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Thread: Dm7 tweeter shellac

  1. #1
    Join Date: Feb 2018

    Location: Hampshire

    Posts: 14
    I'm Andy.

    Default Dm7 tweeter shellac

    I'm in the process of restoring my DM7's. the tweeters work ok but are not performing as they should.
    I have read on a few sites ( maybe even this one - but I can't find it)..) that carefully applying shellac to the silk dome will restore the sound- is this correct? Any advice on how to apply shellac and how many coats would be gratefully appreciated.
    The domes are now available from good hifi in the Netherlands, there's a good 'how to' video on their site, so there is a back up plan..

  2. #2
    Join Date: Apr 2012

    Location: Southall, West London

    Posts: 35,226
    I'm Geoff.

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    My advice would be, don't do it!

    If the tweeters are sounding a bit off it could be a couple of things. If they have ferrofluid in the coil gaps, this could have dried out and be causing fouling/binding of the coil. Or you could have a crossover that needs new capacitors. I'd avoid 'painting' anything on tweeter domes, sounds like a recipe for disaster and once done, can't be undone.

    I'd check the capacitors first. It should be a cheap and easy job.





    .
    Last edited by walpurgis; 05-03-2018 at 09:23.

  3. #3
    Join Date: Feb 2018

    Location: Hampshire

    Posts: 14
    I'm Andy.

    Default

    Hi Geoff thanks for the advice. �� I’m afraid haven’t shared the whole story.. They did work great until I ‘carefully!!’ Removed the debris from the surface with a damp cotton bud. (I know I know ��) so I know the caps are good. I’ve seen a few old threads on different forums so see that it has been done but just wanted the heads up from if someone had actually done it on here. I should have L plates.. ��

  4. #4
    Join Date: Feb 2018

    Location: Hampshire

    Posts: 14
    I'm Andy.

    Default

    I’ve looked at the tweeter specs in the booklet and it doesn’t mention that they have ferrofluid, so I am assuming they don’t.

  5. #5
    Join Date: Jun 2016

    Location: Surfside Beach usa

    Posts: 97
    I'm charles.

    Default

    Quote Originally Posted by Andy1 View Post
    I’ve looked at the tweeter specs in the booklet and it doesn’t mention that they have ferrofluid, so I am assuming they don’t.
    The tweeters do indeed have (had) ferrofluid cooling and it will almost certainly have dried out due to the age of the speakers and HF output will be compromised. They will not be performing to spec. B & W do not service parts for these ancient speakers and moreover even if you were in the position of rebuilding said tweeters there is no data available as to the correct formulation of original ferrofluid used in this tweeter so my advice is to either accept you're listening to compromised speakers or move on.

  6. #6
    Join Date: Apr 2012

    Location: Southall, West London

    Posts: 35,226
    I'm Geoff.

    Default

    If that should be the case and assuming the diaphragm and coil assembly can be removed, there'd be little harm in trying a replacement tweeter type ferrofluid of some sort.

    Cleaning the coil and the magnet gap should not be too hard using non-magnetic tools for the gap. A slice of old credit card or similar might do.

  7. #7
    Join Date: Jun 2016

    Location: Surfside Beach usa

    Posts: 97
    I'm charles.

    Default

    Quote Originally Posted by walpurgis View Post
    If that should be the case and assuming the diaphragm and coil assembly can be removed, there'd be little harm in trying a replacement tweeter type ferrofluid of some sort.

    Cleaning the coil and the magnet gap should not be too hard using non-magnetic tools for the gap. A slice of old credit card or similar might do.
    Switch cleaner and tissues for the gap.

  8. #8
    Join Date: Apr 2012

    Location: Southall, West London

    Posts: 35,226
    I'm Geoff.

    Default

    Quote Originally Posted by 57charles View Post
    Switch cleaner and tissues for the gap.
    Not having done the job myself, I'm sure you are correct. Mind you, I'd consider using dried household wipes rather than tissues. They are lint free, so not bits left behind.

  9. #9
    Join Date: Feb 2018

    Location: Hampshire

    Posts: 14
    I'm Andy.

    Default

    Thanks for all the advice. Replacement diaphragms are availble for these now, (although not genuine) I Finished reassembling them last night and the tweeters don't seem as bad as I thought ( it was most likely my ears plus some paranoia due to ignorance).
    I may order the bits in the future and rebuild them adding some ferrofluid. I've changed a few phone screens in my time- it looks less fiddly than that! These speakers are not so expensive. If I truly cock them up I will indeed move on. Albeit with some new found wisdom!
    All advice here is appreciated guys. Keep it coming

  10. #10
    Join Date: Sep 2014

    Location: brighton uk.

    Posts: 3,289
    I'm jamie.

    Default

    ive done it and on my tweeters is was easy,no soldering required,yours may be different.
    have a look here for a vid.
    http://theartofsound.net/forum/showt...highlight=r852
    My System/ Yamaha NS1000M speakers ,Pioneer PLC-590 turntable,Pioneer PA-5000,Alphason HR-100S-MCS,Zeta tonearms,Denon 103SA Cartridge's,Denon HA-500 Head Amp, John Wood KT88 Valve Amp,Sony 700ES Amp,Sony X555ES CD Player, Nakamichi ca5 pre amp ,

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