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Bi-amping Kef 105.2

 
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qguy
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PostPosted: Wed May 31, 2006 2:13 am    Post subject: Bi-amping Kef 105.2 Reply with quote

Now that I got an extra amp, I am planning to buy amp my kef 105.2. On x-over diagram their is shared capacitors that is used by the entire circuit. On some other sites, it is advised that this part should be removed any thoughts on this ?
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peejay1959
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Location: Bedfordshire UK

PostPosted: Fri Jun 27, 2014 11:33 pm    Post subject: Reply with quote

Bump, I really want to do this using 2 quad 405's
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audiolabtower
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PostPosted: Sat Jun 28, 2014 10:59 am    Post subject: Reply with quote

Do you mean the 900uF (2 x 450 in parallel)?

This is used in the bass equalisation and has a handy benefit of protecting from DC in the event of an amp fault if the SStop fails. If you want the design intent it should be left in. If you want to experiment and bypass it the sensitivity and low bass performance will not be to design but may work in your room.

A further complication is whether the alcaps have drifted over this length of time, but without measuring them you can't tell.

ps I would use a Quad for the B300, and the other channel for the top unit in each channel.
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iso
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PostPosted: Sun Jun 29, 2014 4:21 pm    Post subject: Re: Bi-amping Kef 105.2 Reply with quote

qguy wrote:
On x-over diagram their is shared capacitors that is used by the entire circuit.

Capacitor mentioned is one part of LF-alignment. Without cap Q of resonance will be under damped... Most often under damped alignments have been used to reinforce limited low bass, in designs like LS3/5A and BC1.

You will find more information about this issue at http://hifiloudspeakers.info/Anatomy/KEFDocuments/KEFTopics/KEFTOPICS_Vol_3_No_4.pdf

SG might have better information if it is advisable to feed mid and hf directly to their portions of crossover, bypassing this cap when bi-amping.

Best Regards

Kimmo
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audiolabtower
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PostPosted: Sun Jun 29, 2014 6:53 pm    Post subject: Re: Bi-amping Kef 105.2 Reply with quote

qguy wrote:
SG might have better information if it is advisable to feed mid and hf directly to their portions of crossover, bypassing this cap when bi-amping.


You cannot bi-amp without bypassing the large bass series cap, unless you want to run the B300 and B110 together from one amp, but you would still have to bypass for the tweeter. You don't need it for the B110 and T52, since it has no effect at their crossover freqs and they have their own series caps for possible dc protection. The only thing with bi or tri amping the 105.2 is losing the SStop on one or two units. But the 105 is robust enough not to need the SStop for normal use, and "some" people used to take it out anyway claiming a sound quality "improvement".
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iso
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PostPosted: Mon Jun 30, 2014 6:34 am    Post subject: Re: Bi-amping Kef 105.2 Reply with quote

audiolabtower wrote:
[quote="You cannot bi-amp without bypassing the large bass series cap, unless you want to run the B300 and B110 together from one amp.

I was thinking that large input cap is in series to mid section input cap C6, but I did not calculate effect of input cap removal. However after calculating effect of input cap removal, it appears that removal of cap will alter total capacitance 3-4%. This is most likely insignificant, even original parts were selected to better specs over 30 years ago.

Using one amp for T52 and other one for B300 and B110 is hardly advisable.

My mistake...

Best Regards

Kimmo
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audiolabtower
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PostPosted: Mon Jun 30, 2014 11:31 am    Post subject: Reply with quote

I agree. When I only had 2 amps I also found driving the B300 was better. Usually bi-amping works well at 2-3 kHz since the ears most sensitive range. However the 105 4th order crossovers work so well at integrating the T52 (if crossover still in spec) I think their performance here is better than most other designs. Given the extended bass response available in the 105, and the tendency of smaller rooms to muddle the high bass and low midrange that extra bit of control either side of the 400Hz crossover is more worthwhile.
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speakerguru
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PostPosted: Thu Jul 03, 2014 2:32 pm    Post subject: Reply with quote

There is no easy way to bi-amp LF and MF/HF while retaining the the LF alignment, d.c. protection and S-STOP protection for all units afforded by the series capacitors. You would have duplicate some sections of circuitry.
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audiolabtower
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PostPosted: Thu Jul 03, 2014 2:49 pm    Post subject: Reply with quote

Obviously I kept the large bass series cap for the B300. The midrange has 30uF in series and the tweeter 3.3 uF in series. Providing these are rated at 100 or 150V they should provide reasonable DC protection?

I would have thought the large series bass cap has little effect on the B110 and T52 responses? The loss is the SStop, so to have the same protection as before you would need 3 of these - presumably each specially curved for the voltage and voice coil temperature of the specific units. However I've used my Mk1s for over 30 years with varying amps in single, bi and tri arrangements without the fuses so think those Kef drivers were a well made and reliable bunch.
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peejay1959
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PostPosted: Sat Apr 30, 2016 1:53 am    Post subject: Reply with quote

speakerguru wrote:
There is no easy way to bi-amp LF and MF/HF while retaining the the LF alignment, d.c. protection and S-STOP protection for all units afforded by the series capacitors. You would have duplicate some sections of circuitry.


So would it be a case of adding a second set of series caps for the HF/MF drivers whilst retaining the originals for the LF or is there more to it? I'm not interested in the S-Stop and would be interested in how to remove that completely. Or would it be better to add a precaution cct to the amps and leave out the series caps completely.
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audiolabtower
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PostPosted: Sat Apr 30, 2016 2:08 pm    Post subject: Reply with quote

My Mk1s were easy to tri-wire since the crossover is 3 independent parallel circuits to the input terminals, and the mid and treble does not depend on the large series bass capacitor. They have their own third order circuit blocking capacitors, which proved they worked when an old amp went 45V dc many years ago with no damage to my speakers. The overall response is 4th order with the drive unit characteristics.

The Mk2 is more complicated because the mid and treble sections are wired behind the large series bass cap and relay. The bass series cap is required for the design bass alignment, I have read of people removing it, but looking at the Kef design notes it was there for a good reason and is an expensive component(s), so Kef could easily have left it out if they had wanted to - they did not. When I replaced mine with 360uF of parallel polyesters I did some listening tests clipped either side and decided to leave it in, it was subtle, but a cleaner upper bass I thought.

I would not have thought the bass series cap impedance would have affected the mid and treble sections too much at their frequencies but guru is the expert here. I see no reason why the s-stop cannot just be left open circuit. I assume the 680 ohm is in circuit only when the protection operates so would be circumvented? If you feel there is an imbalance in mid and treble it is easily rectified by tweaking the gain of the 3 amps?
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speakerguru
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PostPosted: Sun May 01, 2016 11:57 am    Post subject: Reply with quote

peejay1959 wrote:
So would it be a case of adding a second set of series caps for the HF/MF drivers whilst retaining the originals for the LF or is there more to it? I'm not interested in the S-Stop and would be interested in how to remove that completely. Or would it be better to add a precaution cct to the amps and leave out the series caps completely.


Yes to the second set of series caps. They could be reduced in capacitance because they don't have to work at the lower frequencies.

I don't know why you would want to remove protection, but if you must, a short circuit soldered across the relay contacts will allow you to live more dangerously.
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audiolabtower
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PostPosted: Sun May 01, 2016 10:25 pm    Post subject: Reply with quote

Just looking at the input caps, the mid in the later crossovers was 450uF in series with 30uF, simple result around 28.2 uF, a significant 6% down? The treble input is 3.3 uF, simple result 3.27 uF, around 1% down.
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