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Advice sought on problem with B200 SP1075

 
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SloopJohnB
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Joined: 09 Sep 2004
Posts: 6
Location: Dorset U.K.

PostPosted: Thu Sep 09, 2004 1:07 pm    Post subject: Advice sought on problem with B200 SP1075 Reply with quote

Hi Everyone,

What a great forum!

I hope someone can help me out here: I recently purchased a pair of Reference 103.2's in original un-molested condition. These were a "dream speaker" for me to own some day and now I have a pair I am not disappointed - I have a sound I am now very happy with indeed Very Happy

But (there's always a but), the B200 in the left speaker has a very slight case of voice-coil "interference" - it's not full-blown rub or off-axis alignment but if you gently move the cone in and out by hand you can hear a faint "click-click-click" as it goes in and out (unless you press in one place only, slightly above the voice coil, then it doesn't do it). The only time this is audible on music is with hollow or echoed low bass (e.g. a decaying drum or 'thud' sound on it's own). Otherwise a sine wave test tone reveals that this distortion is audible only with reasonable cone excursion on frequencies less than 150Hz, where the "clicking" is an added "edge" to each cycle of the sound. Vocals etc not a problem and the cabinets themselves still impressively free of resonances and rattles at all frequencies tested.

So what to do? I've read other posts (this forum) that have told of people removing the drive unit and partial disassembly-reassembly (magnet) and even bending the basket/frame (surely very risky?). I am very keen not to ruin my lovely speakers! The reproduction is sublime!

Is it best to "have a go" myself with the magnet mounting? Do these speakers have any sort of stabilising rod to the back of the cabinet? Any tips from other 103.2 owners? Should I try contacting KEF? Or Wilmslow Audio, or one of the companies that offer repairs to drive units? Are the B200's in these speakers carefully matched like the crossovers? Would major repair work mean the same modifications being carried out on both speakers for them to remain a matched pair?

I am so impressed with these 20 - 25 year old speakers, I had thought that the crossovers with their electrolytic capacitors would be a problem but I can't fault the closeness of matching in this pair: I'll leave those carefully designed crossovers well alone! I use a pair of NAD 214's to drive them and the inefficiency of the design responds well to the huge overhead of "Volts available" in drive, complimenting the "liveliness" of my CD based system rather well - keeping everything nicely controlled (OK I'll shut up now...!)

TIA for replies and suggestions...


Regards to all

Tim
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mech986
Introductory Contributor


Joined: 19 Oct 2004
Posts: 6
Location: La Habra, California USA

PostPosted: Tue Oct 19, 2004 6:45 pm    Post subject: KEF B200 SP1075 voice coil rub Reply with quote

Hi,

Try remounting the B200 in a different position, i.e., turn the driver 120 degrees for about 2 weeks, then again 120 degrees for 2 weeks. The voice coil spider suspension tends to sag after 10-20 years (what doesn't?!!) and the coil can then hit the pole piece. Rotation helps to compensate for this.

I wouldn't mess with the magnet, the frames are not easily bent and it would be hard to determine the alignment.

Hope this helps.
_________________
Regards,

Bart
mech986
Yahoo! LS3/5a newsgroup moderator
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SloopJohnB
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Joined: 09 Sep 2004
Posts: 6
Location: Dorset U.K.

PostPosted: Wed Oct 20, 2004 11:05 pm    Post subject: Re: SP1075 Reply with quote

Hi Bart,

Thanks for replying and for the tips


Tim
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Jb
Introductory Contributor


Joined: 20 Jan 2005
Posts: 6
Location: chicago,illinois

PostPosted: Wed Jan 26, 2005 2:31 am    Post subject: kef-b-200-1075-3-hole-mount-8 inch-woofer Reply with quote

HANG ON SLOOP-B, I have the same problem,I have rotated it, and just recently Armor-alled it,[to condition the vinyl cone]scotch tape works for a song or two,it must be the 3-hole mount,right?My next step will be to drill additional mounting holes through the steel frame,any kef-heads out there have a permanant fix?How about to re-route the cabinet edge and install a round style b-200,[does it have the same range in frequency?]
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SloopJohnB
Introductory Contributor


Joined: 09 Sep 2004
Posts: 6
Location: Dorset U.K.

PostPosted: Wed Jan 26, 2005 9:43 pm    Post subject: Drilling holes? Hmmm, you haven't seen my DIY disasters... Reply with quote

Hi Jb,

Thanks for your advice. Actually the problem really is inaudible in 99.9% of programme material (basically you have to provoke the problem with sine-wave test tones etc to identify it) - I can live with that. I would not wish to change from the SP1075 as originally installed, I would maybe look at a second-hand replacement of the same type or maybe get my drive unit re-conditiond by a specialist. I'm hoping that day is a long way off Rolling Eyes
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clem_o
Intermediate Contributor 25+


Joined: 30 May 2005
Posts: 44
Location: Manila, the Philippines

PostPosted: Mon May 30, 2005 3:38 am    Post subject: Reply with quote

A fix we've tried with some success is to use a hair dryer set to 'hot' and carefully blowing on the spider while 'nudging' the cone to its proper alignment. You have to 'overdo' the position a bit; when the spider cools off it will settle to a position slightly less than what it was when hot. It takes a few tries to get it right, but it does work...

Cheers

Clem

ps: do avoid heating the cone, and don't try this trick on a Uni-Q driver without first removing the tweeter!
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SloopJohnB
Introductory Contributor


Joined: 09 Sep 2004
Posts: 6
Location: Dorset U.K.

PostPosted: Mon May 30, 2005 10:29 pm    Post subject: SP1075 cone alignment Reply with quote

Thanks Clem_o, Def. worth a try when the drive unit becomes unusable due to voice-coil rub! Mine has not worsened (yet). SP1075's seem to be quite rare on eBay etc. They had a very high specification for their day!

Cheers

Tim
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