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Do I do a Lazarus?

 
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Kurt
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Joined: 13 Aug 2007
Posts: 3

PostPosted: Sun Aug 19, 2007 11:43 pm    Post subject: Do I do a Lazarus? Reply with quote

Hi folks, new to the forum which I came across whilst looking for advice on a poorly b200.

Anyway, here goes the background before the questions.

Circa 1988 a friend of mine (a talented guy who was the sound engineer at Manchester's Free Trade Hall) built some custom floor-standers for me. They were 4-ways working on what I believe is the Isobarik principle (bear with me I'm a total novice when it comes to the technicalities).

Each box consisted of:

  • 2 x Kef B200G (SP1075) 8" bass drivers
    1 on the bottom of the front baffle, and 1 on the top of the rear baffle firing backwards. I'm buggered if I know the theory of how they worked but when a bass signal is played they both move in/out at the same time compressing the air in the cabinet, so basically the more bass the more internal pressure. I can tell you they never 'honked' Smile and are pretty flat down to about 30hz
  • 1 x Kef B110B (SP1057) midrange
    Isolated internally via a very thick cardboard tube stuffed with acoustic wool.
  • 1 x Kef T52B (SP1072) tweeter
  • 1 x Coles Super Tweeter (I think), surface mounted on the front baffle
    * KEF 4-way crossovers SP2034 (LF) and SP2035 (HF, MF) (plus something electronic in-line between the two bass drivers.


They are being driven by a Naim 72/Hicap/140 combination.

Anyway, it appears that one of the b200s has developed a distortion/buzz which I believe is either a knackered voice coil or the GSS (Gravity Sag Syndrome).

I've been unsuccessfully trying to track down a replacement sp1075 as they seem to be like rocking horse droppings. So, being the electro-numbskull that I am, could I replace the rear facing b200s (on both boxes) with a pair of sp1014 or sp1054 without too much of a detrimental effect on the sound. I know the 1075 is 5 ohms and the prospective replacements are 8ohms. I've also seen a pair of Peerless 8" drivers on eBay which Wilmslow Audio seem to think are an adequate replacement for the b200s so the same question applies to these too.

Whilst I'm messing with these speakers (which are still used frequently) I'm uhmming and ahhing over whether to banish them to the bedroom and splurge on some Spendors or some Quads, or whether I should take this opportunity to upgrade and sort out some issues that have bugged me for years.

The prime irritant of them sound-wise is that although they have a wonderfully detailed mid and bass with an almost holographic soundstage with relatively uncomplicated music the treble has always let them down when the sound starts to get "busy" i.e. lots of instruments come in etc. It manifests itself as as smearing of detail like high-hats or cymbals. Those same instruments sound very detailed if playing on their own, but throw in more instruments and the detail disappears.

So my query is, would the T52s benefit by being replaced by some T27s (or available equivalents) or is the likely problem somewhere else?

I would prefer to get these speakers working how I like as they have great sentimental value as their designer/builder died last year and they are a sound I have got used to. Not to mention the fact that I'm skint!

Any help would be appreciated, here's some pics of the bits...



The front of the SP2034 x-over (click for larger version)


The back of the SP2034 x-over (click for larger version)


The front of the SP2035 x-over (click for larger version)


The in-line bass doohickey (click for larger version)


Speaker full length (click for larger version)


Speaker Mid/Treble (click for larger version)


The ins and outs of the whole system can be seen at http://www.filmdedications.com/ukra/
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ColinR
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Joined: 31 Jul 2004
Posts: 1175
Location: Staffordshire

PostPosted: Mon Aug 20, 2007 10:07 am    Post subject: Reply with quote

Right you've got five minutes before I go off to work Very Happy .

Your speaker uses KEF CS9 crossovers - B300B, B110B, T52.

The add on board is a standard 0.3mH/0.47uF for a Coles 4001G.

Apart from suggesting David Smith or www.wemblyloudspeakers.com for a £40 plus shipping rebuild or a trip over to the Richard Allen Recone Lab in Huddersfield, I'm stumped.

I don't understand the problem with your T52s, but then again I haven't got golden ears anymore.

Off now to work in Macclesfield Cool.
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ColinR
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Joined: 31 Jul 2004
Posts: 1175
Location: Staffordshire

PostPosted: Mon Aug 20, 2007 7:33 pm    Post subject: Reply with quote

For those not in the know the use of two B200Gs with a CS9 bass crossover is in one of the KEF cabinet design sheets.

Quote:
The in-line bass doohickey


I hope not, as a supertweeter driven on the residual out of phase signal will cause some really wierd effects.
Hopefully the "whatsit" is connected directly to your input terminals somewhere.

Now as your bass units are bolted to the baffles, why not turn the faulty one 180 degrees and affix with three self-tapping screws and see what happens.

If the unit is buggered, spend £40 or look for a particular ePrey auction.

Regarding the T52s, you could always replace them with T33s and add another pcb with the CS7 aB filter section after you've disabled the T52 one.

Wilmslow Audio sell drive units that may work.

In this case, Peerless, NO CHANCE.
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Kurt
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Joined: 13 Aug 2007
Posts: 3

PostPosted: Mon Aug 20, 2007 9:50 pm    Post subject: Reply with quote

ColinR wrote:
For those not in the know the use of two B200Gs with a CS9 bass crossover is in one of the KEF cabinet design sheets.

Quote:
The in-line bass doohickey


I hope not, as a supertweeter driven on the residual out of phase signal will cause some really wierd effects.
Hopefully the "whatsit" is connected directly to your input terminals somewhere.


Yup, you are correct, it was a major brain fart on my behalf. I told you I know little of the technicalities. What made me think it was bass related is that it was attached to the ceiling of the cabinet directly behind the rear-facing bass driver.

Quote:

Now as your bass units are bolted to the baffles, why not turn the faulty one 180 degrees and affix with three self-tapping screws and see what happens.


Yup, already seens that advice here on the forum so about a week ago I removed it from the front and replaced it on the rear (so if it buzzes it would be quite so audible) rotated 120 degrees. Nothing has improved so far but I shall attempt to be patient. Not that I have much choice, lack of funds prevents me from doing anything major anyway.

Quote:

If the unit is buggered, spend £40 or look for a particular ePrey auction.


I'm constantly monitoring the 'establishment' though I'm not holding out any chances.

Quote:

Regarding the T52s, you could always replace them with T33s and add another pcb with the CS7 aB filter section after you've disabled the T52 one.


Now this is where the nomenclature confuses me. I know the numbers relate to millimetres but how do they relate to "quality"? Is the T33 a better driver than the T52?

I have no idea what you mean with regards to the PCB, although I can solder acceptably I have no experience whatsoever about electronics jiggery-pokery. I'm sure I can research it though and there's a new Maplins in Stockport Smile

Quote:

Wilmslow Audio sell drive units that may work.

In this case, Peerless, NO CHANCE.


I'm glad you said that, it saves me bidding on the pair currently on eBay. So I'm presuming the same advice goes for the SP1014 or the SP1054 then?

Many thanks for the advice. It's looking like there aren't going to be too many upgrade alternatives available to me in this instance Sad
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ColinR
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Joined: 31 Jul 2004
Posts: 1175
Location: Staffordshire

PostPosted: Mon Aug 20, 2007 10:25 pm    Post subject: Reply with quote

You have a PM.


The T33 is the soft dome version of the T27 btw and has a square faceplate the same size as the T52 - see drivers section.

The T33 like the T27 tends to be a bit "spitty" with a rising treble response, so benefits from an aB circuit although with a little capacitor swapping you could get the right Bessel circuit on your CS9 pcb - see crossovers section.
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