[Jd007]

hey guys,
 
i'm a bit confused about line level output power. according to wikipedia here http://en.wikipedia.org/wiki/Line_level, line level for consumer audio over rca should be 0.316 Vrms nominal and peak 0.894. but most standalone dacs out there have rca line level at 2Vrms or 2.2Vrms. isnt that over twice the output level of the standard? maybe im missing something here?

 

[jaddie]

  hey guys,
 
i'm a bit confused about line level output power. according to wikipedia here http://en.wikipedia.org/wiki/Line_level, line level for consumer audio over rca should be 0.316 Vrms nominal and peak 0.894. but most standalone dacs out there have rca line level at 2Vrms or 2.2Vrms. isnt that over twice the output level of the standard? maybe im missing something here?

 
Consumer audio, nominal Vrms is .316, but you're considering the Peak value of .894 as a maximum, which it isn't.  It's simply a different way of measuring the same voltage.  You convert .316Vrms to the Peak to Peak value by multiplying by 2.828.  
 

 
However, a DAC may be spec'ed at 2Vrms as it's maximum output voltage, or "full scale" output voltage. It's nominal (average) will still be .316Vrms.  That allows normal levels to average at .316Vrms with roughly 15dB (actually 16dB) of headroom for undistorted short peaks.

 

[Jd007]

Thank you. Another semi related question is how come some balanced dacs the balanced output is not exactly double the SE Vrms, but higher? For example some dacs have 2.2vrms from RCA but 6.8vrms from XLR.

 

[jaddie]

Balanced outputs are intended to interface with professional equipment that uses a higher nominal voltage of 1.228 Volts.  The odd number is because the reference level can be traced back to the days of 600 ohm lines where the source was 600 ohms and the load was 600 ohms, with levels measured as power into a 600 ohm load using dBm (dB re: 1mW).  Studio standard line levels were +4dBm, which was 1.228V into 600 ohms.  Today we don't use 600 ohm matched systems anymore, so only the voltage is important. 
 
In studios there is always an issue using consumer and pro gear together.  For several decades there have been "bump boxes", devices designed to convert ins and outs to and from pro balanced levels and connections.  It's great that a device with both RCA and XLR on it also has the level bumps taken care of as well.  
 
There is no advantage to using balanced connections in the typical home application however.  The only advantage of balanced interconnects is noise immunity, and even then, only when the balanced input is properly designed (many aren't). The potential for stray noise pickup on short unbalanced interconnects is negligible, and creating a differential output and balanced input more than doubles the analog component count vs the raw unbalanced I/O.

 

[Jd007]

Thanks for the answer jaddie. I think with certain headphones (e.g. HE-6) balanced output does have a benefit since it has a lot more power output. SE output of 2W may not be enough to drive the HE-6 but balanced output of 4W is better. but yeah i guess for other types of headphones you can argue that balanced has no noticeable effect.
 
but still, since balanced output is the signal and its opposite phase, ans SE is just the signal and ground, shouldn't balanced out always be double SE, in terms of power? given that they are using the same balanced only circuitry that is, not not a separate SE only circuitry with different power output.

 

[jaddie]

 Thanks for the answer jaddie. I think with certain headphones (e.g. HE-6) balanced output does have a benefit since it has a lot more power output. SE output of 2W may not be enough to drive the HE-6 but balanced output of 4W is better. but yeah i guess for other types of headphones you can argue that balanced has no noticeable effect.

Balancing doubles the output voltage, which would, in theory, quadruple the available output power.  But there are other factors, such as the circuit's current capability, power supply, etc, that may limit that to somewhat less than the expected quadrupling.  You could, however, get the same improvement by just doubling the SE output voltage.  Headphones don't "know" or "care" how the voltage is delivered, the drivers just respond to a voltage across them.  
 
Just because you have an amp with higher output power doesn't mean it will improve anything unless you actually use that power. So the HE-6 with 4 watts is an advantage for certain headphones, because they require that power, but others do not.  You can increase the output power capability infinitely, but what matters is what the load uses.  Consider a 15A  electrical circuit in your home can deliver up to 1800 watts. The average light bulb consumes 40 watts. Changing to a 20A circuit increases the capability to 2400 watts, but the lightbulb still only consumes 40.
 
 

but still, since balanced output is the signal and its opposite phase, ans SE is just the signal and ground, shouldn't balanced out always be double SE, in terms of power? given that they are using the same balanced only circuitry that is, not not a separate SE only circuitry with different power output.
 

Ignoring current source limits, doubling the output voltage will increase the available output power 4X.  Just inverting a SE output with an identical but inverting amplifier doesn't guarantee 4X power, though.
 
As to balancing always doubling output voltage, it depends on how the balancing is achieved.  If you start with a SE output, then go through an inverting, unity-gain amplifier, the difference between the SE output and the inverted version will be twice the SE voltage, and differential.  However, if you run that SE output into a 1:1 transformer, the output will be balanced, but the same voltage as the SE output.  Analog Devices makes (or made) a "balanced line driver" IC in two versions, one was not gain corrected, so you got the +6dB/voltage doubling, the other was compensated so there was no voltage increase.  There are also active balanced output circuits that if connected as a SE output by grounding the unused output, they increase their gain by 6dB to compensate, such that balanced or unbalanced, the output voltage is the same. 

