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Ampeg SVP-Pro+QSC 1450 problems

Discussion in 'Amps and Cabs [BG]' started by SoyBase, Dec 2, 2001.


  1. SoyBase

    SoyBase

    Jul 1, 2001
    Atlanta, Ga
    Hello all,
    I've got a new SVP-Pro Preamp and a new QSC RMX1450 power amp combo. It all sounds great, but it hums through my mesa cab like crazy . I sent the first pre back to Bass Central thinking it was defective. Got the new one and still a hum, so I go and replace the power amp. Still humming. Im using the 1/4 outs on the pre directly into the power amp. I've tried using it bridged and in stereo with the same results. I tried a different pre and had no hum at all, so the power amp is fine. Is it possible that the second pre is also defective or could it be an impedance issue between the amp and pre? Is anyone else using an Ampeg/QSC setup with the similar symptoms? Any advice?
    Thanks
    Tommy
     
  2. Use the DI out of the SVP into the XLR connectors of the QSC.

    The 1/4" is unbalanced and subject to hum. The XLR connections are fully balanced and hum free.
     
  3. SoyBase

    SoyBase

    Jul 1, 2001
    Atlanta, Ga
    Well, I tried that too and no luck. The XLR's get rid of the hum, but I get less than 1/4 output volume this route. I may need to take the power amp back and try a different brand?

    Thanks
    Tommy


    by the way, Bass Central has been EXCELLENT with my purchase of the pre and all my questions, no matter how dumb. Thanks again Gard!
     
  4. FalsehoodBass

    FalsehoodBass

    Jul 22, 2001
    Denver, CO
    i had the same problem with mine right out of the box... i had to take it to an amp shop to get it fixed. Here's what you do... turn the master on the preamp ALL THE WAY up.. and use the volume on the QSC to regulate your level.... if it's not a problem with your preamp.. that's how to minimize the hum... if the preamp hums regardless of the master volume level. .you have the same problem i did or something similar, and you need to take it to a repair place to get it fixed..

    the good news... its still under warranty, so you shouldn't have to pay for it, right?
     
  5. SoyBase

    SoyBase

    Jul 1, 2001
    Atlanta, Ga
    Well, I tried that as well. still hums..even with the master turned all the way down it hums. I dont think its the pre because this is the second one that did this. I can fiddle with the gains on the amp and find a setting that reduces hum, but also isnt as loud as I need to be. What was the problem with your pre, Falsehoodbass? Since it is brand new, I may be able to return it and buy a tube amp like i've always wanted..:D
     
  6. FalsehoodBass

    FalsehoodBass

    Jul 22, 2001
    Denver, CO
    on my pre, the amp tech replaced a preamp tube and replaced an opened (fried) resistor. The problem you're describing sounds exactly like the same one i had... my guess is that the tube got damaged in shipping, which caused the resistor to fry... but i haven't had a problem since i got it fixed. Unplug your preamp from your poweramp, and then mess with your poweramp volume... if it only hums when the pre is plugged in... i say there's your problem...
    It's a great pre.... i hope you can get yours working, or find a suitable replacement..

    Goodluck
    FHB
     
  7. SoyBase

    SoyBase

    Jul 1, 2001
    Atlanta, Ga
    Thanks falsehood. I cant believe this is the second one to do that. The power amp works great without the pre connected, and with other pre's connected it works like a champ. I'm going to plug in to an old Hartke head I have at the rehearsal studio and see if it hums on that one, if it does, hopefully Bass Central will return it so I can buy a Mesa 400+!
    Thanks
    Tommy
     
  8. FalsehoodBass

    FalsehoodBass

    Jul 22, 2001
    Denver, CO
    yea... that's kinda odd that you had 2 in a row with the same problem that I had.... i'm fairly confident with my preamp as it is now... but you have to question the integrity of the equipment if it isn't its best right out of the box.

    Since you just bought it, you can get it fixed for free. As long as you have your reciept it's under warranty. You shouldn't really have a problem returning it either though if you're just over it.

    Goodluck with the 400+ It's not worth the hassle of 12 poweramp tubes to me... but it'll get you some killer sound. post a review when you get it..
     
  9. SoyBase

    SoyBase

    Jul 1, 2001
    Atlanta, Ga
    Well, i sent the pre back to the store today..Ordered my 400+ and should have it for my gig on Friday. I wasnt going to hassle with the tubes and weight of that bad boy but the sound was just too good. Its like pure, creamy butter. I think i did well, 1000 bucks for a brand new unit. They sell at GC for 1300+ Looks like my rack is going to get some wheels this week to save my poor back!
    Thanks
    Tommy
     
  10. lo-end

    lo-end

    Jun 15, 2001
    PA
    The 400+ is a very good choice! :)

    Good luck with your new head!
     
  11. ibanezroadster

    ibanezroadster

    Apr 9, 2012
    The problem everyone is discussing is with out a doubt a earth problem. What the issue is a potential difference in your earth between the preamp and the power amp. What verified this to me was the guys who use the di output don't suffer from this hum. This because there is a isolating transformer between them and the signal. All you need to fix the issue is to purchase a good quality. and lots of car audio stores stock them. A good Earth loop isolator and use this between the preamp and the power amp. Problem solved.
     
  12. AlexanderB

    AlexanderB

    Feb 25, 2007
    Sweden
    There is a chance the issue was solved in the 12 years that have passed...
     
  13. WretchedExcess

    WretchedExcess

    Jul 29, 2013
    Ha! Good point!

    Or maybe there's the possibility that people who mount their gear in racks continue to suffer from ground loop hum, and live with it because they don't know how to eliminate it.

    It's very easy to find rack screws that ground all of the components to each other through the rack. Not so easy to find proper insulating / shoulder washers.
     
  14. B-string

    B-string Supporting Member

    Adding something between two units is not problem solving IMHO, it is working around a problem.
     
  15. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    They're called "HumFrees" and are available from online music sources. I use them as standard when racking equipment.
     
  16. walterw

    walterw Supportive Fender Gold Supporting Member Commercial User

    Feb 20, 2009
    alpha-music.com
    ha!

    i was wondering where this guy was ordering new boogie 400+ amps from!

    (the right answer probably was a trivial ground loop problem, as opposed to amp after amp ordered and sent back.)