SpeakerTalk

Hugues TR4 · Introductory Contributor Joined: 22 Jun 2017 Posts: 9

Hi All,

This is my first post on your forum.
Got your address through a fellow Vinyl Engine member.
Just was given by a friend of mine a battered and dusty pair of KEF Chorale speakers (serial N° 19967, made13/07/1972).
I have heard a lot of good about KEF speakers and would like to compare them with my present Marantz HD400 or my Wharfedale Super Linton's.
Now I'm leaning on a very ill pair of speakers I'd love to bring back to life.
No problem about the woodwork, although it is scratchy and part of the veneer peeling off, this is something I can care about.
Tried to connect them to my Marantz 2245 amp, no reaction.
Opened them up: both crossovers look OK, although the original Elcap capacitors are still present.
The woofers: one is completely non reacting and gives no response to the ohm meter. The membrane was blocked by dust and it took some tweaking to move it. All the other drivers give 8-9 Ohms.
The other woofer reads 8 Ohms but needs being pushed from the inside to work, and still not very well...
The rubber suspension looks fine.
Is there a way to repair a woofer? I've only changed foam rings so far.
Thanks a lot in advance to direct me to a tutorial for repairing this unit.

Cheers,

Hugh.

speakerguru · Posted: Sat Jun 24, 2017 10:11 pm Post subject:

read this "sticky" first
http://www.hifiloudspeakers.info/speakertalk/viewtopic.php?t=1751

I think the Chorale woofer was an SP1014 with a rubber surround stuck directly to the metal chassis using CA (superglue). In which case, you'll have to be ultra-careful with a small scalpel and cut under the surround outer platform away from the chassis. i.e. you are cutting the adhesive layer, just above the paint, NOT the rubber!

Hugues TR4 · Introductory Contributor Joined: 22 Jun 2017 Posts: 9

Hi Speakerguru,

Thanks a lot for your tips.
Since the driver doesn't show any reaction to signal, I suppose it is toasted and good for the dustbin, unless I dismantle it completely and attempt to repair it, if at all possible.
I understand that a blow broke the tiny wire inside the spider, and it is this wire which needs changing (?) Which kind of wire should I use?
I'm a reasonable DIYer but I lack technical knowledge in this field.
Question: what kind of glue should I use with a loudspeaker.
Is white wood glue (Pattex) or similar good enough or should I use contact cement or Superglue?
To loosen the actual glue, could I use aceton or synthetic paint thinner. Possible issue is damaging the rubber or the other materials present in the driver?
Thanks again for your help.
Cheers,

Hugh.

speakerguru · Posted: Tue Jun 27, 2017 8:46 am Post subject:

"The tiny wire inside the spider" can be repaired but do you know which wire? The visible wire from the voice coil to the terminal panel is a special copper-phosphor bronze woven braid with very high fatigue strength. If this is visibly cut or broken it needs to be replaced entirely. If you try to solder or join it with other wire, it will fail quite quickly at the joint due to fatigue.

More likely, it will be the voice coil wire which will have broken at the voice coli former-spider joint. This can happen if the voice coil wire to braid joint has worked loose and allowed the vc wire to move and fatigue. In this case, with nothing to lose, you could dismantle the unit, dismantle the braid joint, pull one turn off the vc, to get some slack, and re-terminate the joint. The braid to vc wire joint must be stuck to the vc former in such a way that only the braid flexes. The vc wire must not flex. It is a very skilled operation. There used to be be many Maidstone ladies who possessed such skills.....

Hugues TR4 · Introductory Contributor Joined: 22 Jun 2017 Posts: 9

Wow!
This sounds like a complicated repair! And I haven't got any Maidstone lady around.
Just saw a pair of Chorale on our local 2nd hand site, with a damaged tweeter for 20€.
Will try and get it, and nevertheless attempt to get into the dead woofer and try a resurrection.
Thanks for your input, taking the liberty of calling again if I get in trouble...
Cheers,

Hugh.

