I did some testing tonight with phantom power noise and difference between hi-lo gain.
Test setup was this:
mic -> Radial ProMS2 "direct 1" -> DR680 channel 1 +P48.
Radial ProMS2 "direct 2" -> DR680 channel 4.
Channel 1+4 = left and right of stereo mix. Direct 2 on the ProMS2 is transformer isolated from the direct 1 that carries the phantom power.
The idea was that if there is a difference between a channel with and without phantom power in terms of noise this test ought to show it. If I am making a mistake in my reasoning, feel free to let me know.
Mics tested: Shure KSM141 cardioid and omni, Rode NT5 omni capsule, Rode NT4 MJE-384K capsule, AT4081, Advanced Audio CM1084 (cardioid) in Bright and Vintage settings.
Result: I could not prove that there is any noise difference between the phantom and non-phantom channels. I did see on most mics a distinct hump around 100Hz on all mics except the AT4081. Perhaps due to environmental noise that the figure 8 ribbon blocks out.
Perhaps when one channel has phantom power all channels suffer the same amount of noise? Or none of the tested mics suffer from this problem, as I understand it varies from one mic to the next.
A second thing I tested was the suggestion that switching from low +15 to high -8 (for example) would make a difference in noise. Here I can say that yes, there is a noticeable difference. On most mics the dfference started around 1000Hz and widened to around 2~4 dB at 10KHz. So in a quiet section of the recording (me not saying anything in my quiet living room) the low +15 channel might be at -114 dB, the high -8 channel would be at -116dB at 10KHz.
The biggest difference was with the CM1084 in vintage setting, Low +20 and High -3. There the difference at 10Khz widened out to around 8dB.
Regards, Christine