rdaneel
100+ Head-Fier
- Joined
- Apr 1, 2008
- Posts
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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!
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!