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Horn Issue

Discussion in 'Amps and Cabs [BG]' started by P. Aaron, Aug 31, 2013.

  1. P. Aaron

    P. Aaron Supporting Member

    One of my LDS cabs has a horn (Selenium) that's buzzing when the dial is turned to add 'high range'.

    Don (@LDS) suggested replacing the diaphragm, which I did. The sound persists. Meanwhile when the horn is zeroed out, the speakers are bassy, solid and punchy.

    Awaiting another reply from Don but thought I'd throw to you guys for any thoughts you may have.

    Replacing the whole horn is about $30.00. But, what if it's an electronic gizmo issue rather than mechanical?

    There's a whole mini-circuit board in there which the crossover runs through. That stuff baffles me.

  2. AstroSonic

    AstroSonic Supporting Member

    Dec 10, 2009
    rural New Mexico
    Might just be a dirty pot. Clean the tweeter level dial (pot). Remove one of the drives so you can see the back of the panel with the tweeter dial. Spray Deoxit contact cleaner (available at Radio Shack and Parts Express among others) into the opening by the terminals, and rotate the knob several times. Inexpensive and worth a try...
  3. Doug Parent

    Doug Parent Gold Supporting Member

    May 31, 2004
    San Diego, Ca.
    Dealer Nordstrand Pickups.
    The tweet is doing it's job, reproducing whatever signal is being sent to it. The source of the noise is elsewhere. Don't shoot the messenger. Don't mess with the pot, crossover or bother replacing the diaphragm. Instead look at your bass for shielding issues or whatnot. The instrument and it's electronics are where the signal chain starts. Just my .02
  4. P. Aaron

    P. Aaron Supporting Member

    The speakers of this cabinet sound full & bassy. The bass sounds fine with my other LDS cabinet. Something in the chain from within the cab to the horn is causing this.

    This has been my main rig for almost 6 years now. I know it pretty well.
  5. With the horn itself the diaphragm is the only electric/electronic part that fails. Once removed it should have visible signs of overheating or charring. If the new one is installed properly replacing the whole horn will yield the same result.
    You could have a bad crossover in the cab but you should try your setup with a different horn loaded cab to be sure the trouble is not the signal being sent to the cab.
  6. P. Aaron

    P. Aaron Supporting Member

    Does it count that after installing the new diaphragm, I plugged the cab into my other Hartke amp, and played my other Precision bass to check the repair yet, am still getting the same result?
  7. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    i have to agree with Mr B's post. With a new diaphragm correctly installed it is the same as a brand new horn.

    I also concur with the thought that the Xover may be the problem. If it is allowing signals through to the horn that are below what it can handle the result would be identical to what you are describing.
  8. That might lead me to look at the crossover in the cab! :)
    You did do these checks with zero effects in the signal chain, only the bass into the amp correct?
  9. P. Aaron

    P. Aaron Supporting Member

    That's how I've been playing since '02. In this case, different amp, different bass, different cord too, same noise.
  10. I had to ask about effects, we even just recently had someone believing they had an amp fault that turned out to be an effects pedal they didn't mention.

    Crossovers only allow the frequencies the horn is designed for to pass to it. If it fails or drifts bad sound and possible damage can follow, they can also cause noise within their passband depending on the failure.
  11. Arjank


    Oct 9, 2007
    Above Amsterdam
    You can also unmount the Selenium horn and connect it to your home-audio system (start with volume knob down), put on a some music and listen to any signs of buzzing. If everything is ok, connect it directly to your bassamp (also, start with the volume knob down). Now play some bass and hear if everything is ok. If there isn't any buzzing in both cases the crossover has probably a bad component.

    I doubt it will be the capacitor, when they get to much voltage they just die. When it's a electrolyt-capacitor it may have dried out and the value isn't ok anymore, but that should not give you a buzzing sound.
    The crossover may also have a (parallel) coil in the tweeter section. I have never seen a "baked" coil in a tweeter section, so I do not think the problem lies there.
    Then there could be an L-pad(two resistors), but since it sports an attenuator I think there won't be one.
    The attenuator could be bad, like someone allready mentioned, try some contact cleaner. (I never ever use attenuators in my builds)
  12. P. Aaron

    P. Aaron Supporting Member

    Finally found the problem.

    Replaced that dome thing in the horn, nope.

    Replaced the L-Pad, nope.

    Finally took it in to Huber & Brese in Fraser, MI. A solder joint on a capacitor connected to the crossover board had come loose so I had it replaced ('cause part of it had broken) and that solved the problem.

    While I was there I fell in love with a '57(?) Reissue P-bass that was white & maple w/gold pg. weighed about 7lbs. Hubba, Hubba!
  13. Crossover eh? :D Glad you are back in business!