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: