Control voltage step-up module
DC-coupled audio interfaces, such as the MOTU 828 MkI that I own, are capable of outputting voltages that can control audio hardware such as Eurorack modules. However, most Eurorack modules expect a CV range of -5v to 5v. I measured the MOTU as outputting -2.88v to 2.88v.
This project contains Eagle files for a Eurorack-mountable opamp circuit with a gain that will scale four MOTU outputs to the full CV range. It uses a single TL074 quad op-amp and a few resistors. Calculations for the resistors were made using the calculator at http://earmark.net/gesr/opamp/gain_offset.htm
There is also a rudimentary 8HP front panel design in an Illustrator template.
On October 13th 2015, PCBs were ordered from OSHPark and panels from Ponoko. A single channel has been successfully tested on a breadboard, and used to correctly track over 8 octaves of pitch control on an Arturia Microbrute using Silent Way's Voice Controller plugin in Ableton Live.
On October 27th 2015, the PCBs arrived and the first one was assembled. All four channels worked correctly.
![Assembled board] (assembled-board.jpg)
![Assembled panel] (panel-assembled.jpg)
![Completed product in rack] (panel-in-rack.jpg)