I know this subject has been beaten to death, but I can't find specifics. Customer wants to add a phono plug to their 40-180. Ron posted a schematic a looooooong time ago, but it doesn't seem to be accessible.
What's the best way to do this? And no, they don't want to use a transmitter.
Add a spdt switch at top of volume control which in one position connects cap 38 to vol control 42. Add cap to to other position and route to an input jack on rear panel.
This mod uses a closed circuit 1/8" (3.5mm) stereo jack instead of an RCA jack. The jack takes care of the switching so you are correct, no additional switch is needed with this design. Just make sure you wire it up correctly.
I believe the 1/8" jack was chosen to not only provide the automatic switching, but also to better match the input from an iPod or other MP3 player. You can also use this to add Bluetooth capability to your radio.
There are three terminals on the 1/8 in. jack. One is for left and one for right. Put one resistor on each and connect the two loose ends together, then attach capacitor. Third terminal is ground. It is less complicated than Ron's schematic shows.