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Refirbushing Kef 105.1, NEED CROSSOVER SCHEMATIC, etc..
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proffski
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PostPosted: Sun Feb 22, 2009 10:10 pm    Post subject: Reply with quote

Thank you! Nice bit of work there. Let us hope somebody can provide inductor values.
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audiolabtower
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PostPosted: Mon Feb 23, 2009 12:24 am    Post subject: Reply with quote

BobL wrote:


Interesting that my xover is not exactly the same as that described.
Bob.


Your crossover is exactly the same as I described in my post above, just the acoustic butterworth capacitors and zobel network are added to the T52 section, requiring a necessary change in one filter capacitor value, as appears to be the case with some selection of tweeters but not required by all. Also the bass section damping resistor has changed by a preferred step in value, again obviously to suit the selection of those particular B300s.

The inductor values have all already been given in my previous post!

However the 2.5kHz and 400Hz inductors will have been selected either higher or lower than centre value depending on whether the corresponding capacitors are lower or higher than centre value.

Just changing components based on their printed value will unbalance the design and the speaker will no longer meet the very tight original spec in terms of flat frequency response because of the tolerance matching and total system design. This explains why every crossover was not the same, the values were chosen to negate the effects of the measured drive unit variability.
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eardrum
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PostPosted: Mon Feb 23, 2009 5:56 am    Post subject: Refirbushing Kef 105.1 Reply with quote

I would like to Sincerely Thank you guy's for the important info that you have provided me here! I am "Shane" and I am the one that has been in need of this Schematic. Prior to just returning here, I traced the mid-hi board; sp1100 and can confirm all that was said here. Colin, is corect about the hf values. Also, Audiolabtower's description of all circuit part locations are very descriptive. And thanks for the coil values! I really was not sure until recently, how the Lf; sp1101 was layed out. Then, I got it! And it is also, "exactally" as shown in BobL's schematic. BIG THANKS!! But, I've gotta tell all that wish to replace these caps and they DO need replacing. "All there values will measure high". Considering centre value shifts only confuses things. Again, all my caps measured high! In the order of 18-22%. All mylar's drift in this direction over time and you can hear the non-linearities in the overall response. Anyway, I want to also, echo that the modern Propylene replacements will be much larger and you will have to go "external" with the Crossovers. The only caps of good quality and fair price $330.00 for all, were rated at 250v. The 100uf caps alone measure 2" in dia. and 3" long! I'm in the process of building the boxes and have many pictures of the process, that I would be happy to share with anyone here.. eardrum...
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BobL
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PostPosted: Mon Feb 23, 2009 10:57 am    Post subject: Reply with quote

Some time in the early 80s Raymond Cooke (yes, I know terrible name dropper) sent me a diagram for an active version of R105/2 which he said would be fine with the Mk1. I had to redraw it due to it fading and being too large to scan.

I have calculated the changes to make it crossover at 400Hz (Mk1) and not 150Hz (Mk2). I don't think the mid enclosure is as large in the Mk1 as the Mk2 and therefore the B110 would struggle to get down to 150Hz IMHO.

So one time only active xover at http://www.mightyoak.org.uk/kef/Active105.jpg and the response graph http://www.mightyoak.org.uk/kef/ActiveGraph.jpg I would'nt think kef would be too bothered about some die hard enthusiats having this nearly 30 yearold diagram.

Webmaster please take copies for your site if you so wish.

Enjoy.


Last edited by BobL on Mon Nov 14, 2011 3:41 pm; edited 1 time in total
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audiolabtower
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PostPosted: Mon Feb 23, 2009 12:09 pm    Post subject: Reply with quote

Thanks for that active circuit - that is worth having since I drive each unit through its own power amp now anyway (having tri-wired the crossovers externally at the amp outputs). The graph responses look just about right to balance this speaker.

