HELP COMPUTER: modding a Boss pedal

[Doog]

GIJoe.jpeg (38.69 KiB) Viewed 1340 times

Hey gang, seeking some specific advice or even offers of handsomely paid service here, so I'd be grateful for any input at all.

So, I love a good Big Muff-based circuit, namely due the fact there's some filtering happening early on in the circuit dulling the sharp attack of the input, resulting in That Muffled Thing It Do.

That's key to me as I run a very sharp clanky 'clean' sound into the Muff, and I really want a lot of contrast when it's on, all while still keeping that clanky OD on to goose the Muff. Sounds so sick, bruh.

Up until now, I've been using a Boss LS-2 to switch my Muff O'Choice in and out as, sat next to my OC-5 and TU-3, it makes turning multiples of these on and off together a snap.

However, I've really wanted to replace that system with a standalone Boss pedal to keep things lighter and simpler, but literally every Boss distortion or fuzz I've tried (I've honestly tried pretty much them all at this point, even weird rare ones) maintains or even BOOSTS that sharp attack. I guess that's the nature of distortion really.

I'm mostly likely looking at a Boss HM-2 or MD-2 Mega Distortion as they have great EQ and gain characteristics.

I've done some simple mods to the MT-2 and DS-1, but they're generally subtractive, just removing caps etc. to tweak the sound to sound, uh, better.

I feel like, all this needs to be is adding a cap to the right place in the circuit, but I'm a bit too green to scope out any schematics and relate to the circuit currently.


Thank you! xo

[plopswagon]

Doog gonna cap that bitch!

[NickS]

Sounds like you want a single transistor input stage with that negative feedback cap that simulates the Miller effect you get with valves and germanium transistors.

[dub]

Feels like it would be easier to stick another circuit and/or foot switch into a muff enclosure than trying to mod a completely different circuit into something it isn't? Plenty of space.

[NickS]

Looking at the circuit diagrams for the SD-2 and HM-2, the HM-2 has a similar input stage to the Big Muff Pi. You might try increasing the value of C10, currently 100 pF, if the other aspects suit.

[Doog]

Feels like it would be easier to stick another circuit and/or foot switch into a muff enclosure than trying to mod a completely different circuit into something it isn't? Plenty of space.

But my point is I want the Boss enclosure because of the form factor and those 2 Boss pedals I mentioned CAN get close enough for me, but just need a bit of a help.

I had previously thought about rehousing a mini Muff pedal into a Boss enclosure, but as the whole bypass system is different, as soon as you start having to fuck with that - now having to operate the Frankenstein'd BossMuff different because of a 3PDT switch hiding in there -, it just introduces a different flavour of problem.

Looking at the circuit diagrams for the SD-2 and HM-2, the HM-2 has a similar input stage to the Big Muff Pi. You might try increasing the value of C10, currently 100 pF, if the other aspects suit.

Ooh that's very interesting, thanks Nick! Based on the circuit, would you foresee any problems with me just running some flying leads out to a pot and a cap, so I can experiment before settling on a specific cap value? It's just sorta working as a guitar tone control at that point, no?

I'll likely pick up a Behringer copy and fuck around with it before sinking a ton into the real thing; based on the mod I did to a Behringer Superfuzz, they're relatively friendly to work with.

[BearBoy]

I've honestly tried pretty much them all at this point, even weird rare ones) maintains or even BOOSTS that sharp attack. I guess that's the nature of distortion really.

Did you try the PW-2? It was, IIRC, supposedly their attempt at a Big Muff style pedal.

Hurb did an demo of the Behringer clone:

[Doog]

I've honestly tried pretty much them all at this point, even weird rare ones) maintains or even BOOSTS that sharp attack. I guess that's the nature of distortion really.

Did you try the PW-2? It was, IIRC, supposedly their attempt at a Big Muff style pedal.

Hurb did an demo of the Behringer clone:

Yeaaaah, I so badly wanted this to be solution but no dice; there's still looooads of attack coming through. I've not tried one (Boss or Behminger), but they do still sound quite different in this and other demos.

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In general, I guess likely down to the the buffer and/or input impedance of Boss pedals, so the 'tamping down' needs to happen inside the circuit for sure.

[BearBoy]

Suspected it probably wouldn't have escaped your attention but thought it worth mentioning just in case.

Hopefully Nick's suggestion will help you wreck an expensive vintage Boss pedal get the sondz you need.

Behminger

Not sure if deliberate or typo but

[Doog]

[NickS]

Feels like it would be easier to stick another circuit and/or foot switch into a muff enclosure than trying to mod a completely different circuit into something it isn't? Plenty of space.

