"Mike McKelvy" wrote in message
ups.com
Cal:

Take a look at the specs for just one class of the QSC line.

They are quite clearly capable of delivering clean undistored power.

Note that they give 2 specs for THD one for the whole frequency range
and one for 1kHz.

http://www.qscaudio.com/products/amps/cx/cx2/cx2.htm

QSC specs are IME very conservative. I've only had the QSC amps I own on the
test bench, but in addition to sounding good, they also measure quite
nicely. For example, the front panel clipping indicator comes on some place
around 0.01% THD.

Cal's comments about junction temps in convection-cooled QSC amps are
completely off the wall. My USA 400 convection-cooled amp's heat sinks don't
run exceptionally warm at all. It turns out that the USA-400 and USA-850s
are packaged in the same case. The heat sinks are about the same size, just
a lot more output transistors and a bigger power supply along with a fairly
quiet 2-speed line-voltage operated fan in the approximately 3x powered 850.
If the fan goes into high speed it's a bit audible. However, I've never seen
that happen except on the test bench while grinding out more than half a
kilowatt.

There's a well-known audiophile in the Chicago area that uses a USA-1250 I
believe it is, to power portions of his floor-to-ceiling ribbon-based
systems. The amp is mounted in a cabinet with the rest of his components,
centered between the speakers. Not a chance of hearing the fan whether
there's music playing or not.

I've had a Pro-grade power amp with a noisy fan, namely my Mackie M1200. In
the interest of truth, I'll admit that it was not a wise choice. Besides the
noisy fan, it suffered from the well-known Mackie ribbon cable problem,
which resulted in one channel that came and went. Before the ribbon cable
problems it was a great sounding amp if you kept it out of earshot.