SVP-PRO hum?

Discussion in 'Amps and Cabs [BG]' started by allan grossman, Nov 7, 2002.

  1. I'm getting some 60 Hz hum from my SVP-PRO. This started happening the last time I moved the rack.

    If you unplug the bass from the preamp it still hums but if you unplug the preamp from the power amp the hum goes away. I've replaced preamp-power amp cables with known good ones and it didn't help?

    Any ideas?
  2. Hmmm.

    There is a QSC RMX2450 right under the preamp - that's got a pretty fair-sized power transformer.

    I don't understand why it started happening after I moved the rack to and from the studio. It was dead quiet and then when I hooked it up in the studio it started humming and has been doing it for about a week.
  3. submelodic


    Feb 7, 2002
    Seattle, WA
    I have the same problem. I replaced the tubes and also tried isolating the preamp from the rack but neither change made a difference.

    It's been suggested that a bad capacitor might be the problem. I'll probably end up taking it to a tech.
  4. ivanthetrble


    Sep 9, 2002
    I had an SVP-PRO and had the same problem. Tried changing the tubes, put rack isolators in and that didn't help either. It wasn't a horrible hum but annoying none the less. I never figured it out but when I made the switch to an SWR Grand Prix pre-amp the hum went away. I always wrote it off as a "tube" thing. :confused:

  5. The odd thing is it just started doing it a few weeks ago - I've had the amp for pretty close to a year.
  6. submelodic


    Feb 7, 2002
    Seattle, WA
    Well, electronic components can fail over time. It's definitely frustrating though. This is the second Ampeg product I've been dissatisfied with.
  7. I also noticed a hum developing with my SVP-pro, and it turned into straight up hiss (coming through when treble was up) after about a week. I took it to my amp tech and it had a whole bunch of bad solders in it, something common to the newer ampeg models he said. I had him go through and resolder everything he deemed shabby and it came back better than new, I highly suggest this.
    It only ran me about $30, I can solder but am no amp tech so I had him do it. I have read quite a few complaints about the Xlr output on these models giving people trouble and I would imagine it is because of the soldering.
  8. I just called Ampeg and found out there's an Ampeg-certified tech where I live :)

    The Ampeg dealer is one town over but the tech is here - so I'm gonna give him the whole damn rack and have him figure it out :D
  9. submelodic


    Feb 7, 2002
    Seattle, WA
    Like you, I keep the preamp in an SBK rack case with the power amp. Maybe the (even slight) shock of moving the rack caused the bad solder joints to weaken. That makes sense. Thanks for pointing that out, CzarMike.
  10. Fixed. Bad tube.

    I pulled the preamp out of the rack and replaced the tubes one at a time with a known good one. the 12AX7 in the #5 slot was causing the hum.

  11. seamus


    Feb 8, 2001
    Glad to hear the problem was remedied.
  12. Mine buzzed really bad when I got it. I took it to an authorized tech to have it fixed under warranty.

    Three of the tubes were bad.

    Now it only buzzes a little.
  13. It seems like alot of people have problems with buzzy SVP-Pros.

    Ampeg should wake up.
  14. 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.