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# Need some help comparing amp output (Emotiva XDA-2 vs. Schiit Asgard)

As a relative newbie to full-size headphones, I'm not very clear on the wattage/voltage/impedance relationships and how to evaluate different amps for my HE-400s.  I currently feed my cans from an Emotiva XDA-2 DAC/digital preamp, which has the following output from its headphone jack:

1.9 VRMS max into 10 Ohms @

< 0.02% THD (360 mW)
2.25 VRMS max into 47 Ohms @
< 0.015% THD (100 mW)
2.25 VRMS max into 100 Ohms @
< 0.01% THD (50 mW)

I'm assuming the output at the 35 ohm impedance of the HE-400 is going to be somewhere around 2 or 2.1 vrms.  I played with a spreadsheet from apexhifi.com and tried to make the relationships between VRMS, p-p voltage, impedance, and wattage all make sense.  The Schiit Lyr, for example, is rated at 40V P-P at 32 ohms, and my calculator says that corresponds to 6200mw - right about the 6 watts claimed by Schiit, so I think I'm not screwing this calculation up too badly.  Using that calculator, it seems that the output of the XDA-2 (2.1 vrms at 35 ohms) is only 126mw.  That's twice what I need to drive the HE-400 to 110dB (not that I want to listen at 110, I'm just using 110 as point of reference).  I want to compare that to the Asgard.  If the Asgard is putting out 20V P-P at 32 ohm (the Schiit site doesn't say 32 ohms, but that is what they quote for the Lyr voltage measurement), that's 1562mw - more than ten times the current output of the XDA-2!  I've heard class A amps output about 10% of the power draw.  The Asgard draws up to 35 watts, so 1.5 is only 4-5%, but seems in the right ballpark.  Does this sound right?  The XDA-2 is reputed to have a decent hp output (and I'm not saying it doesn't!), but I'm surprised that it would have only 10% the output of the Schiit.

I have no idea if that difference in current matters or not, but I'm hoping someone can help confirm that these calculations sound reasonable.  Unfortunately, posting this in the HE-400 thread didn't result in any response, but that thread is so crazy I'm assuming this question wasn't read by many.

Thanks in advance for any help!

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Anyone have any thoughts?
I really just want your honest assessment on xda2 vs bifrost sound quality through headphone outputs. What do you think?

I admit, sometimes I get too caught up in the technical specs of things when I should just be listening.  If you like the sound of your Emotiva, stick with it.  If not, look for a new amp.  Amps color the sound to some degree. Find the amp that colors the sound to your liking regardless of technical specs.

JT, I wish I could offer that comparison, but I have heard only the XDA-2. It can certainly play loud enough, but my HE-400s require most of the available power. My general impression is that amps sound better when not pushed to the limit
Quote:
Originally Posted by rdaneel

JT, I wish I could offer that comparison, but I have heard only the XDA-2. It can certainly play loud enough, but my HE-400s require most of the available power. My general impression is that amps sound better when not pushed to the limit

Sorry...meant compared to Asgard, but nevertheless...XDA-2 is all you have.     As far as being pushed to the limit, I am not sure this is valid.   My understanding is the XDA-2 is attenuated in the analog domain by a ladder/resister step device.      This means the amplifier is always going full output --- and all the volume control does is dump unwanted signal to ground as the volume is turned lower.     This is why the older pots always sounded better turned all the way up --- since the resistance introduced in the outputs is lower and perhaps less noisy.      Just my understanding, anyone care to correct?

I have the Asgard 2 and I think it sounds better than the headphone out on the XDA-2.  With the Asgard 2 gain switch on low it gets loud enough with my AKG-702's.

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