Constructional Difficulty: Easy but with many surface mount parts.
The 6HP wide Oakley Sound Eurorack Multimix is highly useful mixer module that can be used to process both control voltages (CVs) and audio. It is based on the original 'Stooge' version of the Oakley Multimix for 5U.
The unit features three identical channels. Each one has its own level control pot and an invert switch. The pot controls the signal level running through that channel. The gain of the channel can be varied from 0 to 1.1 (+0.9dB) The invert switch when clicked to its downward position inverts the signal so positively going voltages become negatively going voltages. For example, +1V on the input can become -1V at the channels output. All output circuits are 'line driver' type and thus will not droop when loaded with any reasonable demand.
When the input socket of any channel is not used then the channel's output will become a fixed voltage source. The actual voltage is controlled by the pot and its polarity via the switch. Stable voltages from -5V to +5V can therefore be created.
The output of the third channel 'Out 3 / Mix' acts as a summing point for the other two channels should their own output sockets not be used. The output signal at the 'Out 3 / Mix' socket is then the mix of all three channels controlled by their respective pots and switches.
The module also features two output level LEDs. These monitor the signal level at the 'Out 3 / Mix' output socket. The 5V one lights when the signal exceeds +/-5V. The peak one lights when the output signal is getting near clipping, ie. around +/-9V. Special circuitry is employed to ensure that either LED does not cause any power supply disturbances when they turn on or off.
The module's current draw, with no signals passing through, is -26mA and +31mA at +/-12V.
The PCB Set
The Multimix comprises of two printed circuit boards (PCBs) connected together with five 0.1 (2.54mm) single in line (SIL) headers and sockets. The main board on the rear of the module houses the power input and conditioning, the three channel output circuits, and the signal mixer. The pot board has the pots, switches and sockets that are attached to the front panel, as well as the input circuitry for all three channels. The main board is a four layer design, while the pot board is a two layer design. Each board is the same size; 29 mm x 107 mm.
The majority of the components are surface mount parts. The ICs are SOIC, while the resistors and capacitors are 0805. All components are standard parts.
Click here for how to order.
Multimix (Euro) main board issue 1 PCB........................................... 10GBP
Multimix (Euro) pot board issue 1 PCB ............................................... 5GBP
Both boards are required to build the Oakley Multimix for Eurorack project.
All other parts can be purchased from your usual electronic component supplier.
All prices include VAT at UK rates. Shipping and postage is additional to these prices. Click here for full price list and ordering details.
Multimix (Euro) Builder's Guide
Construction Guide Our handy guide to building Oakley DIY projects
Parts Guide Our handy guide to buying parts for Oakley DIY projects
Schematics are available to purchasers of the PCBs and will only be sent via e-mail when the board(s) are shipped.
Front Panel database
A Schaeffer front panel can be made for this module. The database can be found by downloading the following link:
6HP Eurorack format in natural silver
To read, edit and print this file you will need a copy of 'Frontplatten Designer' from Schaeffer. Panels can be ordered via Schaeffer's website.
Schaeffer are based in Berlin, Germany and can send panels to anywhere in the world. Delivery to the UK normally takes around ten days. For North American users you can order your Schaeffer panels from Front Panel Express.
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