2 circuits + shared supply = no workee

Discussion in 'General Electronics Chat' started by qlocs, Mar 30, 2014.

  1. qlocs

    Thread Starter New Member

    Jan 27, 2013
    Just for fun I pulled a stereo amp out of an old computer, one of those TEA jobs that run from 3vdc to 12. I hooked up a little dollar store FM radio (TEA 7088T)to it and everything works great as long as each circuit gets its own battery. As soon as the battery is shared, nothing happens. I thought it was a current prob @ first because I was using tiny batteries, but after hooking up a pair of D cells, I decided current wasn't the issue. Anyone have any ideas?
  2. MrChips


    Oct 2, 2009
    You are probably shorting the battery via the audio connections, i.e. the grounds (COMMON) are not the same.

    If you have two or three wires from the FM radio to the stereo amp, i.e. Left and Right channel plus GROUND. Try disconnecting the GROUND wire.

    Or try isolating the ground connection by putting a 10μF capacitor in between the two grounds (COMMON).
  3. atferrari

    AAC Fanatic!

    Jan 6, 2004

    Would you mind showing a sketch of that, MCH? Gracias.
  4. qlocs

    Thread Starter New Member

    Jan 27, 2013
    You guys have the right answer, which I figured out last night by trial and success. One thing though, when the ground is lifted (on the 3 wire audio) the volume isn't as strong as when I use separate batts. Any particular reason for this?