Mixing 3 audio signals + power amp

Discussion in 'The Projects Forum' started by odinhg, Jan 22, 2010.

  1. odinhg

    Thread Starter Active Member

    Jul 22, 2009
    Hi. I just got an AY38910 PSG IC which have 3 audio outputs. I was thinking of using a LM386 to drive a 250mW, 8ohm speaker. But I was thinking of mixing the 3 outputs together first. I've made a schematic (attached) from different application notes and other resources on the web. Is it possible that the circuit will work? If so, is there any improvements I can do?

    Thanks in advance :)
  2. ifixit

    AAC Fanatic!

    Nov 20, 2008
    1. Use a newer opamp. eg. TL072
    2. Decouple the LM386 input with 0.1uF.
    3. The opamp needs a negative 5 volt rail.
    4. If you don't need to invert the signal then eliminate the opamp altogether.
    5. Add a volume control to reduce the signal level. The LM386 will only need approximately 70mV max.
    Good Luck
  3. Audioguru


    Dec 20, 2007
    The output of the sound generator (awful-sounding square-waves) has DC on it so it will bias the input of the opamp. Then the (+) input of the opamp must also be biased to a similar voltage. Then the opamp will not need a negative supply.

    The output of the opamp will then have a DC voltage so a coupling capacitor is needed to feed AC audio but not the DC to the input of the LM386 amplifier.