Thats when i was told i could do this by my better half...LOL
Sorry if i seem pig headed about this, but i did state that the 504 WILL drive the M80's...to be honest, the volume may be fine for some people..just not me. Plus i find nothing wrong with the M80's at all..they don't come across as a bright speaker, at least to me.

The 504 has been used HARD for 25 years easy. To think anything in the amp is up to spec..probably not close at all at this point. But it will go upstairs and just drive the Advents or Polks at lower volumes. Which it dose fine.

The QSC was designed to handle 4 ohm loads. It's not a bad amp at all and should work fine with the M80's. I just have to sit here and wait.

i think i told you some time ago, but i'm not sure:

i have not heard any difference in sound between my QSC and my Hafler; this is how it should be generally if amps are not overdriven.
the only con in the QSC is the fan; you might hear it or you might not. i hear mine a bit, when the sound is of very low volume.

if you ever want to change the fan, i can tell you which one to get, but don't forget that the change might (might) void the warranty.
so far, watching movies that play quite loud, the air exiting the amp is usually about 3-5C. higher than when the amp is idling.

if you're in the U.S.A., you can extend the free warranty to a total of 6 years, though i haven't checked lately if it is still offered.

Thanks J...Yes you did say that, about the Hafler. The fan noise, i will never hear. I never play anything at that low a volume, unless it's really to much for low passages on classical.
But the system is sitting at least 10 feet away also...so unless this is really loud..don't see a problem.

Not sure about the QSC, but don't some pro-amps use either a two stage fan, or a fan that only activates when certain temps are reached? could have sworn I've seen some like that somewhere.

Who was it that runs the QSC from our forum, the name has escaped me?

I believe he removed the fan or installed a thermal switch to keep the fan off till it is really required.

Charles(Zimm) had a QSC(GX3?), but I don't know if he swapped the fan out or not.

Re: pro amps:

it all depends on the make and model of amp.
some don't start unless the temp goes high enough;
some have only 1 speed;
some have stepped speeds;
some have continuously variable speeds.
some are louder than others and, by extension,
some are quieter than others... ;-)

My Hafler has a 3 speed fan; always on low speed
unless temps get too high.
the only times the fan was at the highest speed was when i connected 2 electric bulbs on the outputs and fed them with 60 Hz sine waves.

Again thanks J for the info. I don't remember the QSC stuff being that loud, fan wise...but you never know. It should be here sometime next week. If it is too loud, would love to know what you recomend as a fan. By the way, were do you set your volume controls on this? I could always set them full on, as the volume is controled by the preamp any way, but i figure, set them at the 3 o'clock position, should be way more then i need.

These are what I use and have two of them.www.hometheatercooling.com/

My computer fans are WAY louder than these, I can barely hear them when it is dead quiet.

quote bobt: "By the way, were do you set your volume controls on this?"

what is recommended by Bob Lee, engineer at QSC is that you set everything in the signal chain to the max volume that will ever be used as long as this will not drive any piece of equipment into clipping.
then, you set the amp sensitivity (gain) according to the max SPL level you want to get out of your system.

this ensures that you will have the best S/N ratio all along the signal chain.

on my system, the only piece of equipment that can be adjusted for level is the preamp.
i set the preamp vol. at 12 noon and the amp gain at -12 db.

-12 db was chosen for the fact that at that gain level on the amp, most of what i watch or play on my system at a preamp vol. level of 12 noon is just about the right volume. Some i have to play less loud and some i must increase the vol. level.

if i was to use the amp at max sensitivity, then i would have to back up the preamp volume too much and then the vol. control would be too sensitive to small adjustments, because i adjust volume for music or movies to within one tenth of a dB, very small adjustments, and doing this at the bottom of the range would be very difficult. it's difficult enough when it's at noon position.
my preamp is analog, no precise digital steps as on modern pre/pros; and at the lower vol. positions, the scale is more compressed than at high vol. positions. example: one notch difference at the top of the scale will make a difference of about 1 dB;
one notch difference at the lower end of the scale will make difference of about 3 or 4 dB.
not very useful...

i would recommend that you first set the amp's sensitivity control to -10 dB and do a system calibration. after that, adjust as necessary.

hope i made this clear and easy to understand. :-)

i can't find the info about the fan, will look for it and come back later.

fan for the QSX GX series can be had here:http://search.digikey.com/scripts/DkSearch/dksus.dll?lang=en&site=CA&KeyWords=P9739-nd&x=24&y=15

noise level is around 21 dB. :-)
also, the fan's voltage is the same as the original.

people who have installed it say they don't hear anything.

J thanks again for the info. The amp should be here on Tuesday.
I'll see if i can hear the fan. I do sit 10 feet away, so it may or may not, show up on quiet passages. I'll start the QSC off at -12db and see were that puts my Preamp volume. The QSC has way more power then i need, but more power is always better then not enough.