Boss - Metal Zone MT2 mods

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Re: Boss - Metal Zone MT2 mods

Postby blackbunny » 12 Mar 2011, 02:46

Thanks Saul T. This is a great tool for we who tweek MT-2's, will surely save mucho trial and error and help us to focus our breadboarding time. And fun as well.

I don't suppose you could apply this program to the BD-2 Blues Driver, perhaps?
There seems to be hundreds of mod tips and Boo-tweekers offering mods for the BD-2, but I have yet to hear any 'magic' tonal breakthroughs for that pedal.

sault wrote:As an added bonus I also show how the frequency response changes when you lift C2 or short C1 (which is a mod that you never hear about with this pedal!), and included preset buttons for the Metal Zone stock values and the Diezel mod values.


I got quite a surprise when I pressed the MT-2 preset button for the stock 'low' gyrator and saw the EQ graphic image.

Is it really shaped like that? Looks like a boost at 100 Hz or so with an amazingly narrowly Q!
Surely that would simply make a couple of notes seem to jump out while doing little to add to the general fatness?

Is that a mistake?
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Re: Boss - Metal Zone MT2 mods

Postby sault » 14 Mar 2011, 09:31

I don't suppose you could apply this program to the BD-2 Blues Driver, perhaps?


Hmmm. Having absolutely no experience with the BD-2, I had to look up the schematic to see what there was under the hood. The schematic is a little blurry, but it looks like C9, C16, R10, and R21 do form a gyrator based around Q7... the values that I'm looking at are 0.056 uF for "C1" and "C2" on my calculator, and 470k for "R1" and 1200 for "R2".

It's a little nutty, and it is enough to make me stop and think... the results that I'm getting are a peak frequency of 120 hz, with a Q of about 20! It is enough to make me wonder if my sources are correct. Jack's calculator does match up with my results, though, so... see my explanation below, that's the best I can come up with.


Is it really shaped like that? Looks like a boost at 100 Hz or so with an amazingly narrowly Q!
Surely that would simply make a couple of notes seem to jump out while doing little to add to the general fatness?


(talking about the Metal Zone) So, umm, yeah. I do believe it is correct... 105 hz, Q of 14 or so...

What I think I'm seeing is that most of the low end is rolled off when the signal hits the pre-emphasis gyrator, ie the range between 800 and 1200 hz is boosted but very little so far below.... Basically, the note contributes harmonic content, but is itself basically filtered out. This matches up with what my ears say, that the low end isn't well-defined (a little boomy/flabby), and with the basic idea that filtering out the low end is exactly fitting the spirit of this pedal - high gain, 80's metal, with lots of articulation and treble response, and no muddy bassiness to pull down headroom. The difference between pre- and post-distortion EQ, right there...


An interesting mod would then be to modify the 'pre' filter... a 0.1uF cap for C1 and a 3nF cap for C2 would keep the resonant frequency in the 900 hz region, but would lower the Q to just under 1, meaning a range of 500-1600 hz. This would indicate to me a fuller tone, albeit one that might not be as trebly and articulated.

Ha. Would never have thought of that one, right? This also makes me think about some of the inter-stage filters, too... hmmm....

It's funny... this is what really interests me these days, trying to understand what the circuit is doing on a fundamental level. I am a little frustrated that I don't have a complete understanding... I can't tell you what the impedances are, or what the gain figures look like, or describe how the curve looks around the corner frequencies (correctly, at least)... but I can at least get us this far. I'm slowly teaching myself the math and electronic theory to go further, but.... well, it's not simple. Well, at least its something to do, right? :D


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Re: Boss - Metal Zone MT2 mods

Postby blackbunny » 15 Mar 2011, 00:55

sault wrote:I don't suppose you could apply this program to the BD-2 Blues Driver, perhaps?

Hmmm. Having absolutely no experience with the BD-2, I had to look up the schematic to see what there was under the hood. The schematic is a little blurry, but it looks like C9, C16, R10, and R21 do form a gyrator based around Q7... the values that I'm looking at are 0.056 uF for "C1" and "C2" on my calculator, and 470k for "R1" and 1200 for "R2".


I recall Brian Wampler pointing out in his stage-by-stage analysis of the Blues Driver that the circuit boosts the low frequencies and severely cuts the highs before the overdrive stages, which is very unusual.

