I use a professional audio soundcard / USB DAC that has XLR outputs. My preamp has RCA inputs.
There are commercial XLR to RCA cables available. They all connect in the same way, i.e. XLR 2 (+) goes to the tip of RCA, XLR 3 (-) to the ground at the RCA end, and XLR 1 (gnd) goes to the shield (gnd).
The reason to join the XLR 3 (-) to ground by the manufacturers is to reduce noise, so that XLR 3 (-) will not be floating.
But this is to short the XLR 3 (-) to ground! would this burn the output stage / +/- converter of the USB DAC? How does it work?
There are commercial XLR to RCA cables available. They all connect in the same way, i.e. XLR 2 (+) goes to the tip of RCA, XLR 3 (-) to the ground at the RCA end, and XLR 1 (gnd) goes to the shield (gnd).
The reason to join the XLR 3 (-) to ground by the manufacturers is to reduce noise, so that XLR 3 (-) will not be floating.
But this is to short the XLR 3 (-) to ground! would this burn the output stage / +/- converter of the USB DAC? How does it work?
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Generally the output resistance of the source driving XLR pin 3 is high enough that grounding it won't damage the circuitry. On some XLR outputs pin 3 isn't driven actively and is grounded via a resistor. No issue in that case.
In any case, I don't think it's good practice to pull the pin 3 output to ground in this way and I modify XLR/RCA adaptors to remove it or when building cables leave it unconnected.
Some professional equipment senses this type of pin 1/3 short on XLR outputs and reprograms gain to increase automatically.
Input RCA/XLR adapters are another case. 🙂
Dave.
In any case, I don't think it's good practice to pull the pin 3 output to ground in this way and I modify XLR/RCA adaptors to remove it or when building cables leave it unconnected.
Some professional equipment senses this type of pin 1/3 short on XLR outputs and reprograms gain to increase automatically.
Input RCA/XLR adapters are another case. 🙂
Dave.
It all depends on whether the XLR driver is balanced or merely biphase.
If balanced then grounding the - signal to convert to unbalanced is both necessary and harmless.
If biphase then grounding the - signal to convert to unbalanced is unnecessary and may be harmful.
The big snag is that people do not distinguish between balanced and biphase so many cheaper 'balanced' outputs are in fact biphase.
If balanced then grounding the - signal to convert to unbalanced is both necessary and harmless.
If biphase then grounding the - signal to convert to unbalanced is unnecessary and may be harmful.
The big snag is that people do not distinguish between balanced and biphase so many cheaper 'balanced' outputs are in fact biphase.
In this case, the manual of loudspeaker processors like BSS or Beringher shows the 'hot +' and 'cold -' of their balanced output only connected to the unbalanced input, the screen being left unconnected.
It doesn't matter whether it's balanced or biphase. And it's not an either/or situation....balanced might be bi-phase, and bi-phase might not be balanced.
What matters is the tolerance of the (-) signal output to a short circuit being placed upon it. In some cases this might be an active circuit with no build-out resistor. In that case you would not want to attach a short circuit to it. Actually, I don't think it's wise in any case, but a build-out resistor at least isolates a zero ohm load somewhat and would probably prevent damage to an active driver circuit.
The issue in the OP's case might have more to do with the type of interconnect being used. If it's a twisted-pair shielded the (-) conductor should probably be returned to ground at the source end.....but not by grounding the output of an active driver stage to do it.
Dave.
Some of all of it ;-)
In a proper balanced output, the signal is carried as the difference between the two signal wires, with no reference to ground. In such a case you can ground either signal with no adverse consequences. Problem is as DF96 alluded to that many are not truly balanced configurations and in such a case, depending on implementations, you may see problems.
Although, have done a lot of XLR to RCA adapters and cables, I have never seen an actual problem. YMMV.
Jan
In a proper balanced output, the signal is carried as the difference between the two signal wires, with no reference to ground. In such a case you can ground either signal with no adverse consequences. Problem is as DF96 alluded to that many are not truly balanced configurations and in such a case, depending on implementations, you may see problems.
Although, have done a lot of XLR to RCA adapters and cables, I have never seen an actual problem. YMMV.
Jan
I'm not sure why the appropriate qualifiers here are so difficult to grasp. 🙂
Forget, for a second, about whether the source is balanced or bi-phase or unbalanced or whatever. IF the circuit sourcing the (-) polarity on pin 3 of said XLR is an active circuit, is it okay to place a short circuit on its output? That's a question we don't know the answer to unless investigating that particular piece of kit.
All I'm saying is that if we DON'T place a short on its output we will be okay.
Regarding any balanced/unbalanced interface concerns.....it's fairly irrelevant at this point since the interface being created is unbalanced. I'm only thinking about safety concerns with the circuitry within the source component.
This concern is exactly what the OP was alluding to with his original query.
Cheers,
Dave.
