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High frequency noise on active bass, help!

Discussion in 'Pickups & Electronics [BG]' started by Cavant, May 4, 2017.

  1. Cavant


    May 4, 2017
    I have a Thunderbird Pro IV active bass, love the sound and everything but unless you roll completely back the high frequency knob there is a very audible buzz, when i up the volume on my amp the same noise becomes audible again, which means it's always there but at low volumes the eq makes it imperceptible.
    I have some experience with electronics and have tried to diagnose it myself but so far i haven't been able to pinpoint the cause, is this a usual problem with active instruments? Has anyone found this kind of problems before?

    Some notes on what i've already checked based on other threads and forums:
    - Already switched both cables and amps so the problem must be on the bass itself.
    - Originally the bass also had ground noise, i made it go away by connecting the bridge to ground as it was ungrounded. This noise seemed out of place to me as the pickups are humbuckers but this solved that problem.
    - I've already checked the soldering and grounding on every component, everything seems in order, nothing is loose nor rusty.
    - Another thread recommended wiring the positive pickup wire to the battery but this made no difference. By default i believe this connection is not made as the eq is active but the pickups are passive.
    - When using a (very) short cable the buzz is reduced greatly, this has lead me to believe it might be picking up radio frequencies or something like that. When connected to my full pedalboard or a long cable the noise becomes louder.
    - Another for the radio frequencies: once had a gig near a radio tower and the bass picked up a lot of radio noise, ground lifting de DI didn't help at all. Ended up having to play with a passive bass.

    I'll really appreciate any ideas or suggestions! I really like the tone of the bass and i would hate to end up selling it because of this problem. Thanks in advance.
  2. bassbenj


    Aug 11, 2009
    Since you are somewhat experienced in electronics, you should know that some really difficult noise problems take magic to fix them. (Or at least things you can't explain).

    First you need to figure out what the noise is and where it comes from . Does the noise change volume or go away when you touch ground? If yes, it's a shielding problem. OR can you make the noise go away when change orientation of the bass (not necessarily in a playing position) . If so It means the humbuckers are not quite canceling hum. Or is there any hint of voice or music in the noise? Or does the noise tend to be present in one location and not at another location (say another house or venue). That could be RF pickup. Voice or music in the audio is a sure sign, but not required. There was some kind of industrial welder or something in my neighborhood that put out a huge buzz as various times of the day. I tried for years to track it down but never could.

    If the length of cable makes a difference, you may need to try a more expensive cable. Some cables do not completely shield all electromagnetic noise. Radio station noise (RF) is usually a problem with active basses unless your amp is the problem (which does not seem to be the case) the Input stage of the preamp acts like a detector. Hence one possible thing to try is get some small ceramic caps like say a couple hundred picofarads and solder one across the bass jack, IN fact solder them between all the terminals! In fact (and this is where "magic" comes in) randomly try them across pickups and various other places you can think of to try. IF something works, don't question it and just leave it that way. How much shielding so you have? What is it? Paint? Foil. Remember to keep noise out ALL ELECTRONICS must be enclosed in a waterproof copper (conductive) box to work right. Of course tops of pickups have to stick out, but you need to get it all enclosed as best you can. Any gaps or holes and the noise eill crawl right in there! Note that noise can actually travel up the OUTSIDE of the cable and into the bass! Hence jack must be firmly connected to shield to block that (also the previously mentioned caps.

    If the problem is not shielding. Namely that you find a position for the bass where hum goes away, then your pickups are not properly canceling noise. They may be wired wrong, but more likely it's just the way they are! You may need to change the pickups in that case.

    This isn't much help. but he secret is just keep trying things until you find something that works.
    Zooberwerx likes this.
  3. Cavant


    May 4, 2017

    Thanks a lot for the comprehensive response! The orientation of the bass seems to do nothing, I've played the bass at different places and the noise never goes lower, so i'm betting on the shielding (paint), i'm definitely going to isolate it with foil as soon as posible. Also the cap thing I had tried only in the input jack but I'm going to cap every single thing on that bass, hopefully with those two things the noise will go away. I'll place my results here as soon as I have time to tinker with it in case anyone else runs into similar trouble.
    bassbenj likes this.
  4. bassbenj


    Aug 11, 2009
    If orientation makes no difference then the problem is shielding and not single coil hum. So a full foil shield job may help . My Fender Deluxe V (active) had paint shielding and sort of worked but there was always a bit of hum coming through. So I gave the full copper foil treatment and that last bit of hum was gone. Also I have a G&L L2500 which in spite of copper foil treatment tended to pick up RF noise in active mode. So I put the small cap across the output jack and another one from the preamp input to ground. That fixed the problem. Like I said you sort of have to keep trying things until you find it.

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