DIY Factory

Talkback Project
A project brought to you by Kev.
Updated 31 December 2005

A simple DIY Talkback Unit that uses the Analog devices SSM 2142 and 2143 line receiver and driver chips with the addition of a relay to provide a user set duck or dim and also makes use of the SSM2019 mic-pre chip.

General Description

The magazine advertising would have us believe that a simple USB interface and a computer is all you need to record your #1 single at your first attempt. Parts of what they say just may be correct but then they sell you on the idea that with a few additions like quality Mics and Mic-pres the whole process becomes a walk in the park.

As we found with the addition of the DAW monitor switcher Mk1 or Mk2 and the Main Monitor Controller, the average DAW software and hardware combination becomes much easier to use. It doesn't take long for a soloist singer song writer to think about including some friends on their recordings. The problem is that the simple computer and interface set up is probably only ready for a single individual user. Unless you are willing to open the door and let your friend fly the controls and add the tracks the way they want and the way they want , you have a problem. Sure you could add a second set of headphones and an extension lead, lean back in the chair and yell instructions down the hallway and probably get by but it does become tiring very soon.

A better idea is this simple stereo unit with talk over facility.

Basic block diagram

You can use the main stereo mix or create a separate cue mix via two additional outputs of your DAW's interface. I tend to use the main stereo mix as often as possible as it keeps things very simple but more on that later. The balanced stereo enters the unit and is unbalanced by the Balanced Line Receivers and put past the two relays. A relay for each channel either for a stereo mix or for two independent mono talkbacks. This signal is then mixed with the control room mic pre-amp, then balanced and sent out by the Balanced Line Drivers. Each relay is double Pole and it is the separate poles that provides the facility for the signal from the Mic to Line Amp to be switched onto the mix bus and also the additional function of dim to the main program mix.

Block diagram of the talkback unit internals

The Mic pre-amp has a 25 turn pot to set gain to suit your talkback mic. The amount of DIM at the relays is also set with a 25turn trim. It is possible to bring these controls to the front panel but I find that having these things inside and away from tampering fingers makes for a much smoother recording session. The GPI (General Purpose Interface) control is a simple contact closure so it is easy to have a couple of switches paralleled to provide a talkback control at the Producers Couch , yes a luxury. Additionally it is possible to use a latching switch at the control position so as to leave the talkback open without holding your finger on it. Perhaps you want to make some of that Phil Collins AIR , of course you will also need THAT compressor.

Schematic
a very quick one, so do double check it
DIY0239_schematic.pdf

Parts List
a very quick, short parts list and as above, do check it first

DIY0239_bom.txt

Downloads

PDF's - right click

Check Plot - DIYF0239_CP.pdf
Top Overlay - DIYF0239_TL.pdf
Bottom Layer - DIYF0239_BL.pdf
Bottom Layer 2 - DIYF0239_BL2.pdf
I think the hole size on BL2 is smaller
but really I can' remember why I exported two bottom layers

SSM2017 - Analog Devices - self contained microphone pre-amp
SSM2019 - Analog Devices - self contained microphone pre-amp
SSM2142 - Analog Devices - balanced line driver
SSM2143 - Analog Devices - balanced line receiver

LM833 - National Semiconductor - dual opamp

Pics
not much yet, but here is is

Additional comments
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none yet

ERRATA

So far so good.  Check back for any updates in this area.

Contact : Kev for more info

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and more will be added

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