First step is to get some soft bodied 3.5 mm plugs.
Unscrew the shell from the plug. Cut the flexible end off the shell, just after the hexagonal body moulding. Cut the earth tag off the plug, right near the threads. Solder a 1" insulated wire to the center pin of the plug and fold the tag flat over the center, making sure you don't short it to the outer part of the plug. Take a Johnson banana socket and fold the part of the tab with a hole in it back on itself. Screw the shell back onto the 1/8" plug with your wire poking out the end. There should be just enough length to be able to solder the wire to the banana socket. Once soldered, push the banana socket into the plug shell. You may wish to shave the threads off the Johnson socket to make it a better fit.
And there you have it.
Readers are permitted to construct these circuits for their own personal use only. Ken Stone retains all rights to his work.
- Banana to 3.5mm adapter plug for music synthesizers. (archived) by Ken Stone, 2006, with permission of the author