So let me get this straight....
With my simple "rig" (see my signature), as long as I get adequate levels on the D7 (going line in), there is no reason to get a preamp, and I am actually better off without one?
So why do so many people typically run a preamp? Is it because most mics are not as sensitive as the AT's and do not provide a strong enough signal? Is there that much difference in the sensitivity of the various mics? In other words, I have the D7 on, say, 4 and I'm getting good levels at a particular show. I switch to some AKGs or ADKs or Studio Projects or whatever, add a phantom power box, and I can no longer get adequate line-in levels, even turing the D7 up? That's when the pre becomes a "necessary evil"?
Sorry for the stupid newbie questions!
An external pre-amp adds degrees of freedom. I.e. it gives you more choice in configuring
the recording chain.
The possibility of adjusting the signal levels (gain & attenuating pads) is only one of many features but admittedly
it might be the most important one especially with low-output mics.
The potential for using truly dedicated circuitry within the mic-pre, resulting in cleaner
sound, lower noise floor, deeper bass, less low end rolloff (phase delay) etc is there but
the purchase price of those mic-pres quickly get pretty dedicated too.
Then there are issues of transformer/non-transformer, solid state, tube, large geometry
discrete devices, no-global feedback, voltage feedback, current feedback etc etc ad infinitum...
The possibility of tailoring the sound with bass rolloff filters, high boost filters exist but now we start
to get into issues that are very mic dependent.
The next level would probably be to optimize the sound of a mic & mic-pre combo where the mic-pre
"compensates", "corrects" or "adds/subtracts" to the sound of the mic. A condensor mic is after all a highly complex
acoustic-mechanical-electrical transducer where the designer needs to wrestle with a slew of competing
issues. (Look at actually measured non-averaged frequency responces as a function of incident angle for a few
directional mics and you start to see why this topic contains way more surprices than any episode of temptation
island... )
Benefits:
The benefits of a mic-pre is self-evident if the levels need to be boosted
or the quality of the external mic-pre is such that the overall sonic result is improved.
An external mic-pre is also beneficial if the higher signal levels allow use of a cleaner, higher quality signal path
downstream (in the recorder all the way up to the ADC itself).
In consumer gear the mic-input is often a highly compromised port with little headroom,
poor linearity and scads of self-noise. On the other hand, if the line-input on the ADC is
of compromised quality then an external mic-pre will not be able to improve much on the overall
signal path because you can't wire around that weak link.
Drawbacks:
All else being _equal_ a mic-pre will add noise, coloration, bulk, power needs etc etc ... Some also present
rather low impedances to the mic bodies (or active heads) which then must work hard to drive the mic-pre
input.
To conclude:
The pre / no-pre issue really becomes an exercise in carefully evaluating the benefits of a mic-pre
up against the drawbacks. A mic-pre shouldn't be necessary if the mic is a perfect match to an already
existing high quality gain/line/buffer/ADC stage.
Regards
Jon