Modifications on a Boss MT-2

[Shlafenflärst]

Hi everyone !

I have a Boss Metal Zone, on which I want to make these modifications :

• Putting it in a new box (because if I don't there won't be any room for my mods)
• Adding a toggle switch to disable the C35 capacitor (a known mod on this pedal, said to turn it into the Waza Craft version)
• Adding a second loop in parallel to mix the distorted sound with a clean sound, to get a less agressive sound and save the low frequencies when I use it with a bass (I currently do that outside of the box, with two loops coming out of my multieffect pedal, one going through the MT-2 and the other one through a tuner that serves as a killswitch, and then straight to the amp).
• Why not making it true bypass ?

For the first two points, I have no question, they are pretty obvious. But for the last two, not that much.

For the clean channel, I thought about simply adding a wire between the jacks, with an on/off footswitch and a volume pot (or possibly a balance pot also connected to the PCB output, or maybe no pot and just the switch), but I'm wondering, when the switch is closed and the pot at full volume, would it make a shortcut that would bypass the PCB ?
If so, what would I need to make sure the sound goes trough both the PCB and the clean channel ?
And if not, what would the pot resistance need to be ? (I know all about these things inside basses and guitars, but not when it comes to pedals)

Now for the true bypass thing, I'm not sure that's necessary, or even possible, and if it is it seems complicated, but I'm curious.
The footswitch connected to the PCB is temporary, so replacing it is not the solution. The easiest thing I can think of is cutting the signal that goes to the PCB and making it go straight to the output jack, but that would mean the PCB is always activated, which would use power. So I could also cut the power supply. But when the power is back, the effect is off, so I would need something to turn it on. Has anyone thought of a solution for that ?

Thanks in advance !

[Fancy Lime]

Hi Shlafenflärst,

you are fairly new here so let me say: welcome to the nut house!

Please post or link the schematic you are working with, so there are no mix ups with part numbers. A lot of avoidable errors happen when two people both talk about "R13" (or whatever other part) but refer to schematics with different numbering.

Turning any pedal into true bypass is very simple. You just need a 3PDT foot switch. Then you simply bypass the whole board, buffers and all. We can talk you through that if you want but quite frankly I would advise against it. True bypass usually makes more problems than it solves especially when modding a pedal that already has a perfectly fine bypass system.

I see no point in moving to a new enclosure. All you need is a little space for a switch, a pot and a little bit of wiring (and a 3PDT foot switch if you really want to do that). People have fitted that sort of thing and more on the sides or on the foot switch area of Boss pedals. Look here: https://www.youtube.com/watch?v=tHkJKAxhr9M

Not sure what you mean by "disable C35". Do you mean disconnect it or short it? Do you have a detailed description for that?

Due to the buffered in- and outputs of Boss pedals, installing a clean bypass loop is quite simple. I would take the clean signal after the second clean buffer (Q004 in the schematic here: https://www.hobby-hour.com/electronics/s/boss-mt2-metal-zone.php) and connect it with the output of the volume pot via a new pot (board connector 3), which then acts as the additional clean volume. You also need to add two resistors, one after the volume pot and the other after the new pot, to keep them from shorting each other to ground if one is set to zero. If you like I can make you a detailed drawing of that but I won't have time to do so before sometime next week.

Cheers,
Andy

[FiveseveN]

For the clean channel, I thought about simply adding a wire between the jacks

It has to be buffered first, but like Andy said, you already have a buffered clean signal in the pedal, you just need to tap it. If I'm reading the schematic right the effected signal should be in phase, so no worries there.

Why not making it true bypass ?

Why yes? What's bothering you about the current bypass system?

but that would mean the PCB is always activated, which would use power. So I could also cut the power supply.

Study the schematics of some effect pedals. You will find that absolutely none cut the power during bypass (even with true bypass). Why would the few mA drawn by the circuit be a problem? Are you running it off a solar panel? Stirling engine? Hand crank?

[Shlafenflärst]

Thanks for your answers !

you are fairly new here so let me say: welcome to the nut house!

I am quite new here indeed (and also new at modifying or building pedals), but I already like the place !

Please post or link the schematic you are working with, so there are no mix ups with part numbers. A lot of avoidable errors happen when two people both talk about "R13" (or whatever other part) but refer to schematics with different numbering.

Not sure what you mean by "disable C35". Do you mean disconnect it or short it? Do you have a detailed description for that?

That mod idea comes from this video and this one. The mod consists in simply removing the cap. And the C35 doesn't comme from any schematics, it's written on the PCB. On your schematics it's on the upper left hand corner (assuming the numbers on the schematics fit with the ones on the PCB, is that right ?)

Turning any pedal into true bypass is very simple. You just need a 3PDT foot switch. Then you simply bypass the whole board, buffers and all. We can talk you through that if you want but quite frankly I would advise against it. True bypass usually makes more problems than it solves especially when modding a pedal that already has a perfectly fine bypass system.

Why yes? What's bothering you about the current bypass system?

