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104.2 bi-wires repair/upgrade

 
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WTG
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Joined: 01 Feb 2006
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PostPosted: Wed Feb 01, 2006 8:07 pm    Post subject: 104.2 bi-wires repair/upgrade Reply with quote

I've owned these since new & just recently the bass surrounds & foam centers fell apart. They are in a Kef authorized repair shop. While there I was considering changing the wiring to mil-spec teflon insulated wire (either bare or silver-plated copper) and silver-soldering all connections (eliminating terminals). The shop said they would do a frequency sweep on the cross-overs to check them. Is this a reliable check? I don't think they have a schematic of values to check each component. What does one do when a mid driver goes bad? I believe they are not available. Does anyone have a schematic or list of values of the cross-over components? Does anyone recommend any upgrades while they are apart? Any opinions on going to larger gauge wire or to wire such as KimberKable inside?
Thanks
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dublin78
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PostPosted: Tue Mar 21, 2006 11:47 am    Post subject: Reply with quote

Hello
I am also considering upgrading some of the components in my 104/2s.
Mine are circa 1992 and the LF units look in good shape.
Someone has already replaced the HF units with KEF NT25 SP1353. Does anyone have any opinion on these?
I am also looking for a schematic of the crossovers, as I believe that there must be some improvements to be made with modern capacitors (Jensens?).
It has been recommended to me that I replace inductor L2 with a 6 mH air-core copper ribbon from Jensen Capacitors. Opinions?.
I would also like to replace the internal wiring with something better. Ideas?
Finally, how do you remove the crossovers? It looks like a nightmare.
Best wishes to all. I am a new member and this looks like a very helpful forum.
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Last edited by dublin78 on Fri Feb 25, 2011 10:01 am; edited 1 time in total
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oplancq
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PostPosted: Tue Mar 21, 2006 5:10 pm    Post subject: Reply with quote

dublin78 wrote:

Someone has already replaced the HF units with KEF NT25 SP1353. Does anyone have any opinion on these?


I bought a pair of those to replace one blown tweeter. I have used those during one month. In the meantime I found a spare SP1191.

SP1353 is going louder than SP1191. Impressive at the beginning. But I feel happier with the original.

I don't know what is the sensivity of the 1353 or if sensivity of 1191 has been somehow reduced because of its age.

I probably would need to pad it...


Olivier
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dublin78
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PostPosted: Tue Mar 21, 2006 7:52 pm    Post subject: Reply with quote

Hello Oliver
My KEF NT25 SP1353s are slightly "Over The Top" also. I suspect that they are a higher sensitivity than the original units. I would be grateful to find out the sensitivity of these for the record.
Wilmslow Audio recommended ScanSpeak D2905/9500 units at ?88 each. I think that I may try these at some stage, or even the D2904/9800 aluminium dome units.
All the best.
Michael
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ColinR
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PostPosted: Tue Mar 21, 2006 9:12 pm    Post subject: Reply with quote

Olivier you probably need to attenuate the tweeter by -3dB.

Which is Cool , a 1.2 Ohm resistor in series and 10 Ohm resistor in parallel with the 4 Ohm unit.

The 104-2 should have 5 and 11 Watt resistors on the original pcb's, so try to use 9W resistors.

Crimp/solder automotive spade/blade connectors on the ends of the series leads (a bit of heatshrink over the bare wires would be a good idea) and get four "piggy back" connectors for the parallel components.
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ColinR
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PostPosted: Tue Mar 21, 2006 9:27 pm    Post subject: Reply with quote

Quote:
I am also considering upgrading some of the components in my 104/2s


I wouldn't bother with "snake oil" components, unless you want external crossovers to begin with, for two of the series capacitors would be the size of Bean tins and a couple of the others you'll have to "make-up" banks to get the correct values and all will have to be within 1% of the original values, unless you've got a good LCR meter to take exact measurements.

