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SVP-Pro crackling

Discussion in 'Amps and Cabs [BG]' started by morebass!, May 29, 2003.

  1. morebass!

    morebass! I'm all ears Supporting Member

    May 31, 2002
    Madison WI
    My SVP-Pro preamp suddenly developed a crackle! I checked the bass, the cords, and the cabinet and they are all fine. It must be either the Ampeg or the power amp (my venerable Crest). It seems to happen only when I'm playing and it is intermittant. Is this a loose tube? I bought it used about a year ago and haven't changed the tubes but have a set. Any ideas?
  2. Chuck M

    Chuck M Supporting Member

    May 2, 2000
    San Antonio, Texas
    It could be a tube not making good connection in the socket but it is more likely a tube going bad.

    Disconnect the SVP from the power amp and 110V. Remove the top from the SVP. Reconnect it and turn it on. Use a plastic pen to gently tap on the tubes one at a time and you'll probably find that you hear the noise when tapping on the tube that has gone bad.

    Be sure to use a nonconductive plastic pen or something similar to tap on the tubes. There are dangerous voltages inside the preamp.

  3. As an SVP owner, I can help.

    Take the svp out of the rack. Does it still crackle?

    If so, unscrew the top. By now the crackle should be gone.

    Close the top, but don't screw it on tight.

    place in rack, and see if adjusting the rack screws makes it start or stop happening.

    I just twist the rack screws until it goes away. If i were to tighten them fully, mine would have this same problem.

    Keep a screwdriver with you when you play just in case it comes back.
  4. NJL


    Apr 12, 2002
    San Antonio
    i am experienced with this as well.

    it was in the shop for a month (warranty) - those guys didn't have the slightest clue!

    you guys think it's pressure on the tubes? or the face?

    please let us know, this would be a great help on this issue.

    BTW, morebass!, do a search for svp-pro crackle, there is one more thread on this issue, but let's keep this one going.

    the crackle on mine is so bad i can't stack it on the cab. sometimes when i turn it on, the peak light blinks on its own, even if you don't touch the pre-amp, it still makes very loud crackles!!!

    ampeg needs to fix this crap!!
  5. Flight Time

    Flight Time

    Aug 29, 2002
    Mine did the same thing. If you have your rack on top of your cabinet, try putting a layer of foam between your rack and cab. Foam insulation about an 1-1/4" thick worked for me.
  6. NJL


    Apr 12, 2002
    San Antonio
    the foam is and has been a great idea. i've read about that one before (i think you were the one who posted). where do you get the foam?

    also, can you guys elaborate on the pressure on the tubes and face plate, pleeeeeeeeeeeese?

  7. It's something to do with pressures, but i'm not sure what...
  8. NJL


    Apr 12, 2002
    San Antonio
    :rolleyes: :D ;) Duh!!!

    is this a surefire way to get rid of the crackling on your pre?

    i actually tried this on my pre (took out of rack and took the top off) but it would still do make the crackling. so i decided to leave the dam thing on over night.

    the next day, the crackle was very small.

    i wonder if the crackle goes through the DI out as well or just in the 1/4" outs?
  9. Josh Curry

    Josh Curry

    May 29, 2003
    Frisco, TX
    I just recently bought a SVT-5 Pro and had a similar thing happen, I don't know if this is exactly what your is doing, but, I noticed that the input was clipping, my bass has really hot pickups, so I used the -15db cut switch and problem solved. I had to turn the gain up to get a good level, but I havent seen that crackling problem again. Mine was a very violent crackling, something that you know would damage the speaker if not fixed. Hope this helps.
  10. I would guess it does go out the di outs as well, although I havn't tried. my fix is just adjusting the rack screws until it goes away. Mine has been crackle-free for a long time, but all it takes is a twist of the screw to bring it back.
  11. Flight Time

    Flight Time

    Aug 29, 2002
    Home Depot or any other hardware store would have it. I bought mine at ACE Hardware.
  12. NJL


    Apr 12, 2002
    San Antonio
    really??? that is too cool - i'm going to try your method tonight!!

    i really hope it works on mine
  13. Fuzzbass

    Fuzzbass P5 with overdrive Gold Supporting Member

    FWIW: my SVT3Pro had intermittent crackling from the get go. Not louder than my playing, not loud enough to cause speaker damage, but still annoying. I tried the 24-hour burn-in trick (leaving the unit on 36 hours, actually) and now the crackling is very rare and very mild when it does occur. Saved me the cost of new tubes (for the time being anyway). No guarantee that it'll work for you, but it's worth a try...
  14. morebass!

