Thanks for your reply!
I would use it primarily with T-Peos H-300s which are pretty bright so I'm looking for an Amp/dac that would counter that. I am also curious about a battery life comparison, idevice changing comparison, power differences, and noise floor comparison.
I don't think either device is going to suit your needs that well...
Amp/DAC to counter brightness:
SDT output impedance is 10ohm so you're going to get the opposite of that with your 22ohm H-300s.
720 isn't going to add or remove much in the way in the brightness. Its pretty neutral but can actually sound a little light on the bass (which sometimes make it seem brighter) with some combinations (I'm looking at the LCD 2's here but that could just be a power limitation)
Battery life comparison:
This is the reason I originally bought the SDT. with most of the other Amp/DAC combos sporting a 6 hour battery life I wouldn't of got through the day at work without having to put them on charge at some point. The SDT gives me enough juice to last me a full 8 hours at work & travelling there & back too. I've not timed either device as this was good enough for me.
The 720 should give more a load more juice but TBH I've never let it die completely on me...
One thing of note on this topic is that the SDT can be charged from a PC via the USB micro (Which is also the DAC connection) where as the 720 needs its own power adaptor to charge...
I'm not really sure what you mean here sorry. The only iDevice I've used with either is an iPod Touch 5th gen 64GB.
If you mean iDevice charging then the 720 does charge the iDevice while in use but not while you're charging it. On the other hand while in use the SDT does not charge the iDevice but if you pug the SDT in via USB to charge it then once its own battery is full it will then charge the iDevice via the connected cable.
The SDT doesn't have enough power to push all cans. In high gain I can max out the volume pot with my LCD 2's & although its too loud to listen to comfortably with a modern day recording it also has a fair amount of distortion. The 720 can push even the 600ohm T1's in medium gain just fine. I think it has a little extra bass impact in high gain though so I use that & less of the volume pot...
Noise floor comparison.
SDT is dead silent with all my IEMs & full size headphones. 720 has a distinct hiss with all IEMs but is silent with full size cans.
Regardless of this the 720 sounds so god dman good with my JH13 I tend to use it more than I do the SDT & put up with a bit of hiss. Its something you need to experience for yourself to decide if its too much for you or not I think...
Hope that helped.