#1
Hello,
I bought a DOD Death Metal FX86 a couple years ago for 25 dollars. It's a decent pedal, but the gain and noise is ridiculous.
That is why I am adding a gain control and replacing two op-amps.

Modded:

Original:


I took the gain control from the DOD Grunge pedal. The 50p capacitor near the second op-amp is replaced with a 1M capacitor. The 120K resistor is replaced with a 10K resistor and I added a 100K pot in series with the 10K resistor.
Would anyone be willing to verify that this will work?

I've done research on mods for this, and one of them said to replace the KA4558 op-amps with a better one. I chose the NE5532 op-amps. They are labeled U1 and U2 on the schematic.

I wont be able to get this done untill Tuesday or Wednesday as the electronics store is closed on the weekend and have the shittiest hours possible when it is open.

--timbit
..I was watching my death.
Last edited by timbit2006 at May 20, 2011,
#2
Damnit Photobucket, why do you have to shrink my pictures?
I have to fix that...
..I was watching my death.
#4
Quote by zero_sith
wow! You can upload a video to see how your pedal sounds ?

I don't think I'll do a video, but there will be sound clips.
I was planning on doing a before and after comparison, but now that I see it laying on my desk like a lobotomy gone wrong... I don't feel like re-assembling it.
..I was watching my death.
#6
Thanks for telling me. I've been looking at the MT-2 mods a little bit and found some that can make it sound American or British. If I feel adventurous I may do this with a toggle switch to turn it on and off.
Hopefully I'm getting to the electronics shop today.
I'm getting a holder for the op-amps so I can switch them out easily.
Can you switch between two op-amps with a switch or does this present a problem?
I would need a big switch, and I would only switch half of the dual op-amp. Unless I can find an 8PDT switch.
..I was watching my death.
#7
Quote by timbit2006
Thanks for telling me. I've been looking at the MT-2 mods a little bit and found some that can make it sound American or British. If I feel adventurous I may do this with a toggle switch to turn it on and off.
Hopefully I'm getting to the electronics shop today.
I'm getting a holder for the op-amps so I can switch them out easily.
Can you switch between two op-amps with a switch or does this present a problem?
I would need a big switch, and I would only switch half of the dual op-amp. Unless I can find an 8PDT switch.


Never used a switch to swap op-amps. My guess is there is going to be a loud pop. Maybe not if you don't switch the power pins.
#8
Alright, thanks.
Maybe I should experiment with keeping the power on and only switching the rest. I'll get a circuit tester board as well. Then I can start prototyping circuits.

Do you see any transistors that would change the tone that could be switched? I know they can be switched with a 3PDT.
..I was watching my death.
#9
You can keep the ground on the op-amps always connected also and should save a row of lugs.

I wouldn't worry about any transistor swapping. You'll get most out of switches if swapping parts in the gyrators. There is a couple gyrators that are pre-distortion that are cool to switch in/out of the circuit. C20 and C24 if I remember correctly.
#10
I'll have to do quite a bit of research on how op-amps work. I really haven't done anything with them. I'm at a novice electronics experience level. Started a couple years ago, haven't really done anything major untill recently.

I'm not to sure as to what a Gyrator is. Could you explain further please? Like I said, I'm still learning. I will do some research on it though, sometimes it's best to have someone show/tell you as well. It helps me alot rather than reading an extremely detailed Wikipedia article.

I've read about diode switching mods for this pedal as well, I'm going to look further into that.
..I was watching my death.
#11
As far as op-amps go, google the datasheet for the one you have in there and the one you want to swap it for. It should be a dual op-amp. It will have two inverted and two non-inverted inputs each having it's own output (so two outputs on the dual opamp). These are going to be what you are wanting to switch out. You can leave both the power and ground supply directly connected to the board. Again, I've never done this but this is how I would do it. Might be able to use a 4pdt switch if my count is correct.

Gyrators are an EQ basically. Here is how you apply the mod I was talking about to the MT-2. See the two transistor circuits? That is two gyrators. One starts at C024 and the other at C020. This could be directly applied to the Death Metal. The switchs turns each one on/off. I think I have a Death Metal schematic somewhere on this computer. If you need me to, I'll try to find it and tell you what components it is on that pedal.

#12
I'm at school and the bell is about to ring, so don't think I am passing over some of your paragraphs.
Is you FX86 schematic better than the one I've found? The one I have doesn't label any of the parts, only a select few.
If you have a better one, I'd greatly appreciate you posting it.

Thanks for all your help.
..I was watching my death.
#13
No, I don't have one that is labeled with component reference. I'll make one for you really quick if you want me to.
Last edited by Griffin Effects at May 24, 2011,
#14
Quote by timbit2006
Damnit Photobucket, why do you have to shrink my pictures?
I have to fix that...

tinypic ftw. also, do NOT post huge pics. link to them instead. it is so friggin annoying to have to side-scroll every 2 seconds to read the posts.
#15
Quote by Invader Jim
tinypic ftw. also, do NOT post huge pics. link to them instead. it is so friggin annoying to have to side-scroll every 2 seconds to read the posts.


It fits on my monitor perfect and mine's not even widescreen.

Quote by GriffinEffects
No, I don't have one that is labeled with component reference. I'll make one for you really quick if you want me to.

Don't worry about it. I'll do fine with my current one.

I don't think I'll mod the gyrator as you described. There just really isn't too much room in the pedal after I put in my gain potentiometer. There may be room, but I'll wait and see.
..I was watching my death.
#16
My first trip to the electronics store was unsuccesful...
They one had one NE5532 Op-amp but the end of the month is nigh.
I was also in a rush and bought a pot which is too big...
I got the Cap and Resistor succesfully though!

I have what I bought currently soldered.
I would like to take this time to say: Chips are a pain in the ass to desolder... Especially when the legs are bent to hold the chip in.
When I get home, I'll take pictures of what I have done already.

I think I may do the gyrator mod now that I have some time before I go to the store.

Griffin, the picture you posted above isn't working. If I remember correctly it was the gyrator mods in a MT-2.
..I was watching my death.
#17
Yeah, the server was down. It's working right now. It's the mod on the MT-2 but can be applied to the Death Metal. You don't have to do a switch. You can test it first by lifting the leg of one of the caps and try the pedal to see if you like it. Then lift the other leg and test it with both out. Then put the first one back in and test it and see if you like it. Make sure it's worth drilling for switches for you first.
#18
Which Gyrators am I modding?
Perhaps I would benifit from a labeled schematic if that's possible.

What do you think of having sweepable highs?
I would do a concentric pot. Do you think this would be relatively easy to do?
Sweepable mids are much more pratical, but the highs look easier to change.

Thanks for all your help, it's greatly appreciated.
..I was watching my death.
#19
The Death Metal has Bass, Mid and Treble control. What do you want to add? What's lame about it is it doesn't have a Gain control.

Give me a little bit and I'll do up a schematic. The Grunge pedal is about the same also so I may incorporate that into the schematic to make an all in one kind of deal. It depends on how much time I have. The both use the same circuit board.

You would disconnect the gyrators at the 13n and the 1.5uf on the third op-amp (triangle thing) from the left on this schematic. FX86 Schematic

Disconnect the side that's connected to the op-amp. I'll get a labeled schematic for you to make it clearer and easier. Give me a few minutes.

EDIT: Here you go: DOD FX86/FX69 Labeled Schematic

You lift the leg of C14 where it connects to R18, C13, and pin 2 of IC2A. The other one you would lift the + leg of C16.
Last edited by Griffin Effects at May 30, 2011,