Engineer Sam Kent has designed a modular Eurorack-compatible stereo DJ mixing system, featuring XLR and line-level outputs, a cuing system, and volume meters.
"Inspired by Eurorack modular synthesizers and the boutique mixer market, the project aims to design and build a simple and customisable DJ mixer," Kent explains. "The design is op-amp based, with filters implemented as 12db/oct active inverting filters, 10k ohm output impedances, and buffered potentiometers acting as voltage dividers for the controls."
The idea behind making the mixer modular isn't new, even among commercial designs, but with one key flaw. "Ripping the faceplate off most mixers the design is already fairly modular," Kent says, "but only in that mixer's specific form factor."
Kent's design, by contrast, adopts the popular Eurorack standard and targets full customisability — offering N channels which can be mixed and match across isolators, filters, effects units, and other Eurorack hardware.
The project has already resulted in several modules: A two-band isolator channel with on-board VU meter; a main channel, with stereo VU meter; and a power supply, though Kent notes that "thanks to the modularity of Eurorack any modular power supply can be used," with the custom version offering 18-36V input and +/-12V and 5V supplies plus two phono preamps — a bonus feature which may move to a channel board in the future.
Kent has released the designs and created initial prototypes, and has gone into quite some detail on the troubleshooting process that resulted and the design mistakes that needed to be fixed — everything from a lack of clearance between the PCBs and the rack rails to problems soldering the LM3914 PLCC package. "[It's] supposedly a package that is socket and SMD compatible," Kent writes, "but it's a definitely a pain to do by hand."
"As it stands," Kent concludes, "it's a working mixer that I use day to day. However, there are a few changes for future versions," including more robust potentiometers, reducing the chip count, using a different VU driver, and replacing all filters and attenuators with VCF/VCAs in their place.
The full project write-up, with links to download the KiCad project files, is now navailable on Kent's website.