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Crossovers

 
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ColinR
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PostPosted: Mon Aug 01, 2005 1:21 pm    Post subject: Crossovers Reply with quote

I was a little perturbed yesterday when an old pair of KEF Concerto DN12 SP1004 crossovers was sold for over £25 on ePay.

If you take the target values for the inductors on the later DN12 crossover as 5mH, 0.5mH, 5mH and 0.25mH from the measurement of seven such crossovers dating from 1976 to 1980.

L1 5 to 7.5mH, L2 0.43 to 0.51mH, L3 4.7 to 5.8mH, L4 0.25 to 0.31mH.

The sample size is too low for meaningful statistical analysis but you're only going to have a sample size of two!

So, if you must buy this "old tat" get crossovers from the 1980's that have colour coded inductors.

Alternatively buy a new pair of crossovers numbers 6 or 33 from Falcon Acoustics and mention that you are going to be using the original KEF connector when ordering.
This is so that you get a pair that you'll just be able to slot in, for the Falcon 3A circuit board is the same width and has the same edge connections as the original KEF unit.


Just before someone points out that the stated values of L2 and L3 are different from those on the specification sheets in the "Technical Section" of the site, 4mH and 1mH inductors should be found on early versions of Concertos with "wide skirted" B139A's.
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proffski
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PostPosted: Fri Aug 26, 2005 1:04 am    Post subject: Re: Crossovers Reply with quote

Gosh Colin, I agree, KEF did go through a dizzy stage once or twice.
I find the Falcon components 1st class, but still try to err away from electrolytics werever possible. The 1st generation of the wide B139s are quaint but not a patch on the later versions no matter how beefier they look!
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Wouter
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PostPosted: Fri Aug 26, 2005 9:04 am    Post subject: Reply with quote

Hello Andy,

Is there a quality/sound difference between the 6171 and SP1044?
I thought, it was only a difference of 'look' and not of sound...?


Thanks,
Wouter
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IsakAlexander
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PostPosted: Tue Jun 12, 2007 11:54 am    Post subject: Reply with quote

On the dn12 I got, the values are different from anything I`ve seen around. The capacitor for the midrange are 60mfd, not usual 30..
Also the polarity are not reversed(marked on the back). Confused The Concertos were made in 71-72, if I remember correctly.
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IsakAlexander
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PostPosted: Wed Jun 20, 2007 8:33 am    Post subject: Reply with quote

Weird, one of the dn12 had following values: 7, 4.7, 12, 80 and 60mfd.
Confused To bring the filters up to date, I can change them to 5, 5, 7, 60 and 30uF? The early versions of concerto had different crossover points than later models then? Confused
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ColinR
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PostPosted: Wed Jun 20, 2007 9:29 am    Post subject: Reply with quote

Quote:
The early versions of concerto had different crossover points than later models then


No.

A number of varients exist within B139 and B110 drive units, plus three types of T27, leads to a significant number of possible permutations for the Concerto design.

So I stick to a smaller set of SP numbers and date codes covering a ten year period.
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proffski
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PostPosted: Wed Jun 20, 2007 11:45 am    Post subject: Reply with quote

Now I learn that there were Three variants of the T27, oh my brain hurts.
Where will it all end...
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Wiesiek Lipowski
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PostPosted: Thu Jun 21, 2007 9:57 pm    Post subject: Reply with quote

I believe the SP1002 Concerto xover had 60uF in the mid section.
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ColinR
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PostPosted: Fri Jun 22, 2007 10:26 am    Post subject: Reply with quote

Quote:
the SP1002 Concerto xover had 60uF in the mid section


Yup, with a couple of resistors to pad down the B110, as the A6362 and some of the SP1003s used had magnets as big as the cutout.
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IsakAlexander
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PostPosted: Fri Jun 22, 2007 12:54 pm    Post subject: Reply with quote

I have changed the capacitors in the tweeter circuit and the 7uf one on the midrange. The cabinets had the early version of the t-27, now replaced for a pair made 18 februar 1977. Should I replace the 60uf for 30uf in the midrange also..? Marked at the back of the crossover, the midrange are not reversed in polarity as in newer ones..
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ColinR
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PostPosted: Sat Jun 23, 2007 9:59 am    Post subject: Reply with quote

As your speakers are 71-72 vintage i suspect you have a large magnet A6362, so replace the capacitors like for like.
Don't bother about the phase of the crossover until you've got your T27s installed then have a look at the "hints and tips" page at falcon-acoustics.co.uk and test accordingly.
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IsakAlexander
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PostPosted: Tue Jun 26, 2007 6:35 am    Post subject: Reply with quote

The label on the b139 fell off some time ago, it`s the one with wide chassis. The b110 do have a very large magnet, sp1003. Guess I will have to try different crossover versions. 5, 5, 7uf and 7, 5, 12 and 5, 4.7, 8.... And the other: 80, 60 and 80, 30 and 60, 60 Razz
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ColinR
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PostPosted: Tue Jun 26, 2007 8:00 pm    Post subject: Reply with quote

Quote:
The b110 do have a very large magnet, sp1003.


This is the same unit as the A6362 btw.

Quote:
Guess I will have to try different crossover versions. 5, 5, 7uf and 7, 5, 12 and 5, 4.7, 8.... And the other: 80, 60 and 80, 30 and 60, 60


Try whichever combination is close to 4, 4; 30, 4.5, 5; 80 - values pinched from a similar crossover design using the same drive units.
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