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Concerto Crossovers

 
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tsgoss
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PostPosted: Thu Jan 22, 2015 2:05 pm    Post subject: Concerto Crossovers Reply with quote

Hello all,

I've recently obtained some 1970s Concertos, more specifically I believe they're the later revision (with the all black, less rounded drivers). I'm happy to post some pictures if I'm being unclear.

The crossovers on them are original and starting to show their age. I've also heard that the crossover design was never spectacular in the first place. So I've been looking at options to replace them, and it seems like I have a few:

Option 1:
I can refit the existing crossovers with new components. It probably wouldn't be that hard, but I'm more or less stuck with the current crossover design.

Option 2:
There's a crossover design at Wilmslow Audio. It's fairly expensive (compared to the other options), but it's an off the shelf product and presumably made from better components to justify the cost (?)

Option 3:
There's a number of crossover designs at Falcon Acoustics, each with different revisions. It looks like there's three designs, the 5, 6 and 33 series. Each series has different options within in, for example the 5C vs 5 vs 5aB. Falcon look cheaper than Wilmslow (even after accounting for the single unit pricing), but because there's so many versions it seems like it's more important to choose the right design. I haven't found any guidance on this.

So, there's a lot of options on the table. I'm pretty convinced that it'd be worth it to buy a new crossover (rather than recap my existing one).

I'm hoping to start a discussion which might help me answer the following questions:
    (Broadly) what are are the differences in components/design between Falcon and Wilmslow?
    What are the differences between the various Falcon crossovers?
    All things being equal, if you had to install a new crossover in your Concertos tomorrow, what option would you use?

I apologise if this has been asked and answered before, but I couldn't find it after a few searches.

Cheers,
Tristan
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iso
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Joined: 29 Aug 2011
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Location: Finland

PostPosted: Mon Jan 26, 2015 9:14 am    Post subject: Reply with quote

First I´d like to say welcome to this forum.

This issue has been discussed earlier. When I tried to find answer to your question few years ago, it appeared that AusKef/Falcon53 would be ultimate development of commercially available Concerto crossover. However it was discontinued. Only few CS7 crossover boards were available these days from Falcon, but no one was willing to share the original schematic.

As far as I remember, Colin Royle mentioned that Falcon 33 with acoustic Butterworth option would be as close as you can get to original AusKef/Falcon53. Falcon 33 options are numerous as it was used also Webb/Williamson TL speaker with super tweeter. I ques that Colin did mean that 33Mc was way to go...

http://www.falconacoustics.co.uk/crossovers-ls35a-networks-filters-falcon/kef-concerto-upgrade-super-power-kit.html

Let us know how things will proceed... especially if you can open can of worms and do find schematic of mysterious AusKef/Falcon53 crossover.

Best Regards

Kimmo

PS I gave up and did Cantata rebuild as this one shared similar crossover topology and happened to be available
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habrune
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PostPosted: Thu Apr 16, 2015 4:36 pm    Post subject: Reply with quote

Hi Tristan,
I completely agree with Kimmo.
I worked trough subsequent versions of the B139/B110/T27 XO layout.
Tried to find the indeed mysterious AusKEF version, the supposed end to all queries....to no avail, so if you find this layout please contact me.
I ended up with a Cambridge R50 TL XO, with modification: I followed an old leaflet once made public by Falcon on the Falcon site. Ask them. Falcon crossovers IMHO are very good, strongly advised to use them.
B139: 6mH and 60uF. T27: The usual 2x 4u7 in series with T27, and from between both 4u7F's a 0,25mH coil to earth. +Modification: the two 4u7F's are bridged by one 0,47 uF cap, thus making a-kind-of aB filter. This is the easy way, you can keep the existing DN12 components. Better: replace this total HF section by the T27 104 aB section.
The MID modification was: B110A (A!, SP1003) 12dB highpass, 18 dB lowpass. In the Cambridge XO I replaced the 0,6mH series coil with an 0,82mH one. I increased the cap to earth (3u9F) to a 10uF one. Next I inserted a 0,4mH coil in series to the B110. To do so you have to interrupt the lead on the print to the B110. The zobel network (10R + 10uF) has to remain parallel to the B110, so after the interrupt. Bridge this interrupt with the 0,4mH. So: 0,82mH and 0,4mH are in fact in series, and between them only 10uf and 3,4mH parallel to earth (4mH from the DN12 will do also). Be careful to line the coil out, in a way non-parallel to any other (big) coil. I kept the 30uF series cap from the DN12.
B110A and T27 are connected in opposite phase w.r. to the B139 section.

