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KUBE 107 Power Supply

 
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Chris_S
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Joined: 06 Mar 2007
Posts: 3
Location: Blackheath , Australia

PostPosted: Sat Mar 10, 2007 6:12 am    Post subject: KUBE 107 Power Supply Reply with quote

I have just been given a pair of KEF 107s with a KUBE 107 unit. The speakers are in great condition except for the rubber surrounds for the bass drivers (currently being repaired) unfortunately the external transformer used with the KUBE is missing. The legend on the back of the case says 18vac but looking at the circuit inside it appears to be set up for a center tapped transformer. Does anyone have a schematic for the KUBE 107 or can tell me its voltage needs? I am very keen to hear them for the fist time.

Thanks, Chris
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ColinR
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Location: Staffordshire

PostPosted: Sat Mar 10, 2007 12:47 pm    Post subject: Reply with quote

I think Proffski mentioned it some time ago.

Doing a google leads one to the diyaudio.com thread where a 103.4 requires a psu.

Andrew a former KEF chief engineer states that the psu is -23 - 0 - +23 and it's regulated down to -18 - 0 - +18.

PM Speakerguru (former KEF employee) or Parts (107 man) for assistance.
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Parts
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PostPosted: Sat Mar 10, 2007 7:54 pm    Post subject: Reply with quote

Hello,

Do you have the original Kube with attached RCA leads or one with RCA in and out sockets ?

Steve.
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Chris_S
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PostPosted: Sat Mar 10, 2007 10:53 pm    Post subject: Reply with quote

Mine has the RCA in and out sockets. I did see the information regarding the 103.4 but I would like to be sure before powering it up.
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speakerguru
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PostPosted: Sun Mar 11, 2007 10:33 am    Post subject: Reply with quote

The first Kubes with external transformers used centre tapped transformers. They used TL072 ics powered by +/-15 v regulators. I forget what the ac input was. (I'm still using one of the early 102 Kubes with internal mains transformer and I'm not taking it apart to find out).

The later big Kubes (200 and 107) used NE5532 ics. They were run at +/-20V. They also needed more current, hence the larger 23V ac external transformer. I remember the transformer at this stage became a single winding to reduce cost.

I have a schematic of the psu but not of the external transformer, so I can't give you chapter and verse but, I remember that a lot of thought went into making everything forward and backward compatible or at least failsafe whatever vintage of Kube and voltage or winding type of transformer were connected together.

Therefore, as you say, the power supply will work with the old centre tapped transformer BUT it was designed for use with a single winding by half wave rectifying and voltage doubling. Hence the use of 4 x 1000uF capacitors instead of the 2 used in previous Kubes.

I hope that all makes sense.
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proffski
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PostPosted: Sun Mar 11, 2007 8:28 pm    Post subject: DIN Type C 5 Pin. Reply with quote

If I remember correctly my KEF 107/2 Kube (SP2163 Ser No: 02390) utilised the DIN type C - 5 pin plug.
Pins 1 & 2 were used and I applied 21 Volts AC.
The KUBE stipulated '23V Volts AC'.
As has been rightly already pointed out the KUBE uses some fair current as I managed to burn out a winding on my first transformer.
I never measured the actual current used.

Remember that the pins go in the following sequence and should be marked on the plug itself. 1 - 4 - 2 - 5 - 3.

Good Luck!
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Chris_S
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Joined: 06 Mar 2007
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Location: Blackheath , Australia

PostPosted: Mon Mar 12, 2007 6:47 pm    Post subject: Reply with quote

Just to clarify things, mine is the KUBE 107 SP2105 marked 18VAC with the TL072 ics and 2 x 1000uf capacitors and RCA in/out sockets.

I have just received a reply from the KEF agent in Sydney who had contacted the factory in the UK. It states the following: For the 23VAC version, connect 23VAC between pins 1 & 2. For the 18VAC version, 18VAC+ to pin 1, 18VAC - to pin 3, 0V (the centre tap) to pin 2.

AC PSU to be at least 300mA or 9VA

I am happy to email the drawing they sent me to anyone who would like a copy.
Thanks for everyones help.
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