Curbside Recording Mic Splitter


The top row of connectors are DB-25 connectors wired with the standard Tascam pinout. These allow one to plug in small 8 pair stage boxes that can be spread around the stage.

The other connectors are ProCo 120 pin Helix connectors. The input can be connected to a 40 pair snake that goes to a stage box. The outputs can be connected to 40 pair snakes and fanouts. The inputs and direct output have all 40 pairs connected. The isolated ouputs only have the first 32 channels connected.



The back of the splitter has the switches for setting up the splitter.

There are separate ground lift switches for every channel of each isolated output.

There are also 20dB pad switches in the control section for Isolated Output 1 that pad both outputs. The pads are intended to be used when a remote mic preamp is used on stage (upstream from the splitter). This way the remote mic preamp can operate at full line level without overloading the splitter. The pads can also be used for other line level equipment. Pads will be a requirement for putting A/D converters on the stage and shipping digital audio to a remote truck via fiber.

Now, let's take it apart.

Here we can see that a PC board assembly handles 8 channels of split. Boards for Isolated Output 1 are fully populated, while those for Isolated Output 2 don't have the input connectors, pad resistors, and switches.

As you can see, the interconnections are done with ribbon cable. Each ribbon cable carries 8 pairs of signals (with ground). The signals in the cable are assigned so a standard DB-25 ribbon cable connector will map to the standard Tascam pin assignments.




And now we unscrew the front panel for more access.

The case is a standard product from Buckeye Shape Form with custom punching and painting on the panels. The artwork was done by HR Music Systems in Vectorworks.


Here it's easy to see the strip of low density foam that provides shock protection for the transformer cases.



The mounting brackets for the PC Boards were designed by HR Music Systems and manufactured by Century Metal Products of Lowell, Massachusetts.

Some of the Ingredients


Here is a better look at the adapters that translate the 120 pin Helix connectors to 5 ribbon cables. These sheet metal brackets were also manufactured by Century Metal Products.

We also have a closer view of the printed circuit boards (there are 3 different kinds). The boards were designed by HR Music Systems using McCAD PC layout software and were manufactured by Sierra Proto Express.

Other parts include Holco Resistors, C&K Switches, and of course, Jensen JT-MB-CPC Transformers.




All the vendors (Sierra Proto Express, Century Metal Products, and Buckeye Shape Form) did an excellent job and come highly recommended.

This design is available for sale or license.

HR Music Systems

PO Box 610072
Newton MA 02461