This is a very rewarding layout, specially if good caps and aircoils are used.
No quacky mids from the B110A, or rough and tizzy sounds from the T27.
This is the best I made with these units so far.
Can only be further improved (recommended) by insterting an 18dB CS7 section to the B139 (3,5 + 7mH / 82 or 100uF). When inserting this option, all units are connected in the same phase (all red dots to +). Might come close to the Falcon 33 crossover?? Ask them.
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Wiesiek Lipowski
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PostPosted: Fri Apr 17, 2015 1:43 pm    Post subject: Reply with quote

Why don't you try adding z Zobel to the B139's?

8R+15uF shunt at the speakers or x-overs can make the male and female vocals less bassy.
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proffski
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PostPosted: Tue Apr 21, 2015 11:48 am    Post subject: Reply with quote

I cannot remember the actual frequency but when I built my Labyrynth /TL monsters I ended up choosing a much lower crossover frequency for the B139, possibly around 100 or 150Hz. It removed a lot of strange behavior from the bass driver! End design got rid of passive crossover and ended up with custom 24dB octave active system with Tri-Amping.
http://s891.photobucket.com/user/AndyGoloskof/media/Richter%20%2819%29_zpsa3196232.jpg.html?sort=6&o=62#/user/AndyGoloskof/media/Richter%20%2819%29_zpsa3196232.jpg.html?sort=6&o=62&_suid=142961320238807283929023654905
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Wiesiek Lipowski
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PostPosted: Tue Apr 21, 2015 1:13 pm    Post subject: Reply with quote

Hi Andrew,

What cap and resistors values did you apply over there? Regards,
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proffski
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PostPosted: Tue Apr 21, 2015 3:23 pm    Post subject: Reply with quote

Wiesiek Lipowski wrote:
Hi Andrew, What cap and resistors values did you apply over there? Regards,


Do you mean the whole crossover or just the bass section?
Now you are asking me something I did circa 1979/1980!
I tried Linkwitz-Riley, Butterworth and Bessel configurations, I think that the final was Linkwitz-Riley… I’ll have a look when I get home tonight.
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Wiesiek Lipowski
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PostPosted: Tue Apr 21, 2015 3:30 pm    Post subject: Reply with quote

I mean just the bass section. I followed the advivce as per over here http://www.trueaudio.com/st_zobel.htm
and the data in the B139 leaflet.
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proffski
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PostPosted: Tue Apr 21, 2015 6:01 pm    Post subject: Reply with quote

I've found some of my notes but not all.
Started with 13µF and about 10Ω, but I went higher after listening tests.
I had trouble getting the damping right, lots of trouble (remember it was half wave column). As the damping changed so did the need to keep tweaking the Zobel network. WHY?!!!

All this was insignificant once I got an engineer to design the active crossover for me as I made a mess trying it myself, he specialised in filter design. Then Tri-Amping and the rest became history.

The B139 in my most humble opinion never was happy working right up to 400Hz, especially when hammered!
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Wiesiek Lipowski
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PostPosted: Tue Apr 21, 2015 6:12 pm    Post subject: Reply with quote

Thanks.

So I think I will also try to do some listening tests.

Fortunately the x-overs of my PRO9TL's are outside.
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proffski
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PostPosted: Tue Apr 21, 2015 6:42 pm    Post subject: Reply with quote

So were mine, big and heavy!
Please keep us informed, I still find the subject fascinating.
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proffski
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PostPosted: Wed Apr 22, 2015 8:43 am    Post subject: Reply with quote

Wiesiek Lipowski wrote:
Why don't you try adding z Zobel to the B139's? 8R+15uF shunt at the speakers or x-overs can make the male and female vocals less bassy.


Have you seen the Zobel Values for the CS7 kit?
http://passthrough.fw-notify.net/download/532077/http://www.kef.com/uploads/files/en/museum_pdf/80s/Constructor_Series_Model_CS7.pdf
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Wiesiek Lipowski
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PostPosted: Wed Apr 22, 2015 9:19 am    Post subject: Reply with quote

Do you mean R1=1,5R and C1=100uF?
Yes, I have.

I have just added a 8R/15uF at the crossover bass output. I did not alter the original values of the PRO9TL crossover, so the C1=80uF is still there.
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