Help needed to design OD1/OD2 pedal from MG100DFX Amp

R

Reconciledheart

New member
Good day everyone

I hope this message finds you well.

Over the last year I started getting into guitar pedal building and truly enjoy it, but have not been able to find a pedal build that has the exact sound I am looking for. I have built a Kliche, Julia Clone, Face Melter, ADHD, Thermionic Distortion and a Spatialist Reverb. All are brilliant and I cannot choose between them so all of them are on my board.

My absolute favorite overdrive/distortion is the OD channel 1/2 on a MG100DFX.

Would it in any way be possible to isolate that part of the schematic and have a design drawn up and schematic and gerber files made to include the layout with a switch to toggle between OD1/OD2, Gain, Bass, Middle, Treble, Contour and Volume controls? If it would be, what would the costs be and who would be able to provide this service? It won't be commercial, just for me and a few friends but after hearing horror stories about scammers on Fiverr it's safer for me to not go that route. I have a quality schematic that I can send of the MG100DFX as well.

Kindest Regards, John
 
Feral I am sorry, I am still limited to sending direct messages to Admin at the moment.

Thank you very much for your comment on my post with regards to possibly making a design of a MG100dfx OD1/2 pedal.

Would you be able to design a schematic of a pedal based on it and if you can, what would the costs be? Thank you😀
 
I have a PCB for a similar Marshall amp circuit somewhere.... I don't think it was the MG100 but the circuit looks close. Maybe it was a practice amp sized version of the same line? I can't recall, but it might be possible to modify it into what you're wanting.

I'll do some digging and see if I can find it. My track record ain't the best here lately though, so don't turn down any offers in the meantime. :ROFLMAO:
 
I can see the potential for this, but I'm not far enough down my own Pedal-Path to wrangle this to submission.

Someone else want a crack at it?


anyone.gif
 
Robert said:
I have a PCB for a similar Marshall amp circuit somewhere.... I don't think it was the MG100 but the circuit looks close. Maybe it was a practice amp sized version of the same line? I can't recall, but it might be possible to modify it into what you're wanting.

I'll do some digging and see if I can find it. My track record ain't the best here lately though, so don't turn down any offers in the meantime. :ROFLMAO:
Click to expand...
I would truly be grateful, thank you for being willing to help:D
 
I played around with this a bit, trying to make it a unipolar supply (just +9V) which looked reasonable given the clipping diodes in the main gain stage anyway. (caveat: I have no idea what I'm doing) When I simulated it in kicad I got all kinds of trouble, tho, but I'm not sure how much of that is my limited experience in playing with the simulator. I'll see if I can breadboard something in the next week or so if I get a chance.
 
z2miller I am really sorry for my late reply I missed the notification on my mail. I am truly grateful for your time and being willing to assist me and for coming so far:D
 
@Reconciledheart I did play around with this on the breadboard a bit this weekend for funsies,
with a bipolar supply (+9/-9V). I got as far as the main gain stage, I haven't gotten through the
whole tone stack part yet. I might try it again next week with a unipolar supply + vref
to keep the parts count down but I'm heading out of town for a week so it'll be a bit.

It is clippy asf, almost a square wave coming out of the gain stage, but maybe that's how
it's supposed to sound. (metal!)

One hassle about this is that it has so many controls, any more than 6 controls and it gets harder to fit
in a 125B. (looks like it has Gain, Treble, Mid, Bass, Contour, Volume, and then the OD1/OD2 switch).
Are any of these controls like set-it-and-forget-it, like you always leave it on OD1 or OD2?
If one of the controls stayed internal, it'd be easier to lay out.

(Yeah, could do another footswitch or something for OD1/OD2, or an offset layout, as well...)
 
I haven't gotten this all breadboarded, but I just yolo'ed a through-hole PCB layout and will order a stack of 'em next time I order from JLCPCB, and see how it works. If it makes any reasonable noises I'll release the gerbers for people to try out.
 

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I dunno if @Reconciledheart is still around, but I'm going through and cleaning up my old crappy schematics and repositories one by one and ran into this one again. I did a little troubleshooting with simulations and as far as I can tell, it's supposed to clip into near-square-wave-territory really easily. So anyhow, I haven't had this fabbed yet but I'm just going to release the whole thing as-is.

Notes:
* I tried to make this support either PedalPCB style (GND/9V up at the top, 4 pins for footswitch at the bottom) or my JST-PH header style. The gerbers for my footswitch breakouts are in my pedalfx repo.
* It's a conversion from a +/- 15V effect and I've tried to maintain maximum fidelity with the original. You can run this on 9V but that might change the tone a bit since the first stage is more likely to clip. If you run this with an 18V adapter it should be completely true to the original. Sure I guess I could tone down the first gain stage to try to match on 9V, or go nuts and make the board a foot long with a charge pump on there, but I didn't.
* I added a bunch of power supply filtering (not exactly in the original since it brought its own power supply that was filtered however it wanted). What's on the board is a capacitor multiplier that buys quite a bit of extra power supply ripple rejection at the cost of some extra components and a little bit more voltage drop (about 1V total including the reverse polarity diode). If you've got a clean power supply that's only 9V and want to buy some more headroom so the first stage doesn't clip, you can replace the resistor with a 47R or something, leave out Q1, and jumped Q1 pins 2 and 3 which buys you ~0.3V or something. Or you can totally raw dog it and jumper straight from the input side of the protection diode to a jumpered Q1. But really you should just run it at 18V.

Here's the whole KiCad project (CERN-OHL-P-2.0 license):
github.com

GitHub - z2amiller/fx-mg100dfx

Contribute to z2amiller/fx-mg100dfx development by creating an account on GitHub.
github.com github.com

I generated the gerbers in case you can't be arsed to get KiCad working so you can order it (relatable):
github.com

fx-mg100dfx/GERBER-fx-mg100dfx.zip at main · z2amiller/fx-mg100dfx

Contribute to z2amiller/fx-mg100dfx development by creating an account on GitHub.
github.com github.com

Interactive build doc:

I'll probably throw this in my next JLC order and try to build it, but Idunno when that'll be. If you decide
to order/build it, let me know how it goes!
 
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