KEF 104B crossover schematic needed !

measured values for L from early 104aB

dave
 

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I really wish I could help you right now, but it was in a book had and sold on ebay last year by MARTIN COLLOMS, called "high performance loudspeakers":goodbad: perhaps a library near you may have it on it's shelves.... etc, etc, hope you find it as the 104 ab x, over as well as the spendor bc1 and 111 are also featured in there... cheers and best regards :devily: TC
 
I happen to have analysed the 104aB filter as a start of my 'career'. The LF filter is simple and consists of a 3rd order filter with a resistor parallel to the second inductor. The values are:
L1: 2.7 mH switchable to 3.6 and 2.0
L2: 500 uH (with 10 ohm parllel)
C1: 5 uF

The HF filter is as shown above. with the following values:
C1: 3.3 uF
C2: 10 uF
C3: 10 uF
C4 (the one pareallel to C1 and C2): 600 nF
R1 (parallel to C3): 3 ohm
L1: 2.4 mH

The inductors where rather high resistance iron core ones. It seems that the speaker doesn't improve with better components but I never tried that. Theh capacitors I could not identify but where not much better I suppose.

The tweeter is indeed a T27. I'm not sure as to the B200 and the size of the cabinet. I sold mine some time ago.
By the way. The acoustic responses weren't that good. The B200 has some nasty break up frequencies.

Good luck.
 
:xeye: Yes DICK, you are right on the money as far as the B200 is concerned I know the early MONITOR AUDIO MA 4used it [ btw designed by the same erstwhile audio journalist; MARTIN COLLOMS ] who wrote the book I mentioned above in my prev post] using this driver had to be heavily equalised in a similar fashion because of this.... probably the same reason he did not use the venerable and much over rated T27, Choosing the isophon kk 8 or was it 10? in this design instead: and BTW the 104 ab used the T27, for sure regards to all TC:D
 

bdgdpc

Member
2008-11-19 6:36 pm
Re: kef 104

ANTHONY2181 said:
Hi i have a pair of kef 104 speakers they use a B200 BD139 passive radiator and a T27 tweeter i have the crossover design + i know the guy that was on the design team at kef in the 1970s

I've just signed up for a new account - I'm looking for some help. Can I convert KEF 104's to 104ab's by replacing the crossover? From the threads it looks like they have the same drivers....

David
:smash:
 
[IMGDEAD]http://www.hifiloudspeakers.info/Anatomy/Crossovers/104aB/KEF104aBcrossover.gif[/IMGDEAD]
KEF104aBcrossover

Hi,

Make sure you have the correct specification Kef drivers.
(Tapped inductor is some form of contour control built into 104aB's.)
If you do not have the correct specification drivers then its likely
better to use a KEF crossover for that specification driver.

:)/sreten.
 
Re: Re: Re: kef 104

planet10 said:


Yes. I'd build one from scratch with better parts. The box could use some work too.

dave

I just picked up a set of KEF Cantata's (the bigger 3- way boxes) at the local goodwill for $25, on a 50% sale day. Since 'regular' folk don't understand these things (can't recognize quality audio gear) too much it went like this: I drive to the store to find out..that..at 8:30pm at night, 1/2 hour before closing - the parking lot is still full. I told myself, 'well, I'm sure there's no neat toys left there today, if there were any at all.' And there they were ..where they had been sitting all day...a set of KEF speakers which sold for $1500 in Canada at the time (1978-1980) they were new. A nice little treat for the end of the day, except for the part of trying to shove these things into my car.

Sometimes I wonder what I miss at these stores..stuff that is really cool, I'm sure...but I'll just end up hurting myself if I spend too much time pondering such things.
 
KBK, have you no shame? It is early morning here, still waiting for the caffeine to kick in and I have just logged on. I think your recent post was quite uncalled for!!!! As my teenage children would say "too much information". If you were an American there would be a queue of lawyers about to sue you for "cruel and unusally punishment"! (Although, to be fair, I shouldn't throw too many stones as I did pick up a JLH Class A Amp for $25 myself one day.......)
We can all dream I suppose. Jonathan
 

bdgdpc

Member
2008-11-19 6:36 pm
sreten said:
[IMGDEAD]http://www.hifiloudspeakers.info/Anatomy/Crossovers/104aB/KEF104aBcrossover.gif[/IMGDEAD]
KEF104aBcrossover

Hi,

Make sure you have the correct specification Kef drivers.
(Tapped inductor is some form of contour control built into 104aB's.)
If you do not have the correct specification drivers then its likely
better to use a KEF crossover for that specification driver.

:)/sreten.

Thanks! I've just stumbled on the same diagram from www.hifiloudspeakers.info/Anatomy/Crossovers/AnatomyCrossovers.html and also got a schematic of the contour control from Mr Watson (!) from KEF (I was going to attach it but it's too big - e-mail me if you want it), via Neil Smith from Wilmslow Audio - very helpful people. They do a manufactured pair for £120. I can see that the 3-position control knob will sit on the positive supply of the circuit diagram, selecting between 2/2.7/3.5mH inductors that feed the B200 mid driver. I guess a simple 3 pole switch would do. Just about to bid for a pair of 104's......

David
 
the extra components on the T27 section were the famous "acoustic butterworth" components of that time. The T27 fundamental resonance was around 1.2 kHz and even though about 30 dB down the slope of the crossover spoilt the sound. The extra AB components nulled the effect of the resonance and did give a better smoother sound through the crossover region than before. Kef did a reasonable trade in upgrade kits of the crossover for self fit since the 104 was a popular speaker of that era.
 
I forgot, the outside of the box was 63 cm by 33cm by 26cm deep. It was made with rather thick flooring grade chipboard, braced around the middle with internal volume of 35.5 litres filled with heavy grade foam. You do need the later higher power B200 since the crossover lower section was designed for it. Also the passive B139 ABR suspension was tuned for the volume so you would need to stick fairly close to the original if you have the same unit.
 

hondeoren

Member
2016-06-04 1:25 am
NL
In my opinion, the 104ab is a superb reference monitor. With tight low and mid-low bass, and a very open wide mid-high and high band spectrum . I've tested it with several amps: Akai am2400, Yamaha CR 420 and Harman Kardon HK6300 (bizarre fresh opensound!) and very satisfied with it.
Does the fact that it is a closed box with passive radiator have an effect on the crossover? Or could I rebuild a box with the same speakers (T27, B200 SP1039) vented / leaving out the passive radiator?
Thanks for all the info on this forum, I like reading it!
 

Deano452

Member
2016-12-08 9:30 am
In my opinion, the 104ab is a superb reference monitor. With tight low and mid-low bass, and a very open wide mid-high and high band spectrum . I've tested it with several amps: Akai am2400, Yamaha CR 420 and Harman Kardon HK6300 (bizarre fresh opensound!) and very satisfied with it.
Does the fact that it is a closed box with passive radiator have an effect on the crossover? Or could I rebuild a box with the same speakers (T27, B200 SP1039) vented / leaving out the passive radiator?
Thanks for all the info on this forum, I like reading it!
It would 1000 percent necessary to include the passive radiators in to your design why would you even consider removing it . Perhaps putting it on the back might work but that would change phase a bit .