Hugues TR4 · Introductory Contributor Joined: 22 Jun 2017 Posts: 9

Hi speakerguru,

So I bit the bullet and, since the driver is fried, attempted, with some success to reach the voice coil.
Unglued the dust cover with cellulosic thinner and got it off OK.
Then used the same product to loosen the spider and the surround rubber suspension.
Connected to my amp, after unwinding a small amount of the copper wire and soldering them to the terminals, I got some faint sound (!?)
Question: how free should the voice coil be in the main magnet groove?
How high should it stick out from the spider?
Mine was full of old melted glue and didn't move at all. Cleaned it with cellulosic thinner and got it smoother but it still doesn't really move freely.
Is there a way?
Have to go step by step as my skill in speakers is very limited.
I'm more a mechanical man, no problems to service and repair a Dual or a Thorens turntable.
Thanks a bunch to help me out (or at least try to...)

Cheers,

Hugh.

speakerguru · Posted: Wed Jul 05, 2017 7:36 am Post subject:

Assuming the vc is still circular, it is centered using a 0.007"' shim between it and the magnet centre pole. When the glue is set, pull out the shim and glue on the dust cap. It should be completely free to move with no scratchy sounds.

speakerguru · Posted: Wed Jul 05, 2017 7:40 am Post subject: Re: KEF Chorale.

Hugues TR4 · Introductory Contributor Joined: 22 Jun 2017 Posts: 9

Hi speakerguru,

Thanks a bunch for your lecture!
Well, I think I'll have to give up on this project!...
Lack of skills, vision getting weaker...(75)
I'd like to ask the expert one more question though.
I might have a solution: replace both woofers by a pair of Wharfedale (also British sound) Super Linton woofers I still have here lying around.
They are matching fully working Linton W30D's of which one of the fried egg type tweeter is toasted, and very difficult to fix or replace.
What would the expert think about the idea?
Don't know about the sensitivity and impedance of the Wharfedale, and whether they would match with the crossover board of the KEF...or would I have to use the Wharfedale crossover (looks rather basic though).
Do you know about the Linton?
Wouldn't it be a crime (and a counter-performance) to mix two different British brands?
Thank you very much for your precious help!

Cheers,

Hugh.

speakerguru · Posted: Wed Jul 12, 2017 1:53 pm Post subject:

No, sorry. I know nothing about Super Lintons.

Hugues TR4 · Introductory Contributor Joined: 22 Jun 2017 Posts: 9

Thanks for your reply.
Will try and find a source for a pair of SP1014.
Do you know any through this forum?
The Wharfedale's have an impedance of 6 Ohms and wouldn't probably meet the KEF specs.
The boxes are restored and re-polished and look almost like new, so I would hate throwing them away...
Thanks again for your input.
Cheers,

Hugh.

speakerguru · Posted: Thu Jul 13, 2017 3:19 pm Post subject:

eBay is probably the best source for woofers.

6.5 Ohms d.c. is the typical resistance for an "8 Ohm" driver and one to be used in a nominal "8 Ohm" system.

happy hunting

Hugues TR4 · Introductory Contributor Joined: 22 Jun 2017 Posts: 9

Thank you Guru.
Will start looking.
I'll keep you informed about the further developments.
Thanks again for your hints and advice.

Cheers,

Hugh.

Gary · Posted: Wed Sep 13, 2017 1:30 am Post subject:

Any luck with the speaker search?
_________________
Sometimes I lie awake at night, and I ask, "Where have I gone wrong?" Then a voice says to me, "This is going to take more than one night."
-- Charles M. Schulz (as Charlie Brown)

Hugues TR4 · Introductory Contributor Joined: 22 Jun 2017 Posts: 9

Hi Gary,

I was just about to send you a post.
Tried unsuccessfully to repair the damaged woofer. This tweaking with these tiny wires is definitely not for me!
The second driver is shot as well: coil half stuck in the spider. It doesn't go up again after pushing the cone down. It also makes a rubbing sound when moving.
Should I throw them both away, or is there still anything I can disassemble and keep for further repair work? (the rubber suspension for example?)

Finally found a nice pair of SP1014 for 35€ and fitted them on the boxes: what a fabulous sound, deep bass, presence and channel separation!
Listening to them at the moment, in place of my previous set of Marantz HD400: quite a difference!
Is there an other affordable model of vintage KEF's I should look for? (these ones are belonging to a friend).
Am presently on an ad from Holland selling about six SP1014 for 20€ a pair...

Other question: the B200 type uses several different SP drivers (SP1039, 1022, 1054, 1063 ...) Are they all compatible with the Chorale?

Thank you for teaching me! It's the first time I come across KEF's, but I had heard about their qualities.
Thanks again,

Cheers,

Hugh.