I finally got around to rebuilding my audio amp/signal tracer box. The amp has volume and 3 gain settings (20, 50, 200).
The box has a 1/4" , 1/8" and probe inputs
I also made a custom ring modulator, similar ones was used to make the voices of the Dalek from the Dr. Who TV show. You can here a sample here. My "Ring Thing" has 6 variable frequency wave forms, effects, export its wave forms to other devices, or you can use any external wave form source such as a keyboard.