I resurrected my project about making a midi controled preamp, like the Mesa Triaxis, ADA MP-1, Marshall JMP-1, and a few other. I call it as the Variamp.

This one also will feature full preset recall like the old ones, the main control electronics are much more modern as it has a single Atmel AVR microcontroller instead the IC based control electronics. I'll use photoresistive optocouplers for controlling the preamp electronics. Also the whole project is open source so feel free to reuse it, helping me out, or just laught at me doing a probably pointless project in the age of digital modelling.

The control electronics are partly modular, thanks to the modern technology. This allows the module to reuse for other projects easily. The only built in devices are: port decoders for the channel select out (it helps the preamp have ut to 16 channels, probably even more by different tricks), a port decoder to the keyboard/led matrix (up to 32 LEDs and buttons), and the midi port (in the future). The microcontroller also allows the use of a USB port, I'm still not sure if I'll implement it. It may sacrifice the external EEPROM use.

Here's the proposed PWM board for the project. These use the microcontroller's PWM outputs and create a DC voltage for the LEDs of the optocouplers from the 5V digital supply (a buck converter). The mosfets are pretty low power, but it don't really have to have an output higher than 100mW (which would burn the LEDs out), and the microcontroller isn't designed to have "high" current outputs. The most possible change would be on this board is larger inductors.