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Thread: Technical help

  1. #1
    Join Date: Nov 2014

    Location: Torquay,Devon

    Posts: 58
    I'm peter.

    Unhappy Technical help

    Anyone any ideas on this problem?
    This is the third I have a problem with woofers blowing on left hand channel- this time all 3 woofers have blown on left hand channel – luckily I think the separate subwoofer has survived.
    Was listening quietly to a cd, then experienced horrible loud humming then speaker blown - smell of cone burning – I have a video- had phone close to hand(cant download it here) – hope this gives you an idea of problem. This is now third time this has happened

    Can anyone please advise with any technical expertise out there whether there is any possibility this could be a fault with the subwoofer, amp or speakers – if not, then any advice on what could be the cause(eg. Faulty amp or faulty speakers)would be much appreciated – I think one of the subwoofer engineers mentioned last time that it sounded like amp was going into DC mode??

    The dealer has, I believe approached both manufacturers of amp(musical fidelity m6i) and speakers(Focal Chorus 836vw) and am awaiting their feedback The subwoofer is a BKxxls400

    Thanks for anyone who can help with this https://theartofsound.net/images/smilies/17428.gif

  2. #2
    Join Date: Oct 2012

    Location: The Black Country

    Posts: 6,089
    I'm Alan.

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    Sounds like you possibly have some dc component going into the amp, can't tell from the user instructions to whether the amp is direct connected or not.

    Get hold of a multimeter of find a friend who has one, then measure to see if there is any dc present on the input leads/connectors.

    I love Hendrix for so many reasons. He was so much more than just a blues guitarist - he played damn well any kind of guitar he wanted. In fact I'm not sure if he even played the guitar - he played music. - Stevie Ray Vaughan

  3. #3
    Join Date: Nov 2014

    Location: Torquay,Devon

    Posts: 58
    I'm peter.

    Default Technical help

    Thanks for reply Alan
    I have attached photos of connections of speakers and Subwoofer- don't know wether this makes it any clearer
    Peter
    Attached Images Attached Images

  4. #4
    Join Date: Oct 2012

    Location: The Black Country

    Posts: 6,089
    I'm Alan.

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    I don't think it has anything to do with your connections, which look fine.

    On re-reading it sounds like the amp is probably at fault, do not switch it back on with speakers connected until you have it checked out, it could blow more speakers.

    I love Hendrix for so many reasons. He was so much more than just a blues guitarist - he played damn well any kind of guitar he wanted. In fact I'm not sure if he even played the guitar - he played music. - Stevie Ray Vaughan

  5. #5
    Join Date: Mar 2012

    Location: Gloucestershire

    Posts: 3,377
    I'm Paul.

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    DC on the output, sounds like your amp has developed a fault and fried one of its output transistors, op amps or an output smoothing cap may have developed a short. Best not connect any more speakers until the amp is repaired. Your tweeters will have been protected by the crossover capacitors. This can be a common problem for anyone buying used old amps which haven't ever been serviced or checked or where the amp has been run into an over-demanding load which has caused the output stage to fail. I've lost count of the number of times I've seen this.

    To check the amp; use a multimeter set to DC, then switch to the voltage on the lower range (0-10V something), place an 8 Ohm resistor across the output terminals of each speaker output on the amp, rated for 20W, have the volume fairly low, say 1/4 volume, and put the multimeter across the terminals in parallel with the load resistor. If you're getting anything much over 0.1V on each channel, you've a fried output stage component or components so you'll know its the amp needing a service.

  6. #6
    Join Date: Oct 2012

    Location: NE England

    Posts: 4,173
    I'm Jez.

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    95% likelihood of blown output transistors. The mains hum as it blew is a dead give away as well. I'd loose the sub if I was you.... or at least power it from a line level output.
    You can indeed check for DC with a meter. You don't need any load resistors or anything. Don't connect any speakers to it as you'll almost certainly blow them!
    You can't check for likelihood of output transistors failing or for signs of abuse in the past I'm afraid. Nor will servicing mitigate against it. Either they blow or they don't and that's that.

  7. #7
    Join Date: Feb 2008

    Location: South Wales

    Posts: 9,151
    I'm NotTakingLifeTooSeriouslyTheseDays.

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    Really sorry to hear this,
    Yep,
    Agree with the advice given, That is unfortunetly the main reason i bang on about Transistor amps having DC detection circuits on their outputs!
    Like Arkless has stated, you never know when an output Transistor is going to fail.
    FET output amps are safer to a degree, as the device just stops conducting, where as with Bipolar devices, they generally go dead short, and seen as most conventionally designed bipolar output stages have an NPN and a PNP device [or banks of them] when one or the other goes, you get the full power supply voltage, and current capability of either the positive or negative rail on your speakers.
    A...
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  8. #8
    Join Date: Jan 2008

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    I'm AudioAl'sArbiterForPISHANTO.

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    Yes, and another good tip is not to have inflammable curtains...

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  9. #9
    Join Date: Feb 2008

    Location: http://www.homehifi.co.uk

    Posts: 6,288

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    This used to be quite a regular problem that I used to come across when I was in the audio repair business. Almost all of them were due to soldering dry joints, especially around transistors and voltage regulators in the power supply and the output stage. As the amp heats up during play, the solder at a dry joint location starts to separate. That's when you start hearing the hum, which normally is soon followed by the protection relay cutting in. But if your speakers are blowing before the relay trips, I would head straight for the output stage and resolder any non-shiny soldering spot.

  10. #10
    Join Date: Feb 2008

    Location: South Wales

    Posts: 9,151
    I'm NotTakingLifeTooSeriouslyTheseDays.

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    Yep,
    I remember my Dad repairing a lot of solid state stuff in the 70's 80's, and as you say, some of it was indeed down to bad joints etc, mostly in high powered Amps used for Disco...
    Quote Originally Posted by StanleyB View Post
    This used to be quite a regular problem that I used to come across when I was in the audio repair business. Almost all of them were due to soldering dry joints, especially around transistors and voltage regulators in the power supply and the output stage. As the amp heats up during play, the solder at a dry joint location starts to separate. That's when you start hearing the hum, which normally is soon followed by the protection relay cutting in. But if your speakers are blowing before the relay trips, I would head straight for the output stage and resolder any non-shiny soldering spot.
    "Today scientists have substituted mathematics for experiments, and they wander off through equation after equation, and eventually build a structure which has no relation to reality"
    Nikola Tesla



    Its now a conspiracy theory to believe that the Immune system is capable of doing the job it was designed to do.
    A fish is only as healthy as the water its swimming in ! [Dr Robert Young]


    www.tubedistinctions.co.uk

    Matthew 5:10

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