Approximately one forever ago I was asked to modify an E-Mu 0404 USB to have subwoofer and balanced output. Certain parts of the project were relatively straightforward, others took forever. (I started in fall of 2007.)
The rear of the unit uses Neutrik 1/4 TRS plugs to connect the emu to crossover. The left pair of Neutrik XLR connectors are the balanced subwoofer output. There is also an unbalanced Cardas RCA connector for unbalanced use.
The right pair of XLR connectors are the main channel output, left and right. Power goes through a Corcom input module to provide power switching, RFI filtering and a fused AC input.
One of the more difficult parts of the project was locating an enclosure that would be simple to work with during construction and hold all of the parts securely. The active crossover is mounted to the lid of the enclosure. The power supply is on the bottom and the balanced output modules are located at the back.
I originally built a linear power supply with a toroidal transformer and LT1085/LT1033 regulators, which worked well -- but when all was done, I had some issues with heat and what I thought was poor regulation, so I switched to a commercially-sourced EOS power supply.
The power supply needs to supply +5Vdc for the E-MU 0404, +/- 12V for the active crossover and +/- 15V for the balanced output units.
All wiring is silver-teflon twisted pair.
The crossover is a 4th order Linkwitz-Riley 2-way active crossover from audio-kits.com. The crossover was built with Burr-Brown OPA2134 op-amps in through-board sockets. The resistors are Vishay precision 1% units and the capacitors are Wima polypropylene film capacitors where available.
The crossover is fed by the 0404 and provides unbalanced output to four THAT1646 balanced line driver ICs. These had slightly better specs than the TI DRV134 or AD SSM2142. The circuit boards are mounted and connected directly to the rear of the XLR jack.
How's it sound? Well -- I need to get started on version two, I'm going to miss this one. Version two will revert back to the original linear power supply, I don't think there was anything wrong with it to begin with. I'll also switch to silver-teflon coax for the interconnects instead of twisted silver-teflon pair.
This page last modified Sun Apr 19 19:54:18 CDT 2009 by timc!