NiMH battery may go up to 14V in fresh charged state, that is higher than 13V spec for DR 680, but slows down after some days through self discharging or under load; that may be the only limit for that battery, but you can use it down to 9V for DR 680. I am using NiMH too but always in conncetion with a voltage multimeter to control the voltage.
For my battery setup I found the following configuration:
- take two sets of NiMH batteries linked together via two switches and two diodes
- start up with first battery set switched on. If voltage drops down to 9v switch on second battery set and switch off first set afterwards. That will give you an uninterruptd supply over the switching process. The two diodes will avoid high "charge" current to the lower voltage battery during switching and on the other hand due to their 0,7 V drop will avoid the 14 V overvoltage.
For my use I built up the following configuration based on that battery power supply solution and realizing a redundant recording via second recording device (as I had two lost sessions through Edirol R 44 failure):
- Mic 1 - 4 goes into an RME quadmic mic amplifier
- Mic 5+6 are connected to Mic input 1+2 of a Focusrite Scarlett 18i6 which runs standalone even if netbook failed and from scarlett output to DR 680 channel 5+6 input
- Quadmic line outputs are devided throug symmetric y-cables to the 4 inputs of DR 680 and Scarlett 18i6
- Scarlett 18i6 runs with a simple netbook for recording via reaper, DR 680 runs in parallel for recording on their SD card
- all devices including batteries are build into a case and connected together - so for recording connect the mics, switch battery set and devices on and record. Netbook gives you a recording tim of 4-5 h through his Li Ion battery
Gain of DR 680 has to be set to +10 for reaching 0dB in both recording "channels" and in addition you will have good peakmetering through netbook too for both recording channels
This gives you a setup which is easy to use for recording performances f.e. in churches (organ, oratorio,..) indepent of AC supply in the church (which may be instable in older churches) and quick to install with good recording quality based on the mic preamplifiers in front of the recording devices going directly into both devices - without running throug internal reording devices AD-DA - and more "security" through "switchable" battery supply andredundant recording.
Best regards
Grosse_j