 

[Steve Eddy]

Thanks for the answer jaddie. I think with certain headphones (e.g. HE-6) balanced output does have a benefit since it has a lot more power output. SE output of 2W may not be enough to drive the HE-6 but balanced output of 4W is better. but yeah i guess for other types of headphones you can argue that balanced has no noticeable effect.

Output power can be whatever the amp designer wants it to be, whether "balanced" or single ended. You can achieve all the output power you will ever need with a single ended design. I could design a single ended headphone amp with more output power than any existing "balanced" headphone amp if I wanted to. Output power is just a design choice, not a matter of "balanced" versus single ended.

but still, since balanced output is the signal and its opposite phase, ans SE is just the signal and ground, shouldn't balanced out always be double SE, in terms of power? given that they are using the same balanced only circuitry that is, not not a separate SE only circuitry with different power output.

That may hold true for a given amp. But you can't say brand X's "balanced" amp will always have more output power than brand Y's single ended amp.

se

 

[UltMusicSnob]

Output power can be whatever the amp designer wants it to be, whether "balanced" or single ended. You can achieve all the output power you will ever need with a single ended design. I could design a single ended headphone amp with more output power than any existing "balanced" headphone amp if I wanted to. Output power is just a design choice, not a matter of "balanced" versus single ended.
That may hold true for a given amp. But you can't say brand X's "balanced" amp will always have more output power than brand Y's single ended amp.

se

Ditto Steve Eddy above.
 
I use balanced TRS in my home studio, but that's only for the purposes of carrying signals downstream of the mic preamp into my other gear--tiny tiny voltages, in other words, compared to speaker driver lines. The noise-canceling feature of balanced connections is the only reason I know of to use them.

 

[Steve Eddy]

I use balanced TRS in my home studio, but that's only for the purposes of carrying signals downstream of the mic preamp into my other gear--tiny tiny voltages, in other words, compared to speaker driver lines. The noise-canceling feature of balanced connections is the only reason I know of to use them.

Yes. And the reason I use "balanced" in quotes is because the first "balanced" headphone amps (and the bulk of those on the market today) are what the rest of the audio world would call a "bridged" amplifier. And of course bridged amplifiers don't offer any common mode rejection because the inputs aren't differential.

And to be fair, "balanced" headphone amps were never promoted on common mode rejection, but rather doubling the output voltage swing. However the industry continues to misuse the term "balanced" so it can cause some confusion for those who come to the headphone market from other audio disciplines.

se

 

[jaddie]

However the industry continues to misuse the term "balanced" so it can cause some confusion for those who come to the headphone market from other audio disciplines.

se

And doesn't the word "balanced" have a nice warm and pure feeling to it? Who wouldn't want to be balanced?  
 
Doesn't "unbalanced" sound just horrible?  "Single Ended" just sounds sort of prejudiced somehow.  Love the terms, though. "Star-Quad" is just wonderful!

 

[Jd007]

That may hold true for a given amp. But you can't say brand X's "balanced" amp will always have more output power than brand Y's single ended amp.

I understand this of course. but i was talking about the output of a single balanced DAC, where the SE output is 2.2Vrms and XLR output is 6.8Vrms. There are multiple DACs that do this, and I was wondering why the two power outputs are not in the normal 2x relationship. Thanks for the answers above.

 

[Steve Eddy]

And doesn't the word "balanced" have a nice warm and pure feeling to it? Who wouldn't want to be balanced?  

Doesn't "unbalanced" sound just horrible?  "Single Ended" just sounds sort of prejudiced somehow.  Love the terms, though. "Star-Quad" is just wonderful!

How 'bout "Balanced Star-Quad"?

se

 

[Steve Eddy]

I understand this of course. but i was talking about the output of a single balanced DAC, where the SE output is 2.2Vrms and XLR output is 6.8Vrms. There are multiple DACs that do this, and I was wondering why the two power outputs are not in the normal 2x relationship. Thanks for the answers above.

I don't know. That's just plain weird. What DACs do this?

se

 

[jaddie]

  I understand this of course. but i was talking about the output of a single balanced DAC, where the SE output is 2.2Vrms and XLR output is 6.8Vrms. There are multiple DACs that do this, and I was wondering why the two power outputs are not in the normal 2x relationship. Thanks for the answers above.

 
Pretty sure you got it, but just in case: two different reference levels, one for SE, one for balanced.  They are standards based on the market each serves, and have nothing to do with simply changing to a different output configuration.  
 
Ever heard of a balanced output at .00123 volts?  Sure you have, it's a microphone.

 

[jaddie]

How 'bout "Balanced Star-Quad"?

se

 
Heaven.  Sheer heaven.