Any suggestions for a modern equivalent to the 351? presumably not needing frequency compensation? I used a 4562 in the output stage of a Beresford 6/4, but 9 of those would start to be expensive Smile

The point about drift with age is a good one, and there will be a problem measuring the original caps at this age. Curiosity made me dig out my notes from years ago and it turns out every value I measured was in tolerance spec, most were slightly high (maybe 2 to 4% high), the 80uF was exactly 80.2 and 79.5, and the 100uF was deliberately low at 95.6 and 95.3. The 120uF were all 122 to 125 uF. The tweeter caps were obviously selected especially high for my T52s since they were 3.52/3.55 and 3.82/3.85 uF at that time.
These were measured when the speakers were only a couple of years old, and as explained earlier the values were Kef chosen for the drive units in my speakers so may not be the same selection in other examples.

I decided on reflection Kef knew best and kept the 360uF and each was made up of twelve large 30uF polyester caps which we used in a product at that time. the 24 were measured and selected into pair groups to add up to the median of the 2 original values. Thus was youthful enthusiasm in copying the Kef approach! They had to be stacked onto the pcb space and ended up with 4 layers of "skyscraper" soldering the axial leads together tightly in a kind of mesh to make a rigid assembly. But with external crossovers they were in any case not subject to the pressure levels inside the cabinet.

I have the original Kef crossover drawings sent by Laurie Fincham and Mike Gough at that time but they are eight times A4 size (A1?) and I have no way of scanning them. They are pretty faded now but just about still readable.
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ColinR
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PostPosted: Mon Feb 23, 2009 12:40 pm    Post subject: Reply with quote

Quote:
I would'nt think kef would be too bothered about some die hard enthusiats having this nearly 30 yearold diagram.


I think not.

I'm currently trying to tease the original designer away from his public multi screen HDTV designs back through the automated public laser light show control systems to this particular active speaker design, which he sent to KEF (unsolicited) whilst designing active sound and light systems for clubs and discos, etc.

It's not a KEF design, but it is "type approved" Cool .

Quote:
The tweeter caps were obviously selected especially high for my T52s


My poking about inside many KEF designs tends to confirm your observation.
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audiolabtower
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PostPosted: Mon Feb 23, 2009 3:22 pm    Post subject: Reply with quote

[quote="ColinR"]
Quote:

I'm currently trying to tease the original designer away from his public multi screen HDTV designs


Would that be Andrew Jones (who also designed the cubes)?
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ColinR
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PostPosted: Mon Feb 23, 2009 3:38 pm    Post subject: Reply with quote

Quote:
Would that be Andrew Jones (who also designed the cubes)?


From our email exchanges quite a few other bits of kit too Very Happy .
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audiolabtower
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PostPosted: Mon Feb 23, 2009 3:50 pm    Post subject: Reply with quote

Please ask him why 150Hz in the original active, since both the 105-Mk 2 passive crossovers shown here are 400Hz between the B300 and B110... ?
I'm interested now Smile
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BobL
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PostPosted: Mon Feb 23, 2009 4:47 pm    Post subject: Reply with quote

audiolabtower wrote:
Please ask him why 150Hz in the original active, since both the 105-Mk 2 passive crossovers shown here are 400Hz between the B300 and B110... ?
I'm interested now :-)


Sorry but I don't think that is correct. I'm pretty sure the Mk1 R105 was the only R105 to have the crossover set to 400Hz. The Mk2 R105.2 always had it set to 150Hz and so did the active version. If you look at the specifications you will see that the volume of the mid enclosure on the Mk2 is considerably larger than on the Mk1. This is because the mid enclosure in the Mk2 includes the tweater housing which it does not in the Mk1. Hence, the Mk2 B110 can deliver down to 150Hz.

Sorry to rant on a bit.


Bob.
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audiolabtower
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PostPosted: Mon Feb 23, 2009 5:50 pm    Post subject: Reply with quote

have a look at both passive networks for the 105 Mk 2 here:

http://www.hifiloudspeakers.info/Anatomy/Crossovers/105.2/105.2CrossoverIndex.html

for a first order approximation I make the 1st version bass rolloff around 500Hz and the B100 high pass around 300 Hz.

Likewise the 2nd version has the B300 rolloff around 560 Hz and the B110 come in at around 340Hz.

Only approximations based on the printed values of course, and as we know these can vary with selection, but I can't see how these can be as low as 150Hz?
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BobL
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PostPosted: Tue Feb 24, 2009 10:43 am    Post subject: Reply with quote

audiolabtower wrote:
Only approximations based on the printed values of course, and as we know these can vary with selection, but I can't see how these can be as low as 150Hz?