I guess I'm just being lazy asking for a simulator, as there's more than enough info available on the BD-2 already so that I could figure out the frequencies stage-by-stage with a little bit of calculating.

sault wrote:(talking about the Metal Zone) So, umm, yeah. I do believe it is correct... 105 hz, Q of 14 or so...

What I think I'm seeing is that most of the low end is rolled off when the signal hits the pre-emphasis gyrator, ie the range between 800 and 1200 hz is boosted but very little so far below.... Basically, the note contributes harmonic content, but is itself basically filtered out. This matches up with what my ears say, that the low end isn't well-defined (a little boomy/flabby), and with the basic idea that filtering out the low end is exactly fitting the spirit of this pedal - high gain, 80's metal, with lots of articulation and treble response, and no muddy bassiness to pull down headroom. The difference between pre- and post-distortion EQ, right there...


An interesting mod would then be to modify the 'pre' filter... a 0.1uF cap for C1 and a 3nF cap for C2 would keep the resonant frequency in the 900 hz region, but would lower the Q to just under 1, meaning a range of 500-1600 hz. This would indicate to me a fuller tone, albeit one that might not be as trebly and articulated.


Experimenting with the midrange pre-emphasis seems to be the way to go, with a lower Q. Since the tone controls are fairly powerful Baxandall types, and are near the end of the circuit, maybe a bit less fixed low- and high-frequency boost from the post-clipping gyrators will make the bottom end a bit tighter and the upper midrange a bit less annoying.

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Re: Boss - Metal Zone MT2 mods

Postby Seven64 » 22 Mar 2011, 07:17

im a pretty big noob at this, but what size resistors are in this pedal? 1/4w or 1/8w?
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Re: Boss - Metal Zone MT2 mods

Postby blackbunny » 22 Mar 2011, 12:43

All the MT-2 boards that I've seen have had 1/8 watt resistors. You can use 1/4 watt resistors for some modifications by mounting them 'standing up', or in many places on the board you can get them to fit horizontally by carefully bending the legs to achieve the shortest overall length possible.
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Re: Boss - Metal Zone MT2 mods

Postby Seven64 » 22 Mar 2011, 20:11

ok, cause i cant seem to find 1/8w at any of my retailers....funny thing is they easiest place for me to find them is radio shack
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Re: Boss - Metal Zone MT2 mods

Postby Seven64 » 22 Mar 2011, 21:07

holy cow! i was searching around for mods for it when i stumbled across the griffin death metal mod. I am going to search more to see if i can figure out a parts list and whatnot, but it sounds incredible! im temped to just buy the mod kit when i get paid again!

http://www.youtube.com/watch?v=gBoGnWanqUs

and the griffin site


http://griffineffects.goshopper.net/i/1 ... od-kit.htm
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Re: Boss - Metal Zone MT2 mods

Postby ckyvick » 23 Mar 2011, 08:57

If anyone is curious these are the pedaldoc mods. I chose this one because it had the best reviews on hc of all the mt-2 mods. Smooths out the pedal and makes it a lot more usable. Not sure if anyone's posted this before. Reviews: http://www.harmonycentral.com/products/106612
Mods:
Change to red leds - D3,D4
R30- change to 2k2
Remove- C25, C35
Change to .22 uf- C8, C20
Change to .1uf polyester- c9,c36, c42
Change to .47uf- c17
Change to 1uf tantalum- c11, c37, c39
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Re: Boss - Metal Zone MT2 mods

Postby diggum12 » 19 Apr 2011, 16:17

Saul, or anyone else, can you give me a detailed description of how the Mid-Freq components work? I've developed a good mod for the pedal, but when I dial that control below 12 o'clock it sucks out all the bass and is painfully shrill.

I get how the mid control works, but the Mid-Freq part loses me. I would LOVE to learn more about it.

download/file.php?id=11741&mode=view
"Now we cheer if someone get's a tweed champ working. I feel like the future was here and we traded it away for trinkets." -diagrammatiks

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Re: Boss - Metal Zone MT2 mods

Postby blackbunny » 14 Jun 2011, 16:33

diggum12 wrote:Saul, or anyone else, can you give me a detailed description of how the Mid-Freq components work? I've developed a good mod for the pedal, but when I dial that control below 12 o'clock it sucks out all the bass and is painfully shrill.

