We managed a classic last year. It was the third or fourth gig with Jenny, we opened as a a five piece (four now, we cut a guitarist) for the first set, then Jen came on to front the second. We started her set with 'White Rabbit'. Now this was in my local pub, 200 yards from my house, full of people from my village I drink with nearly every day...and who have had to put up with me going on about how great our new singer is etc etc.
So expectations are high, and reputations in the balance (mostly mine). Bass, drums and guitar play the intro, she steps up to the mic and gives it everything....the audience look unimpressed, some of my friends are shouting to turn her up, so one of the band ups her mic level on the PA, not enough, they want more...they can hear her as she reaches the crescendo, but it's not enough. Harp player/PA man returns to stage and casually mentions that he turned the power amps off during the break (never done that before or since) so Jenny was doing her best to make herself heard unamplified over the full band thumping away behind her.
No further complaints about her volume once the amps were back on. And her voice is so powerful that we didn't realise she had no amplification as she sounded fine to us!