Modular Summing Amp Buildout

Well, I finally got to it and started putting together the modular summing amp I'd had brewing in my mind for the last couple of years.

I had a chasis from an old project my grandfather had been working on in the early 70's, which consisted of 10 "modules" using 44 pin card edge connectors. I was able to source some prototype boards that fit the modules, and went to town.

The first module was the power supply which gives +/- 18V, +/- 24V. and 48V rails.

Then I built out the "sum amp" module, consisting of Hardy 990s in a VE / ACN configuration, with Jensen Output transformers.

That left input modules. The first one I built was a simple 8 channel input module based on INA134s, and simple LCR bus assignment switches. I'm probably going to build some more robust 4 channel input modules with discrete 2550 type receivers with pan and gain for each channel.

Because it's modular, as long as I respect the basic topology, also have the ability to swap summing amps with different components.

Did my first full "system" test this evening, and so far, extremely please with the results!

PSU Module

Summing Amp Module

8 Input Module

A very interesting project. I am curious about the 44 way edge connectors. Google seems to think they find use mainly in arcade games. Your mechanics looks very much like a standard 3U sub rack.

Cheers

Ian

My grandfather used to do engineering work for a number of TV stations in the 60s, and was involved with the conversion of the Johnny Cash show to support color television sometime in the early 70s.

He died of a heart attack pretty suddenly in '74 (before I was born), and my understanding was that this unit was a tape automation machine he was building. It was pretty ground breaking for the time, but nothing but a curiosity now. I saved all the old PCBs he built, and salvaged a number of the components.

The truth is 44 pins is way more than I need for any of the modules. This is a case of making the project work with the chasis I've got.

I would love to make use of some of the components salvaged (there's hundreds of old transistors and diodes in there, but most of what he was building were logic circuits, from what I can tell most of the components are spec'd for switching as opposed to audio amplification.

I may start up another thread to investigate the usefulness or lack thereof in that stuff.