Svp-Pro hum issue

Discussion in 'Amps and Cabs [BG]' started by groovecat, Feb 20, 2005.

  1. groovecat


    Jan 5, 2002
    In the past, I read posts of quite a few guys having a hum issue with their Svp-pro. Some said tubes, others said tubes didn't work. I have one that has the hum problem.I changed the tubes and it made no difference. It even hum's when the preamp is shut off. Could some of you guys let me know how you solved your problem? I would really appreciate it. I'm thinking mine needs a good service tech. Geo
  2. I just bought one the other night that did this....

    My first problem is that I tried to run the output to a regular bass amp....this will not work. The output on the SVP-Pro is enough to run a regular bass cab. If you have to do it this way, run it into the effects return and bypass your bass amps preamp. This worked wonders Friday night in eliminating buzz and hum. Second, if you have a cab with a tweeter, turn the tweeter off. My Ampeg cab has such a sensitive tweeter, that when it is full on, it drives me up a wall! Now it has always done this regardless of the amp I used, but was worse with the preamp.

    I use mine primarily in church, so I need it to be dead quiet. I found that the DI is nice an quiet. Works great with no noise at all.

    So give this a shot....hook it straight up to a QSC power amp and a cab, and try that....I think you will be happy then...

  3. notanaggie

    notanaggie Guest

    Sep 30, 2003
    That might be your first clue that what you have is NOT RELATED to the preamp itself. It is a system issue.

    If power is shut off, then no amount of tubes etc can fix it. It isn't an electronic problem.

    It sounds like a "pin 1" problem (shield grounding issue) with the unit that you are plugging into.

    It could even be a bad cable.

    Can you explain what you are using it with? Cable types, equipment type, what input you used, etc.
  4. groovecat


    Jan 5, 2002
    I am using a 1.5' instrument cable to input it to the power amp in on an ampeg b2 combo. This does shut off the b2's preamp and runs it directly into the b2's power amp. I tried 3 different instr. cables and they all do the same thing. I am waiting for my power amp to come in and I wanted to try the pre amp.I don't really know what is causing the objectionable hum. Any ideas? thanks for the help, Geo
  5. Try out the system in another building. Sounds like you may have a grounding issue there. Make sure there are no lights on dimmer switches nearby, and no computers or TVs....
  6. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    Grounding does sound like the issue. Sounds like an extra ground current is flowing in the cable shield.

    The power switch turns the unit completely off, no circuits have power. So there is nothing active in the pre to make a buzz.

    When connecting ANY equipment with unbalanced lines, both power cords should be plugged into same outlet strip. Different outpets may create ground currents, which flow through the cable shield and insert noise in the signal path.

    There also may be a difference in noise depending on exact position of the signal cables relative to the equipment. Move them around.

    BUT, DON"T remove the grounding pin on the plug. It's there for a reason, which is safety. Leave it in place and solve the problem another way.

    Unbalanced connections on any equipment are sensitive to externally induced hum and noise. Might come from a power transformer on the equipment, or some ground current in the building, etc.

    Basically, that is why balanced lines were invented. But they are not the standard for typical instrument amps, so we have to deal with it.

    System hum is often odd, even in simple systems. I have even seen hum induced from putting a preamp over a big power amp. The transformer in the power amp induced hum directly into the preamp circuits, again with or without power to the preamp.
  7. groovecat


    Jan 5, 2002
    Guys, thanks for taking the time to help me out. I will try a few of your ideas to see if I can shake the hum. Nothing like bass players for helping their playing brothers,
    Muchas Gracias Geo
  8. inazone


    Apr 20, 2003
    I had a new svp-pro and the hum was huge. I tried new tubs and lots of gear and couldnt get it to go away. I took it back and got the svp-cl and problem solved. The way i take it, some of the svp-pros hum more than others. Good luck.
  9. groovecat


    Jan 5, 2002
    Guys, It worked!!! I did have the preamp plugged into a different outlet. I plugged into the same as the amp and it took away 95% or more of the hum. Simple minds, simple matter. I'd like to thank everyone who helped out with this, special thanks to Scott and master Jerrold.Guys like all of you make this the great site it is. One happy bassman, Geo
  10. Got to give credit where it is due....Lord Valve helped me with my problem in the middle of the night last week, so he should get the credit. Make is easy on yourself now that you have a rack. Go buy a Ferman power conditioner for $39 and plug everything into that. It looks nice in the rack and gives you a convenient swith to turn it all on with.

  11. groovecat


    Jan 5, 2002
    Scott,I have one waiting with my skb rack. As soon as my power amp arrives it's all going together. I also bought tubes from Lord Valve,was very helpful and he never steers you wrong.Thanks ,Geo
  12. groovecat


    Jan 5, 2002
    I hooked the svp-pro up to my just recieved carvin Dcm600, sounds real nice.This is "the sound" .The dcm600 is a real nice
    piece. Geo
  13. 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.