​54 Channel Three-Way Splitter

This custom project was done for The Showbox in Seattle, WA . The Technical Director at the time was looking for an audio distribution set-up for their PA system that was more than a plain old resistor/ Y split.  They also wanted it to be flexible enough to insert additional mixing consoles, without breaking down the house setup up every time a band brings in their own mixing console.  Nearly all splitting/distribution snakes currently available, suffer the same problem; signal loss due to resistive coupling/decoupling of two or more signal paths.  This is in addition to the biggest existing problems; multiple audio connections, ground loops, and HF interference.

The main objective was to come up with a solution so the house set up, a Gamble front of house and a Midas monitor console, could be installed while still having one auxiliary audio path for any additional mixing/ recording console to be inserted.  Several outlines were made to come up with the best solution and a user friendly price tag.  After calculating every set-up, from simple buffers, active line drivers, etc. we settled on a transformer balanced split.  One direct line to front of house plus two galvanic decoupled channels, one for monitor the other one as an auxiliary.

Due to the hard conditions in live situations, a solid aluminum enclosure was chosen, cut out of 4'x 8' solid 8mm plates.  All of the openings for connectors and holes were machined and than welded together.  A custom hinged front plate was made to house all 54 male and 54 female XLR connectors for the auxiliary output.  Front of house and monitor are connected through Ramtech RAMX025 connectors.  Before the final assembly, the housing was black anodized.  The cable lengths were 25' for monitor and 250' for front of house with 54 pairs of Flexalloy wire bridges the distance stage/monitor/front of house.

All 54 decoupling transformers are screwed to the back of the front plate.  Audio connections are soldered via a hardpaper plate with press-in stand offs on the top of each transformer. The basic design of the transformer is an EI625 two chamber square nickel core with each primary split in half and both sides are wound out of phase and than electrically connected in phase.  This keeps the stray field as small as possible so that there is no cross talk between channels and external hum strayfields are rejected. The transformer layout was chosen such that all windings have the same DC resistance and a short impedance of 600 Ohms.  This way every signal, from mic level to line level can be split with minimal loss of signal.  The bandwidth of all three channels is 20 to 20 @+12dB (+0/-0.5dB) at any load from 600 to 10kHz, the perfect set up for live recording.  Phantom power can be applied via front of house or build in "Power One" 48V/3A supply.

All connections are made through 16AWG silver plated Teflon wire.  Designed in the old fashion style, the AC and audio ground are pulled separate to two big brass ground plates with a single termination for every reference point. Via three main ground switches, AC and Audio can be lifted, a scenario that is only needed in the most difficult set-ups.

Even with the complex transformer set-up, the finished splitter is able to withstand a direct magnetic strayfield of 100mG and is immune to HF interference caused by dimmers in show light equipment.

​The whole project took from design to final assembly about 4 months.  With a price tag of about $14K (in 1998...), it was not a cheap solution, but it takes care of all possible live set ups and problems.