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Fan noise on a QSC PLX-2402

Discussion in 'Amps and Cabs [BG]' started by mgmadian, May 16, 2002.

  1. mgmadian


    Feb 4, 2002
    Austin, TX
    I recently switched my rig to a Kern IP-777 powered by a QSC PLX-2402...great combination, with one lone complaint. In low-volume situations (e.g. when practicing alone in the studio) the noise of the QSC's fan is very noticeable and I'd love to either (temporarily) turn it off, or somehow minimize the noise (e.g. turning the fan down).

    Is this at all possible? Truth be told, it's not horribly loud, and it's probably not as loud as other power amps on the market...but it bugs me none the less. Anyone know if you can open up the amp and disconnect a jumper switch or something...or if doing so would ge HUGELY unadvisable? Any alternative solutions/recommendations (aside from saying "dude...don't worry about the dang fan noise...just be happy with the overall rig")?

  2. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Commercial User

    Jul 3, 2001
    Santa Ana, Calif.
    Former Technical Communications Developer, QSC Audio
    No, the fan needs to run, even at slow speed, to keep the components cool.
  3. FunkySpoo

    FunkySpoo Supporting Member

    Feb 6, 2002
    Hey Bob. I don't have a rack system but am seriously contemplating it. As far as power amps go QSC is at the top of my list. I've read lots of positive posts about your amps but the one and only complaint about them seems to be the fan noise. Now I haven't even started trying out amps yet so I haven't heard how loud it actually is. Having said that, is there any R&D going on at QSC for a quieter fan? Seems to me if the fan were quieter there would be nothing to complain about (wouldn't that be nice?). If there is some R&D going on make sure the older amps can be retrofitted. Just an idea.
  4. chucko58


    Jan 17, 2002
    Silicon Valley, CA, USA
    I paid for all my gear myself. Well, me and MasterCard.
    In trying to hush the computers at home, I've found that fan noise is often conducted from the fan to the surrounding sheet metal, which happily radiates it. This can be reduced by isolating its vibrations from the chassis. Rubber bushings, felt pads, etc. all help with this. Once you've dampened these sympathetic vibrations, all you should have left is the noise of the fan itself.

    Don't expect to gain much by replacing the fan. The quietest fans at a particular air flow rate are maybe 2-3 dB quieter max than cheaper fans. The ultra-quiet fans sold for cooling PCs flow much less air than the fans they replace. I would not risk reducing the airflow on a multi-kilowatt power amp!
  5. bben


    Feb 28, 2002
    Santa Fe, NM
    I tried all sorts of things to make the fan in my PLX 1602 quieter. (Before Bob Lee gets excited, let me say that I have been poking around in the innards of amps for years, know what I am doing, realize that I voided the warranty, and don't necessarily recommend that anyone else do the same!)

    The fan is a good-quality Panasonic, and if you take it out and run it off a power supply, it is very quiet. When you put it back in the amp, the amp acts as a sounding board and greatly increases the sound, so chucko is right on.

    At first, sitting on top of a speaker, the amp buzzed and rattled loudly in sympathy with the speaker. I used foam tape in the cabinet joints to stop them from buzzing, and pieces of eraser between the cabinet and the circuit board to shut it up. I also put silicone globs on the ceramic stand-offs for the output coils, since they buzzed, too.

    Then I was concerned with the fan noise in a quiet room, so I tried damping down the fan, the plastic shroud that it mounts to, and the cardboard shroud that contains the airflow, with a combination of silicone and moretight, but with limited success. The plastic shroud the fan mounts to presses up against the amp case, which transmits the noise.

    I bought a ProTec case and put the amp in it, and that helped some. And I turned the fan around so it sucks air from the front and pushes the air (and more of the noise) out the back. Finally, the combination of all these things have gotten the noise down to a level which is acceptable to me.
  6. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Commercial User

    Jul 3, 2001
    Santa Ana, Calif.
    Former Technical Communications Developer, QSC Audio
    Everything else was cool, Ben, but turning the fan around severely reduces its effectiveness in removing heat from the amp. Because the heat sinks will tend to be warmer, the fan will run faster, too, which will tend to make it louder.
  7. lneal


    Apr 12, 2002
    Lee County, Alabama
    I have noticed the fan noise on my PLX but not so much for its level as its unusual droning sound. Hey Bob, is that a brushless motor? If so that might explain it.
  8. If you disconnect the fan, be sure to get it on video tape...I wanna see this! :D
  9. VicDamone


    Jun 25, 2000
    Is there anything being done by QSC to minimize fan noise in future models or as a retrofit for existing products?

    I guess this isn't exactly a cable question which might explain the lack of response.
  10. bben


    Feb 28, 2002
    Santa Fe, NM
    Thanks, Bob, I was wondering about that. I will turn the fan back around again.

    Ineal, yeah, mine drones in the key of B, if I remember right.
  11. ganttbos

    ganttbos The Professor Gold Supporting Member

    Dec 18, 2001
    New Orleans area
    FWIW I compared my 2402 fan noise to my Crown Power Tech 3 - the 2402 is no louder (except that it's variable speed and may get a little louder if it's running hot.) So it's not like the QSC is noisy in comparison. Now my computer!!!:p
  12. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Commercial User

    Jul 3, 2001
    Santa Ana, Calif.
    Former Technical Communications Developer, QSC Audio
    We do try to minimize fan noise--that's why all our amps have variable-speed fan cooling--but first and foremost we also must make sure there's enough cooling, even at idle.

    Even less than a cable, a fan would not cause any deficiencies in response; perhaps you have some EQ settings that need tweaking.
  13. VicDamone


    Jun 25, 2000
    Bob Lee:

    I ment response from you, in a feeble sarcastic way. Please forgive me, I apologize for that remark.

    Vic, a contented QSC owner.
  14. Lumberg


    Nov 25, 2001
    at the risk of redunancy...

    I have been very interested in getting a QSC for quite some time, but am now having reservations because of the fan noise everybody is talking about.
    So my questions is, is the fan noise in the PLX's any louder than other fan-cooled amps?
  15. LowRanger


    Dec 24, 2000
    I sold my Eden WT-800 because the fan came on constantly, and sounded like a margarita stand when it did. I've since been using both a Mackie 1400 and QSC-PLX3002, and found the fan noise (in a "live" setting) for both to be negligible. And I'm pretty picky.

    I haven't tried recording/miking the setup, but would think that there are several techniques to mitigate fan noise if it was a problem.

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