Sorry, I could not find a descriptive subject line, because I need help with something I don't really understand.
I am connecting a device which outputs an audio signal to an amplifier, and then to the speaker. It works fine.
Then I wanted to power the device with the same power source of the amplifier (this power source is a set of Li ion batteries). The device powers on ok, and it outputs a nice test sine wave as it should.
But when I connect this audio signal to the amplifier, something strange happens. The speaker starts to jump, the power led on the device starts blinking. Eventually the amplifier breaks down (I think this is what broke the amplifier, though I can't be sure).
I have installed a brand new amplifier and it behaves the same, although I disconnected it before it broke!
In summary, the amplifier works fine, the device works fine and they also work fine together as long as they are individually powered.
I have attached a diagram to show what I want to do. I can't do much testing for fear of the new amplifier will break too.
Any suggestion will be appreciated!