Click here to read part#1

Click here to read part#2

Click here to read part#3

Some great feedback was solicited from the first three posts.

  1. Control Room monitor output should be attenuated 20dB when the talkback microphone is enabled.
  2. Cue output should not simply switch back and forth
  3. Balanced system only required on i/o, entire system needn't be balanced.

Lets address each of these

1 -  Control Room Monitor should attenuate 20dB

A simple H pad and a relay thats controlled when the user pushes the push to talk button. It does mean additional connections on the back panel.That feeds the concept that this is a rack mount unit. A remote makes sense, but switching still needs to happen in the rack.

2 - Cue output should not simply switch back and forth

The original switch used a relay to switch between mic and line.

Two people contacted me on facebook suggesting that the cue should be a mix between mic and line.

That suggests that the line in select relay and mute relay are still valid, but a mixer should be set up between the mic and line ins. I figure this could be done using a TL072. Cue mixes don't require 0.000x% THD.

I figure a simple mixer like that shown on http://sound.westhost.com/articles/audio-mixing.htm will do the trick.

The mix level for microphone input can be set by setting the gain in the mic pre. Alternatively, trim pots could be provided.

3- Balanced IO

Easy Peasy Lemming Squeezy. Get an I/O board with XLR's on it, with INA134's to receive and a DRV134 to transmit.

More sooon. Cheers


Written by Dafydd Roche — September 17, 2013

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