#1
I have a Digitech grunge pedal, but im not really satisfied with the tone.

If i use it on the clean channel of my amp, i cant get distortion without the tone going all fizzy.
Also, the gain itself is VERY limited, it's too much. I want a more versatile gain, that can go as low as i need it to.

MODS I WANT:
1. More versatile gain
Clip and replace any "minimum value" resistor there might be, so the pot can give me a wider range of gain. Maybe also change the pot to compensate.

2. Less noise (if possible)
Replace the ceramic caps (wherever possible) with film caps of same value.

3. Asymmetrical distortion
Switch out one of the clipping silicon diodes to a germanium diode (or maybe an LED) for asymmetrical distortion.

4. LED replacement
Change out the boring red LED to a bright blue one.

Any suggestions?
Last edited by unet at Jan 1, 2009,
#2
Find a schematic first

For more versatile gain play around with the diodes or pot tapers
For the mids alter the tone stack?
For less noise try replacing the cheaper parts with high quality parts of the same values (change ceramics to film caps etc.)
Last edited by Sunburst PR at Dec 31, 2008,
#3
For the pot tapers, increasing the value would give me a wider range of gain right?

And what change would silicon diodes to germanium make?
If there are only two, would changing only one to germanium make a significant difference?

Also, why are film caps less noisy?!
#4
Silicon to germanium would cut the output as they are about half the voltage. Unless you put 2 in series each way. But with the diodes on full time its gonna be hard to completely get rid of the "gain" from the pedal. It might be better to find a pedal kit that you can do some tweaking to. I built a doubleD from run off groove. With the mods I did it will do just about anything. The clipping is on a switch with silicon or germanium diodes or off with a saturation control to dial in the amount.
#5
I could get a pedal kit, but not right now.

Right now, i want to mod this pedal so it can get closer to the tone i want.

Sooo....
Quote by unet
For the pot tapers, increasing the value would give me a wider range of gain right?
If there are only two, would changing only one to germanium make a significant difference?
Also, why are film caps less noisy?!


Also, im going to take photos of the circuit board if i can, but i can't get the freaking screws out!

ANY MOD SUGGESTIONS AT ALL??
#6
by tapers i meant keeping the same value, but switching from Audio(log) to Linear or vice versa. This changes how the pot changes its resistane and can lead to a broader range of useable tones.

Changing to germanium diodes will reduce the output, but I personally find germaniums to be a little bit smoother, better for overdrive than distortion. Replacing only one (or even adding one to an existing side) will produce assymetrical clipping, which some ppl find to be pleasing.

as to why film caps are less noisy, i dont know the facts, but consider how ceramic caps go for a few cents, and film caps go for around 10, companies mass producing tend to cut as many corners as possible to reduce costs, and ceramic caps are cheap not necessarily better
#7
Quote by Sunburst PR
by tapers i meant keeping the same value, but switching from Audio(log) to Linear or vice versa. This changes how the pot changes its resistane and can lead to a broader range of useable tones.

Changing to germanium diodes will reduce the output, but I personally find germaniums to be a little bit smoother, better for overdrive than distortion. Replacing only one (or even adding one to an existing side) will produce assymetrical clipping, which some ppl find to be pleasing.


What i was thinking was since the gain doesn't go below a certain value, i think there are a few fixed resistors in the gain stage, and a pot in series to adjust further.
If i replace this with a value that is lesser, or even a jumper, i'd considerably alter my gain range right?
(Obviously i'd have to get a higher pot value to compensate...)

I play quite a bit of metal.
Would making the clipping asymmetrical affect the compression or the overall amount of gain on tap?
Also, if it did, would i be able to compensate with the pot?

EDIT:

SCHEMATIC for dod grunge (mine's digitech...i hope they forgot to change the design.)



I see the diode clipping section.
I think thats going on my mod list. Add a germanium diode for asymmetrical clipping.
Last edited by unet at Jan 1, 2009,
#8
Changing the diodes will change the character, but i think some of the op-amps are distorting too. Try it without those diodes in and see how it sounds.
#9
The opamps as far as i can see are all setup for some gain.
I don't want ot mess with any IC's in the circuit unless the change would be very drastic.

What are all the FET's and BJT's for?
Also, can someone figure out WHICH opamp IC is being used, as well as the diode type.
I haven't been able to open the pedal yet.

Also,
MOD list in the first post!
#10
Quote by unet
The opamps as far as i can see are all setup for some gain.
I don't want ot mess with any IC's in the circuit unless the change would be very drastic.

