Crossover for KEF 103 Ref (Mid 70,s Model)

[bencat]

I have tha chance of getting what looks to be a reasonable pair of KEF speakers the original KEF 103 Reference.

However given the age of these units I will need to do a complete check on the crossover and ensure that all the components are still within spec and reaplce were needed.

If anyone has circuit diagram for the crossover that would be a real help .

[Phil Y]

Hello bencat,
Have you tried contacting KEF ?
Many years ago I got in touch with them with some DIY questions and they were quite helpful. With your speakers the main concern would be electrolytic caps and I doubt a REF model would have any in the x-over. I would expect it to be those black cylindrical polyester jobs that were popular at the time, they should be fine. The internal wiring could well be skinny with push on tags which would be well worth replacing with something chunkier and soldered at both ends though.

Regards, Phil.

[Richard]

Hi Bencat,

Also have a look at this site and their forum, maybe ask there or email the site owner.

There's the 103.2 xover linked below. Even if you don't find the circ though the checking will be pretty much the same. The inductors may not be marked but will more than likely be fine. The elctrolytics will be marked with values so check with the meter and change if needed.

It may be surprising though, I've checked many from that era expecting them to be bad but they were all fine. Changing electros for plastic film types though can bring some fine detail and control to the sound but you will have to decide whether you want that or Kef's original sound I suppose

http://www.hifiloudspeakers.info

http://www.hifiloudspeakers.info/speakertalk/

http://www.hifiloudspeakers.info/Ana...overIndex.html

[Phil Y]

Circuit diagram with lots of electrolytics.
I'll get my coat.

[bencat]

Thanks for this I have found through these links some pictures of the inside of the Kef 103 and the full circuit diagram

On looking at the pictures I think Phil Y is spot on . Wiring looks to be very thin and to be push on clips.
All capacitors seem to be plastic film which should be okay measurement wise but might be swapped for some modern ones just to be safe . The two resistors are 5 watt and look like carbon 5% one. Might well be worth seeing if there are any 1% Metal Film ones that could be used.

Only thing I am less sure about is the inductors which I am not sure if there are better quality ones around to replace them .

[Richard]

The caps will be electrolytic I think. Old Kefs used black ones with red resin ends labelled Elcap as Phil says but they were electrolytic afaik and could go high.

Later caps may be blue, labelled Alcap, but again both are electrolytics afaik.

I've some of the blue ones swapped out from a xover years ago and still measuring fine.

Of course you might want to change them and the wiring etc whatever they are but I'd be careful not to lose the Kef sound if that is the attraction of them.

Bear in mind any replacement inductors will likely have a different DCR so you will be changing the xover. Unless you play them at massive levels they are unlikely to saturate so I'd leave them and focus on the caps.

[Phil Y]

For some reason I had always thought those caps were polyester.
Every day is a school day !

Thanks for putting me right Richard.

Phil.

[bencat]

Originally Posted by Richard

The caps will be electrolytic I think. Old Kefs used black ones with red resin ends labelled Elcap as Phil says but they were electrolytic afaik and could go high.

Later caps may be blue, labelled Alcap, but again both are electrolytics afaik.

I've some of the blue ones swapped out from a xover years ago and still measuring fine.

Of course you might want to change them and the wiring etc whatever they are but I'd be careful not to lose the Kef sound if that is the attraction of them.

Bear in mind any replacement inductors will likely have a different DCR so you will be changing the xover. Unless you play them at massive levels they are unlikely to saturate so I'd leave them and focus on the caps.

I am in two minds over this as there are two issues . One as mentioned is that if I like the KEF sound then changing things may just make things different but not better .

The other idea or option I am considering is to construct two complete new crossovers using Clarity Caps , decent resistors and full set of Inductors if possible the same as those in the original . Then mount them in a box and just disconnect the original and wire directly to the speaker connectors and use the outboard crossovers. I can then do any changes to resistor values (to compenstate for the different caps ) and any other things easily but if I decide either to sell the speakers or do not like what the new crossover does I can reconnect the old ones inside the speaker and back to original state .

What do you think ?