Another project we have been working on here at WindWorks Design is building our own production intercom interface. Clear Com, Production Intercom, and Telex all use the same standard, and each requires a headset (earpiece & microphone) as well as an interface box, also called an intercom “station” or “belt pack”. Headsets are not too expensive at around $100US, but the intercom stations and belt packs are typically selling for more than $200. Here is the beltpack Production Intercom BP-1:
This price got us looking for an affordable alternative in a shop built solution. As it turns out, there is more to an intercom interface than just some simple circuitry. While not too complex, designing from scratch didn’t seem worth it. Ultimately, the solution we found was Richard Crowley’s Comclone, a great website that describes the circuit and operational theory, schematics, parts lists, and a link to buy a simple one sided PCB that we could assemble ourselves. Here are the links we found most useful:
Theory (my favorite page)
The project was a success. We built two and both successfully tested the first time. After bench testing, our friend Max B helped us with the testing in our theatre. Both worked just fine. About the only quibble is the sidetone nul pot doesn’t seem to do much. I was expecting this to be a more significant adjustment for sidetone – how much of yourself you hear in your own earpiece. But that’s only minor, as the ComClone circuits clearly work well and do everything needed.
Next up is to package the boards into enclosures. We had some sleek euro style enclosures in the leftovers box that are nearly perfect except for being about 2″ longer than desired. But since the were already in the shop, no point in buying anything else. Here’s a fit test into the enclosure:
One of my favorite things about the project was learning more about theory of operation, and understanding how stupid simple it is to add a beacon/flashing light just by adding a relay and larger light. Likewise, we enjoyed reading how Richard Crowley added jacks to use simple low cost headsets instead of the (better) pro headsets.
In a later posting, we will follow up with photos of the finished project. But for now we remain delighted with the project so far and the excellent resource from Richard Crowley’s ComClone pages. Thanks!