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KEF 103/3 studio monitors

r50bike

Member
I have a pair of 103/3's. These have an active equaliser called a Kef cube connected between the pre amp out and main amp in.
I cant quite remember when I bought these(1980?) and have lost all the paperwork.
The speakers still perform well and I am reluctant to change them until I have replaced all of my electronics.
As I upgrade my amp and pre amp the noise coming from the Kef cube electronics is now at a higher level than the noise floor of a modern amp/pre amp. I have tried to get a circuit of the Kefcube from KEF to see if I can improve the signal/noise ratio of the cube, but no luck so far.
Anyone have any info on 103/3 and Kefcube or anyone tried the 103's without the cube for a prolonged period
IanMac.
 
The KUBE was als sold with the104/2s - I bet the schematic is on the web somewhere! IIRC it uses TL072s, not the quietest devices, so there's one avenue to pursue.

Equally, many prefer(red) KEF speakers without the KUBE - while it flattened and extended the bass, it really did seem to throw the baby out with the bathwater too often to be more enjoyable with it in circuit IYSWIM.
 
Will keep looking on the net. CCT diagrams for Hi Fi equipments seem to be well kept secrets. I had quite a hassle prising one out of Linn for my Karik.
Will try my 103's without the cube for a while.
Ianmac
 
have logged onto the suggested Hi Fi LS site but the administrator seems overloaded as I cant get registered.
I have been and listened to a few Loudspeakers in local Hi Fi dealers and was quite dissapointed, most were pushing B&W ( some of their latest models appear to be made in China) I had a preference towards Spendor but they are expensive. My old KEFs stand up better than I though against modern speakers and I have decided that I will upgrade the KEFCUBE with lower noise I/c's and power supplies. I need a circuit for a 103 Kefcube if anyone can help
Ianmac
 
Registration does take a while, I seem to remember not getting a confirmation that my account had actually been activated either. Give it a week then try logging in.
 
The KUBE was als sold with the104/2s - I bet the schematic is on the web somewhere! IIRC it uses TL072s, not the quietest devices, so there's one avenue to pursue.

Equally, many prefer(red) KEF speakers without the KUBE - while it flattened and extended the bass, it really did seem to throw the baby out with the bathwater too often to be more enjoyable with it in circuit IYSWIM.

How difficult is changing the OP amps? I myself use the R107, and have a couple of issues my 107 Kube.
 
Have been unable as yet to get a scematic of the KEFCUBE for the 103.3
I have communicated with people who have changed the op amps from the NE5532 fitted by KEF to Low noise OPA 2132's. This also requires the Power supply to be lowered slightly. Have also been advised that it is a pig to change the op amps due to the flimsy double sided PCB but I think if one cuts out the old chip it should be possible to remove the pins without damaging the PCB.
My intention is to build another cube using the KEF frequency contour circuit with low noise chips audio friendly capacitors and PSU. eliminate the tape circuits and the extend button which I never use. ie minimise the electronics and switches the audio signal passes through.
I have had no luck in obtaining a circuit for the Cube or Crossover Unit.
May have to dismantle my cube and trace the circuit the hard way
Ian
 
Ian, it might be worth fitting some dil sockets in place of the 5532s so that you can try different OP amps without further damaging the board.
 
The 5532 and the 2132 are both rated for +/- 18V, so there shouldn't be an issue there.

Another good sub for the 5532 is the OP275, rated at 22V.

Snip, desolder and socket is the way to go.

I don't know what a Kube looks like, but I would have thought upgrading the opamps, caps and bypassing anything not needed would be better than rebuilding the thing.
 
Hi,

If it's of any use, I can tell you a lot about the KEF KUBE's as I used to be KEF Product Manager for 7 years and was always advising people about them...!

Basically, in speaker design terms, to increase bass response, you have to efficiency (for a specific size/type of drive unit). And likewise, if you want a smooth mid-band response in the mid, then you usually have to attenuate any nasty peaks in the mid, using the passive crossover.

