How to drive a sub woofer in addition to satelite speakers

Discussion in 'The Projects Forum' started by ioncore, Jan 12, 2012.

  1. ioncore

    Thread Starter New Member

    Jan 11, 2012
    My Polk Audio 2.1 Speaker system broke down. The stereo speakers are in perfect condition, and so is the sub woofer. For some reason, the sub woofer is working fine, yet there is no sound from either of the stereo speakers -- but when I test those separately (by plugging in the jack into a MP3 player), they're working fine.

    I opened it up thinking maybe I could spot a burnt out capacitor/resistor/etc and replace it, however the entire circuit is in original condition and nothing seems to (visually) be out of place.

    Thinking maybe it is the pre-amps/power-amp that got shot internally, (and for what it's worth a good learning opportunity) I'm thinking about rebuilding the entire amplifier from the ground up -- nothing fancy, just very very crude/basic. I've been searching up on the various types of amplifier chips and found the TDA2009A at the local electronic store. The data sheet offers a good schema of a basic amplifier and I think I'll implement that.

    (A cleaner version is here: )

    Now the problem is, the amplifier will be capable of driving the stereo speakers, but what do I do about the sub woofer? The sub woofer has a resistance of 4ohms, the stereo speakers are reading somewhere between 3 and 4. Is there a circuit I could build to drive the woofer from the same input? Or some how augment the above schematics to allow for the woofer?

    Just some FYI: The original circuit was driven by a LA4485 and a bunch of C4570ha.

    As you can tell I'm very new to this stuff, but have some elementary exposure to electronics. Any help or pointers would be greatly appreciated.

  2. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    If the sub still works, use the existing amplifier for the sub, and you can buy a 10Wx2 channel prebuilt amplifier board to run off the power supply in the sub, it would be like the schematic you show, but per-assembled and tested if you don't have any equipment at the moment..

    First, we need to know the voltages of the power supply in the sub, there may be a + and - supply, measured from ground.
  3. crutschow


    Mar 14, 2008
  4. wmodavis

    Well-Known Member

    Oct 23, 2010
    " but what do I do about the sub woofer?"

    The signal to feed the woofer should be a monaural mixed signal from both left and right stereo channels so you will have to add left + right and amplify it to feed woofer.