Boss - MT-2 Metalzone [schematic]

[gnognofasciani]

I was thinking: why does it always have almost the same amount of gain even when the gain is at min?
I just don't understand: at min it should have a gain of 1 and at max 200...

http://www.freeinfosociety.com/electron ... php?id=138

Can anyone help me understand please?

Thanks!

[pz]

The minimum gain at the second stage is 2x to be specific.
There's also a 35dB peak around 900Hz, take a look at the first input tone shaping opamp stage with a gyrator.

[gnognofasciani]

Ok, so it is due to the input tone shaping as I suspected...
Thanks

[pz]

Yes. In fact, thats the main reason why MT2 sounds as it does. I'm thinking about lack of dynamics and response to the playing techniques. Imho it's designed for young metal players, who want a good palm muting sound and scooped mids But it's only my opinion.
Some years ago i experimented with this tone shaping stage. A little bit flattened response brings a lot of life to this pedal. A simplest mod would be to attach the series R+C in parallel to the gyrator and reduce the feedback resistance.
F.e. reduce the feedback R from 220k to 100k-150k, attach 2k2+ trimpot 22k + 470n between the -input of the opamp and the ground. The trimpot will regulate the amount of the full frequency range boost.
If the gain range will be too small you can tweak the 10k+10k divider just after the input stage or increase the gain in the second, clipping stage.
I think, only decreasing the gain of tone shaping stage, preventing it from clipping and making it deliver only a little bit shaped and boosted sound to the main clipping stage can improve the sound a lot.

[gnognofasciani]

Pretty much what I was thinking to try, thanks for your great help!

I'm drawing a pcb but it will take some time as i want to keep it as small as possible

[soulsonic]

I will work on modding one of these soon myself. I will share the results of my experiments.