Would this be a good deal...QSC amp

[BIG BLUE2]

Hello,

It's been a long time since I've posted here. I have a set of Kg4's and I am considering buing and hooking up to a QSC amp. I have a Yamaha pre amp that I can use. Mainly I use this for parties and the kids using this in the basement to kick out the jams.

Here is my question. I have an opportunity to buy a QSC MX 1500 amp for $200 used. This is the older version not the 1500a. This is a very lightly used piece as I know the guy who was using it as a slave amp for a few gigs with his guitar rig. At 500w into 4 ohm I'm thinking this would fair nicely with the Kg4's. I also have a pair of Cornwall II's (circa 1985)...I wonder how it would sound with those....Hmmm.

Any advice on the price and or mating with the Kg4's would be much appreciated.

Thanks,

Big Blue2

[Arky]

I have never heard kg4's. I own a QSC plx 2402 & it sounds very nice with my cornwalls & cornscalas.

[stereohermit]

I used to use quite a few of those 1500's back in the '90's. The original version had separate power supplies, and was rated for 2 ohms.They cut costs and weight with the 1500a. They shared the transformer. Please bear in mind that the output drvices are no longer made for that amp, so if you blow one, you'll have to put in all Motorola MJ15024's and 5025's ...and there are 12 outpits per channel. Same as early Adcom amps, it uses Toshiba 555, 424 compliment. The QSC is capacitor coupled, so the frequency extremes can be a little soft. Running bypasses across the cap banks can help quite a bit. I had great reliability with the ones I had in the field,... dont remember a single blowup. The price seems fair, although its amazing what yiou can buy for the money, these days!

[djk]

The QSC MX1500 has a DC coupled output, there is an electrolytic cap in the feedback loop around the opamp.

Putting a small 0.1µF film bypass on the cap in the feedback loop will make the amp a lot clearer and cleaner sounding.

Putting mid-value bypass caps (22µF~100µF) on the main power supply caps will make the bass sound tighter.

http://www.qsc.com/support/library/schems/Discontinued/MX%20Series/MX1500.pdf

The outputs are in groups of three, a total of twelve per channel. If one of the three are blown then all three in that group should be replaced. QSC now uses the On Semiconductor MJ21193/94.

This amplifier has enough power to launch a pair of KG4 into low earth orbit, I would fuse them with a 2A fast-blow type fuse.

[BIG BLUE2]

Hi Guys,

Thanks for all of the feedback. I figure at this price it's not a bad deal, but I will be certain to check and see if my friend has had any "repair" work or any mods done to the amp.

I like the idea of adding a 2A fast-blow type fuse, but do not know how to go about doing this type of mod. Any instructions you can point me to?

I appreciate the help.

BIG BLUE2

[dollar bill]

I have two of the original QSC 1500's running bridged to power a system with two 15" bass cabs, two 12" with HF horns and sometimes a pair of Yorkville "Sibilance Projector" super tweeters as well.

The one QSC 1500 running in stereo is enough to run this system, but liked having the extra headroom.

Only issue I had with the QSC's is one flakey input jack and fans needing to be cleaned/re-lubed after years of hard use.They do have a hard clip/thermal protection, but that would never be a issue in your case.

I also have a pair of Kg 4's and 50 watts a side with a old "Black Jap" Rotel RX-602 was more than enough to take 'em full tilt at noon and not over drive them.

Mind you, this system is in a smaller room and as soon as I finish getting my Sansui AU 20000 tweaked, I'll be trying 170 watts a side, but doubt that I'll ever run them that hard.

The QSC 1500 would be more at home with some LaSala's, but even then is more power than you need.

But for $200 or less, grab it now and you may get better use/application later.