Speaker crossover overload circuit.

Discussion in 'General Electronics Chat' started by redrooster01, Sep 3, 2015.

  1. redrooster01

    Thread Starter Member

    Jul 15, 2014
    84
    1
    A friend of mine asked me to see if I could fix one of his Yamaha S250X P.A. speakers for a concert this weekend.He said it was crackly and he could hardly hear anything coming through it and admitted that he had been running them flat out when it failed.I took it apart and tested the components in the crossover and the drivers but everything was OK except for one of the bulbs was blown in the speaker protection circuit which comprises of two sets of interior car lights in parallel and series. So I thought the signal power isnt getting through the single bulb properly and because theres no markings on the bulbs to find out what value they are to replace it he asked me to solder a 1 amp fuse across the blown bulb? I did that but Im having second thoughts now. What if the two bulbs by itself are a weak link? Should I have soldered the 1 amp fuse across all the bulbs? Ive taken a photo of the bulbs but I cant upload it here for some reason so I drew a diagram in Paint and I cant upload that either? Any ideas, suggestions?
     
  2. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
    1,438
    368
    The bulbs are supposed to be a weak link as they are there to protect the speakers not by blowing but by heating up, it would have taken considerable abuse to cause a bulb to blow. It doesn't make sense to bypass the bulbs with fuses as you would be effectively protecting the bulbs at the expense of the speakers.
     
  3. redrooster01

    Thread Starter Member

    Jul 15, 2014
    84
    1
    I realize what your saying but there not my speakers and the owner asked me to solder the fuse across the bulb.What I need to know really is if enough signal power is going to get through with one set of two bulbs in parallel instead of the two sets in series it had origonaly? I wish I could upload a picture. A pictures worth a thousand words.lol
     
  4. #12

    Expert

    Nov 30, 2010
    16,248
    6,745
    The fuse has a lot less resistance than the bulbs, so the power will get through. Watch for him needing new speakers next week.
     
  5. GLPro

    New Member

    Aug 21, 2014
    4
    0
    The lamps are used as current-limiting devices and if you still have one of the two paralleled lamps remaining, then signal will continue to pass to the speaker....you didn't say how the lamps are wired into the circuit path, regarding where they actually are (before the crossover circuits, on the high side or low side, etc)....I'm assuming they are intended to protect the compression drivers (only place you would need them), but you don't say; it's difficult to know why just one lamp has failed, but they will not last forever (it may have nothing to do with your crackling); speaker lamps are common in some speaker crossover circuits built now days to protect tweeter drivers from excessive current. You know that your crackling noise may be generated by another source (connectors, jacks, wiring, solder joints, amplifier, mixer desk, etc), especially since you have determined that the network circuit components are good. To replace you lamps, look at the power rating on the driver and that will be your limit power-wise....eg. for a 20W driver, you might have had 2 10W lamps in parallel, etc. My gut feeling is that your 1A fuse will simple render the remaining lamp useless. One thing to look at is what is going on upstream of the speaker enclosure....do you have proper headroom at the desk, is the power amp under rated (most common cause of driver failures), a need for a compressor/ limiter between the desk and the power amps or speakers; a multi-band compressor/ limiter would be my go-to tool first and foremost (set the attack for fast for your frequencies over the 2.5khz and slow for the lower ones and a compression ratio of 20:1 or higher....good luck
     
    Last edited: Sep 4, 2015
  6. redrooster01

    Thread Starter Member

    Jul 15, 2014
    84
    1
    I dont think you understand what Im saying here? If I could upload my photo it would become clear what Im talking about? Instead of 2 sets of bulbs,each of them being in parallel,Ive only got one set now for the signal to go through (less resistance) The other pair has a 1 amp fuse across it because 1 bulb of the pair blew.
    He has tested the speaker and its working OK but he is only using it for voice anouncements for now.I didnt mention the bulbs were to protect the horn tweeter because I thought that was obvious? The bulbs are 12v car interior lights,5W by the looks of them? It is a crackling noise and I can hardly hear the volume, was how he described the fault to me,when I looked inside I found the back of the horn tweeter screws had vibrated loose a bit so I tightened them up,maybe it was that causing the crackling noise plus the spade lugs to the horn tweeter were loose? I know he is using a 400W a channel amplifier and he has been doing gigs for years but thats all? Ill check out whats what and see if he has a compressor/limiter,multiband or not? So if the horn tweeter is 20W I use two 10W bulbs in parallel? Ive asked on two audio sites about what bulbs to use and all the different answers have made me completely confused, thats why Ive come here because I tend to get the right answers here. Thanks for the advice on the compressor/limiter settings Ill pass them on next time I have a yarn with him.
     
