A couple of notes I have after doing some of my own tests today:
- It does work fine on a 9v DVD battery.
- With 8 AA batteries installed (internally) I pulled the external plug out and it continued recording without a hitch. So internal battery back-up works fine.
- Without batteries installed I pulled the external plug and it shut down. The WAV files were saved fine. The header was fine too. The files were not corrupted.
- The pre-amps are not noisy.
- There is plenty of gain in the LOW mic setting. I wasn't able to check if my mics overloaded it with concert level volume.
- The screen back-light stays on when using the external power source (9v DVD battery or AC). So that will negatively effect external battery life.
- It's fairly easy to use right off the bat. I did read the manual inside and out a number of times before it arrived.
- I like it.
I doubt I'll have much more time to mess with it before I use it to record this weekend.
A couple of things to be wary of, if the power operations are anything like the HD-P2. The HD-P2 would automatically choose (and seamlessly switch between) the power source with the highest voltage. So even though an external 9V battery would "work", some people had issues when using an external 9V and AA's loaded at the same time. The 8 internal AA's would provide 12v, so even though a 9V external was connected and people thought that the deck was running off the external, the power was actually coming from the internal AA's. Also, some people found that if they left dead AA's inside the deck, and tried to power the deck with an external 9V, the deck still saw a higher voltage from the dead AA's (even though they were dead and had no juice), so it would try to use the internal AA's instead of the external 9V battery. This would result in the deck just not turning on until the internal battery's were removed.
So, all that said, while a 9V battery might work with the DR-680, if you are planning to use internal AA's as a back-up power source, it would probably be a good idea to get a real 12v external battery. There are plenty of fantastic 12v battery options now that don't involve lead-acid (the tekkeon, for example. there are many others as well).
On the other hand, maybe the DR-680 doesn't handle power sources in the same way as the HD-P2, and everything I just wrote is irrelevant. but I wouldn't want to find out at a show during a live recording, so it's probably worthwhile for someone to test the internal/external battery operation at home to determine what really happens and where the DR-680 is really drawing power.
the other thing that i would be concerned about is that 6 channels of phantom power turned on might be too much for a 9V battery. maybe I'm wrong and all 6 channels of phantom operate within spec (48v +/- 4V) with a 9V battery, but it's probably something else that should be tested. Also note that some mics are more amenable to a lower phantom power voltage than others.