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

    Distinguished Member

    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

    AAC Fanatic!

    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.