Tom Ball is one of the top acoustic harmonica players working today, as visitors to our Pro Pages know well. Tom posted this message to the Harp-L list recently; it’s re-posted here with Tom’s permission. (Don’t ask what we had to do to get it . . .) If you want a clean sound off a PA, here’s yer Bible.
Regarding the search for a "clean sound":
I agree that the best option is a good vocal mic played (from about 6 inches away) through the PA (not through an amp.) In general, you may have to goose the EQ on your PA so that you have a little more bottom, a little less top, and some reverb.
I’ve found that if I’m feeding back I’m probably playing too close to the mic, or the PA’s simply too loud. If I’m 6 inches away from the mic and still feeding back, it’s time to experiment with
the speaker placement and/or turn down (or reposition) the monitor(s.)
Here’s another couple of mic options:
1. If your PA accepts high impedence phone jacks, then rather than using a low impedence Shure (like a 57 or 58,) you might try to locate a Shure SM-54. Believe it or not, these are excellent mics! They don’t make them anymore, but used ones pop up pretty regularly in stores and on eBay. I used one of these in performance for over 22 years before finally upgrading just a few months ago, and I still use it for noisy gigs. They are workhorses. As you can imagine, over the course of 22 years of gigging it’s been dropped, run over, spat upon, fallen in snow, filled with dirt, soaked with beer, and generally tortured in all manner of inhumane ways, yet it keeps on ticking… sounds fine, too. In addition I have the habit of turning it off and then on again after every song, so that I can talk to Kenny… (Hmmm… let’s see… 3,500 gigs, times maybe 30 songs per gig, means that I’ve flipped that off/on switch over 200,000 times and it ain’t broke yet.)
2. What I finally upgraded to is an AKG C535EB. A bit pricey (lists at about $370 but can be had WAY cheaper.) Outstanding; used as a vocal mic by both K.D. Lang and Sting amongst others. Very happy with it in almost every respect loud, crystal clear, excellent sounding and never seems to feed back. Great frequency response! But (and this is a big but) it’s a condenser mic requiring phantom-power, which means there’s no off/on switch; and you can’t install an off/on switch because it would make a very loud snap noise every time it was turned off and on, due to there being an actual flow of power through the line. S0… since it’s "on" all the time, and since it is very omnidirectional, it picks up all kinds of ambient noise crowd noise, belching, motorcycles driving by, Kenny and I discussing the girl in the third row, etc. Means that I can’t use it at noisy gigs, but it works just beautifully at quiet concerts. And it’s also a superb vocal mic, a very good recording mic, as well as the best sounding acoustic guitar mic I’ve heard (outside of Neumanns or some other $2000+ tube mics.)