->AB, QSC, or Crest Amplifiers...which one is the best?
James:
AB really only makes one good product, the 1620, and it's one a heck of an
amp - around 1200wpc/8ohm.  I believe it's SRP is around $2100, making it
a good bit cheaper than it's competition.  I've had it side-by-side with
both QSC MX-a gear and Crown VZ stuff, and performed remarkably well in
that company.
QSC has always made good, reliable product.  The "number" series (1400,
1700, et.al) were tough (if heavy) amps that were sold with great
success in the 1980's.  If you find 'em used, they make great hi-mid
amps, and killer passive monitor amps - and they'll be cheap buys, to
boot.  QSC's original MX series was the successor to the "number"
series, and had a fair amount of low-end strength (for the late '80s),
but mediocre reliablity coupled with weak driver protection makes the
MX series a poor choice for your used equipment dollar.  The EX series,
which was the successor to the MX line, had wuss-poor low end when
compared to the closest pricepoint competition - Crown's Micro-tech
line, and quickly dissapeared from the market in the early '90s. Then,
finally, with the MX -a series, QSC had a winner. The MX -1500a is a
great 500wpch/4ohm amp, with plenty of low -end reserve, and run-for-days
2ohm ability.  Ditto for the MX-3000a, but at 1300wpch/4ohm.
If you're the one bearing the brunt of moving your amp rack in and out
of venues on a daily basis, QSC's latest venture, the Powerlight series,
is the best buys for your new equipment dollar. With all the light weight
of the traditionally bass-wimpy Carver products, and with the punch of
Crown's VZ gear, QSC is, as we speak, sweeping the professional audio
market with their Powerlight 1.8 (500wpch/4ohm/18#) and Powerlight 4.0
(2400wpch/2ohm/28#). But it's going to cost you a lot to lose that weight!
The PW amps SRP at nearly half again as much as the comparable MX-a
product.  A MX-1500a SRPs for around $1300US, the PW1.8 sits at $1800.
Actual street prices are around $750/1400, which means my money's on the
MX-a gear - until my back gives out!  
Last on your list, but certainly not least, is Crest.  If you can find
any used Crest product in your market, especially the x001 series (8001,
9001, 10001) - suck it up _quick_, if you can afford it.  The 8001 is
one awesome low-end amp, and sounds even better if you pay low dollar
for it.    However, you won't want to buy any new Crest gear - not
at their high prices, anyway.  Crest is more expensive than Crown, and
both of them are higher-priced than QSC's PW series, which performs as
well, if not better, than the competition.  Of course, there's something
psychological about a rack full of 8001's that just makes the low end
sound tighter... :-)
So, in short, if you're searching the used market for a big amp, seek
out a Crest 8001 or QSC MX-3000a (or a pair of MX-1500a's).  You won't be
dissapointed.  If you're shopping new, still consider the MX-a gear, and
don't forget to look at AB's 1620 - it's a cool piece of gear at a cooler
price.  If weight's an issue, the only way to go is with the Powerlight
stuff.  And lastly, if you're looking for smaller amps, consider QSC's
MX-a line, again.
Regards,
Tim ==
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