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In Reply to: RE: Balanced/Unbalanced Simultaneously posted by John Elison on September 29, 2015 at 03:55:31
You described a good test, but your conclusion is incorrect.
In most cases it is perfectly fine to use both outputs simultaneously, even if they are not buffered. Typical inputs are purely resistive, so you just need to make sure the total load is not below minimum recommended for that preamp.
There is one small caveat - some solid state amp inputs might become non-linear when the unit is powered down. Whether this is or is not a problem for you is another question. But this is a small concern.
Follow Ups:
Then running a single-ended output at the same time should not be possible, unless the unit either has a buffered single-ended output or does not support the balanced line standard (AES file 48).
Now if it supposed to be balanced and does not support the standard, then the issue is that the balanced outputs are referenced to ground. One side is then going to be loaded harder than the other and this will unbalance the signal to the balanced amp.
The degradation might be slight, depending on the the CMRR (common mode rejection ratio) at the input of the amp, but could be audible.
Thanks, Victor.
I disagree with you. First of all, I didn't say it would hurt anything to connect both components simultaneously. I said it would create an unbalanced load on the preamplifier. Furthermore, it would be more than a restive load because the unbalanced cables to the sub have capacitance and if they happen to be 25-feet long like the cables to my sub, this presents significant capacitance. I like my sub to be placed on a rear wall behind my listening position. At any rate, placing different loads on each leg of a balanced connection kind of defeats the purpose of a balanced connection. It basically negates the word "balanced." ;-)
Best regards,
John Elison
Figure, 100 Ohm output resistance.
It doesn't matter what the output resistance is for the preamp; you no longer have a balanced connection because you no longer have a balanced load. That may or may not make an audible difference, but it is definitely not ideal. The two outputs should be buffered if you intend to use them simultaneously. On the other hand, if you can't hear any difference, it might not matter to you. It just depends. I, personally, wouldn't be happy with such a configuration.
Best regards,
John Elison
But you just wrote earlier:
" Furthermore, it would be more than a restive load because the unbalanced cables to the sub have capacitance and if they happen to be 25-feet long like the cables to my sub, this presents significant capacitance."
After which I asked you to describe their effect. You then stated, totally incorrectly, that the output resistance does not matter.
OK... I am out of this discussion.
You stated that the imbalance from the load of the sub was purely resistive and I was pointing out that it also had a reactive component due to cable capacitance. Regardless of whether the load is purely resistive or partially reactive, it constitutes an imbalance to a supposedly balanced connection. The reactive component will create phase shift to the audio signal on one of the supposedly balanced legs. My point is that I, personally, would not be happy with that situation in my audio system.
> OK... I am out of this discussion.
Well, it's about time!
Good luck,
John Elison
My sub cables aren't particularly high end (though I could dig out some that are probably of better design/manufacture, like Canare), but the run is only about 8'.
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