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All about the Audio Companion

Posted by Bryan, 02 December 2017 · 549 views

Audio Companion AC Sound

The Audio Companion board is designed to be a simple way to add high quality sound to Atari consoles and computers lacking a sound output (predominantly the 2600, 5200, 7800, 400). It can also be used in any system as an audio mixer. For example, a stereo Pokey setup can be mixed to a mono output without affecting the separation of the 2 stereo channels. Two boards can be installed to provide multiple different outputs as well.
 
The most common question is, "What makes this better than the audio modifications currently being done?" There are three main advantages:
 
1. The AC board installs very simply without cutting or removing anything on the board. The AC board gets its power from being soldered across a power decoupling capacitor and its high impedance inputs don't disturb the existing audio circuits. The board can be removed at any time without the need for any repairs.
 
2. The AC board uses an op-amp to provide a buffered line-level signal. This gives the output a consistent quality when driving various amplifiers and cables. Picking audio off without a buffer can give inconsistent results.
 
3. The AC board has 4 additive mixing inputs designed to preserve the system's intended audio functions. This means the AC will play 7800 games with cartridge audio intact. The AC will provide the 400 with audio that includes the cassette audio track. Other sources can be mixed in as well if desired.
 
Installation is simple. Find a power supply decoupling capacitor near the audio circuits or power supply input (these caps will usually be 0.1µF and may be marked '104' to denote this value). Determine which side has 5V with a multimeter and solder the board across the cap observing the polarity markings. Run wires from the AC inputs (A-D) to the appropriate signal points for your system and another wire from the output to your audio jack. Then run a ground wire back to the AC board ground pad or a nearby ground point on the system board.
 
There are 4 inputs on the Audio Companion. Using the correct input is important for proper level matching (input iD is marked on the board for reference).
 
A - Input for Pokey or TIA audio.
B - Second input for Pokey or TIA audio.
C - 7800 cartridge audio input.
D - 400 SIO audio input.
 
There is one audio out pad (marked out) that can drive one or two audio jacks.
 
On the back of the board is a gain pad that can be cut to provide a 3dB output boost if desired.
 
Here are pictures of the board and schematic:

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Great work Bryan! Will be ordering one soon!

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Hi Bryan (or anyone else who knows), I’m just curious why the audio only has one output?

I have a SynthCart which I believe is capable of splitting two separate audio signals to left and right outputs, so that I can capture the two signals separately into my computer audio interface or one of my hardware samplers for further processing.

I intend to install this on an Atari 2600 Jr for ideal portability, with either a single trrs output jack (with a trrs to 3 rca breakout cable) in place of the original 2600 Jr rca out, or possibly by adding two separate 1/4” audio output jacks, keeping the original rca for composite video output only. Stereo audio is my prime objective, but nice clean video would be a bonus.

I’ve PM’d Bryan, but as he’s busy, if anyone with info or suggestions could comment it’d be greatly appreciated. Thanks!
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Deleted double post

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The AC mixes one or more sources into a single channel because mono output is used far more often in Atari systems than stereo. Two of them could be installed for stereo, but you could also wire in stereo audio directly from TIA and then use an AC to generate an alternate mono signal. To do this, follow the mod described here:

 

http://atariage.com/...-mod/?p=2545630

 

Then run left and right (before the output capacitors) into AC inputs A and B to mix them without affecting the stereo signal.

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