  7. #12

    Expert

    Nov 30, 2010
    16,248
    6,745
    It's always great to start the day with a coffee and a laugh, just not at the same moment.

    No, we are not mind readers.
    Even if we were in the trade for 40 years, manufacturers are constantly introducing new models to the market. In fact, the 200W amp in my living room has fuses for the bass speakers. How am I supposed to guess where your fuses are?
     
    absf likes this.
  8. redrooster01

    Thread Starter Member

    Jul 15, 2014
    84
    1
    You have got to be joking! If you are seriously saying you thought the bulbs were to protect the woofers, you know less than I do about this?
     
    Last edited: Sep 4, 2015
  9. #12

    Expert

    Nov 30, 2010
    16,248
    6,745
    Are you seriously saying that everybody should know that no designer, anywhere on the planet, ever has or ever will use a light bulb to protect any part of an audio system except a tweeter?

    Everybody doesn't know. New designs happen every day and there are tens of thousands of designs that I have not seen. Every designer does not think the same way and every design can be protected in several different ways. Some of the designs are suspiciously ineffective and some are actually bad designs. I have to give Yamaha credit for having good designers, but everybody doesn't know that, either.

    I'm seriously saying, "Better information gets better answers", even if all it accomplishes is verifying we both have the same thing in mind. If everyone that would happily assist you is required to already know that an incandescent lamp has never been used in a woofer circuit, you are seriously limiting the number of people that can assist you.

    This sentence actually creates room for doubt. If a speaker cabinet has two (2) sets of protective devices in a cabinet with two (2) speakers, there is room to wonder if both protective circuits are connected to only one (1) of the speakers.

    GLPro pointed this out by saying,
    He's new at this site, but his post seems perfectly valid to me. Still, he arrives at the word, "assuming". Assuming is always second best to knowing for sure.;)
     
  10. redrooster01

    Thread Starter Member

    Jul 15, 2014
    84
    1
    I was addressing the question to the experts that dont have to assume anything? I dont need and I dont want advice from someone who hasnt a clue of what Im talking about.It leads to confusion and doubt.
     
  11. Sinus23

    Member

    Sep 7, 2013
    160
    378
    You do realize that we are not there as in having the speakers in our hands ( pretty much crystalballing since there isn't even a picture of that said speaker). Have you ever had to fix your grandmothers computer via phone;) Talking about confusion and doubt:rolleyes:

    "A friend of mine asked me to see if I could fix one of his Yamaha S250X P.A. speakers for a concert this weekend.He said it was crackly and he could hardly hear anything coming through it and admitted that he had been running them flat out when it failed"

    What does running them flat out mean?o_O
     
  12. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,766
    928
    Please forgive the impertinence of our members. We live to serve.

    How can we help you sir! It is our pleasure to provide instant, knowledgeable answers to all our superiors. Please let us try again. I promise we will do better at guessing what you need and supplying it instantly.

    It's FREE too! :rolleyes:
     
    blocco a spirale and Sinus23 like this.
  13. redrooster01

    Thread Starter Member

    Jul 15, 2014
    84
    1
    Ive had my question answered on another site in a normal civilized manner,without any of this silly,juvenile,sarcastic,trolling etc... Why this is allowed to happen here I dont know? but I do know that it brings this site into disrepute.
     
  14. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
    1,438
    368
    I have just read through your posts again (for free, you're welcome) and their is not sufficient information in them to provide a definitive answer to your questions; You said you would upload a diagram and you never did. The quality of the answers is dependent on the quality of the question, and you got out what you put in.

    Please, provide a link to the site that provided the answers that meet your strict criteria for free advice?
     
Loading...