I get how the mid control works, but the Mid-Freq part loses me. I would LOVE to learn more about it.

download/file.php?id=11741&mode=view


The Mid Freq control changes the centre frequency that the Mid control is boosting or cutting. If you have the Mid Freq control between 7 and 11 o'clock, the Mid control should be able to cut or boost the low mids, say between around 120 to 400 Hz.

To quickly check if these controls are working properly, leave the Low and High controls at 12 o'clock (straight up), turn the Mid Freq control to 8 or 9 o'clock and turn the Mid control all the way down and hit a low chord on your guitar. The guitar should sound thin and bright. Now, while hitting a fat low chord on your guitar, turn only the Mid control slowly clockwise until it is at 3 or 4 o'clock. The sound should get fatter as you turn the Mid control up, getting muddy by around 3 o'clock, and increasingly "woolly" or "muddy" as you turn the Mid control up past 3 o'clock.

Then, with the Mid control at 5 o'clock, turn the Mid Freq control slowly up and you will hear a "wah" effect as the Mid Freq sweeps from the low mid frequencies to the high mid frequencies with the Mid boosted. You can then turn the Mid control all the way down, and slowly sweep the Mid Freq control anti-clockwise (back) from 5 o'clock all the way down to hear the tonal changes as it cuts first high-mid frequencies, sweeping through to low-mid frequencies.

This should help you understand how the Mid Freq and Mid controls work.
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Re: Boss - Metal Zone MT2 mods

Postby diggum12 » 14 Jun 2011, 22:03

Thanks for the reply blackbunny, but what I meant was schematically I'm not grasping how it works. :)
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Re: Boss - Metal Zone MT2 mods

Postby blackbunny » 15 Jun 2011, 03:09

diggum12 wrote:Thanks for the reply blackbunny, but what I meant was schematically I'm not grasping how it works. :)


Damn, sorry about that. I didn't understand your question.

The Mid Freq control is a basic swept-midrange bandpass filter, similar to those found on most low cost mixing desks. It does an OK job of cutting and boosting frequencies in the sweepable range between approximately 120 and 2Khz.

You can experiment with the capacitor and resistor values around the dual pot to get wider or narrower bandwidth of frequencies and / or a different range of sweepable frequencies,
but the Mid / Mid freq control is probably not the reason your MT-2 sounds shrill....it's more likely to be in the relationship between the pre-emphasis (mid boost) at the beginning of the circuit around transistor Q10 and the amount of high-mid and high frequency boost in the post-distortion stages around transistor Q8.

Having said that, it would be wonderful if you found a magic notch frequency / bandwidth combination by modding the Mid Freq control that got rid of that shrillness.
That's what most of the 'boo-tweakers" are trying to convince us they have done so that we buy their mods, and pretty much none of them have nailed it. It's not easy to get rid of the shrillness without turning the pedal into a mud machine.
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Re: Boss - Metal Zone MT2 mods

Postby diggum12 » 15 Jun 2011, 03:57

Having said that, it would be wonderful if you found a magic notch frequency / bandwidth combination by modding the Mid Freq control that got rid of that shrillness.
That's what most of the 'boo-tweakers" are trying to convince us they have done so that we buy their mods, and pretty much none of them have nailed it. It's not easy to get rid of the shrillness without turning the pedal into a mud machine.


Nailed it right there sir. That's precisely what I'm trying to do. I agree, no one has really found a magic formula yet, that I have found, which is why I've been trying so eagerly to understand this. Sault did help a lot, but honestly I've forgotten everything I thought I understood about it already. Ha! I need to stare at it again, but I've been working on too many other fun projects lately. I really do need to come back around to this. Part of my lack of motivation is that I don't really like the sound of the pedal anyway, even with all of my modifying, and none of the mods floating around have caught my interest... To be continued...
"Now we cheer if someone get's a tweed champ working. I feel like the future was here and we traded it away for trinkets." -diagrammatiks

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Re: Boss - Metal Zone MT2 mods

Postby blackbunny » 15 Jun 2011, 05:32

diggum12 wrote: Part of my lack of motivation is that I don't really like the sound of the pedal anyway, even with all of my modifying, and none of the mods floating around have caught my interest... To be continued...


