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One for the Isobarik Experts

Discussion in 'audio' started by Richard Lines, Mar 3, 2020.

  1. Richard Lines

    Richard Lines pfm Member

    Good Evening All,

    I am in contact with a guy who has a pair of Isobariks circa Serial No. 007800+ who is getting a reading of 8ohms across the banana sockets for the bass drivers on both speakers.

    I have two pairs of Isobariks here and both are showing something in the region of 4ohms which would be consistent with a pair of B139's mounted in parallel.

    The readings he is getting across the midrange and tweeters are constant with what you might expect so it doesn't appear to be a faulty meter.

    Anyone care to offer up any theories?

    Regards

    Richard
     
  2. JensenHealey

    JensenHealey pfm Member

    We are assuming that there is a fault with the speakers?
    If so, what are the symptoms?

    If you read 8 Ohms then it would indicate that one of the drivers or the lead to one of the drivers is open circuit. Would be odd for both to have the same issue. Not altogether familiar with Isobariks - are there any fuses?
     
    Chris likes this.
  3. Richard Lines

    Richard Lines pfm Member

    No fuses involved - an open circuit driver is a possibility but on both?

    It is difficult to diagnose at a distance.

    The owner posted on here back in January 2011:-

    Many thanks fot the intrest my bricks serial no 007854 and yes the old style 250 keeps tripping. I do like to hear them loud and am a little disapionted particualy with the base which seems to be just warming up when the amp trips.

    It is possible that there has been a problem here for a while?? Not easy to believe defective woofers could have remained undetected all this time?

    The speakers have had alternate midrange and tweeters fitted by a reputable firm and you would think an obvious fault in the bass department might have been uncovered?

    The speakers were originally sourced from a dealer as far as I can tell.

    Regards

    Richard
     
    Raj sondh likes this.
  4. Raj sondh

    Raj sondh Member

    Hi Richard
    My guess is that one of the bass units may have blown (ive done it a twice a couple of years back and luckily ive had spares) or the solder connections to one of the units has seperated.

    I used a tone and connectivity meter to test each unit. If the bricks are passive you'll need to place bricks top down so you can access the crossover and wires and test them. But you may need to seperate the cables to the drive units.

    Same with an active setup.
    What ive done is separated connections to all drive units and added banana plugs to each. Its a lot easier to test all the drive units with bricks placed as they are.

    If the bass unit is blown. The front ones are easy to remove. The the inside one takes a lot if effort though.

    You can get replacements from https://www.falconacoustics.co.uk/d...8-ohm-kef-b139-sp1044-replacement-woofer.html
    Hope this helps
     
    Last edited: Mar 4, 2020
  5. david ellwood

    david ellwood Kirabosi Kognoscente

    Take a picture of the wiring behind the removable panel in the base.

    Its either a blown driver, disconnected wire, or deliberately split between the spare connector to facilitate an individual amp per driver (nice)

    Or maybe some idiot removed the rear drivers?
     
    Raj sondh likes this.
  6. YNWOAN

    YNWOAN 100% Analogue

    In my experience, and this is true also of Sara’s, if Briks are overdriven the internal bass driver is the one most likely to fail. Unfortunately, the only real sign of this is to measure them (as above) - it’s also a proper PITA to repair.
     
    Raj sondh likes this.
  7. david ellwood

    david ellwood Kirabosi Kognoscente

    The good news is new replacements are available and are much higher excursion and power handling. (They do fit)
     
  8. Richard Lines

    Richard Lines pfm Member

    Good Morning All,

    If the bottoms in a later model are removable then that is a start.

    I would be looking to replace the KEF drivers with Keltik or TDL/ Elac ones anyway........ all I need to do is source some ;)

    Regards

    Richard
     
  9. Richard Lines

    Richard Lines pfm Member

    The only positive I would take from that is that you don't need to be too subtle removing the rear unit, yes you don't want to damage the cabinet but you could just cut through the driver......

    Regards

    Richard
     
    Raj sondh likes this.
  10. Raj sondh

    Raj sondh Member

    Yes def. The ones from falcon . Can take some serious power and i've found tightness of the bass to be superior to the original b139's
     
  11. Raj sondh

    Raj sondh Member

    the mastic/glue that sticks the driver unit to the cabinet is the issue. Otherwise its dead easy to take out.
     
  12. martin dawson

    martin dawson pfm Member

    I had a problem about 5 years ago where the right hand speaker mid / tweeters failed. It was a dry joint on the printed circuit board, resoldered and back in business.

    Regards,

    Martin
     
  13. Richard Lines

    Richard Lines pfm Member

    Good Morning All,

    Didn't the later units resort to gaskets did I read somewhere?

    Regards

    Richard
     
  14. Richard Lines

    Richard Lines pfm Member

    Good Afternoon All,

    I've never had cause to take the bottom panel off my Isobariks before -

    [​IMG]

    It should be pretty easy to determine which of the two woofers is at fault or even if both are connected.....

    Regards

    Richard
     
  15. Raj sondh

    Raj sondh Member

    Hi Richard

    Connections look sound. One way to determine which drive unit it is. Is to run a tone through the connections. ( Tone generators like the ones bt use are fairly cheap and is a very useful tool). (,iv

    When running the tone. Determine if the sound is coming from the rear drive unit by placing your ear on the cabinet at the back where the rear drive unit is located.

    Youll know get some indication bit to be perfectly sure you'll need to desolder the bass drive connections and test each one sepertaly.

    Once fixed your bass will sound ballistic.
     
  16. Richard Lines

    Richard Lines pfm Member

    Raj,

    I can knock up a 555 based tone generator for this coming weekend - good idea thanks.

    Regards

    Richard
     
    Raj sondh likes this.
  17. david ellwood

    david ellwood Kirabosi Kognoscente

    Looks like you’ll soon have it licked
     
  18. martin dawson

    martin dawson pfm Member

  19. david ellwood

    david ellwood Kirabosi Kognoscente

    That’s an old boy
     
  20. Richard Lines

    Richard Lines pfm Member

    Good Evening All,

    Having sent the vendor a couple of photo's and the old Linn Speaker Service manual he has removed the two front woofers and determined that both are dead. As you can imagine he is disappointed to find this out about them after owning them for over 10 years.

    I strongly suspect that they were like this when he bought them (I'm not going to name the sellers but it wasn't Audio Projects so those that know Leeds will have a fair idea who the other vendor was).

    He is still selling the speakers so I will be down at the weekend to collect them.

    Thanks for suggestions/ comments.

    Regards

    Richard
     

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