apr 2013, 07:04

Hi there!
I'm planning to mod a DOD Buzz Box (Octaver/distortion) that I have, and I'm asking for help here because the distortion section on it is a copy of a DOD Grunge. (brilliant, don't you think? jajaja)
I'm just a beginner, but i've been looking at the mods suggested here, and i think there are some components that are the same. Here I've pointed them in a pic i got from internet (don't have a decent cam, sorry).

Image

Chips are 4558.
I've seen that, for example, C24 has the same "name" and same position as in the picture in the first post (Grunge).
I "deduced" the position of R16, R19 and D2, based on the other components close to them. I could be wrong.
C6 and C19 have the same "name" as in Grunge's pic, too.
Again, I could be wrong :roll: :mrgreen:
The jumper substitution is another mod i want to make for a better blend between octaved and distorted signals. I plan to replace it with a 82k/100k or a trimpot, so I can "calibrate" it.
I also would like to know the purpose of the two diodes I've pointed in green.
If someone has any kind of suggestion, please, let me know. Here is the original pic so you can point me any detail.

Image

Please, excuse my english. I'm working on it (and in my soldering skills, too. jajaja)

EDIT: :slap: I think I was wrong (told you so jaja).
Maybe D2 is the one closer to C19. And R19 is on it's right, in vertical position (yellow, violet, orange, gold). Makes more sense.
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Re: so, i broke a new dod pedal tonite..but found cool mod..

Postby astrobass » 12 Apr 2013, 13:54

The two diodes in green are both oriented the same way so not sure what their purpose is. If you look up and two the left under U2 there are two diodes quite close together going opposite directions. That looks like it's probably the clipping section.

Life would be easy if it turned out that they numbered their parts the same way they do on the Grunge, and added the octaver second, counting up from there. We can test if that's the case by removing a single part:
Try removing C19. The pedal should immediately seem less hissy and screechy.

You don't need to replace it or jumper it, just remove it and it should sound more mid rangey and normal.

If it does, try a few more mods (ONE AT A TIME) based on the part IDs used in this thread. If that doesn't work, put it back in. If that's the case, I don't know how you'll do this without a schematic.
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Re: so, i broke a new dod pedal tonite..but found cool mod..

Postby P3pp3r » 12 Apr 2013, 21:29

Last night I sent an email to Digitech, and surprisingly they gave me the schem for it! Also for my DOD flanger and my Meat Box :D
(Don't know how to reduce the image)
Schem:
Image

Bill of Materials:

Image

Hope it helps. I'm trying to understand it jajaja
I'm going to take your advice and replace C19 first.
I think you are right about the clipping diodes.

Thanks!
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Re: so, i broke a new dod pedal tonite..but found cool mod..

Postby astrobass » 13 Apr 2013, 04:22

Just checked the schematic and C19 is definitely the same in that schematic as it is in the Grunge. You can remove it to make the pedal WAY less obnoxious, or replace it and C20 to tweak that filter. C20 is the other cap in that gyrator filter, if you use the calculator I linked you can figure out which values work for you. R24 is R1 and R22 is R2 for that calculator, C19 is C1 and C20 is C2.

C6 is the same as it is in the Grunge too, so if you want to do the fuzz mod, that one will work too.

D2 and D3 also line up the same, so if you want to change the clipping diodes, those are the ones.
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Re: so, i broke a new dod pedal tonite..but found cool mod..

Postby astrobass » 13 Apr 2013, 04:32

Also, I'm pleasantly but QUITE surprised that they just sent you the full schematics and BOM. That's really awesome.
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Re: so, i broke a new dod pedal tonite..but found cool mod..

Postby P3pp3r » 15 Apr 2013, 21:36

After a few days, i'm back with good news!
I modded my buzz box and now souds a lot better than before!!!
First (and probably most important thing) was to change a jumper with a resistor for a better blending between the distorted and octaved signal. Before this, the octave sounded WAY more loud than distortion.
Second, I removed C19, and that added more mids to the sound. So i continued with the mods, and replaced all of the components mentioned. Put a green led in D2, and made it a more controllable distortion.
I even replaced C6 for a "fuzzy tone". And it works. I mean, it's not a fuzz face, but something close to a "creamy" "nasty" Big Muff (some settings remind me of Siamese Dream). And when i add the lower octave (the blend knob beyond 8 ) it's pure madness! :twisted:
Now my idea is to put a toggle switch so I can select the caps for C6, to have fuzz and distortion.
And I think i´m going to try with other led/diodes for clipping.
I want to say thanks to astrobass for your help, and to everyone who made a contribution to this mod.
I'm going to make a new topic explaining it for possible owners of a Buzz Box.
astrobass wrote:Also, I'm pleasantly but QUITE surprised that they just sent you the full schematics and BOM. That's really awesome.

Yes, I was surprised too! :whappen:
Now i will try to mod the flanger because it produces a noticiable volume boost when turned on.
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