Todd R, when the inputs to a mike preamp overload but the microphones themselves aren't near their own overload point, switching the preamp to line levels is often a poor alternative from a signal-to-noise standpoint. Sometimes you would get better results with in-line resistive attenuators at the inputs of the preamp, leaving the preamp set for "mike in."
This varies case by case and should be worked out by actual measurement--but if for example you are only overloading the preamp by, say 6 - 8 dB on peaks, then a 12 dB pad will fix that problem. The mike-to-line stage may amplify signals by (say) 40 dB--and if so, should you take that gain out of the picture by using line inputs, suddenly you'll need to make up that gain somewhere after the line input which your mikes are now underdriving by more than 30 dB. So you're amplifying a noisy signal, and boosting that noise along with the signal.
If the extent of the overload is more severe--if it's 20 or 30 dB, for example--then it gets silly to pad the microphone signal down so far just so that you can boost it up again. And in that situation, all other things being equal there would also be less of a noise penalty for using the line inputs as you suggest.
For any pair of microphones and any pair of microphone inputs, if you know the sensitivity of the mikes in mV/Pa and the overload point of the inputs in mV, you can determine the sound pressure level that would cause those mikes to overload those inputs. And if you know the maximum SPL for the microphones, you will then know whether that sound pressure level is within the range that those microphones can handle or not. That's important information to have for any microphone/preamp or microphone/recorder combination.
For example, with a few simple measurements and a bit of listening through headphones for distortion on steady tones (which is very easy to hear), I determined that no matter how loud a sound may be that I'm trying to record, my Schoeps microphones simply cannot overload the inputs of my Lunatec V3 preamp as long as my levels are set properly in the first place (not quite reaching 0 dBFS on the loudest peaks). It's one thing that I never have to worry about, and I'm grateful for it.
With other recorders or preamps, and/or other microphones, though, that wouldn't always be the case. If I was going to record with a setup that could have this problem, I would sure as hell keep a pair of in-line pads in my kit bag--and with some combinations of microphones, expected sound pressure levels and recorders or preamps, I would plug them in "pre-emptively."
--best regards
Topic: Serv4U XLR248HD phantom/pre (Burr Brown) - Beachtek DIY knockoff? (Read 5926 times)