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audiolabtower
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 Posted: Tue Mar 03, 2009 8:16 pm Post subject: |
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| speakerguru wrote: | | I haven't spoken to Andrew Jones recently and I only have a dim recollection that he'd done an active 105. Was it before he joined KEF? |
Hi, the date on the Kef response graph of the active circuit is 1982 if that is any help. |
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audiolabtower
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speakerguru
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| Posted: Mon Mar 30, 2009 8:42 am Post subject: |
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| I spoke to AJ last week. He didn't remember an active 105 either. I've sent him the link to this thread so if he does remember anything I'm sure he'll chip in. |
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ColinR
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| Posted: Mon Mar 30, 2009 10:07 am Post subject: |
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| Quote: | | I spoke to AJ last week. He didn't remember an active 105 either |
He probably wouldn't  , having found my original paperwork is David (no surname yet thanks to Tiscali) still working at Electrosonic in Dartford?
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AndrewJ
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| Posted: Tue Mar 31, 2009 9:59 pm Post subject: |
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AJ here !
I just read this thread after speakerguru forwarded to me.
I did indeed join KEF in "83 and no, I had no involvement in any active 105, nor ever knew of such a beast. I certainly doubt that it had ever been an in-house project.
Interestingly, small world that it is, my brother worked at Electrosonic around that time! |
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audiolabtower
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| Posted: Tue Mar 31, 2009 11:12 pm Post subject: |
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Hi, and thank you very much for joining in. The circuit and response graphs of the active 105 are on page 2 of the thread here and it would be very interesting to hear of your opinions with your experience in the Kubes etc. I am in the process of getting all the components together and intend to build it and try it out.
We think that even the 105 Mk1 would be fine with the B110 down to 150 Hz for instance, and maybe this crossover was better, just difficult to achieve with passive components so compromise of 400 Hz was chosen for the commercial version??
If it is any clue to the design history the initials on the response graph are EC, Jan 82.
Thanks again for taking the trouble to reply  |
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AndrewJ
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| Posted: Wed Apr 01, 2009 5:21 pm Post subject: |
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The date of Jan 82 definitely puts it before my time at KEF. I joined May '83.
As for a passive xover at 150Hz, yes this is always much more difficult than at 400Hz becuase not only do you have interaction with the coil inductance, but very strong interaction with the motional impedance, ie the resonant peaks in the impedance due to the driver and vent coupled resonances. These unless fully conjugated will play havoc with the network response.
Of course, later KEF models did xover this low, certainly the 104.2 and the 107, but they did incorporate quite complex conjugation networks.
AJ |
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speakerguru
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| Posted: Thu Apr 02, 2009 8:11 am Post subject: |
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| audiolabtower wrote: | | If it is any clue to the design history the initials on the response graph are EC, Jan 82. |
EC would be Enrico Cecconi, who was at KEF from '75 to '99, but he definitely didn't design an active 105. His first active systems were the P60 and KM1 professional products.
Speculating, often Raymond Cooke would get given designs on his travels and then he would pass them on to the lab on his return. Maybe EC got the job of evaluating and measuring that design. The only other contributor I can think of was Seigfried Linkwitz, who had his active T27, B110, B139 sub-sat system published in Wireless World, but that was much earlier, in the 70s. |
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audiolabtower
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| Posted: Thu Apr 02, 2009 10:48 am Post subject: |
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| speakerguru wrote: | | The only other contributor I can think of was Seigfried Linkwitz, who had his active T27, B110, B139 sub-sat system published in Wireless World |
I remember being very impressed with the Linkwitz design but since young at the time could not afford to take it further It must have been one of the best clones of LS3/5a inspired designs with added subwoofer ever!
Nevertheless looking at the response graph of the active 105 it seems very reasonable. The tweeter shaping looks spot on. The midrange seems to have more slope than I would have imagined but this may just be compensating for the rolloff running down to 150 Hz. I've more or less decided that 150Hz is a better crossover fequency and should not compromise the B110 power handling unduly. I think 400Hz would need a redesign of the B300 low pass to 3rd order with the first RC values selected to match the B110 rolloff and this is beyond my measurement capabilities, theoretical 3rd order values might end up a worse total design than the passive version.
I've built one channel, now waiting for OPA134's on order to finish off, super regulators for the power supply and other hardware. Unfortunately my only test equipment nowadays is a multimeter, but a test tone cd should be enough to confirm the basic response shapes. |
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BobL
Intermediate Contributor 25+
Joined: 27 Jan 2004
Posts: 39
Location: West Midlands, UK
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| Posted: Mon Apr 06, 2009 1:51 pm Post subject: |
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| speakerguru wrote: | | I spoke to AJ last week. He didn't remember an active 105 either. |
The original diagram though a bit faded now does have a 'drawn by' signature. Like the response graphs the diagram is on official Kef paperwork.
I'll see if I can scan the signature.
Bob. |
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BobL
Intermediate Contributor 25+
Joined: 27 Jan 2004
Posts: 39
Location: West Midlands, UK
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| Posted: Mon Apr 06, 2009 1:55 pm Post subject: |
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| audiolabtower wrote: | | I've built one channel, now waiting for OPA134's on order to finish off, super regulators for the power supply and other hardware. |
I have to admit I'm almost excited to hear how you get on with this. It may make me dig out the vero board versions I made 25 years ago.
Bob. |
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BobL
Intermediate Contributor 25+
Joined: 27 Jan 2004
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Location: West Midlands, UK
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audiolabtower
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| Posted: Mon Apr 06, 2009 8:35 pm Post subject: |
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| BobL wrote: | I hope you all see them as a usfull resource.
Bob. |
they are, thank you |
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speakerguru
Über Contributor 1000+
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Posts: 1192
Location: Green Hut, Tovil
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| Posted: Tue Apr 07, 2009 11:48 pm Post subject: |
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| BobL wrote: | | The signature which looks like DJ Grainger to me is in lower right. |
That's P. J. Granger. Phil was a technician at KEF. He would have got the job of building the circuit, I guess. |
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