NOTE: Due to overwhelming demand (one email, which actually is overwhelming for this website), Ratty is posting instructions for the 2600 stereo mod.
First find the TIA chip which is one of the big ICs. Look for the one with pins 12 and 13 shorted together (they will also have a 1k pullup to 5v). If you're not sure how to find pin 12, go to the side of the chip with the dot or indentation and start counting clockwise. Make a sketch of which way the chip is facing and slowly remove it by prying up with a flathead screwdriver. Then bend pins 12 and 13 up, and attach them to the circuit below. You can also buy a 40-pin dip socket, bend up its pin 12 and 13 instead and put it in the middle. NOTE: A 2600jr is not socketed, so you'll have to cut the two pins and bend up instead.
Give them each a 2k (ie 2x1k) resistor pullup (1.8k is standard value and close enough), dc blocking caps (any cap value from .1uf to 10uf will work), and tap out with rca jacks (remember to ground the other connector of the rca jacks), and a switch to short them together when you want mono. Plug the TIA back into the socket (check your sketch!) and power up.
I didn't make a note of what pin was right or left, so try it with Combat and see what output the right tank makes noise on. Make sure you play Turmoil also, it's got a great echo effect.
This circuit can also be used on the 7800 but you'll have to connect the external audio signal to either the right or left output. I kept the standard external audio resistor, but not sure if that's the best choice. For the 5200, the audio channels all come out the same pin, so it's not doable.
+10uF TIA12<----------------------------|(-------------->Audio R? | | 5V o | | | 1.8K | | |--/\/\/--' SPST \ | SWITCH \ |--/\/\/--, | 1.8K | | | +10uF | TIA13<----------------------------|(-------------->Audio L?
Here is the original post from Kevin Horton (with comments added by Rob Mitchell):
From: firstname.lastname@example.org (Kevin Horton) Date: 21 Jan 1996 02:20:11 GMT Also, it's confirmed: You *can* get stereo out of a 2600!!! Both sound channels exit the TIA seperately. To get two seperate audio outputs from a 2600: Lift pins #12 and #13. Tie each to 5V through a 2K resistor. Attach two .1uf caps to the two joins formed by the pin and resistor. Attach two audio cables to the free ends of the caps and ground the shields of the audio cables. I suggest adding a switch to short the two pins together (that's what was done in the 2600) for mono sound. You'll need mono for things like Pitfall ][, unless you like your music in one side and all the sound FX in the other! :-)
The original 1977 six switch consoles have openings in the top deck for two speakers! Obviously Atari nixed the built-in speakers and went with the sound through the TV speaker. So that is why the Atari 2600 has a "speaker grill" as its top! Rob Mitchell, Atlanta, GA