While I was looking at the intellivision service manual I noticed the sound chip has 3 outputs all tied together along with the external audio. I decided to try and put together a stereo mod to go along with my rgb mod and this is what I came up with. It seems like the three outputs are part of an internal DAC so I took the output of pin 3 and blended it into pins 4 and 38. This seemed to provide the most uniform sound output from either channel. The external audio is blended into both channels and has a 10pf capacitor to ground to eliminate hum. The two signals are then fed into a common base amplifier.
Attached at the bottom you can find the audio recordings and other relevant info. Enjoy!
This is a recording of the intro music from the crimson tower. The mono sample is taken from the solarfox av mod circuit.
Here is the intro music to frogger. The mono sample is taken from the solarfox av mod circuit.
Here is some audio from pitfall. The sound order is two log hits, jump, vine swing, then game over. Notice how only one channel is prominent in the stereo recording. Adding a jumper wire between the two emitters resulted in dual mono signals, so add either a switch or blend pot to the emitters if you like.
This is the intro from b-17 bomber to demonstrate external audio. It's dual mono regardless of the emitter jumper discussed earlier.
Edit - the 10pf capacitor should be 1nf
Edited by emerson, Sat Jan 12, 2019 12:29 PM.