Forget, for a second, about whether the source is balanced or bi-phase or unbalanced or whatever. IF the circuit sourcing the (-) polarity on pin 3 of said XLR is an active circuit, is it okay to place a short circuit on its output? That's a question we don't know the answer to unless investigating that particular piece of kit.
All I'm saying is that if we DON'T place a short on its output we will be okay.
Regarding any balanced/unbalanced interface concerns.....it's fairly irrelevant at this point since the interface being created is unbalanced. I'm only thinking about safety concerns with the circuitry within the source component.
This concern is exactly what the OP was alluding to with his original query.
Cheers,
Dave.
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Anybody who sells an audio signal source that will be damaged by grounding any of its outputs is sure to be rewarded with warranty return financial losses.
Therefore one finds very little commercial gear with this problem.
Dave, as I noted, balanced outputs carry the signal as the difference between two lines. That means that these two lines can carry (and often do) appreciable common mode noise and hum, which of course is cancelled by a balanced receiver.
Now if you only use one signal line and let the other float, you have just converted all that CM junk to DM and input it into your preamp. I would assume you don't want that. Connecting the unused signal line to your preamp reference (ground in the RCA case) you preserve the CM suppression.
It may mean the difference between failure or succes.
Jan
Jan,
Yeah, I'm well familiar with the concept.
The OP is specifically asking about an interface with an unbalanced receiver. "My preamp has RCA inputs."
In this case (and with the cable configs he mentioned) it won't make a bit of difference (CM or DM wise) whether the (-) source of his XLR outputs is brought to ground. It MIGHT make a difference to the source circuitry though if doing so.
arnyk is certainly correct that decent commercial gear should be able to tolerate this. I'm playing devils advocate here.....I thought that was obvious. 🙂
In many instances the balanced output of a component is a dual op-amp stage. Even though we might not damage it placing a short circuit on one output, it might degrade the performance of the other output that is still being used. (I've seen this previously on a few occasions.)
Now, if we were in the other case......an unbalanced source driving a balanced receiver...then we would surely want to ground the pin 3 input on the balanced input receiver.
Cheers,
Dave.
Yeah, I'm well familiar with the concept.
The OP is specifically asking about an interface with an unbalanced receiver. "My preamp has RCA inputs."
In this case (and with the cable configs he mentioned) it won't make a bit of difference (CM or DM wise) whether the (-) source of his XLR outputs is brought to ground. It MIGHT make a difference to the source circuitry though if doing so.
arnyk is certainly correct that decent commercial gear should be able to tolerate this. I'm playing devils advocate here.....I thought that was obvious. 🙂
In many instances the balanced output of a component is a dual op-amp stage. Even though we might not damage it placing a short circuit on one output, it might degrade the performance of the other output that is still being used. (I've seen this previously on a few occasions.)
Now, if we were in the other case......an unbalanced source driving a balanced receiver...then we would surely want to ground the pin 3 input on the balanced input receiver.
Cheers,
Dave.
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Your use of the word 'biphase' is like cheering on self invented emperors new underpants.
As I said, this is incorrect. If the output is a transformer balanced output then to convert to unbalanced requires us to place a short on one of the wires - without that there is no output! A true balanced output will not be upset by this, whether it uses a transformer or some other method. A biphase output may be upset, depending on how carefully it has been engineered.Davey said:
So, a short on one output may be required or prohibited or tolerated.
How does this answer the OP's question, except that it is 'best' to use a xformer?
Jan
Did I say anything about a transformer balanced output? A transformer output is obviously a different situation.
I said an "active circuit" and I qualified it by saying we don't know exactly what it is unless investigating.
Are you actually reading my posts?
Your final sentence I do agree with though.....since it basically qualifies everything. 🙂
My goodness.
Dave.
Maybe the "it is 'best' to use a xformer" is the best option?
HiFiNutNut has a tough question that has been going around for a long time. I hope a
wrong connection does not damage his equipment.
PeterC
HiFiNutNut has a tough question that has been going around for a long time. I hope a
wrong connection does not damage his equipment.
PeterC
I recommend reading the "Theory of Operation" section in the THAT1646 data sheet: http://www.thatcorp.com/datashts/THAT_1606-1646_Datasheet.pdf
Tom
Tom
Amazing thing audio. Ask a simple question and get a dozen differing responses.
Grounding pin 3 is commonly done in the pro audio world for balanced to unbalanced. Many manufacturers recommend it. Whether or not it's ideal, it gets done without catastrophe all the time.
For the overly cautious, you can tie pin 3 to ground via a 10K resistor. I've done that, not sure it made any difference. But I felt better. 🙂
Grounding pin 3 is commonly done in the pro audio world for balanced to unbalanced. Many manufacturers recommend it. Whether or not it's ideal, it gets done without catastrophe all the time.
For the overly cautious, you can tie pin 3 to ground via a 10K resistor. I've done that, not sure it made any difference. But I felt better. 🙂
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