Quote:
6 mH air-core copper ribbon from Jensen Capacitors


Hmmm, the only series component in the bass section optimized to operate at >20kV, er I don't think so unless you want to convert a silk purse back into a sow's ear by knackering the voicing.
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dublin78
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PostPosted: Tue Mar 21, 2006 9:35 pm    Post subject: Reply with quote

Thanks for the info Colin
What would you suggest is the best way to get the most from these loudspeakers with the aid of modern components. I would not be sad to hear that it is best to let sleeping dogs lie, if that is indeed the case.
Michael
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Last edited by dublin78 on Fri Feb 25, 2011 10:02 am; edited 1 time in total
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ColinR
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PostPosted: Tue Mar 21, 2006 10:47 pm    Post subject: Reply with quote

I would initially suggest leaving them alone, for with my older birds only a very few of the original components have actually gone off, but they used 150V, 100V and 50V capacitors.

However, later KEF crossovers used 25V and 50V capacitors so have a look at C6, C7, C13, C14, C15, C16 and advise me via email.

If some series components indeed need replacement, you'll end up with a brighter sounding design because of lower internal resistances.

The internal steel wiring was included in the original design "target function" so I wouldn't play with that unless you can find the right sized blade connectors.

Binding posts are a posibility if you're handy drilling pcb's.
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dublin78
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PostPosted: Tue Mar 21, 2006 11:28 pm    Post subject: Reply with quote

Thanks again. This seems very sensible.
How do I check the caps? Do I need an LC Meter?
Best wishes.
Michael
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Last edited by dublin78 on Mon Mar 14, 2011 10:43 am; edited 1 time in total
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ColinR
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PostPosted: Tue Mar 21, 2006 11:42 pm    Post subject: Reply with quote

Quote:
How do I check the caps?


Just look at the condition and note the voltage.

Quote:
Do I need an LC Meter


A £20 multimeter that measures capacitance is a good investment even if it's only use will to be just to check household fuses.

You'll have to unsolder one leg of each capacitor to check it's value.

A >£150 LCR meter is useful if you're going to build loudspeakers or work out crossover schematics Shocked .
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oplancq
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PostPosted: Wed Mar 22, 2006 8:15 am    Post subject: Reply with quote

ColinR wrote:
Olivier you probably need to attenuate the tweeter by -3dB.

Which is Cool , a 1.2 Ohm resistor in series and 10 Ohm resistor in parallel with the 4 Ohm unit.

The 104-2 should have 5 and 11 Watt resistors on the original pcb's, so try to use 9W resistors.

Crimp/solder automotive spade/blade connectors on the ends of the series leads (a bit of heatshrink over the bare wires would be a good idea) and get four "piggy back" connectors for the parallel components.


Thanks Colin...It's worth a trial...
Are you sure for the 3dB figure ? Does that mean NT25 SP1353 have 96 dB as sensitivity ?


Olivier
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ColinR
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PostPosted: Wed Mar 22, 2006 10:58 am    Post subject: Reply with quote

Quote:
that mean NT25 SP1353 have 96 dB as sensitivity ?


Er no, you've gone in the wrong direction, lower numbers are more sensitive.

As the Ref 104-2 has a 92dB sensitivity and the Uni-Q animals 89dB, I sort of pulled the figure of 3dB out of the air for a point of reference.
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oplancq
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PostPosted: Thu Mar 23, 2006 9:28 am    Post subject: Reply with quote

ColinR wrote:
Quote:
that mean NT25 SP1353 have 96 dB as sensitivity ?


Er no, you've gone in the wrong direction, lower numbers are more sensitive.
.

Euh ? I'd say the opposite.

[quote="ColinR"]
Quote:
that mean NT25 SP1353 have 96 dB as sensitivity ?
As the Ref 104-2 has a 92dB sensitivity and the Uni-Q animals 89dB, I sort of pulled the figure of 3dB out of the air for a point of reference.


We would need to look at the Xover used in UniQ series before making this kind of conclusion. I guess tweeter in UniQ series is attenuated.


But I'm surprised and disapointed that KEF did not mention this...Unless my 1191 are too much attenuated because of ferro fluid waxing...

Olivier
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ColinR
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PostPosted: Thu Mar 23, 2006 11:15 am    Post subject: Reply with quote

Confused Ooops, looks like I'm going to have to put my brain in gear in future Wink .

I was thinking about maximum spl's and writing about sensitivity, the Uni-Q's go louder than the 104-2's, so as the R1548X is currently too loud, attenuate by 3dB and listen to the result.
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