Modding Kef 105 speakers

[flinx]

Have a pair of kef 105 mk1 speakers they are working fine with original crossovers with protection circuit and facility to select power rating of amp used. I cant help thinking they would sound better with a 'simplified' crossover without protection circuit and amp power selection. Would like to here from anybody with experience of these speakers and modding them.

 

[Robert]

If you go to the KEF main website you can download the old Keftopics technical papers on the 105 design and the associated protection circuits. Great reading:

http://www.kef.com/gb/about/keftopics

 

[martin clark]

I'd be wary about modifying without taking much time to understand/trace what each bit does, because this design effectively comprises a lot of EQ and was one of the first 'conjugate-match' crossovers from KEF. That's not to say that better parts wouldn't be better (esp. replacing any electrolytic caps at nearly 30yrs old)- but it may just turn out to be rather more sensitive to exact values than most.

Nice link Rob - thanks.

 

[flinx]

Thanks for the advice and link guys. I guess I was wondering if the mods would make a worthwhile and cost effective improvement, as i def dont have the know how to do them myself and once modded i suspect their value would be decreased. so it would be a gamble to mod them or not

 

[James]

I would recommend a refresh of electrolytic caps only, and perhaps changing the lower value one (<20uF) to film caps. Inductors and resistors don't deteriorate, and won't need changing.

Modding the XO in any other way, including the removal of congugate filters and seemingly redundant bits would require a complete redesign with measurement, modelling and many evenings of fine tuning. If you don't have the know how, I'd recommend leaving the classic as KEF intended.

 

[Yank]

I would recommend a refresh of electrolytic caps only, and perhaps changing the lower value one (<20uF) to film caps.

Are there any caps in a KEF of that vintage that aren't electrolytic? I thought they used those black "Elcap" NP 'lytics with the red end-fill everywhere?

 

[James]

Are there any caps in a KEF of that vintage that aren't electrolytic? I thought they used those black "Elcap" NP 'lytics with the red end-fill everywhere?

I can't be sure, not having seen the insides of too many KEFs. Electrolytics themselves aren't an issue if they are used to shunt a leg of the circuit to ground. The character of caps come into play in MF and HF circuits, where there is at least one in series to form part of the high-pass filter.

 

[flinx]

So it looks like modding the XO is a big job and not really practical. Replacing the caps seems fairly straight forward and I may even attempt it myself.For a complete novice to matters of DIY audio is it possible to identify from pic which components it is recommended to replace and any recommendations for a particular brand to use would be helpful.

 

[Yank]

Well, all the black tubes with red ends are ELCAP non-polar electrolytic caps, and I'd replace them all with the same type. I'm sure Falcon Electronics still sells them? The two colorful ones with the stripes look like Mullard "goldfish" polyester film caps, and I think you could get away with replacing those with any modern polypropylene film-and-foil "audiophile cap du jour" type film cap without doing any damage.

The received wisdom is that in these KEF crossovers, the filters were optimized around the particular characteristics of those ELCAPs, and changing them to supposedly better cap types may result in deleterious effects on the frequency response of the system.

The inductors (coils of magnet wire around an iron core) do not degrade with age and don't need maintenance unless they've been overheated. The green wire-wound resistors should be good for life too.

 

[flinx]

Thanks Yank thats the kind of info a novice such as myself needs.