Constructional difficulty: Easy
A simple but effective four channel mixer for use with control voltages and audio. Each channel has an independent level control that goes from fully off to unity gain.
Two outputs are provided. OUT (MAIN) is a low impedance driver that simply presents the sum of the input signals as controlled by the level pots. The other, OUT (SOFT), is also the sum of the inputs but this time the signal is passed through a special 'soft clipping' circuit. This soft clipper is designed to sound like an overdriven valve amplifier and adds a form of harmonic distortion that is musically interesting.
If no jack plug is inserted into the IN 3 socket then by adjusting the LEVEL 3 pot you will add a positive offset voltage to the output. Likewise, if no jack plug is inserted into IN 4 then the LEVEL 4 pot will control the amount of negative offset that is added to the output. Each pot therefore can either act as a constant voltage source which can be added to other CVs for controlling other modules. Furthermore, it can also be used to generate asymmetrical signal clipping in either any following modules or by using the soft output of the Fourmix itself.
The module also features two output level LEDs. These monitor the signal level at the main out socket. The 5V LED lights when the signal exceeds +/-5V and indicates that soft clipping is about to take place from the soft output. The peak LED lights when the output signal is getting near hard clipping, ie. around +/-11V. Special circuitry is employed to ensure the LEDs do not cause power supply clicks when they turn on or off.
To allow all the functions required by this module we have had to reduce the spacing between the pots. Instead of our usual 1.625" (41.3mm) we have opted for the smaller 1.375" (34.9mm). Used in conjunction with smaller 20mm (13/16") diameter knobs this still allows for an attractive module design and finger friendly tweaking.
The module accommodates either our standard Oakley/MOTM power header or a Synthesizers.com power header. Current consumption is approximately 25mA per rail.
The PCB is 7.8cm (deep) x 12.3cm (height). The four pots are normally board mounted for speed and simplicity
As with all Oakley projects the PCB is double sided with through plated holes, has tough solder mask both sides, and has bold component legending for ease of construction.
The Oakley Fourmix as a single width MOTM format module in a natural finish Schaeffer panel. Note also the use of our optional Sock6 socket board to help keep the wiring to the sockets neat and tidy.
Click here for how to order.
Fourmix issue 1 PCB
Sock6 issue 1 PCB ........................................................ 6GBP
Fourmix pot bracket kit ............................................. 0.75GBP
The optional Pot Bracket Kit contains the three 16mm Alpha pot brackets required to complete one module.
All other parts can be purchased from you usual electronic component supplier.
All prices include VAT at UK rates. Shipping and postage is additional to these prices. See also the FAQ page.
Ready made modules may be available from Krisp1.com.
Fourmix issue 1 Builder's Guide
Fourmix issue 1 User Manual
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 databases can be found by downloading the following links:
5U format 1U wide Fourmix module in traditional black
5U format 1U wide Fourmix module in natural finish
To read these files you will need a copy of 'Frontplatten designer' from Schaeffer. The program also features on-line ordering, so its now even easier to buy your panels from Scheaffer.
The company are based in Berlin in Germany and will send out panels to anywhere in the world. Delivery to the UK normally takes around ten days. For North American users you can also order your Schaeffer panels from Front Panel Express.
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