stv014
Headphoneus Supremus
- Joined
- Jul 17, 2011
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The HE-400 is one of the more efficient and relatively easy to drive planar magnetic headphones, the O2 should be plenty enough.
It's not really an external power supply that the O2 uses. The external unit the O2 uses is just a transformer, to step down the voltage from the wall to something like 13.5-20V AC. Hence you'd need a different transformer in a country with 115V power as opposed to 230V power. I think for size and weight concerns, maybe regulatory too (?), the transformer wasn't put inside the chassis. You can get an upgraded transformer if you really want though; in fact, it's recommended for bench testing or running the planar magnetics run at a loud volume. Difference in price is only like $5.
WAU12-200
WAU16-400
The power filtering is on the PCB inside the amp. There are some filter caps and 7812 / 7912 linear regulators. Power consumption of the O2 is in general pretty low—it's not class A, it only runs off of +- 12V rails, etc.—if it were a power hog, batteries would go out really fast, so it's not. If the power supply were inadequate, then you think that there would be performance issues under high load, right, or maybe some noise? I don't think there's evidence of that. So I think that concerns over power supply quality are not really that well founded.
I can understand the reservations about having another fat plug-in thing to deal with though.
Why would sticking a bigger AC/AC adapter do anything to boost amplifier output? Isn't the "power supply" of the O2 basically 2 9V batteries (so, 18V)? The O2 definitely measures more peak power on AC than battery power, but its hard to imagine a 20 V adapter is going to somehow turn the thing into a beast. Maybe a battery charging beast.
First off, as I mentioned, there are +-12V regulators on board. The output of all of that is what is connected to the op amps (so they are running off of +-12V). That's also what charges the batteries. 12V is higher than 9V or so, so you can charge the battery off of that supply. On battery operation, there is no 12V to charge the 9V battery, so the op amps are getting voltage from the batteries and thus see +-9V or so (actually a little less as the batteries discharge). That difference in supply voltage is why the max output is higher on AC power.
The difference between 700mW and 450mW is 10*log(700/450) = 1.92 dB. It's probably a stretch of the imagination to call a 2 dB difference in SPL a big deal; just open up a player with volume control denoted in dB (e.g. foobar) and turn down that slider 2 dB and see for yourself. Log scale on power may be more appropriate.
Is the ODAC+O2 combo able to be powered solely by the USB input?