I always wanted to add a line in jack to my AJ 9200R Radio. I went to the junkyard and purchased an extra one, along with the wiring harness so that I could experiment with it on the bench. I then went to a local thrift store and bought a 12 volt, 3 amp power supply that was originally intended for some type of gaming console.
I spent a significant amount of time poking around and studying the circuits and I think I came up with the best solution-I then modified my actual radio. Here’s what I did:
- Locate the 4 blue coupling capacitors on the front of the board, just to the right of the Dolby chip. They are polyester film types and they appear to be 470pf.
- The first and last capacitor in the row couple the radio output to the preamplifier. One is for the left channel and one is for the right.
- Unsolder the side of each cap that connected to the radio output.
- Take a thin shielded stereo cable with conductors for left and right; solder each of the two conductors into the holes left behind from where the capacitor was lifted. These will be your radio out connections.
- Take another think shielded stereo cable with conductors for left and right; solder each of the two conductors onto the ends of each capacitor that was lifted. These will be your line-in connections.
- Connect the shields from both wires to the radio chassis.
- Take both wires and thread them through the front of chassis and out to the right hand side where the faceplate screws on.
- Drill a hole in the upper right hand side of the faceplate.
- Solder the two stereo cables to a stereo switching 3.5 mm phone jack. There are 5 connections-L signal in, R signal in, L signal switched, R signal switched, and ground.
- Put everything back together and reinstall the radio.
In operation, plugging in to the new jack, your sound source such as a smartphone, will disconnect the AM/FM tuner from the preamp, and feed in your sound source. That way, there is no bleed through from the tuner, tape player, or CD player. You will find that while you have your sound source plugged in you can still toggle between the CD changer and the cassette without having to unplug your sound source from the new jack. You only have to unplug from the jack to re-establish the tuner.
My smart phone sounds fantastic this way! The quality is way better than the previous configuration which was through a cassette adapter. I also like the fact that the cassette player doesn’t have to spin unnecessarily any longer.