On Oct 11, 1:46*pm, DaveC wrote:
A set of Harman Kardon Soundsticks are obsolete with most modern computers.
They originally took digital audio via USB output from the computer and fed
it to a multi-channel audio amplifier chip which drove 2 desktop speakers and
a sit-on-the-floor subwoofer. USB drivers are no longer available.

I'd like to make these work again by connecting the audio-out jack from the
computer to the appropriate points on the Soundsticks' PCB.

The main component on the PCB is the amplifier:

http://oi55.tinypic.com/egrdyg.jpg

My question is basic: how do I connect to both stereo inputs (inputs 1 and 2)
and at the same time connect to the subwoofer input (inputs 3 and 4)?

Think a bit here -- the rationale for a common woofer is that the low
frequency sound is common to both left and right channels. Therefore,
all you need is a low pass filter from either channel 1 or channel 2.
The input impedance of the common amp has to be much higher than
anything you could make with resistors.


I presume the answer is a simple resistor network mixing the 2 signals for
input to 3/4?

And yes, there's filter networks there, too, and it is important to know the
appropriate "injection" point, which will take some time.


Assuming there's a low pass filter circuit on the board somewhere,
connect channel 1 to its input.