Very little info around on this late 70’s / early 80’s unit. Check the FSB thread for details. I snatched the image off from fxdb…
Now. What’s this all about.. The way i see it, we have a buffered OD250/Dist+ gain stage (including clipping diodes shunt to ground), followed by a sort-of active BMP tone stack and an output buffering. It may not sound all that great as it is, but there is a lot of room for your own improvements. First of all, one could up the input cap for 47n or 100n and up the 47n coming from distortion control for 220n or even 470n to get a lot more lows through. Next, the tone stack is quite abysmal. I would probably double the cap values there too. Then the unity amplifier making the tone stack active is what it is – an unity amplifier. Either lower the input resistor from 100K to 47K or up the feedback resistor from 100K to 220K. That should make the circuit roar. Also, for added stability, up the filter caps to choice. And finally, try on a few different diode setups for the clippers. Not all of these may be required to nail your new favorite tone, but most of them should be worth a try. Anyway. Maybe you should try and have your way with this one.
