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XLR and RCA, and gain differences

Keith_W

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I have a quick question about XLR and RCA.

This is the scenario: I am using a Merging NADAC MC-8 DAC (i.e. 8 channels of DAC).

Channels 1-6 are output via XLR. The output gain is 18dBu.

Channels 7-8 are output via RCA. The output gain is 8dBu. I have no choice but to use RCA because the amp that I am using has RCA inputs only.

Obviously, there is a gain difference between XLR and RCA. If I were to fabricate a cable so that it had XLR on one end (the DAC end) and RCA on the other (the amplifier end), would I get 18dBu gain, or 8dBu gain?
 

Blumlein 88

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You are most likely to get 12 dbu from the XLR set up that way.

BTW, you can buy cables that go from RCA to XLR. Just make sure if you want the XLR to be male or female for your purposes.

Monoprice cables are inexpensive, well shielded and have very good quality ends.
 
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Keith_W

Keith_W

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Thank you Blumlein. Can you please tell me your reasoning behind getting 12dBu gain if I were to do this?

This is mine (most probably wrong): XLR has 3 cables - + phase, - phase, and GND. At the receiver end, the + and - phase are summed. If the transmitting end puts 9dBu into each + and - phase, then the sum is +18dBu. If you were to only take one signal, then it should be 9dBu.

Please don't jump on me, I don't know if my reasoning is correct or not which is why I am asking. I genuinely want to know why you think it is 12dBu.
 

RayDunzl

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It halves the signal voltage, and that is a 6dB loss. 18 - 6 = 12.

http://www.sengpielaudio.com/calculator-gainloss.htm

upload_2016-9-15_4-37-9.png


I'd assume that's his thinking...

If the transmitting end puts 9dBu into each + and - phase, then the sum is +18dBu.

Taking this calculator - http://www.sengpielaudio.com/calculator-db-volt.htm

Using 9dBu (unbalanced)to find the RMS voltage, and doubling that (balanced) in the volts RMS to dBu calculation, gives 15dBu.

9dBu + 9dBu does not equal 18dBu, in other words, as I see it.
 
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RayDunzl

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Good! Because I'd hate to try to explain my explanation.
 
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Keith_W

Keith_W

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Can you try to explain why you'd hate to explain your explanation then? ;)

I get it. Logarithmic scale for dB. Forgot about that one.
 

Phelonious Ponk

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So you get 6db more, but you'd get another 6db if you had balanced output? Is it the same if you go through a direct box?
 

Blumlein 88

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So you get 6db more, but you'd get another 6db if you had balanced output? Is it the same if you go through a direct box?

Not sure I understand your question. In the OP's question he is taking something balanced and going to RCA. Normally that is done by grounding the negative portion of the balanced signal. So you get half the voltage. So instead of putting out a balanced 6.2 volts by having +3.1 volts and -3.1 volts you ground the minus leaving +3.1 volts and ground. You have cut the voltage differential in half and therefore have 6 db less signal. 6.2 volts is very approximately 18 dbu. Now the RCA outputs are apparently not just half the balanced outputs on his NADAC. They have a different gain. So just doing an adapter to RCA from the balanced outputs will leave a difference between that and the provided RCA outputs.
 

RayDunzl

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