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How to get the most out of 105.2?
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andrelly
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Joined: 28 May 2007
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PostPosted: Tue Jun 12, 2007 7:58 am    Post subject: Reply with quote

Update report:
I opened the head module. Was quite surprised that factory had put some sort of damping in the back half. Cool I put on Acourete resin damping sheet in the front half of head module (stick it on any space available). Now the head module is less resonant (knock on it with your fingers, yields a low thud).
Also put damping sheet at the bottom & top of disc, bottom of head module (exterior), and on same parts of the supporting arm.

Results: Clarity and definition improved! Musical delineation now much easier to follow. I am happy. Very Happy

Question: there is a small pcb in the head module. What is it for? anything to with mid/hi frequency crossover?

Cheers...
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qguy
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PostPosted: Tue Jun 12, 2007 10:07 pm    Post subject: Reply with quote

Thats the STOP circuitry

andrelly wrote:
Update report:

Question: there is a small pcb in the head module. What is it for? anything to with mid/hi frequency crossover?

Cheers...
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speakerguru
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PostPosted: Wed Jun 13, 2007 9:43 am    Post subject: Reply with quote

The S-Stop protection circuit had parallel thermal modelling sections so that if either the tweeter or midrange units were in danger of thermal overload the relay would switch in a series resistor. I can't remember if there was thermal protection for the woofer. I suspect not. The B300 has a very big voice coil.

Another parallel section sensed overvoltage to protect the xo capacitors and finally an over excursion section prevented woofer bottoming.

This last section was not popular because it could be tripped even when the woofer did not sound like it was in distress. It was disabled in later production and for any early customers who complained of premature S-Stop operation. Don't hold me to this but I think it was done by snipping the red wire going to the head unit. This would be the sense wire coming from the non-common side of the woofer. N.B. do this at your own risk.
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andrelly
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PostPosted: Wed Jun 13, 2007 11:19 am    Post subject: Reply with quote

qguy: Oh, the S-STOP circuitry. A malfunction of this circuit means that my tweeter/mid/woofer would not be functioning? Also it means that there is no way of overdriving the spkr drivers? I am worried as I read in other forums that availability of KEF drivers is very scarce.

Speakerguru: Yes, I have been experiencing pre-mature s-stop going active even though level is not too loud. Thanks for the info! I guess that disconnecting the red wire (going to head module) on the x-over pcb would be it.
BTW, the damping mod improves the treble that I don't find it to be lacking anymore!
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ColinR
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PostPosted: Wed Jun 13, 2007 8:22 pm    Post subject: Reply with quote

Quote:
snipping the red wire


If you do this remember to install a Polyswitch first.
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speakerguru
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PostPosted: Thu Jun 14, 2007 8:26 am    Post subject: Reply with quote

ColinR wrote:
If you do this remember to install a Polyswitch first.


Why's that then Question Cutting the red wire only removes the over-excursion limit in the woofer passband. The thermal and overvoltage protection is still there.

You're a better man than I, if you can find a polyswitch which can match both the tweeter and the midrange thermal time constants at the same time Exclamation
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andrelly
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PostPosted: Thu Jun 14, 2007 9:06 am    Post subject: Reply with quote

BTW, what is a polyswitch? Shocked

I am using McIntosh 2205, a solid state 200W amp which has output transformers (just like tube amps) with multiple taps for 2ohm, 4 ohm, 6ohm and 8 ohm speakers. Hence DC would certainly not be an issue here?
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ColinR
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PostPosted: Thu Jun 14, 2007 9:19 am    Post subject: Reply with quote

Embarassed
Quote:
ColinR wrote:
If you do this remember to install a Polyswitch first.


Why's that then Cutting the red wire only removes the over-excursion limit in the woofer passband. The thermal and overvoltage protection is still there.

You're a better man than I, if you can find a polyswitch which can match both the tweeter and the midrange thermal time constants at the same time


I meant to say "remember to install a Polyswitch in series with the T52" the B110B is robust enough to look after itself.


Quote:
BTW, what is a polyswitch?


Look here

http://circuitprotection.com/polyswitch.asp

and do a Google Smile .
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speakerguru
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PostPosted: Fri Jun 15, 2007 8:22 am    Post subject: Reply with quote

ColinR wrote:
I meant to say "remember to install a Polyswitch in series with the T52" the B110B is robust enough to look after itself.

OK, well that makes slightly more sense, but what I said still stands; disconnecting the red wire only affects the woofer exc protection. Thermal protection on both the tweeter and midrange would still be active. Fitting a polyswitch as well, is for real pessimists (you know, the sort of people who like to use belt and braces on their trousers) Laughing
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proffski
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PostPosted: Fri Jun 15, 2007 8:40 am    Post subject: Reply with quote

A Pessimist is only an Optimist with lots of experience...
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andrelly
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PostPosted: Fri Jun 15, 2007 11:42 am    Post subject: Reply with quote

To bypass one thing and add another seems to be redundant. Rolling Eyes
....unless the polyswitch does not degrade the sound? Shocked

Cheers...
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proffski
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PostPosted: Fri Jun 15, 2007 12:15 pm    Post subject: Reply with quote

What if the protection circuitry is faulty or no longer workinng to original manufacturers specifications? Confused

Is there a teest routine that one could dare try without frying the driver units? Shocked
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proffski
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PostPosted: Fri Jun 15, 2007 12:15 pm    Post subject: Reply with quote

What if the protection circuitry is faulty or no longer workinng to original manufacturers specifications? Confused

Is there a test routine that one could dare try without frying the driver units? Shocked
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speakerguru
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PostPosted: Fri Jun 15, 2007 1:03 pm    Post subject: Reply with quote

proffski wrote:
What if the protection circuitry is faulty or no longer working to original manufacturers specifications? Is there a test routine that one could dare try without frying the driver units?

Yes, but I don't remember the figures. Laughing

You would have to replace the units with dummy loads and then apply sinewaves in each unit's passband; say 800Hz for the MF and 8kHz for the HF. You then measure the time it takes for the relay to trip at ever increasing levels. If your maths is up to it, you can then see if this stacks up with the published KEF data on drive unit thermal time constants and maximum long term voltage rating. The modelling is such that the time to trip halves for each doubling of voltage above the threshold. (You'll need a big amplifier.) This will have to be repeated for both the HF and MF sections. If the S-Stop unit trips below about 10 V rms for the tweeter then most likely one of the high voltage relay drive transistors has blown (as was surmised somewhere up this thread). If it never trips then that is a potentially bigger problem for the units and probably due to open circuit transistors. Not that I'm suggesting this was common. It wasn't. The transistors were high voltage and very reliable. I have never come across a case of the thick film thermal models ever developing a fault.
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proffski
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PostPosted: Fri Jun 15, 2007 1:13 pm    Post subject: Oi, oi, oi... Reply with quote

Surely dummy loads will not exhibit drive unit characteristics anyway?

Hm, I think that trusting ones ears and not running small amplifiers close to clipping is a much more safe & sound philosophy somehow.
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