Like I said, I wasn't sure about this part, and I have no problem with the current bypass system, I was just curious.

I see no point in moving to a new enclosure. All you need is a little space for a switch, a pot and a little bit of wiring (and a 3PDT foot switch if you really want to do that). People have fitted that sort of thing and more on the sides or on the foot switch area of Boss pedals. Look here: https://www.youtube.com/watch?v=tHkJKAxhr9M

Didn't think about putting the second footswitch there... I could do that indeed. I just thought having a large enclosure with plenty of space between the two footswitches would be more comfortable, since I have big feet. But I could try making the mods in the original enclosure, and move to a larger one if I don't like it.

Due to the buffered in- and outputs of Boss pedals, installing a clean bypass loop is quite simple. I would take the clean signal after the second clean buffer (Q004 in the schematic here: https://www.hobby-hour.com/electronics/s/boss-mt2-metal-zone.php) and connect it with the output of the volume pot via a new pot (board connector 3), which then acts as the additional clean volume. You also need to add two resistors, one after the volume pot and the other after the new pot, to keep them from shorting each other to ground if one is set to zero. If you like I can make you a detailed drawing of that but I won't have time to do so before sometime next week.

It has to be buffered first, but like Andy said, you already have a buffered clean signal in the pedal, you just need to tap it. If I'm reading the schematic right the effected signal should be in phase, so no worries there.

I'll study the schematics and come back to you if I don't understand something.

EDIT : I think I understood what you said. I made the modified schematics. I also added switches for the C20 and C24 caps they talk about in the first video, not sure I will actually do that but I might, I'm curious to see what these do.



What do you think ?

[ElectricDruid]

This idea of chopping out C35 is quite interesting. I've got LTSpice sims of most of the bits of the MT-2 left over from my analysis of the pedal, so I tried it.

Here's the response of the Pre-distortion tone circuit without the mod - gives a serious midrange peak. It's been described as "nasal" by people who aren't fans of the pedal.


Here's what happens when you take that cap out. The response widens out and smooths out, but the mid boost remains. It drops to 18dB instead of 24dB, but +6dB in this pedal isn't a huge amount, given the rest of the gain.


From these graphs, it's certainly something I'd want to try. You could even just lift one end of the cap and then add a SPST toggle to be able to switch it in and out.

[iainpunk]

the mod i really like is taking out C017 and C025, this takes out the huge bass and treble boost, giving less of a scooped character after the distortion. i never understood why people would take out C035, i find that it makes the circuite even more scooped than it already is... and you'll get lost in the mix even more.
i also like changing R045 to 47K instead of 10K, this tames the overall gain a bit more

cheers,
Iain

[Shlafenflärst]

Well, I should also try that. That's a lot of options to test. Don't know how I'm going to do this, perhaps by adding a bunch of switches and then removing the ones I don't find useful...

[Fancy Lime]

Shlafenflärst,

your schematic would work as you drew it, I think. However, you will get better results by putting the extra resistors after lug 2 of the Level and Clean pots, respectively, instead of lug 1. I also see no real benefit in having an additional switch on the Clean Pot. You can just turn Clean to zero if you want no clean added.

Andy

[Shlafenflärst]

you will get better results by putting the extra resistors after lug 2 of the Level and Clean pots, respectively, instead of lug 1.

You mean like that ?

I also see no real benefit in having an additional switch on the Clean Pot. You can just turn Clean to zero if you want no clean added.

I want to be able to activate or deactivate the clean chanel while playing, so I need a footswitch.

[FiveseveN]

One more thing to think about: do you want the footswitch to just enable/disable the added clean signal or should you also compensate for volume? Because clean + distorted is going to be louder than distorted alone. How much that matters very much depends on how you set your controls (mix ratio in particular).

[Shlafenflärst]

You're right, compensating for volume could be a good idea, if it's not too complicated...

[Fancy Lime]

you will get better results by putting the extra resistors after lug 2 of the Level and Clean pots, respectively, instead of lug 1.

You mean like that ?



...

Yes, exactly like that. I would suggest a resistor that is about as big as the pot. So 47k for the 50k Level pot. It is easiest to make the Clean pot 50k as well and use a 47k resistor there as well. If you only have a 100k pot for the Clean volume, use 100k resistors on both pots.

A foot switchable clean channel should indeed probably have a volume compensation. That means you need a 3PDT foot switch and one more pot. The additional pot would be a second level pot wired like the original Level pot. Then the 3rd foot switch function would switch between the outputs of the two Level pots.

Andy

[Shlafenflärst]

Great, that's easier than I expected. I think I have all the information I need now. Thanks everyone !

[PRR]

> bypass  ....that would mean the PCB is always activated, which would use power. So I could also cut the power supply. But when the power is back, the effect is off, so I would need something to turn it on.

"ALL" audio circuits take some time to power-up from cold, and usually thump.

Some more than others. Yes, you can devise mutes and kick-start add-ons to get up to speed faster with less drama. It realy is not worth it.