Boss Metal Zone Mod for Bassguitar

[dighom]

I found the Boss MT-2 works great for bassguitar, but I missed a few pounds of bass, so I decided to mod it a bit.

Here are two schematics:
http://scaai.org/mt2_a.gif
http://scaai.org/mt2_b.gif

The first one shows, where the bass frequencies are reshaped after the distortion circuit. Unfortunately I don't really understand the part of the circuit, except it is a highpass. So I experimented with some values and came to those, which I wrote in mt2_a.gif.
If anybody knows what the circuit does in this section and how to calculate the values for a given Q and F please let me know.

The mt2_b.gif shows a simple active filter 2.order and Bessel. It is signed to F about 105 Hz. With the active filter calculator at http://www.analog.com/Analog_Root/static/techSupport/designTools/interactiveTools/filter/filter.html
I changed the F to 40 Hz and so changed the values of R12 and R13 as shown in my gif.

The bass comes better than before now, but I still miss a bit of punch. May be I've gone to far down, 'cause I know that the punch of a bassguitar lies around 50 to 65 Hz.

To all professional engineers, who are writing to this forum: Please, if you have any suggestion to make the MT-2 even more punchy, let me know.
Thanks

BTW the numberings of R and C are like the numberings on the pcb of the MT-2 - man, it ate a lot of time to find the exact places ;-)

[Duff]

Did you check all your MT-2´s circuit with the schematic you have?, cause I want to build one but I have 3 schems and they all have differences, could you tell me from your pedal, how´s the output section part, from the volume pot to the out jack? And also something confusing, do you know what components of the FET switching do I have to take out if I were to use true bypass?(only from the vol pot to the out, I know all the other mess)

[spongebob]

The first one shows, where the bass frequencies are reshaped after the distortion circuit. Unfortunately I don't really understand the part of the circuit, except it is a highpass.

It's more of a band-pass actually, it creates a peak in the frequency response at a certain frequency. Here is the freq. response of the first stage in the MT-2 for example.

If you want more low end, you could move the resonant frequency down a bit by increasing the 2K resistor at the emitter. A 6.8K resistor for example would set the frequency to around 600 Hz. These numbers are from looking at the frequency response in a circuit simulator, I could not find any exact information on this kind of circuit on the web.