But my point is I want the Boss enclosure because of the form factor and those 2 Boss pedals I mentioned CAN get close enough for me, but just need a bit of a help.

I had previously thought about rehousing a mini Muff pedal into a Boss enclosure, but as the whole bypass system is different, as soon as you start having to fuck with that - now having to operate the Frankenstein'd BossMuff different because of a 3PDT switch hiding in there -, it just introduces a different flavour of problem.

Looking at the circuit diagrams for the SD-2 and HM-2, the HM-2 has a similar input stage to the Big Muff Pi. You might try increasing the value of C10, currently 100 pF, if the other aspects suit.

Ooh that's very interesting, thanks Nick! Based on the circuit, would you foresee any problems with me just running some flying leads out to a pot and a cap, so I can experiment before settling on a specific cap value? It's just sorta working as a guitar tone control at that point, no?

I'll likely pick up a Behringer copy and fuck around with it before sinking a ton into the real thing; based on the mod I did to a Behringer Superfuzz, they're relatively friendly to work with.

There's no harm in trying, but keep the leads as short as possible.

[NickS]

Looking at the circuit diagrams for the SD-2 and HM-2, the HM-2 has a similar input stage to the Big Muff Pi. You might try increasing the value of C10, currently 100 pF, if the other aspects suit.

Ooh that's very interesting, thanks Nick! Based on the circuit, would you foresee any problems with me just running some flying leads out to a pot and a cap, so I can experiment before settling on a specific cap value? It's just sorta working as a guitar tone control at that point, no?

Well, sort of. Where it is you get a filter effect that is larger than you might think, as the value of the cap is effectively multiplied by the gain of the stage (the Miller effect).

HM-2 input.png (85.89 KiB) Viewed 1225 times

In this diagram the high frequency cut-off in the input stage is pretty much determined by the values of R19 and (C10 x gain).
Notice that right behind that input stage is another similar stage around Q7 (upside down, PNP transistor) but with lower gain so the effective cut-off frequency would be higher; maybe if the input stage goes into clipping that takes some of the edge off the clipping? I really should learn how to use SPICE or some other circuit emulation.

There are a whole bunch of variations of the Muff input stage, though, so I'm not quite sure which you prefer; see http://www.bigmuffpage.com/Big_Muff_Pi_ ... part1.html

I did add a small feedback cap to the silicon Fuzz Face clone my son built. The Fuzz Face has variable gain on the input stage so as you turn the gain up the cut-off frequency comes down.

[Johno]

Would a Boss Metal Zone provide the answer?

[Doog]

I do have one that I modded (Simpledog mod, clipping a few caps), and it’s grand but not quite there.

I’ll likely try to mod it further - less scary when they’re so cheap and abundant - with NickS fantastic guidance, as the EQ section really is great.

[Doog]

There are a whole bunch of variations of the Muff input stage, though, so I'm not quite sure which you prefer; see http://www.bigmuffpage.com/Big_Muff_Pi_ ... part1.html

Ooh yeah; I prefer the Russian variants generally (lower gain, more mids and bass, v wooly), but I'm not really sure how much of that sound is down to this input stage per se?

[Doog]

So I sat down with a few videos and Electrosmash pages about both the MT-2 and the Big Muff to understand the circuit/s a little more; how RC filters really work, and noting how many stages of lowpass really happen in the Muff circuit! Hint: loads.

Used this handy calculator to figure out what value resistor or cap I could sub in to get the frequency response in the MT-2 closer to that in the Muff.

I eventually just realised I could literally just piggyback another capacitor in parallel across the existing input lowpass filter, and just went about mashing various caps to the solder pads on Metalzone PCB, until I settled on some value that doesn't even matter, one that suitably dulled the attack to take on enough of a Muff vibe to keep me happy.

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Screenshot 2024-06-06 at 22.39.30.png (2.2 MiB) Viewed 1155 times

The response is obviously not the same as the Muff as they're very different circuits (even with the Wazacraft mod I did to this already), but it's much MUCH more what I want out of a fuzzy distortion now.

I'll replace the combo with a single cap when I've got a bit more time over the weekend, but I've buttoned 'er up temporarily to mess around with it til then:

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Screenshot 2024-06-06 at 22.39.34.png (1.95 MiB) Viewed 1155 times

The Boss Ghostwatch, named for the 90s 'documentary' that made everyone shit themselves



Thank you for your help, Nick; much appreciated!

[plopswagon]

My son in law is getting his paralegal certification, I asked them if he was going to do ghost law.

[Doog]

Rights are rights, man!

[NickS]

Happy to have helped, glad you've found a solution that suits you.

[Bacchus]

Great work!