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Notch filter on the 105/2?

 
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Lee in Montreal
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PostPosted: Thu Oct 15, 2009 11:52 pm    Post subject: Notch filter on the 105/2? Reply with quote

I was trying to understand the crossovers on the 105/2, is that possible that on the bass driver circuit, C1/C2 + R1 +L1 are a notch filter that takes care of the high impedance of the woofer at the resonnance frequency?

IS so, what is the actual difference between the two version of crossovers, at least sonically speaking?




TIA

Lee
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T.O. Chef
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PostPosted: Fri Oct 16, 2009 2:13 am    Post subject: Reply with quote

Correct me someone please if I'm wrong, but me thinks R1, 680 ohm is the depository for the shunted input signal when activated by the protection circuitry. Severely reduces the system output.

The earlier version 4 capacitor (C1-C4) crossover was just that. 4 parallel capacitors instead of 2 (C1-C2) in the version 2 crossover.
Total combined capacitance of of 480uF in version 1, 450uf in version 2.
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speakerguru
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PostPosted: Fri Oct 16, 2009 8:31 am    Post subject: Reply with quote

T.O.C. is almost correct. The 680 Ohm resistor is put in series with the speaker by the protection circuit when it operates. It is shunted by the relay in normal operation.

In both crossovers L1, L2, C5 make up a third order low pass filter with the woofer/box impedance as the load. There are no impedance compensation circuits (not even a Zobel).

The capacitors C1....C4 give D.C. protection. They also react with the equivalent inductance of the woofer driver mass to give a small boost below resonance, resullting in a third order high pass characteristic; sort of half way between a closed box and a reflex. They have no effect on the midrange or tweeter.
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T.O. Chef
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PostPosted: Fri Oct 16, 2009 4:46 pm    Post subject: Reply with quote

The slight difference in values used in C-1-C2 between version 1 and version 2 (480uF vs 450uF) account for what variances? Was there a change in the B-300 used?

If the B-300 were to be installed in a larger volume cabinet would these values need to be recalculated?
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ColinR
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PostPosted: Fri Oct 16, 2009 5:48 pm    Post subject: Reply with quote

Wrong tree Very Happy .

From the "A History of Kef Drive Units" thread.

Quote:
Our records show that the SP1072 tweeter was used in the 105.2 from SN2966


So the ?s on my schematics can be replaced by 2965 and 2966.
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Lee in Montreal
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PostPosted: Fri Oct 16, 2009 8:48 pm    Post subject: Reply with quote

Is that possible that the differences in the bass and medium circuits are only to accomodate a different crossover frequency from bass to mid? 250Hz and 400Hz or something like that.
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speakerguru
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PostPosted: Sun Oct 18, 2009 8:45 pm    Post subject: Reply with quote

T.O. Chef wrote:
Was there a change in the B-300 used?


No. SP1060 and SP1071 have the same magnet and moving parts. Only the chassis differed.

T.O. Chef wrote:
If the B-300 were to be installed in a larger volume cabinet would these values need to be recalculated?

Theoretically, yes, but the closed box third order alignment is not particularly sensitive to changes in the box volume or series capacitor.
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audiolabtower
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PostPosted: Fri Oct 30, 2009 12:46 pm    Post subject: Reply with quote

T.O. Chef wrote:

Total combined capacitance of of 480uF in version 1, 450uf in version 2.

actually Colin confirms the difference is 480uF to 900uF in another thread - quite a step!
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Lee in Montreal
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PostPosted: Fri Oct 30, 2009 1:23 pm    Post subject: Reply with quote

audiolabtower wrote:
actually Colin confirms the difference is 480uF to 900uF in another thread - quite a step!


What is the impact of the difference in capacitance between both filters - 480 - 900µF?
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ColinR
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PostPosted: Fri Oct 30, 2009 3:48 pm    Post subject: Reply with quote

Quote:
What is the impact of the difference in capacitance between both filters - 480 - 900µF



Nowt, the designs' SP number hasn't changed has it?


If you want to make a difference build a pair of the "KEF type approved" active filters for the Ref 105-2 Cool .

http://www.hifiloudspeakers.info/speakertalk/viewtopic.php?p=4972&highlight=#4972
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Lee in Montreal
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PostPosted: Fri Oct 30, 2009 5:24 pm    Post subject: Reply with quote

ColinR wrote:
If you want to make a difference build a pair of the "KEF type approved" active filters for the Ref 105-2 Cool .

http://www.hifiloudspeakers.info/speakertalk/viewtopic.php?p=4972&highlight=#4972


I read half of the thread and will read some more later. There's so much info to digest that my head spins. That active crossover might very well be what will be used on my experimental set. Not. I don't have three amps or that.

Thanks again for that link. Good reading on the 150Hz vs 400hz crossover frequency.
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