You can build your own ring modulator
3 1/4 inch phono jacks
4 germanium diodes
2 mouser TM014 small signal transformers
Any small signal centre tapped transformer
will do, really, it'll just have different audio properties
Anyhoo... Solder the 4 diodes into a ring with all the anodes
connected to the next diode's cathode
. Form the diode ring into a diamond shape.
Solder the 'north' and 'south' corners to two of the outer terminals of one of the transformers.
Solder the 'east' and 'west' corners to two of the outer terminals of the other transformer.
Each transformer will now have a middle tap terminal between the two outer terminals that you just soldered.
Connect THESE two terminals to one of the phono jacks.
Now solder the other two jacks to the remaining outside terminals on the transformers.
If there is a sixth unused tap terminal on each transformer, dont worry.
Any jack can be used as an input or output. You want two inputs and only one output at any time and this little device does not require batteries.