ProtegeManiac
Headphoneus Supremus
Okay, most of this is a tad over my head, but I get the just of it. So you think my phone will get the 400s up to desirable listening levels? I can trick the phone into high impedance mode with an impedance adapter. This would definitely be the cans I go with if so. I can't do IEMs.
Yes. Just note that at some point higher impedance can cause the output to start trailing off, so you might not necessarily get as much power you were hoping for over the penalty to channel separation and distortion that Quad DAC operation does over just one of the ESS chips running. If you can root the phone so it activates Quad DAC as default instead of relying on a high impedance load to trigger it you won't have to take a penalty on the output power.
On a side note, can anyone recommend other higher impedance, open back cans that will trigger the phones high impedance mode without the need for an adapter? Something only moderately power hungry that will sound good with classic rock.
HD650/6XX has 98dB/1mW sensitivity but at 300ohms impedance the output power could drop significantly, since higher impedance usually means lower output (unless you're looking at OTL amplifiers) that drops faster on mobile devices due to the voltage performance of its power supply being a ~7.2v battery (and in this case the same battery has to run a CPU, a screen, etc).
HD660S has a lower impedance of 150ohms but sensitivity is also a little lower.
I'd really much rather use an HE400S or a Grado RS2 and then an impedance adapter or root the phone.