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KEF 103.2 Crossover upgrade
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proffski
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PostPosted: Fri Jun 13, 2008 7:40 pm    Post subject: Reply with quote

Confused
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tancrède
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Location: Quebec Canada

PostPosted: Fri Jun 13, 2008 10:14 pm    Post subject: Reply with quote

-------
Hi again folks

The crossover is very well glue to the bottom of the boxe. And there's not much place over there.

So how can i pull-it off so i can check the caps individually ?????

Thanks again

Tancrède
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tancrède
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PostPosted: Fri Jun 13, 2008 11:28 pm    Post subject: Reply with quote

--------

Ok I've have succefully pull them out

Tancrède
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tancrède
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PostPosted: Sat Jun 14, 2008 3:58 am    Post subject: Reply with quote

-------

For those you are interest, I will try to understand this crossover.

For the moment, i know why my ohmmeter didn't see around 8 ohms. This crossover have a 600 microF at is end - opposite side of the frivers of course.

What is the use off those caps ? Maybe for the protection circuit ? Dont know yet.

I 've already check a few caps, and there is 2 of them that look like off of their farad limit value. Maybe that's explain why the tweeter are not so bright in high frequencies.

I dont have wave generator to see them work in a benchmark test
So, i think i will change them all. After 25 years, i think it's a logical move to do.


Tancrède
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proffski
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PostPosted: Sat Jun 14, 2008 12:06 pm    Post subject: Reply with quote

Series capacitors in sealed boxes offer improvement and or a tailoring of the LF response below f³.

This method can also be used in other enclosures but the loading will change from third, fourth to fifth order depending upon the configuration.
There is a penalty to pay as the obviously he dB/octave roll off will also change.

Then we have group delay and phase response to worry about.

Give me a well designed Sealed Enclosure any day for a crisp fast bass response!
Anyway, I'm getting out of my depth here, I'm sure that S.G. will elucidate further if he so wishes. Smile
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tancrède
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PostPosted: Sun Jun 15, 2008 7:32 am    Post subject: Reply with quote

----
Hi

My schematic drawing of the 103.2 is the same that Colin Royle:

http://www.hifiloudspeakers.info/Anatomy/Crossovers/103.2/SP1144103.2CrossoverIndex.html

The protection circuit is a little bit hard to understand because some discret components are sealded by Kef

Nevertheless, after the 600uf (2 X 300) there is a R1 = 680 ohms. This R1 is bypass, in normal operation, by a normally close relay. But when the power is to high, the relay work and open the contact. So the signal audio will pass into the 680 ohms and the current will drop a lot to protect the drivers. But enough power to light the red light below in front of the speaker.

Well, i quiet sure that this is the way that work.

I find 4 capacitors off limit value (one crossover for the moment), not very much, but who knows what could be the change after changing them.

Tancrède
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ColinR
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PostPosted: Sun Jun 15, 2008 10:50 am    Post subject: Reply with quote

Quote:
The protection circuit is a little bit hard to understand because some discret components are sealded by Kef


The two red sealed units are reverse biased Zener diodes and resistors which will overload at various currents and voltages.

The rest of the circuit is for half-wave rectification and for driving the relay.

Perhaps somebody who "does electronics" can draw the circuit diagram Rolling Eyes .
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speakerguru
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PostPosted: Mon Jun 16, 2008 10:08 am    Post subject: Reply with quote

ColinR wrote:

The two red sealed units are reverse biased Zener diodes and resistors which will overload at various currents and voltages.

No zener diodes, just regular signal diodes and resistors doing a piecewise-linear approximation to get a d.c. output signal which is proportional to the sum of the rms of the input audio signals across each drive unit, with time constants appropriate to each voice coil's thermal characteristics. When this d.c signal exceeds a threshold, it switches the relay via the other thick film module.

ColinR wrote:
The rest of the circuit is for half-wave rectification and for driving the relay.

Correct. The second thick film module has the relay switch/driver and is the audio-derived psu for the whole protection circuit.

ColinR wrote:
Perhaps somebody who "does electronics" can draw the circuit diagram.
My memory is not that detailed Rolling Eyes What do you want - blood? Laughing
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ColinR
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PostPosted: Mon Jun 16, 2008 1:26 pm    Post subject: Reply with quote

Quote:
ColinR wrote:
Perhaps somebody who "does electronics" can draw the circuit diagram.
My memory is not that detailed What do you want - blood?



No Very Happy , but the contents of my "inbox" demanding schematics of designs I don't own and people having some strange idea that I used to and still design loudspeakers and can scratch build crossovers and supply drive units to order does lead to similar feelings Rolling Eyes .

With postgraduate qualifications in Analytical Chemistry and Production Control plus an LCR meter I do my best, obviously it’s just not good enough for some people Wink .
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proffski
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PostPosted: Mon Jun 16, 2008 1:37 pm    Post subject: Reply with quote

Must try harder... Very Happy
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tancrède
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PostPosted: Mon Jun 16, 2008 6:28 pm    Post subject: Reply with quote

-----------

Thanks folks

I think there is a transisitor in that red sealed pack

Maybe one day, i will depack and draw the protection circuit. In case someone need to repair-it one day

But those protection circuit is good only if you have children around, in case.

Tancrède
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tancrède
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PostPosted: Tue Jun 17, 2008 1:13 am    Post subject: Reply with quote

Hi

Solen, who is a specialist in Crossover and drivers in Quebec, told me that a coil with no core is better than one with.

The guy was talking about saturation and elimination of certain frequencies.

Exemple: B&W and other goods brands use coil with no core.

What does-it mean to you folks ?????

Thanks with anticipation of course.


Tancrède
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tancrède
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PostPosted: Tue Jun 17, 2008 7:37 am    Post subject: Reply with quote

Hi

Long time i didn't play with cut frequencies calculation

About the crossover of the 130.2 at this adress:

http://www.hifiloudspeakers.info/Anatomy/Crossovers/103.2/SP1144103.2CrossoverIndex.html

For he HF, the Fc = 1/2 (6.29) (R) (C)

So, 1/ 2 (6.29) (220 ohms) (0.22uf) = 3.2 Khz

So the tweeter will produce everything above 3.2 Khz. And that's good

But in the vertical branch, going to the return wire, before the tweeter, there's a 2.2 uf and a 10 ohms

If we do again 1/2 (6.29) (10) (2.2uf) we have = 7.2 Khz
So everything higher 7.2 Khz will go thru this branch and not to the tweeter.

So, how can the tweeter can produce 7.21 Khz to 20 Khz ?????


Tancrède
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ColinR
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PostPosted: Tue Jun 17, 2008 9:53 am    Post subject: Reply with quote

Add page 3 of the CS7 Constructor Series to your reading list, then write an essay titled "compare and contrast" Laughing .

At the bottom of the page it has some impedance plots; the schematic is at the top Smile .


http://www.falcon-acoustics.co.uk/Archive/CS7-3.jpg
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tancrède
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PostPosted: Tue Jun 17, 2008 10:20 am    Post subject: Reply with quote

Hi Colin

The Falcon page is allright for me, because the capacitor and resistance is not in parallel with the HF driver

But with the 103.2 it's not the same

I will change the 2.2uf because they're old. But i dont think it's gone change a lot.

I definitively find that those speakers have no high frequencies, and i think i understand why now.
Because they are cut at around 8000 hz

Or maybe there is something i dont understand over here


Tancrède
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