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KEF 103.2 Crossover upgrade
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speakerguru
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PostPosted: Tue Jun 17, 2008 10:51 am    Post subject: Reply with quote

tancrède wrote:

So the tweeter will produce everything above 3.2 Khz. And that's good...............
So everything higher 7.2 Khz will go thru this branch and not to the tweeter........................


No, no, no, Sad Shocked Evil or Very Mad Rolling Eyes Wink . Please don't try to analyse circuits with black and white guesswork. Filters do not work like that. There is no such thing as zero loss passband or infinite cut stopband. Similarly, highpass and lowpass filters do not have infinite slope. Crossover networks do not just frequency divide, they eq as well. Read some filter books and do some measurements if you want to learn more. You can't expect a forum to be a crossover design primer.
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ColinR
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PostPosted: Tue Jun 17, 2008 10:56 am    Post subject: Reply with quote

Well said Very Happy .
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tancrède
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PostPosted: Tue Jun 17, 2008 11:33 pm    Post subject: Reply with quote

Hi

My old notions of electronic begin to emerge

Dont know the value of the coil of the tweeter, but i suppose that at high frequencies, around 10 000 hz and more, the XL impedance of the tweeter is quiet the same as the branch with the 2.2uf and the 10 ohms resistance

So the half of the signal goes in the tweeter and the other branch. So this must be a -3 db filter for the tweeter frequencies.

So in that case everything is allright. Tweter can produce high frequencies to 20 000 hz (20Khz) Ouf, that was scary.

But if i can hear more frequencies then that with the change of capacitors, i will find a way to change that. The bass and mid are very good.

And in case you think that my ears is to old to hear high frequencies, well that's not the case with my B&W 330i and Rogers LS7

Tancrède
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hef
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PostPosted: Sun Jul 20, 2008 1:34 pm    Post subject: Reply with quote

Hey guys, I would like some advice...

I just inherited a pair of 103.2s that were going to be scrapped. After getting them home and testing them out I've found that one cabinet works perfectly while the other doesn't function at all.
I have since narrowed this malfunction down to the crossover board as both the woofer and tweeter in the non-functional cabinet work perfectly when swapped into the other cabinet.

I have thus been looking for a replacement crossover board for this model and cannot find one anywhere. However, I have found a pair of crossover boards on ebay for a Carlton model KEF set. Seemingly the Carlton model uses the same model of woofer and tweeter as these 103.2s so I am wondering, is it a wise idea to replace the crossovers in these 103.2s with the working ones from a Carlton series cabinet? Will there be a massive tonal difference since the crossover is designed for the same drivers?

I'm more inclined to take this route as I get the impression it will be pretty hard to track down some of the components needed to rebuild the original crossovers, but if anyone has any helpful advice towards that end it would also be helpful to me.

Cheers guys.
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ColinR
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PostPosted: Sun Jul 20, 2008 3:25 pm    Post subject: Reply with quote

You want a Carlton III crossover, the ePrey crap artist is flogging a Carlton II crossover which is a different animal.

I’d invest £30 in a bleeping multimeter (continuity tester) and determine whether it is a series component (lead-in wire, inductor or resistor) or a break in the PCB track due to corrosion.

Bypassing it with a short lead endowed with crocodile clips can identify a dead capacitor.

Use a transistor radio personal earpiece socket as your sound/amplification source in every case.

A picture of one of my 103-2 PCBs with a blown then repaired bass/mid unit track is available for those interested in what happens when an old S-STOP electrolytic corrodes what’s around it Shocked .
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Last edited by ColinR on Sun Jul 20, 2008 4:04 pm; edited 1 time in total
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proffski
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PostPosted: Sun Jul 20, 2008 3:29 pm    Post subject: Reply with quote

Agreed, it is not that complicated.

Colin, if the photograph is not on the site I'd welcome a peek at the patient before and after photographs please...
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ColinR
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PostPosted: Sun Jul 20, 2008 4:05 pm    Post subject: Reply with quote

Quote:
a peek at the patient before and after photographs please...


You have mail Smile .
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proffski
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PostPosted: Sun Jul 20, 2008 4:39 pm    Post subject: Reply with quote

Er, nothing in my personal messages folder as yet, and a link to here on my normal email address... Crying or Very sad
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hef
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PostPosted: Sun Jul 20, 2008 5:33 pm    Post subject: Reply with quote

Okay,
I think I have this figured now...

I tried the test you described Colin and get this, there is nothing wrong with the crossover. I took the headphone out of my PC to a mono line on the input of the crossover and instantly had tiny sound. No problem.

So I connected it all back up again, fired up the amp and still, no sound.

The next thing I did was pretty much a bad idea, but has helped narrow the problem down... I tried shorting some of the caps while hooked up to the amp at a super low volume and discovered by accident that shorting resistor R1 (circled below) solves the problem. I get full volume and correct frequency division. This resistor isn't included in the crossover schematic on here.... making me think it's part of the s-stop circuit that i haven't been able to get a diagram of...does this help identify the problem component? Is THAT the problem component?


That's the geezer there circled in yellow.

Cheers.
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hef
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PostPosted: Sun Jul 20, 2008 5:51 pm    Post subject: Reply with quote

Forgot to add, It's marked "ERG 17 ER 680R 5% 7938".
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proffski
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PostPosted: Sun Jul 20, 2008 6:07 pm    Post subject: Reply with quote

hef wrote:
Forgot to add, It's marked "ERG 17 ER 680R 5% 7938".


Looks like a 680Ω Wire Wound resistor then, 5 Watt?
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ColinR
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PostPosted: Sun Jul 20, 2008 8:01 pm    Post subject: Reply with quote

Quote:
discovered by accident that shorting resistor R1 (circled below) solves the problem


A S-STOP circuit is parasitic and in parallel with the crossover, when it kicks in it diverts most of the signal through the 680 Ohm resistor.

You have a fried S-STOP so remove the resistor and replace with a piece of wire.

Some Carlton III crossovers are built on the same PCB btw.

Find some Polyswitch of 0.5 Amp for the T33 and 0.8 Amp for the B200G and solder in series at the +ve to the drivers from the pcb.

Job done.

The bust bit is probably in one of the diode packs in the "black bricks" Cool .
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proffski
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PostPosted: Sun Jul 20, 2008 9:58 pm    Post subject: Reply with quote

Still awaiting the pics...

Agree with the comments, but why or how with any sensebility can you destroy the S-Stop module in a domestic evironment unless you are deaf or daft?
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speakerguru
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PostPosted: Mon Jul 21, 2008 12:35 pm    Post subject: Reply with quote

ColinR wrote:
You have a fried S-STOP so remove the resistor and replace with a piece of wire.

Could also be a dodgy relay. Worth checking.
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hef
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PostPosted: Mon Jul 21, 2008 2:04 pm    Post subject: Reply with quote

Removing that resistor seems to have solved the problem. I'll be keeping an ear on it for a few weeks to make sure it's right but in the mean time, thanks very much for the help guys.
I just had a pretty good listening session. It's amazing how much difference a fresh/different set of speakers can change your listening experience.
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