It all goes back to Dickie's comment:
dickiefunk wrote:To be honest the only hiss I get is when I crank the gain on the preamps of the QU-PAC.
... and his suggestion that he needed a more sensitive mic to deal with distant choirs etc.
As we have probably all experienced, some budget preamps do introduce a lot of noise at max gain. However, although I'm not familiar with the QU-PAC, as James says A&H certainly do know how to build high-quality preamps. Oddly, though, the spec sheet I found for it doesn't provide an EIN figure, just THD+N for 0 and 30dB of gain... Both of those figures are okay, but not high-end performance... And why no figure for the max 60dB gain? Odd...
The problem we have here, though, is that diagnosing these kinds of 'noise' issue remotely is very difficult.
Obviously, if extra gain is needed to compensate for distant mic placement (or low level sources) an inline gain-booster can be a very practical solution.
And if the preamp gets noisy at extreme gain settings it can help there too, by allowing a lower (and hopefully quieter) gain setting.
But if the issue is noise, and its coming from the source rather than the preamp -- either from the mic or the natural ambient acoustic -- then an in-line gain booster won't help. And we have been told it didn't help in this situation.
The only solution for a noisy mic is a quieter one... However, the AT4040 has a self-noise figure of 12dBA, and that is leaning on the noisy side for a large diaphragm capacitor mic. The best are typically around half that at 6 or 7dBA.
But it's easy to get lost in the specs... the reality is that 12dBA is very much on a par with the very best small-diaphragm capacitor mics, and probably 6dB quieter than most. The much-loved DPA 4011 has a self-noise figure of 18dBA, for example, and plenty of choirs have been recorded using that -- including by me -- without noise issues!
So, since the use of a high-quality in-line gain booster didn't improve the noise performance we can probably assume the problem is not at the preamp. And, since the mic is no noisier than many often-used alternatives we can probably assume the problem isn't really the mic either...
Which only really leaves acoustic noise as being the real problem here...