Guitar Loudspeakers

Discussion in 'General Electronics Chat' started by veenife, Sep 17, 2014.

  1. veenife

    Thread Starter Member

    Jan 16, 2014
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    hey, i found this super old loudspeaker at my rehaersal room.... the LS is a teisco checkmate 100 super old stuff like from 67.... it has two pionner speakers on it each 16 ohms and 50w connect in parallel... i then have a marshall g100r cd amp... which is a 8 ohm 100 w amplifier...

    the first time i connected it it made no sound then when i touched the cable it was super super loud and then total silence forever.... i thought then it would be just some bad wired cable and etc... so i ordered new wires and solded everything new....... the only still old part of it is the jack input connector....

    the first thing i did was to sold just one of the speakers... .. and it worked.... i tried it for a few minutes with low volume and it was no problem....

    after that i then connect the second speaker in parallel.... then it kinda worked..... first even with low the volume knob totally down it was still putting out some sound... but then once i turned the amp volume knob up.... it happened exactly the same as the first time i tried it.... just a super super loud sound for a millisecond and total silence after that....

    i thought then i broke it or something cause of too much power or whatever... but to be sure i resolded just one of the speakers again with new cables but no sound came out ....

    after i tried figuring out what could be the cause of the problem... i solde and resolde that thing a million times kick it in all the ways possible...

    an then sometimes actually some really short clicks and sort of distorted low sound came out of it.... and just once again a super super loud sound...

    i dont get it i resolde that thing so many times it cant be a soldering connection problem...
    i have no idea what the problem with that thing is.....
    maybe im missing something....

    and the most weird thing is the loudness thing... cause before i turned the volume knob that thing was working with no problem... which means it cant be the speakers....

    does any one have an idea what it could be causing that???
     
  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,783
    945
    at full excursion the speaker windings may be shorting out. Old speakers often lose the centering due to deteriorated suspension material. High power abuse overheating the coil also caused the insulation to cook off and exposed bare copper.
    Ohm checking the speaker terminals to the frame can find this.
    An intermittant open in the coil is also possible.
    speaker excursion and polarity is often checked by applying DC voltage from a 9 volt battery. Fully pulled in for one polarity and fully extended cone for the opposite polarity. Don't apply the voltage for too long. It is just a quick check, mostly for proper polarity in multi speaker systems.

    Check carvin.com for good quality replacement speakers for the guitar amp. they are reasonably priced as well.
     
  3. veenife

    Thread Starter Member

    Jan 16, 2014
    42
    0
    man, if it is that it will be super sad that thing has the potential to sound amazinly amazing.... seriously....

    i want to run this tests but i didnt quite get it....

    ohm checking the speaker terminals to the frame??? how does one do that... how is the procedure?

    and the thing with the 9 volt battery... you mean i have to once connect + to the battery+ and then another time + to the battery - ???
     
  4. Lestraveled

    Well-Known Member

    May 19, 2014
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    It is an old speaker with old connections. Connect from your amp with a known good cable directly to the speaker. (jumper leads if you have them.) Also check the leads from the speaker terminals to the spider. Sometimes they let go.
     
  5. #12

    Expert

    Nov 30, 2010
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    I read the part about you fixing the cables, so I'm going with Kermit. Try a different speaker and don't crank the volume up to 10. If it suddenly behaves, you know it's bad speakers. If it doesn't, you're going exploring inside the amplifier.
     
  6. MrChips

    Moderator

    Oct 2, 2009
    12,440
    3,360
    Use a 1.5V battery to test the speakers. If you see the cone move and hear it crackle then the speaker might still be ok.

    Don't test either the amp or the speaker at full volume until you are sure everything is ok.

    Is the speaker in a box or cabinet? Check the connections and wiring from the speaker itself to the cabinet.
    Check the flexible braided wire from the speaker connection to the cone.

    Check to feel if the speaker coil is rubbing against the magnet.
    To do this, use both hands, four fingers total, two fingers on each hand.
    Position the four fingers evenly spread around the cone, front side. Press down gently and feel & hear if the speaker coil is rubbing.
    As Kermit says, if the coil is rubbing, you may have a short to the frame. Check for continuity between the coil and the frame.
     
    #12 likes this.
  7. veenife

    Thread Starter Member

    Jan 16, 2014
    42
    0
    the speakers are in a cabinet with opened back...

    i will run this tests then ... thanks for the replies....

    but so then IF i do have a short to the frame.... how do i fix that????

    i not even know what a short to the frame means.....
     
  8. sirch2

    Well-Known Member

    Jan 21, 2013
    1,008
    351
    The frame is the metal framework that supports the speaker cone and magnet. The speaker consists of a coil of copper wire around a magnet. this is inside the "dome" on the back of the speaker. If the coil of copper wire touches the metal speaker frame and the insulation on the wire has failed due to age or wear and tear then this is a "short to the frame" i.e. the electrical energy is short-circuiting to the speaker frame.

    So to test this you need a multimeter or continuity tester (or a battery and a light bulb) to check that there is no electrical connection between where you connect the wires to the speaker and the metal framework of the speaker.
     
  9. Lestraveled

    Well-Known Member

    May 19, 2014
    1,957
    1,215
    Google "speaker reconing". There are a lot of youtube videos that show you how and there are several companies that sell reconing kits.
     
  10. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,783
    945
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