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Kef 104/2 Crossover Schematic

 
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Les H
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Joined: 01 Jun 2006
Posts: 3
Location: Pleasanton, CA

PostPosted: Thu Jun 01, 2006 5:32 pm    Post subject: Kef 104/2 Crossover Schematic Reply with quote

Does anyone have a schematic for the crossover in the Kef 104/2?

I'd like to replace the capacitors in mine and a schematic would help.

Thanks,

Les
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ColinR
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Joined: 31 Jul 2004
Posts: 1175
Location: Staffordshire

PostPosted: Thu Jun 01, 2006 7:56 pm    Post subject: Reply with quote

Quote:
Does anyone have a schematic for the crossover in the Kef 104/2


Yes, of a bi wire version as do several other members, but it's not of a production varient.
Having two bi wire owners compare it to their crossovers, the topography is correct, but the component values aren't, suggesting that it's an alternative "target function" solution.

The single wire schematic is in a book by Martin Colloms I believe.

If you do wish to continue to change the capacitors, you should spend at least $300 on an LCR meter as the component tolerances vary from 1% to 20% to get the exact values required by the original computer model.
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Les H
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Joined: 01 Jun 2006
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Location: Pleasanton, CA

PostPosted: Thu Jun 01, 2006 8:12 pm    Post subject: Reply with quote

Colin,

Thanks much for the info.

I have the single wire version.

I take it then that in effect each crossover is custom built for the individual drivers so I'd have to match the specific values in my unit to avoid degrading the balance.

That could be difficult and expensive - buying many caps of the same value to find the one that matches what's required within 1%.

Maybe it 's better left alone after all. But didn't Kef use non-polarized electrolytics that don't do well over time?

Thanks,

Les
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ColinR
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Joined: 31 Jul 2004
Posts: 1175
Location: Staffordshire

PostPosted: Thu Jun 01, 2006 8:26 pm    Post subject: Reply with quote

You've got the drift Les, KEF's component tolerances cover an A3 sheet.

I've recently frightened a couple of 104-2 owners with the schematic, away from using a foil inductor in the bass section, which by the nature of the design would have totally changed the voicing.

Regarding the KEF "badge engineered" electrolytics, they'll outlast two sets of foams on the bass drivers and the Ferrofluid drying out in the T33mkII.

So unless you work where ther are lots of components around or have a friend who has such a job, are very talented or have "loadsa money" I'd leave well alone.

It's a shame that the "go faster stripes guys" are never ordinary Joe's, but that's life.
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Les H
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Joined: 01 Jun 2006
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Location: Pleasanton, CA

PostPosted: Thu Jun 01, 2006 9:09 pm    Post subject: Reply with quote

Let me sheepishly admit then that I just "upgraded" the NPE caps in my older Kef 104aB speakers with high grade film. I do notice an improvement in transients, dynamics and extension. Of course these speakers are being used as surround channel speakers (with the 104/2 in the front) where the application is much less critical. And I suspect that KEF did not as closely match the 104aB crossovers as they did with the 104/2. Correct if I'm wrong.

It's not the first time I may have intended to improve something only to perhaps have gone backwards, nor will it probably be the last. Ignorance was bliss.

Les
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ColinR
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Posts: 1175
Location: Staffordshire

PostPosted: Thu Jun 01, 2006 9:42 pm    Post subject: Reply with quote

Why be sheepish Les, in a lot of the "older" designs the caps are knackered.
My example is my 1977 Cantatas, which used to live by the seaside, so suffered from sea salt corrosion and the effects of age, so in went the Solens Smile .

My recapped Ref 105-2's were/are a learning experience, for the job was done before I aquired a Meterman LCR-55. On examining the "old" components only one 80uF capacitor feeding the midrange was broke, the rest were o.k. Embarassed

With a more complex design like the 104-2 where the "arms" of the circuit are balanced a bit like the earths on Kelvin Labs monoblocks - high inductor low capacitor, low inductor high capacitor, I wouldn't touch them as I don't have all the bits of test kit that the manufacturers originally used Sad .

However, as they're outside the scope of my KEF driver based collection (~44 pairs), I'm not particularly worried Very Happy .
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