I spent some time going through KEF documents from 1980 and to my surprise I couldn't find a sinle instance of the crossover frequency being quoted anywhere. That leaves me unable to argue with you really as I have no case. All I can say is that at the time I believed they had moved the crossover frequnecy to 150 and it matches with the active version. Why would they change it only for the active version if the cabinet and drivers are optimised for a different frequency. Anyway, you may be right but personaly I still think its 150Hz on all Mk2.

I've updated the crossover diagram to incorporate the inductor values as decsribed in this thread. Hope this helps a little.

http://www.mightyoak.org.uk/kef/R105-1.jpg

Bob.


Last edited by BobL on Mon Nov 14, 2011 3:45 pm; edited 1 time in total
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speakerguru
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PostPosted: Tue Feb 24, 2009 10:59 am    Post subject: Reply with quote

BobL wrote:
Sorry but I don't think that is correct. I'm pretty sure the Mk1 R105 was the only R105 to have the crossover set to 400Hz. The Mk2 R105.2 always had it set to 150Hz and so did the active version. If you look at the specifications you will see that the volume of the mid enclosure on the Mk2 is considerably larger than on the Mk1. This is because the mid enclosure in the Mk2 includes the tweater housing which it does not in the Mk1. Hence, the Mk2 B110 can deliver down to 150Hz.


Sorry but none of this rings any bells with me. I don't recall there being any deliberate increase in MF enclosure volume when it changed from Mk 1 to Mk2. The main thing about the Mk2 enclosure was that it was a tooled up plastic injection moulding rather than the Mk 1 MDF boxes with sheetmetal back covers.

Re xover frequency: It is very difficult to design a passive low pass filter at 150Hz because the inductive part of the voice coil impedance reacts with the shunt capacitors to produce an unwanted voltage peak with an attendant dip in impedance just above the driver/box resonance. The only way to avoid this is to have compensation networks across the woofer to make it resistive (a la 104|2). With an active design you can put the xover frequency where you like and then it is advantageous to xover lower down in a region where the woofer is less directional and there is less time/phase difference between the woofer and MF unit.
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BobL
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PostPosted: Tue Feb 24, 2009 11:13 am    Post subject: Reply with quote

speakerguru wrote:


Sorry but none of this rings any bells with me. I don't recall there being any deliberate increase in MF enclosure volume when it changed from Mk 1 to Mk2.


Okay, I'll bow out on the 150Hz bit although I've got it from somewhere, I didn't dream it up. The enclosure was bigger though as I've already said the Mk2 has the tweeter housing in addition but the Mk1 does not.

speakerguru wrote:



The main thing about the Mk2 enclosure was that it was a tooled up plastic injection moulding rather than the Mk 1 MDF boxes with sheetmetal back covers.


And a pressed steel B300 with a less substantial cabinet and 3 point resiliant mountings.
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audiolabtower
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PostPosted: Tue Feb 24, 2009 11:49 am    Post subject: Reply with quote

Well the passive crossover values speak for themselves at ~400Hz and we have two of them for different production runs, and I also cannot recall any mention at the time of the launch or afterwards of such a significant change in design, just the new enclosures based the the newer decoupling of drive unit ideas at that time and consequent small tweaks to suit that.
You can see the difference even without calculation because all the passive crossovers have 3rd order bass section using the B300 response above 400Hz to achieve final slope, but the active bass section has to have two cascaded sallen key filters of identical values to get a 4th order at 150Hz because of the significant change in frequency from the passives.

The question could be solved by Mr Jones if he is still around as to why the active changed to 150Hz?

The crossover diagram now looks good, and agrees with my samples apart from the tweeter having to have a value change due to the zobel inclusion and acoustic butterworth components, and the bass damping as described earlier. If I may make a suggestion it might be worth indicating that all drive unit positives run through to input positive. Some 3rd order crossovers use a phase reversal in a unit to smooth the response but Kef used the natural rolloffs in the computer optimised design to get their 24dB/octave phase correct design and then put the units in a "linear phase" baffle on top Smile
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