    morebass! I'm all ears Supporting Member

    May 31, 2002
    Madison WI
    Thanks everybody. This is a great site. Sounds like this is a common problem. My ampeg is not new so I don't think the 36-hour burn-in will work. However I like the tube tapping and foam suggestions and maybe the screw loosening idea. I have a mousepad that might work for foam - nice dense, sturdy, compact foam. I'll try these things and report back to the group.
  15. sleazylenny


    Jun 20, 2002
    Mpls, MN
    To those who do a lot of gigs, it could be just road wear. I have an SVT pro 3 and after weeding out all other possibilities, brought mine into the shop. Turns out that it had quite a few "cold" solder joints. Does the crackling or loss of signal happen after you've had the amp fired up for a while or right away? If it happens after you've been running your rig for a bit, it's probably a cold joint. The amp heats up, warms the thin area of the solder, which in turn compromises the connection. Next show comes along and the problem is gone, UNTIL the amp heats up again. I had about five of them in mine. I also had a bad tube socket that had cracked loose. Remember, all that time your amp travels in the trunk of your car or in a trailer, it's vibrating and being bumped around. If you live in a cold weather area ( I'm in Minnesota), it compounds the problem.

    If it's still under warranty, bring it in and get it checked out now. Those problems can be expensive when they come out of your own pocket.

    Good luck
  16. NJL


    Apr 12, 2002
    San Antonio
    here's my report from last night:

    i turned on the pre, still doing the loud crackling.

    i did notice that after i turned up the drive all the way (that's the gain for the 12au7) that the crackling did go away for the most part.

    i turned it off and watched my San Antonio Spurs win. turned it back on and and the crackling was back. so i started to get ready for sleepy time (about 30 mins) came back the the crackling was go for the most part, again. maybe the issue is that you have to have the dam thing on for a while before you turn up your power amp?

    BTW, this was done out of the rack and with the top off.

    i did try tapping the tubes with a pen, but tapping anywhere on the pre (including the case) seemed to trigger some crackling.

    anyone try anything last night?

    morebass!, yes your are correct, this site does rock! :)
  17. NJL


    Apr 12, 2002
    San Antonio
    i have heard that the solder joints with ampeg are lame. thank for the post.

    when i took mine in for warranty, the music store didn't even look at the solder joints.

    its to the point to where i'm going to fight for instore credit back and go for a demeter or aggie, but i must admit, the ampeg, when it works, it does have the sound that i'm looking for.

    i'm fairly sure that i'm going to call ampeg today and bitch.

    i will my fellow talkbassers updated.

    ta ta :bassist:
  18. jobu3

    jobu3 Artist formerly known as Big Joe

    Feb 17, 2002
    Mountain Top, PA
    sounds like you got yourself some microphonic tubes there... a call to lord valve may be in order here! :cool:
  19. jobu3

    jobu3 Artist formerly known as Big Joe

    Feb 17, 2002
    Mountain Top, PA
    try to isolate it to the tube (or tubes) if you can... switching out the culprit tube will be cheaper and make you more certain that it is a tube and not something else (i do think it's tubes though). i got mine new for a steal and was able to swap all five out and still pay less than what MF asks new and i think it sounds awesome!
  20. morebass!

    morebass! I'm all ears Supporting Member

    May 31, 2002
    Madison WI
    ...so I took off the top and tapped the tubes with a pencil and, well, some of the tubes seemed to make a slight crackle when tapped but nothing like what I had heard while playing. I didn't have time to replace and test each tube separately so I slapped a spare set of Sovtek tubes in and put it together (not tightening all the screws all the way. I put it back in the rack and played it for 3 hours at a gig without one crackle. Was it the new tubes? Can't really tell from what I did. It could have been the looser screws. I'm relieved that it doesn't seem to be a bad solder joint. Overall I'm happy that it's fixed but a little disappointed. I like my equipment to be reliable and not expensive to maintain. This unit seems to be from '96 (the number on the inside had a "96" in it. I guess I'm okay with it seeing as how I bought it used, I like the tone, and it seems to be working okay now. I definitely need a backup though because the crackling I had was not tolerable. Again, thanks for all those who gave advice.