Dm7 tweeter shellac

[Andy1]

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? :scratch: 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..

[walpurgis]

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.





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[Andy1]

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.. ��

[Andy1]

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.

[57charles]

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.

[walpurgis]

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.

[57charles]

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.

[walpurgis]

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.

[Andy1]

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 ;)

[karma67]

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

[Andy1]

Hi all.
Charles, you suggested that there is ferrofluid in the tweeters fitted to these speakers, but I cannot seem find any references which support this on the net. I thought the specs in the original manual would Clarify this if this were the case. ( it goes into detail about everything else) Am I missing something? Could I add ferrofluid to improve performance regardless?
I have also read that bypassing the fitted 2a fuse would improve the sound too, which I have done. Would bypassing the 500mA fuse, which I believe protects the tweeter be advantageous too?

[57charles]

Hi all.
Charles, you suggested that there is ferrofluid in the tweeters fitted to these speakers, but I cannot seem find any references which support this on the net. I thought the specs in the original manual would Clarify this if this were the case. ( it goes into detail about everything else) Am I missing something? Could I add ferrofluid to improve performance regardless?
I have also read that bypassing the fitted 2a fuse would improve the sound too, which I have done. Would bypassing the 500mA fuse, which I believe protects the tweeter be advantageous too?

Hello Andy - I'm afraid those tweeters were indeed ferrofluid cooled - and B & W manuals don't state this. Old B & W tweeters are well known for this ferrofluid drying out problem - not just the tweeters in DM7. I've owned DM7, DM6, DM12, DM14 and DM2 series 2 and all the tweeters dried out and none are servicable by B & W. Bypassing the fuse is a complete waste of time.

[Pharos]

Switch cleaners in the coil gap?

Be careful, Kontakt is very vicious and may well remove coil varnish, I would use Radiospares Computer cleaning fluid.

[Andy1]

Thanks gentlemen.
I going to enjoy these for a while and then order the parts and give it a go. The age of the tweeters does show.. (they sound good still, but I know they should sound better). There is a good video available from good hifi.netherlands re replacing the diaphragm. They talk about refilling ferrofluid too. If it goes the wrong way there will be some dm 7 spares on eBay shortly after... I'm not happy unless I'm tinkering