What are all the FET's and BJT's for?
Also, can someone figure out WHICH opamp IC is being used, as well as the diode type.
I haven't been able to open the pedal yet.

Also,
MOD list in the first post!

the two JFETs attached to diodes are for switching (i.e. bypass) the JFETs at the input and output are buffers (to enhance signal quality), same with the BJTs.

I'd say that the op-amps are all duals.

Your mod list seems good, but I think the Grunge uses SMT/SMD components, so you'll need a steady hand for any mods.
#11
Quote by Entrant_21

Your mod list seems good, but I think the Grunge uses SMT/SMD components, so you'll need a steady hand for any mods.


Aww crap!

Are you sure, because if that's the case, i'd be too nervous to touch the damn thing.
Makes sense though...there are too many components for such a small enclosure.

Does no one have a picture of the Grunge's internals?!
#12
thier is a thread of a modded bad monkey might be pretty simular

https://www.ultimate-guitar.com/forum/showthread.php?t=1034068&highlight=bad+monkey+mods
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#13
The clipping diodes are gonna add alot to the distortion even when the gain is turned down. So if you want less gain thats where to go, disconect em and see how you like it. Not much else youre gonna be able to do maybe adjust some of the resister values on the feedback for the op amps. But if its the small surface mount stuff best to leave it alone. That stuff is really hard to work with and the traces are really small, ie easy to make a big non functioning problem. Some of the fets are input and output buffers the others are the flipflop switches to turn it on/off.
#14
Quote by Tackleberry
The clipping diodes are gonna add alot to the distortion even when the gain is turned down. So if you want less gain thats where to go, disconect em and see how you like it. Not much else youre gonna be able to do maybe adjust some of the resister values on the feedback for the op amps. But if its the small surface mount stuff best to leave it alone. That stuff is really hard to work with and the traces are really small, ie easy to make a big non functioning problem. Some of the fets are input and output buffers the others are the flipflop switches to turn it on/off.



Are the diodes SMD also?
I might be able to make that one change if they used regular diodes.

Also, would a professional electronics soldering person be able to perform the changes?
(I could ask a professor...)
#15
Issue with the surface mount stuff is there isnt a hole in the board for the component. Its soldered to a little pad. Be really hard to use a regular diode this way and very hard to drill a hole in the board. Way better to dig around for a schematic you like and build that.
#16
Quote by Tackleberry
Issue with the surface mount stuff is there isnt a hole in the board for the component. Its soldered to a little pad. Be really hard to use a regular diode this way and very hard to drill a hole in the board. Way better to dig around for a schematic you like and build that.


So there are no leads basically...

Yeah....i guess so.
Well at the very least im putting in a new LED!
#17
Heya unet,
Maybe you can help me verify if the Digitech Grunge pedal I have recently obtained has been actually modified. Seller claims he got it from someone who had it worked over. It sounds alright, but I don't have an original Grunge pedal to compare it with. Here is a pic of the circuit board:

Larger image
So far, I'm thinking the only thing modified on the unit I have is the stripped paintjob and the marks-a-lot labeling. The overspray on the inside of the case is purple and the knobs have white lines like the Grunge pedal.

If this has been modifed, what was done?

Thanks
BLAZE ON!

2006 Epiphone '58 Korina V
2008 Aslin Dane Bohemian
Real Sound Mars Twin Tube Distortion/Overdrive
Crate dxj112 amp
Dunlop HighGain used as expression pedal
#18
the necrobump was somewhat resonable, but why couldent you have just sent a PM?
Quote by Scowmoo




You deserved this, Matt.
#19
What? PM everyone that has one of these pedals? Found the this hread through a google search. Was looking for information on modified Digitech Grunge pedals. OP was looking for a pic of the insides of the box, I'm wanting to find out if what mods have been made to the unit I have.

Yeah, the thread is a year old, so? Should I have started a new thread? 'cuz I'm really confused as how a forum is suppose to work. Why do people complain when an old thread is dug up that pertains to what ever it is one is looking for. Isn't this is what a forum is for? To obtain and share information on specific subjects? How about the endless lame threads about, "My knob fell off, what do I do?". If there is so much static about digging up old threads, then maybe the forum moderaters should set the forums to delete after a few months.

Thanks for your advice there metal-matt, guess I'll start a new thread in regards to my question if that'll make ya happy.
BLAZE ON!

2006 Epiphone '58 Korina V
2008 Aslin Dane Bohemian
Real Sound Mars Twin Tube Distortion/Overdrive
Crate dxj112 amp
Dunlop HighGain used as expression pedal