So, what KEF did with the 102, 103/3, 107 and 107/2 was to design a electronic box that could "fill in" for the "missing" bass (by boosting the LF at the same rate as the natural roll-off) and also attenuate the mid-frequencies so as to smooth out the sound. This made the speakers produce a very good LF performance for their size, without trading efficiency, (otherwise this would mean you'd need a far more powerful (and hence more expensive) amp to drive them).

Whilst this worked fantastically well in theory, in practice it was let down by the manufacturing cost of the KUBE's, which someone decided had to be "cheaper" than might have been the case.

As such, the 102 and 103/3 ended up with: low-end audio IC's, cheap plastic cases and low quality outboard power supplies. (The 107 KUBE's were a bit classier, as there was more budget for them).

So, in truth, you really need to use the KUBE with their respective speakers, to get close to the best overall sound...but this will be at the expense of transparency and detail (which get lost in the KUBE!).

Use the speakers without the KUBE and you will lose bass and gain an unbalanced mid-band sound.

The 104/2's were designed before the aforementioned speakers and hence the KUBE was made optional. It only really boosted the bass, with a smidgeon of MF-cut.

Later on, the KUBE 200 and it's cheaper brother KUBE 100, were designed as optional KUBE's for the follow-up range (101/2, 102/2, 103/4, 105/3) and these just boosted the bass - the roll off slopes of all the above speakers were basically the same so a single designed KUBE worked for all of them.

I was working on a SuperKUBE when Gold Peak bought KEF out of administration, but sadly the new owners decided against going into production with it.

As far as electronic schematics goes, I cannot recall these being published anywhere....and IIRC, the design was made more difficult to ensure it couldn't be copied easily...(unless you had the drawing to hand to "follow it").

Hope this helps someone.

regards

Tim
 
These sound a bit complicated with the 'KUBE' involved.
So many variables...
Better go back to the thread on the original 103s.

As my Serbian friend would say, "Keep it simple, man."

Martyn.
 
These sound a bit complicated with the 'KUBE' involved.
So many variables...
Better go back to the thread on the original 103s.

As my Serbian friend would say, "Keep it simple, man."

Martyn.


My experience - best with kube - richer/fuller/more harmonious.

Still missing schematics......

Erik
 
My experience - best with kube - richer/fuller/more harmonious.

Still missing schematics......

Erik

There is some who say that electronic equalisation/manipulation is to be avoided.
The KUBE presumably comes into this category.

I keep an open mind on these things, except for the BOSE system.
My friend in prof. audio quoted me the following.
'No highs, no lows. That's Bose.'
He was referring to Bose PA speakers, not domestic ones.

Martyn.
 
I just bought a pair of 103/3s, definitely a step up from my older and cheaper speakers. My purpose is both general background listening at home but also monitoring once I start doing some recording. Comparing the KEFs with new Wharfdales in the local audio store, I immediately preferred the more transparent sound of the old-timers, without KUBE attached (I have still not hooked it up). But they are rather light on the bass, I can easily hear when I compare the speakers with my AKG K340 or K702 headphones. So I'd like more bass but do not wish to give up detail and transparency. Timbo's post was very enlightening about the tradeoff.
What if I get a third-party equalizer? And/or a subwoofer? Would that give me more bass yet preserve detail? I am no audiotech expert at all, so any suggestions are appreciated.
 
This argument holds if the equalisation unit is not an integral part of the crossover but in this case it is so it's not really an option. On the KISS principle the easiest option here might be to rebuild the crossover in the speaker to avoid the need for the kube. To do it properly you would ideally need the technical specs of the drivers, some measurement equipment and speaker design software. But getting this right now may resurrect a lot of pairs of kef speakers.

There is some who say that electronic equalisation/manipulation is to be avoided.
The KUBE presumably comes into this category.

I keep an open mind on these things, except for the BOSE system.
My friend in prof. audio quoted me the following.
'No highs, no lows. That's Bose.'
He was referring to Bose PA speakers, not domestic ones.

Martyn.
 


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