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-   -   What are the correct output line levels for unbalanced & balanced? (http://www.diyaudio.com/forums/digital-source/7087-what-correct-output-line-levels-unbalanced-balanced.html)

 Brian Guralnick 25th October 2002 03:01 PM

What are the correct output line levels for unbalanced & balanced?

I’m working on the analog end of a audio DA board. What are the correct output line levels? I created a CD which had a simple 60 Hz sine wave for measurement with a standard volt meter. The sine wave went from 32767 to –32767 in amplitude.

Here are some measurements I took:
2.14Vac = Harman / Kardon HD200 CDP
1.92Vac = Sony 209ES CDP
0.93Vac = Sound Blaster Live
0.65Vac = (Line out) Portable Panasonic SL-S360 CDP

You can see my confusion here. What should the voltage be for –10dbm unbalanced out and +4dbu unbalanced out?

What should the voltage between the + & - signals be for –10dbm balanced out and +4dbu balanced out?

Brian.

 ashok 25th October 2002 04:18 PM

Correct levels

0dbm is 0.775 volts ( for 1mW into 600 ohms)
-10dbm is =0.316x0.775 = 0.245 volts.
+4dbm is 1.228 volts.

There is no standard output on most machines. I believe that the Red Book spec for CD's is 2 volts. I have never checked this and cannot be sure. I do not see many machines with 2 volts output. Most are between 1 and 2 volts. Tubed outputs may be higher depending on how they are implemented.

If you keep within 1 and 2 volts you would be following the general norm. If you keep the signal high you can avoid a buffer or gain stage before the power amp .
Cheers.

 Sparhawk 25th October 2002 04:59 PM

clarification

I agree with ashok's post, but here is a little more clarification:

First of all, you have your levels backwards. They are usually specified as +4dBm and -10dBu, not the other way 'round as you have them. These are often called "Pro" and "Consumer" levels, respectively.

dBm is a power ratio relative to 1mW, whereas dBu (or dBv as it is sometimes written) is a voltage ratio relative to 0.775Vrms. (There is also dBV, which is a voltage ratio relative to 1Vrms.)

With a 600 Ohm load, 0dBm = 0dBu = 0.775Vrms. dBu is more relevant to consumer equipment, since the load is never as low as 600 Ohms. -10dBu (0.25V) is supposed to be a normal line level for consumer equipment. I'm not sure what the peak level is supposed to be, or if there is a standard, but 2V is probably more than enough. The exact value isn't critical, as long as it is not high enough to overload the preamp or whatever it is feeding.

 Steve Eddy 25th October 2002 05:15 PM

Re: What are the correct output line levels for unbalanced & balanced?

Quote:
 Originally posted by Brian Guralnick You can see my confusion here. What should the voltage be for –10dbm unbalanced out and +4dbu unbalanced out? What should the voltage between the + & - signals be for –10dbm balanced out and +4dbu balanced out?
Forget about all the dBm and dBu stuff. With digital, it's dB Full Scale or dB FS. 0dB FS for a Red Book CD player is 2 volts RMS. 2 volts RMS from hot to ground on an unbalanced output and 2 volts RMS between the + and - lines on a balanced output.

se

 Brian Guralnick 25th October 2002 06:27 PM

Re: Re: What are the correct output line levels for unbalanced & balanced?

Quote:
 Originally posted by Steve Eddy Forget about all the dBm and dBu stuff. With digital, it's dB Full Scale or dB FS. 0dB FS for a Red Book CD player is 2 volts RMS. 2 volts RMS from hot to ground on an unbalanced output and 2 volts RMS between the + and - lines on a balanced output. se
OK, I can live with the 2 volt RMS.

Now, what should the ouput impedance be?

For example, in the balanced output reference design for Crystal's CS43122 DAC, they use 100 Ohm resistors in series on the +&- outputs. Is this correct. Is it the same for unbalanced outputs?

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