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Did I blow the horn on my Avatar 212?

Discussion in 'Amps and Cabs [BG]' started by DeadRBassistNJ, Jul 7, 2005.


  1. Yesterday I plugged my bass into my Peavey amp and Avatar B212 that has a 4th order crossover that I made and installed. I didn't realize it but the input jack on my bass was loose and somehow the treble on the active pre got turned up all the way. When I picked up the bass and turned the amp on, the horn started making a super high pitched noise, which usually means I didn't push the patch chord all the way into the bass. I started fumbling with the chord and jack on the bass and after maybe 3 seconds the noise stopped and smoke started pouring out of the unused 1/4" jack on the cab. I thought something was on fire but I took the control panel off right away and everything looked ok. The L-pad which is still the stock 15w was warm but looked ok, the horn looked normal, and I'd have to take a speaker out to inspect the crossover, so I didnt get to check that. I havent tried using the cab since. Any ideas as to whether it was the horn, crossover, or L-pad? Thanks
     
  2. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    You can check the tweeter with an ohmmeter, you should read 5 to 7 ohms, if there's no reading it's dead. The LPad might have taken the hit, but it's unlikely that it would go and not take the tweeter with it.
     
  3. Checked the horn out. Its not reading any ohms or any circuit between the two terminals, so I guess I burned it out somewhere. Can I just tape off the two wires and use it without the horn for now? I have practice in an hour and I can live without the horn for now.
     
  4. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    Not a problem, but other stuff could be toasted as well. You can easily test the LPad but not caps unless you have a fairly sophisticated DMM. If they're 200 volt rated or better I doubt there's a problem, though, as your amp can't generate that kind of output voltage.
     
  5. Yeah the caps are 250V rated and the inductors are 800W so they should be ok. A new Foster horn is only $26 so I'll probably just cheap out and replace it with that. Thanks for your help.
     
  6. random question, but i heard in harmony central reviews that turning off the tweeters on teh cab would cause it to blow? is this still an issue? i'm considering getting a cab and since i don't use tweeters in my rig anyways (because they don't have any), i figure i could live with the tweeter off anyways, but i don't want to have to worry about things blowing up on me.

    how does a tweeter work anyways (ie how does the cab make the cutoff on what frequencies pass trough teh speakers and what frequencies are sent to the tweeter)?
     
  7. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    Turning your tweeter's attenuation knob all the way down placed a lot of strain on the L-pad and can burn it out. It you really, really want the tweeter to make no sound, disconnect the wires. Or install a true bypass toggle switch.

    Most bass cabs today have a partial crossover. It's basically some capacitors and inductors arranged in such a way that it blocks the low frequencies from reaching the horn. The values of the capacitors and inductors, and the nominal impedance of the horn determine the frequency at which the crossover starts to block the lows. That's the quick answer. Crossover design can get quite involved and indeed there are entire chapters of books dedicated to it.
     
  8. so simply put it puts out a certain amount of high frequencies out through a tweeter, and the l-pad will basically act as a filter for the freqs; when cranked fully all of the sound (or signal) will try to go through the tweeter, but turning it down will restrict the signal from coming out.....and how does it strain it? sorry, i'm slow.....i'm usually just running through peavey 15 inch speaker tweeterless combos and i don't have to go through the entire "well if you do this, that will happen" process.

    maybe i'll just spend money and when all the equipment comes i'll worry about it then...keeping the tweeter low (1/4 or less) won't hurt the ears much will it? i'm gonna be using a lot of heavy overdrive in my sound
     
  9. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    Not quite. All the L-Pads does is act as a volume control. It allows you to turn the tweeter down. The blocking of the low frequencies is done by the crossover, specifically the capacitors with some help from the inductors.

    The L-pad uses resistors to reduce the amount of electrical energy that reaches the tweeter. The more resistance, the less signal that pass through, but the more work the resistors have to do. When you turn the L-pad all the way off, the resistors can struggle to absorb that amount on electrical energy, especiall an L-pad rated at a mere 15W.
     
  10. Yeah I have to replace the 15W L-pad with a 100W to be safe, and maybe wire in a bulb so I don't blow it again. Any info on the bulb would help.
    I figured out the jack on my bass actually had nothing to do with the horn going out. When I stand next to the transformer side of the head my bass picks up a lot of noise and the amp clips at some really high frequency, with the built in DDT limiter off. I was using the cab tweeterless and discovered it happening again at practice on Friday, I guess the DDT got turned off in transport.
     
  11. so if i disconnect the tweeter from teh amp when i get it, the 2 12s will be the only components getting all of my high and low end right? it just seems that up until now i've been happy without any tweeters and that this would just be troublesome
     
  12. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    Yep, just pull the tweet out, disconnect the wires, then put it back into the cab. The 12's should recieve a full range signal.
     
  13. And put tape over the ends of the wires so they don't touch and short anything out.