help interpreting this schematic?

[ian87]

hey y'all. i've got a Boss MT-2 on the bench right now that i'm trying to mod, and was interested in hot-rodding it a la this schematic, but i can't make heads or tails of it. anyone feel like lending a hand? thanks!

[Marcos - Munky]

This schematic is just a part of the entire schematic. If you want, I have the entire schematic here, just send me a e-mail.

[ian87]

hey, marcos, thanks. i have the other bits as well -- it's just the switching part that i'm having trouble sorting out. can't tell where the toggles go, etc.

[Mike Burgundy]

the schematic seems pretty clear.
Lets start with ocating the connection points in the existing schem? Got those?

[ian87]

the schematic seems pretty clear.
Lets start with locating the connection points in the existing schem? Got those?

well, no. that's part of the problem. i mean, i have that part of the schem, i think, but i'm not sure where this "connects."

i guess it's gotta be the output tone-shaping section, tho, correct?

[Mike Burgundy]

It looks like this would replace the entire opamp section before the output buffer.
This schem is not the same as an MT-2 as far as I know, though. The most important bit of an MT-2 is the parametric EQ section, which isn't there. The diode-to-ground clipper looks the same, though. That's "all" an MT2 is, a simple clipper with some EQ tricks (some of which are adjustable).
It's an opamp stage with some elaborate switchable frequency filters in the feedack loop - I'd say breadboard it, lift one leg each of the 10u going in and the 22k going out of that stage, and hook up the breadboard there. Don't forget 9V, ground and Vref. See how it sounds!
You might want to read up on gyrators and EQ's - great article at GEO on that - 'cause this is what's going on here.
Sw1: around the BC550 we have a gyrator simulating a coil (L), and we have a cap here as well: classic LC filter. The resistors in there do some additional shaping, and the switch alternates between two different responses - modern probably having more of a mid dip but I'd have to look a little deeper when the flu's dropped.
SW2 bypasses a resistor - with the resistor bypassed, the LC filter is driectly hooked up, so has maximum Q (narrow bandwidth). With the R in the circuit (switch open), Q lowers, bandwidth increases.
Sw3 controls how much highs are bled off.
hih

[ian87]

hey, thanks mike. appreciate your help here.

since this is just for a mod, i think i'm gonna skip it this time around. but if i decide to build one, i'll defintely try this.

cheers,
ian

[Mike Burgundy]

did a little update if yer interested - see above