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Leaving space above/below a power amp?

Discussion in 'Amps and Cabs [BG]' started by mgmadian, Feb 20, 2002.


  1. mgmadian

    mgmadian

    Feb 4, 2002
    Austin, TX
    Hi All,

    I've just picked a Kern pre-amp and am looking into various power amps to accompany it...I'll liley go with either a QSC PLX or a comparable PA amp (e.g. Mackie 1400i, Carvin).

    One minor but related issue is how best to rack the resultant combination. I've got a 4-space rack now, and would like to rack also my RNC compressor. So...4-spaces is enough if I completely fill the rack, i.e. no space free above the power amp...but would this fall into the category of baaaaaad ideas?

    Does a power amp like a QSC PLX need to have a spare space above it for proper cooling? If I jammed in the RNC (mounted on a universal rack shelf) directly above the power amp, then the Kerm pre-amp on top of that...am I likely to smell smoke if I ever push the amp to a reasonably loud level? FYI...I'll probably also run a pair of Acme cabs here...so the amp may get pushed somewhat hard. That said, I also play mainly gospel and RnB (no death-metal clubs...yet), but even in a decent-sized church the volume can get pretty loud.

    Thanks!

    Greg
     
  2. RAM

    RAM

    May 10, 2000
    Chicago, IL
    I don't think you'll have a problem. Most rack components other than amplifiers are not that deep. And, most amplifiers have their fans in the back, occasionally on the side, not on top. That way you really don't run the risk of covering up the fans and hindering the cooling effect.

    If you want to play it absolutely safe, there's nothing wrong with leaving a space. You can buy rack spacers that look like a vent, for just a few bucks.

    I just don't think you need to.
     
  3. chucko58

    chucko58

    Jan 17, 2002
    Silicon Valley, CA, USA
    I paid for all my gear myself. Well, me and MasterCard.
    I went with a 6-space rack in a situation like yours, mostly to leave room for a "power conditioner" (well, it turned out to be a glorified outlet strip) and future expansion, but also because power amps can generate strong magnetic fields as well as heat. I put the power amp at the bottom, the outlet strip just above it, the effects just above the outlet strip, and the preamp at the top of the rack.

    This is less of an issue with a PLX or similar lightweight amp with a switching power supply. But if you use one of those heavy amps with a line frequency transformer, you're better off to give it some distance from low-level electronics like preamps and compressors.
     
  4. mgood

    mgood

    Sep 29, 2001
    Levelland, Texas
    Cooling should not be a problem.

    One thing that might be of interest though is that sometimes other gear can get a hum in it if it is sitting too close to the power amp. The big power transformer can induce noise into the audio wiring in the other equipment. Not always, but sometimes. Leavin one or two spaces in between helps avoid this.

    Also, if you get a rack that's just big enough, I can almost promise that in the very near future you'll want to stick another piece of gear in there and won't have room.

    Do yourself a favor and get a rack a couple spaces bigger than what you think you need.
     
  5. QSC amps are rear-to-front cooling and require no spacing above or below. My SWR IOD preamp specifically requires spacing both above and below to vent the heat from the EL84 power tubes at the rear of the chassis.

    If you are running heavy gear, consider using two smaller racks. The plastic SKB racks are rated at 69 pounds maximum weight. I had to replace my 10RU rack with two 4RU so I can manage the weight unassisted. My QSC MX-3000a weighs 69 pounds by itself...