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In Reply to: RE: Balanced/Unbalanced Simultaneously posted by jsr on September 28, 2015 at 23:20:30
You can check to see if the two outputs are buffered by turning off and unplugging the preamp and using an ohmmeter to check the resistance between the RCA center pin and the XLR pins 2 or 3. If you get a reading of zero ohms or thereabouts, this indicates they are not buffered and should not be used simultaneously.
I have a Pass Labs X1 preamp with the same output configuration and it states in my manual that the two outputs are buffered and can be used simultaneously. Therefore, I'm doing exactly what you are doing.
It would be a shame if your preamp doesn't have buffered outputs. However, if it doesn't, then you are screwing up the signal to the power amplifier, but it shouldn't do any harm. You can always remove the cables to the sub and see if you notice any difference in sound quality to the main speakers. The sub would be placing an unbalanced load on the balanced output.
Good luck,
John Elison
Follow Ups:
Thanks! Unfortunately, my meter's in storage.
I will say that the sound quality seems the same, but I will try what you suggest. Is there anything I could physically observe inside the preamp that would tell me they're buffered or not?
Thanks again.
Just buy another meter or else take yours out of storage; then you will be certain. It might be difficult to trace the connection when looking inside. Then, again, it might be quite apparent. Take a look and see.
Good luck,
John Elison
One thing I didn't get into is probably important. When I run the system using both preamp outputs (balanced and unbalanced), the sub puts out much less volume than normal. For instance, if the preamp runs unbalanced to the sub, and then unbalanced from the sub to the amp, the sub is happy with the sub's volume set around 9-11 o'clock. When the balanced outputs are used direct to the amp, and the unbalanced to the sub, then the sub doesn't get happy until the sub's volume is set to almost 3 o'clock. Strangely, the balanced output seems to remain the same (louder than the unbalanced, naturally).
I really like the balanced sound - it is not only louder (which is meaningless as to fidelity), but much, much clearer and with superior resolution, because the noise of an unbalanced connection is gone. I have always liked this in the few truly balanced systems I've had in the past - I don't care what anyone says, truly balanced has always sounded better than unbalanced in every way. No comparison.
Don't know if this info means anything or not.
Balanced outputs are often 6-dB louder than unbalanced outputs. The reason is that each leg of the balanced output is the same level as the unbalanced output but 180-degrees out of phase with each other. The difference between the two legs is therefore 6-dB louder than either of the individual legs to ground.
I know what you mean by the lack of noise in a fully balanced system. I've noticed the same thing in my system.
Best regards,
John Elison
Thanks!
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.
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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