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Sub problem. Something blew.

Discussion in 'Amps and Cabs [BG]' started by odie, Mar 22, 2004.


  1. odie

    odie Supporting Member

    Band has a set of subs. They are Peavey RBS-2 and are bandpass, with 2 15's.
    http://www.peavey.com/support/searchmanuals/list/rbs.cfm

    Well to make a long story short we had to use them at a venue that has subs but theirs were not working. Now we have one that doesnt do anything. Soemthing blew in the sub. It has its own built in crossover, and inside the sub there is a trasformer on the crossover and one mounted to the inside of the sub.

    What blew?? Do you think it is a trasformer?? What should we look at? Ideas?

    Thanx
     
  2. odie

    odie Supporting Member

  3. BruceWane

    BruceWane

    Oct 31, 2002
    Houston, TX
    Looking at the specs for the cab, it says that it has inputs that go directly to the drivers; they bypass the internal crossover. They call them "biamp low" inputs. Have you tried using these? If it works with these inputs, then apparently the internal crossover is blown. If it doesn't, you'll need to investigate further........get an electrical meter and check the resistance of each driver. If it's extremely low, like less than 1 ohm, you've got a shorted voice coil. The driver will have to be re-coned. If it shows infinite resisitance, or a very high number like 999 ohms, that indicates the voice coil wire has been broken. You'll probably need a re-cone here as well, but sometimes you get lucky and the wire has broken somewhere away from the actual coil in a spot that you can repair.


    If the crossover is shot it'll be easiest to order a replacement from Peavey, although you can also probably have it repaired at any shop that repairs amps. What you're calling a "transformer" is probably a coil. They can look kinda similar.
     
  4. odie

    odie Supporting Member

    There is two box like things that look just like transformers. lil plates with copper wrapped around them with wires going to the crossover.

    Also when we hooked it up to another amp to test it, we could see a spark jump from the speaker cable to the cab. This normal?
     
  5. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    Odie NNNNOOOOOO! I'm dying right now! Hopefully there's a lesson learned here. You would have had no way of knowing the specs or indeed the condition of the club's power amps. It's just too risky.

    OK first thing first, check the drivers. You may need to grab a screwdriver and pull them out. You'll also need some lose speaker wire and a 9v battery. I assume you know what to do next. If the speakers are moving then they're fine, start looking for problems elsewhere, probably the crossover. Those passive crossovers work less effectively as the wattage increases so it's possible something in there is burnt out. Find a way to by-pass the crossover components and see if the subs now work.

    Man I hope everything's OK.
     
  6. nonsqtr

    nonsqtr The emperor has no clothes!

    Aug 29, 2003
    Burbank CA USA
    Well, yeah. You'll need to test each speaker individually. That would be the first thing I'd do. I wouldn't use a 9v battery though, that only tests for "continuity" (or the equivalent), and won't really tell you if the speaker sounds right. But, continuity is definitely important, so it wouldn't hurt to use a battery or a meter as your first step.

    Anyway, if the inputs that BruceWane mentioned are there, you can use those, or you can just open up the cab and disconnect each speaker in turn, and test it separately with an amp. My guess is, the speakers are probably fine, those darn crossovers blow more often than the speakers do.

    Just as a wild guess, I don't suppose there's any kind of fuse or circuit breaker in the crossover? Many of them have something along those lines, sometimes there's a fuse soldered directly onto the circuit board. Definitely check that before disconnecting the transformers.

    If the speakers check out, and there's no blown fuses or obviously charred components, the next step would be to check the inductors (transformers) for continuity. To do that, you'll have to disconnect them from the circuit. At this point it would definitely help to have a schematic or wiring diagram for the cabinet. Is there also one or more capacitors in the crossover? If so, you may need to test those too.

    If this sounds like more trouble than it's worth, it probably is, and you might choose to take the cab to a tech. If you choose to do it yourself, you'll need a soldering iron, a multimeter, and an amp with some kind of signal running through it. If you get to the part where you're testing capacitors, you might also need a battery and a small value resistor.

    Edit: by the way, an 8 ohm speaker should have a DC resistance of about 6 ohms (or so), and a 4 ohm speaker should be around 3.2 ohms. In lieu of the battery test, you could trust your multimeter as a first approximation, although again it won't tell you if the speakers sound right (it's possible that the cone could be frozen into place even though the coil is still continuous).
     
  7. odie

    odie Supporting Member

    Took out the speakers. I have not tested them but one has a very distinct burnt smell. I mean it smell burnt. The cab and the other speaker both smell fine.

    Should I assume this is the problem and that it is wired that if one goes nothing works?

    Also where is a good place for a replacement. Do I need a whole new speaker?? Or the basket part. This is all new to me.
     
  8. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    Odie all spread your fingers evenly around the speaker cone and press inwards gently. Does the speaker move freely and are there any grinding or scraping noises? I'm testing for any obvious signs of voice coil damage because that's what the burning smell would suggest.

    Assuming that driver is damaged, I'd look at a re-cone (ie a new cone, surround, voice coil, spider, everything except basket and magnet) It usually costs about half of a new speaker and the results is pretty much the same.

    I'd still like to see you do the 9v battery test.
     
  9. odie

    odie Supporting Member

    Nope they are FUBAR. Took the magnets off and the coil is burnt and crispy. So I need new ones. So do I just look for a new "basket". I thought the basket was the coil, cone etc.

    Also anyone know a good source stateside for Peavey replacements?

    PETE- You rock as usual. I really appreciate all the hand holding on this!!
     
  10. If you're anywhere near any town with more then say 1000 people that has a music store, chances are they're a Peavey dealer. They will most likely have cone/coil replacements in stock. This is an excellent feature of the Black Widow drivers, you can change these yourself in a matter of minutes. If you don't have a local Peavey dealer pretty much any sound company or music store could order them for you. You could also go on E-bay or order them yourself from Peavey. Let us know how it goes!