Romeo Y Julieta

[Wild E]

Several weeks ago I started a thread called "Bad Odie" and was able to make him behave with a breadboard. But his adventures aren't over yet.He has been banished from the ROG site to the Homewrecker site, I can't help feeling responsible somehow. Along the way he met a girl named Ruby and they made beautiful music together. Now they want to get married and live together in a Romeo Y Julieta brand cigar box. But their families resist...
OK enough of the creative analogy. I hooked up my odie to my ruby to 2 12" crate speakers and WOW!This setup cranks! I thought to myself "I need to make this into an amp" so I hooked up an extra battery snap in reverse to jump the power and identified it.I wanted to see if one battery could handle it. Then I hooked everything back up.As I increased the gain on odie it began to oscillate and changed pitch. I tried a 12V power supply with the same result. I guess that I could replace the gain pot with a series of momentary switches with different resistance values to make an"oscillation keyboard", but not now. Maybe not ever. I know that feedback can cause oscillation so I began to ponder. I noticed there were 2 ground paths, sleeve on the output to input jacks and battery snap. I disconnected the sleeve since it wouldn't be there on a single board and might be slightly more positive than with the added resistance from the patchcord. No change. While I was reviewing the schematics I realized the ruby feeds the signal to the inverting input of the 386. Could this be the problem? If so could the solution be as simple as reversing this connection or would I need to make other mods? If not how can I make them "think" they're on separate supplies? I planned to use a wall wart with the option for battery.This forum has really helped me do things on my own so far but I would appreciate some thoughts from people with more experience than I before I continue.Thanks.