Re: Sound card question

[rlharris@oplink.net]

On Thu, October 1, 2015 3:57 pm, Doug wrote:
> I believe that the output of the headphone jack is not impedance
> matched--I expect it's just a voltage source. Wat's more, unless you are
> plugging the same low-impedance devices into both Y outputs, _and_ the
> source is impedance matched, you would not split the power equally. I
> don't know what you want to do with the second output, but it's more than
> likely a relatively high impedance, so it would not load the circuit at
> all. I could be wrong, but it seems logical to me.

With consumer electronics, the source (LINE OUTPUT) typically is of
low impedance, say ten to a hundred Ohms.  And the load (LINE INPUT)
typically is of high impedance, say a thousand to a hundred thousand
Ohms.  Consequently, loading is not a concern: the load cannot draw
sufficient current to affect the source.

Loads typically are connected in parallel one with the other, so no
"splitting" or voltage divider is involved, as would be the case if
loads were connected in series one with the other.

In consumer audio gear, (1) the HEADPHONE output may be driven by a
buffer amplifier stage which is driven from the LINE OUTPUT stage.
The buffer stage typically is able to provide a hundred milliAmperes
or so into any reasonable headphone load.  With this arrangement, even
a dead short across the output terminals of the buffer amplifier
should not affect the LINE OUTPUT.

But it may be that (2) the LINE OUTPUT and HEADPHONE jacks are
connected in parallel, one with the other, across a single output
stage.  Again, the output stage is going to be an amplifier which is able to
provide a hundred milliAmperes or so into any reasonable headphone
load.

So, whatever the case, connecting headphones to the HEADPHONE jacks
should not cause a lower level of the LINE OUTPUT.

RLH