OT: Two PCs, One Speaker System?

  • Thread starter Thread starter (PeteCresswell)
  • Start date Start date
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(PeteCresswell)

Can I run a "Y" cable from each of two PC's sound cards into a single speaker
system without damaging the sound cards?

Simultaneous output isn't an issue hearing-wise, but I'm wondering if the signal
from one PC's output hitting the output side of the other would be a problem.
 
You would be asking for trouble!

Applying a voltage (that's what audio is) to the "output" jacks of an audio
device (in reverse) is never a good idea. That is why the audio industry
markets speaker switches. You apply output from one device at a time to the
speakers, never from both at once.

--

Regards,

Richard Urban
Microsoft MVP Windows Shell/User
(For email, remove the obvious from my address)

Quote from George Ankner:
If you knew as much as you think you know,
You would realize that you don't know what you thought you knew!
 
Richard, in general you're right, but he might be
able to get away with it.

We're talking line level audio here - approx. 1V P-P
when playing. Even if the output of the sound card,
onboard audio, etc were DC coupled (few are as this
requires careful design and more $$$ - something most
PC hardware mgfrs. are loath to do) the audio level from
a PROPERLY DESIGNED "playing" device will likely not
harm a PROPERLY DESIGNED "non-playing" device.

Emphasis is on "PROPERLY DESIGNED". The corner-cutting
of the majority of consumer PC "audio hardware" is enough to make
most analog engineers wince.

If we were talking SPEAKER output levels, after the
above discussed line level signal has been run through
an audio power amp, you would have issues as the voltage
swings and currents involved are much higher.

You can always couple the line out audio with an inline
capacitor to isolate potential DC offsets on the output -
simple & cheap. If you want to get fancier, build a
unity gain buffer out of low-noise op-amps.

Your bigger problem will likely be with possible interference
introduced by directly connecting the outputs of two preamp ckts. together.
This can start all kinds of weird positive feedback oscillations
which CAN kill the circuitry. And, you will double the ckt. noise
("hiss"). Unity gain buffer ckt. will fix the oscillation problem.

Simple solution, if both these PC's are on at the same time, would
be to run the line out of machine #1 to the line in of machine #2,
then the line output of machine #2 to the speakers.

This will double hiss as well, but it may be acceptable depending
on your situation.

My 2 cents worth based on a couple dozen years of building
audio preamp/amp/speakers from scratch...not intended to cover
all bases and/or possibilities.
 
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