[Michael Moroney]

(Don Pearce) writes:

On Wed, 26 Oct 2011 08:50:55 -0700 (PDT), NT
wrote:

On Oct 26, 7:58*am, DaveC wrote:
I want to connect the audio out (headphone jack) of 2 computer sound cards to
a desktop & woofer speaker-amp combination. (The original input was via USB
only and I'm modifying this for analog audio input.)

This is my guess at the necessary resistors to mix down these 4 outputs to
the 3 inputs in the amplifier (L, R, sub):

http://i41.tinypic.com/97mpud.jpg

Lose Rs 1-4, keep 5-8, lose R11, and lose C1,2,3, then itll be good.


NT

Is there something wrong with my browser? I can't see any of these
component references. Actually I see what you mean. One problem here
is that R9 and R10 are going to cause crosstalk. Without some active
electronics there is no way around that apart from taking the sub from
one channel only. This is actually quite common.

I don't see component references, either. However, assuming R1-R4 are
the resistors from the inputs to ground, they may be necessary to provide
a proper impedance to the source driving them.

To reduce crosstalk, I'd replace the two resistors from the 220nF
cap junctions to the pot with four resistors from each of the four inputs
to the pot. Presumably, the output impedance of the amps is low compared
to the resistors reducing crosstalk.

For mixing signals there is a method using amps and feedback where the
connection between multiple sources is at a virtual ground, eliminating
crosstalk.