Loss of Treble Response!

Discussion in 'Pickups & Electronics [BG]' started by rawlsjk, Mar 26, 2005.

  1. Hi, my name is Jason Rawls. About a month ago or so, I noticed that I was no longer getting any treble response out of my bass. I have a Bartolini NTBT preamp (9V system). It worked fine for a year and half. All of a sudden the treble went out on me. I thought maybe a bad pot....NOPE! The potentiometer worked fine. I thought maybe bad capacitors...NOPE! I replaced the capacitors and still had the same problem. Then, I started to believe the circuitry may be shorting out somewhere. So I analyzed that; didn't find anything. So, I ultimately thought that the NTBT module was the cause. I purchased another module, wired it up....IT STILL HAD THE SAME PROBLEM. Right now, I'm completely lost at what it could possibly be. The only electronics on my bass that hasn't been checked or replaced are the pickups (humbuckers). I'm not too sure if defective pickups would have this type of effect on my response, but it's all that I can think of as of right now. HOPEFULLY, there will be someone that will be able to help give me some insight on where I can start to look as far as troubleshooting to come up with a problem, and eventually a solution to the problem. Thanks in advance.

    Jason K. Rawls
  2. Tim__x


    Aug 13, 2002
    Alberta, Canada
    Was it a slow, gradual loss, or a sudden, overnight kind of change?
    How old are your strings?
  3. luknfur


    Jan 14, 2004

    may sound stupid but is the bridge pup working (both coils)? Some guys are heavy on the neck and may not notice a bridge going out. Also, if there's any switching that splits the humbuckers I'd look into that.

    Personally, I'd have replaced the pot before the preamp. Moving parts are always more prone to failure and pots are cheaper than preamps. Preamp failure in one less than ten years old is pretty rare in my experience. I noticed you said you checked that pot out but didn't say you replaced it. The only way I know to check a pot out without playing it is with a meter and no sound comes out of a meter.

    For that matter, I wouldn't rule out the possibility of any new component (ie cap) being defective. In as much, I'd say it would be highly unlikely for both Bart pre's to be bad. I'd probably skip the cap anyway and see what I get.

    I assume you know for a fact it's the bass. Have you played it through another amp? Did you make "ANY" changes that corresponded with the loss in treble - equipment, cords, where you play, outlet you've been using, whatever. I would definetly double check your amp for any switching/adjustments that cut trebles that may have inadvertantly been altered. As simple as my amp is, there's lots of stuff that will cut treble on it that I use on occassion but not routinely and on more than one occassion I've shut it down afterward and forgot about it the next time I fired it up.
  4. Thanks for all the help so far. When I caught the problem, I hadn't noticed it before. So, I really couldn't tell you if it was gradual or sudden. I rarely change my settings because I plug into a direct box and I'm controlled by sound engineers. Regarding the treble potentiometer...I measured the pot with a multimeter. That's how I knew that it was working correctly. Even at that, when I ordered the new Bartolini NTBT, it came with brand new pots, capacitors, and resistors. I installed all new parts in the bass. I went to the music store the other day to talk to some guitar techs there and they had never heard of this problem. So, I plugged my bass in a head and speaker to see how it sounded in a better controlled environment. I noticed that as I turned the treble knob, there was an increase in static in the speaker. However, there was no obvious change in the signal response; it remained the same while I adjusted the pot. So, I'm guessing the pot is working correctly, however there isn't any obvious signal frequency response. Oh yeah, my strings are less than 6 months old. I clean them about every 2-3 months by boiling them in water and vinegar. I hope that might clear up some of your questions. Thanks again for your quick responses. Have a good one!

    Jason K. Rawls
  5. luknfur


    Jan 14, 2004

    Assuming all the coils on the pups are working, sounds like you'll have to isolate the problem. So you basically have to skim electronics down to basics and vary one thing at a time; preferably going with the simples, cheapest, quickest, and easiest varition first.

    I'd probably remove the preamp first and just run the pups (one at a time) straight to the jack and work off amp controls. You get treble reponse there, there's nothing wierd going on with the pups.

    Then I'd run the pups through the pots only (no capacitors) in whatever configuration it took to test all the pots.

    Then I'd throw in capacitors (switching, whatever) one at a time and check.

    Then I'd throw the preamp back in.

    There's always a possibility of a defective batch of whatever (preamps, capacitors, pots). I don't know that's there's any way to check preamps or capactors aside from installing them and I have no idea what quality control process makers use for them.

    I might even take a stab and just jerk the capacitor for starters and check the bass since it's the simplest and quickest mod and you have a treble issue, and treble is what capacitors are about. If the capacitors dead and treble has to go through it to complete the circuit through the treble pot then it's a prime target. Another thing you could do is stick a substantially lower value cap in (like .01 in place of .05) and noticeable more treble should be apparent. Or conversely a higher value (.09) would be bassier.
  6. mrelwood


    Dec 15, 2004
    I don't know what the preamp is like, but the effect of replacing the cap with different value works differently in different situations. The mentioned change would be true with a passive tone control. When rotated anti-clockwise, that is.

    But there are a few other things to check. I have fixed several guitars with treble issues. Most of them were because of faulty wires or rotating vol pot, where the hot tab almost touches the ground. If the output cable is shielded (=has one wire inside the wrap ground), check the solderings and ends very carefully. I recommend soldering the whole cable off and measuring the resistange while twisting. But don't touch the ends, resistance from right hand fingers to left hand fingers is around 600k-800k.

    Other things to measure:
    -Unsoldered output jack + to ground. Should be unmeasurable.
    -Unsoldered pot, tap 1 to 3. Should match the pot value.
    -All shielded wires unsoldered, should be unmeasurable.
    -Pickup DC resistance. Depending on the model. Active 0.5k-2k, passive 4k-25k.

    Also check that there are no solder spills behind the pot taps touching the cavity. And check that there are no screws that could touch any wire.

    Are the pickups active or passive?