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KEF 103.2 Crossover upgrade
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proffski
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PostPosted: Mon Jul 21, 2008 2:49 pm    Post subject: Reply with quote

This is a weird one.
Shorting the resistor removes the problem as does removing it.

Looks like the S-Stop gubbins has thrown a wobbly!
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speakerguru
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PostPosted: Mon Jul 21, 2008 3:45 pm    Post subject: Reply with quote

proffski wrote:
Shorting the resistor removes the problem as does removing it.
Looks like the S-Stop gubbins has thrown a wobbly!

It sounds more and more like a problem with the relay contacts. After all these years who knows what the state of the relay contacts might be. The contacts are most likely oxidized and have probably been disturbed and cleaned by movement during the act of removing the resistor. The contacts are normally closed and thereby short the resistor. When the S-Stop triggers it opens the contacts and the resistor is then in series with the speaker. If shorting the resistor makes a difference to the sound then the relay contacts must be high resistance Q.E.D.
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hef
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PostPosted: Mon Jul 21, 2008 8:17 pm    Post subject: Reply with quote

proffski wrote:
This is a weird one.
Shorting the resistor removes the problem as does removing it.

Looks like the S-Stop gubbins has thrown a wobbly!



Yeah, I thought it seemed a little strange.
I've decided that I'm gonna hunt down all the parts to do a complete rebuild of the crossovers anyway, so I'll just enjoy the fact that it works for now until I manage to find those elusive 4.2uF caps. Nobody around my area seems to carry them.
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proffski
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PostPosted: Mon Jul 21, 2008 9:00 pm    Post subject: Reply with quote

4.2µF Capacitors.

What is their physical size in mm?
I just may have some quality ones in my workshop, you may have to pad them out with a smaller value to make up the 4.2µF, but there is nothing wrong with that as long as there is space on the PCB.
Are they 5% tolerance or better?
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tancrède
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PostPosted: Mon Aug 11, 2008 3:33 am    Post subject: Reply with quote

-------
Hi friends

How can i test the protection circuit of 103.2 without explosing the speakers ?????


Tancrède
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ColinR
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PostPosted: Mon Aug 11, 2008 11:45 am    Post subject: Reply with quote

Essentially you're asking for the circuit diagram with component values or if someone has "reverse engineered" the circuit and determined the current and over voltage conditions for operation.

I suspect a very emphatic NO!

The best you can do is get some 8 Ohm 17W or 20W resistors to replace the drive units and come up with some scheme where you can play something loud and horrible or test tones at measurable levels to get the S-STOPs to operate without blowing them up.

Hope this translates Smile .
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hef
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PostPosted: Fri Nov 07, 2008 4:12 am    Post subject: Reply with quote

Well well, I'm back, and I bring good news.
I bought a pair of NOS KEF sp1144 crossovers Very Happy still in their original packaging!

Seriously.



They arrived yesterday while I was at work and since i was free today I installed the first into the damaged cab.
All was good, so I went ahead and installed the second one into the working cab.

All is still good. Awesome in fact.

After installing the second network I noticed something. The low end of both speakers has lost a little (really little) of the kick it had originally.
As I was sitting here listening with the old crossovers in my lap I noticed something I didn't notice when I first posted here and had to come back to check... and I was right...

The original crossovers in these speakers are different to both the circuit diagram posted by colin in the crossovers section AND from the NOS service parts I have just installed in two ways, the second of which is probably more important.

1. The NOS circuits use ALCAP capacitors which are a nice shiny blue colour whereas the originals use slightly bigger black ELCAP capacitors. I dont know enough about either to know how this may affect their performance but I didn't think it would make them significantly different.

2. As discussed at the beginning of this thread, the NOS networks have two big bad ass 300mfd caps wired parallel in series with the woofer in the exact same place as my original networks had a bunch of slightly less bad ass caps in series, HOWEVER, the bunch of caps in my original units DO NOT add up to 600mfd. There are three 150mfd and one 100mfd, making only 550mfd in series with the woofer.


Top left corner.

What do you guys think about that?
Think either of those would cause me to lose a little of the low end beef from these cabs and should I bother rectifying the problem since it's not that outrageous a difference (it's nothing EQ can't fix)?

Also, do crossovers require/have any sort of burn in/warm up time before they reach their optimum performance? Heh, that's probably a pretty stupid question.

Cheers.

EDIT - Also, I should say, thankyou very much for your kind offer profski. Had I been back in the meantime I would probably have taken you up on that, but it's all good now.
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speakerguru
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PostPosted: Fri Nov 07, 2008 9:01 am    Post subject: Reply with quote

KEF used to buy in all the capacitors at +/-10% or sometimes +/-20%. Then they would measure them all in-house and sort them into 1% bins. If I remember correctly, any parallel combinations would always be sorted to end up with a less than than 0.5dB effect on the response (0.3dB Reference series). In other places the inductors would be wound to compensate. i.e if the capacitor was -6% the inductor would be wound +5% or whatever the calculation predicted would minimise the drift from nominal. All of which is a long way of saying I bet your 300+300 measures pretty much the same as your 150+150+150+100.
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