That's exactly how I feel. I've spent too much time over the last 10 years trying to get various Metal Zones to make magic, with varying levels of success. After I heard my friend's Wampler Triple Wreck, I liked it so much I bought one myself and haven't plugged in to a Metal Zone since.

Another friend has an EH Metal Muff that has a very similar circuit to a Metal Zone. His Ibanez Artist guitar which has very dark sounding humbuckers sounds superb through the MM, much better than it does through a MT-2. The magic seems to be in the combination of guitar & pickups, pedal and amp. :slap:
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Re: Boss - Metal Zone MT2 mods

Postby blackbunny » 15 Jun 2011, 09:57

Back on topic, there are a few things you could try that will give you a quick indication as to whether altering the Q might help. Try increasing C043 from .0082 to .015, and then to .027 or .033.

This should simultaneously increase the Q (narrow the filter bandwidth) and lower the highest sweepable frequency range. If that seems to be going in the wrong direction, reduce the value of C043 instead, to about half of the original value, say .0047, and then half again.

Since this will also decrease the Q (widen the filter bandwidth), you can also adjust C036: increase it to widen the filter bandwidth and decrease it to narrow the filter bandwidth.
The Q of the midrange circuit is pretty much determined by the ratio of C036 to C043 (roughly 5:1) - many simple midrange bandpass circuits seem to use the ratio of 5:1 for a natural-sounding Q of around 2 IIRC.

Decrease the ratio of C036 to C043 for a narrower bandwidth / higher Q and increase the ratio for a wider bandwidth / lower Q.
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Re: Boss - Metal Zone MT2 mods

Postby diggum12 » 15 Jun 2011, 13:57

IIRC, I had increased C43 a month ago. Maybe I posted that on the other forum. Anyway, it did seem to help, but wasn't the fix. I will reexamine all your other suggestions above and below. Soon hopefully. :)
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Re: Boss - Metal Zone MT2 mods

Postby jimosity » 21 Jun 2011, 01:27

What are the parts to change to tighten the bass in a Metal Zone?
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Re: Boss - Metal Zone MT2-DEQ2 mods

Postby ppcnostalgic » 30 Jul 2011, 20:45

Hi. I bought a Johnson DEQ2 (Mt2 clone with 6 knobs) and I can say this one sounds very similar to MT2 but slightly better, anyhow I didn't like the sound as many of you all, I think... So I performed the Diezel Mod plus some variations. C42 and C36 both 0,1uf for less muddy and added a switch to swap C34 from stock 0,027uf to 0,047uf for less harsh, D3 replaced with a red LED and D4 with a 1N4001. The pedal sounds way better than original, a lot more dinamic and usable as you can go from light overdrive to extreme brutal sound and all that lies in the range is very usable and pleasant. I do recommend this mod if you're thinking your MT2 sounds too harsh and you can't use it but for extreme (and acid) tone and you'd like to be more versatile with this stompbox.
BTW: Boss Metal Zone and Johnson DEQ2 are the very same effect with a different pots arrangement only, everything on the 2 boards is quite the same and components' numeration matches perfectly.
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Postby ppcnostalgic » 10 Dec 2011, 22:42

Hi guys, so long and I bought another MT2 for very cheap and (guess what) I did the mods. I can say to you all to replace BOTH D3 and D4 with red LEDs, this did the trick and changed that fuzzy-harshy stompbox into a very good effect, just follow the Diezel mod replacement, then swap both the diodes and finally lower the R41 to 5k or so. You won't believe your MT2 sounded so crappy before the mod, because after it sound AWESOME. I put a Blackstar HT Boost before my modded Metal Zone and I can't stop playing, despite I'm trying it with an old solid state amp I can achieve wonderful tones :lol:
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Re: Boss - Metal Zone MT2 mods

Postby ddpawel » 11 Jan 2012, 02:18

What do you think about this mod?

Image

It allows to switch between normal and smooth Diezel mod.
Added 220pf capacitor filters harsh high frequencies (and noise) in Diezel mode. 1M resistors prevent popping.

Is it possible to further improve this schematic (for better protection of op-amp and optocouplers while switching)?
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