MT-2 Metal Zone Mods

[navvid]

I recently got back my old Boss MT-2 Metal Zone from a student I had lent it to so he could experiment with pedals. I had long ago shelved it since I had "outgrown it", it's tone being far inferior to the tube distortion on the high gain channel of my Marshall by itself. Since it is basically expendable to me, and I have recently started modding my pedals, I wanted to see if anyone had the schematics/instructions for some of the mods available for it. The one I am most interested in is the Twilight Zone Triple Diode Mode, but it seems that most of the mods for it are pretty similar.

Anybody have a Keely MT-2, or info on how to DIY it?

[navvid]

Ok, so I wired it for true bypass and put a Millennium 2 indicator led drive circuit in, and that all works fine. I also did the following mods, which I acquired from the forum at freestompboxes.org:

Diesel Mod

C35 : remove
C34 .047uF
C25 : remove
these three mods remove harsh

C42 1uf
D3 LED
D4 1n4001
------ make the sound more dynamic and full
C36 .1uf----- EQ more usefull

Boogie/Bogner mod:

C35 a enlever
C34 .047uF
C36 1uF
D3 led
D4 1n4001

EN PLUS:
R46 increase values, more pre-distortion + mids
R41 reduce value you obtain more distortion (470ohms to start)


Mods don't have the same sound of diezel amp or Bogner amp, but it can be better tant the stock sound.



Keeley mod:

C20 .22uf
c42 .1uf
c37 , c39 , c17 , c11 1uf
c8 .22uf
c9 .1uf
c20 .22uf
d3 , d4 LED

One other thing you can do to make the unit a little more deadly is to add more gain. If you trace the path of the Gain control (a 200k pot), one end of it goes to a 1k resistor. Replace that 1k resistor with another resistor, anywhere from say 39k to 68k, whatever you have on hand. That will raise the gain of that stage from 202x to 270x (if you use a 68k resistor).

The gain bit is r37/C19

http://img364.imageshack.us/img364/8...ezelmodpc8.jpg


The last part about r37 is from music-electronics-forum.com



Something is wrong. When I turn it on, I hear a rising pitch whine, that to me sounds like a cap charging. It works for about a few seconds (longer if you don't send signal through it), and then the level drops off slowly as if the gain is dropping. If I unplug it or turn it off, then plug it back in right away, it only outputs a barely audible signal. But if I wait a while, then plug it back in, it whines again and it outputs a hot signal that drops off just like before. After watching the led dim down in despair for the nth time, I got the idea to try to check the voltage at the board as it happened, and sure enough the board input voltage drops off at what appears to be an exponential rate until it levels off and decreases very slowly at around 1.1v (that's when I usually get tired of holding the probes and watching the voltage reading, but its still dropping).

It appears to me that I have an input power capacitor problem. Can anyone verify this? I have been going around looking at the caps, pulling and replacing the ones that I have changed, but so far no progress. The only thing I can think is that I did use electrolytic can caps for all of my replacement caps except for the one 0.047uF cap since no electrolytic ones were available. Could it be that maybe one of these has too slow a response time or something like that, causing it to not supply the board with steady voltage?

The fact that I have to unplug it and wait for a while also implies that there is a cap that is discharging, and so it won't give a full signal again until it finishes discharging and recharges.

Any help or idea's is appreciated...