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Ianmac
Junior Contributor 10+
Joined: 07 Aug 2007
Posts: 11
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 Posted: Sat Aug 11, 2007 3:49 pm Post subject: KEF 103.3 KEFCUBE |
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As I upgrade my system electronics the noise floor in todays amps is below that of the KEFCUBE.
I would like to try and reduce the noise in the cube by using lower noise Chips and other components, and improve the powersupply.
Am looking for a circuit diagram.
KEF have not replied to my emails.
Anyone out there have one
Ianmac |
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proffski
Über Contributor 1000+
Joined: 22 Aug 2003
Posts: 1297
Location: Tewkesbury UK
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| Posted: Sat Aug 11, 2007 7:21 pm Post subject: KEF 103.3 KEFCUBE |
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I cannot help you with the diagram, but...
Some advice.
I did once help and repair a KUBE. Unusually one of the op amps had popped.
Removing the 8 Pin DIL component I damaged the double sided PCB badly.
It did not take kindly to having bits removed.
There is a happy ending as in the end the repair was managed and a high quality turned pin socket soldered into the board.
Now with eyesight even worse than it was ten years ago I would refuse to offerany any such help. Maybe other KUBES used more robust tracks on the PCBs, I cannot even remember which one it was that I worked on.
These particular tracks lifted with the least provocation!
_________________
I contend that for a nation to try to tax itself into prosperity is like a
man standing in a bucket and trying to lift himself up by the handle.
-Winston Churchill
Last edited by proffski on Mon Aug 20, 2007 10:38 am; edited 1 time in total |
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speakerguru
Über Contributor 1000+
Joined: 18 Nov 2005
Posts: 1192
Location: Green Hut, Tovil
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| Posted: Mon Aug 20, 2007 9:31 am Post subject: Re: KEF 103.3 KEFCUBE |
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Just back from hols. I will look for a circuit diagram, but don't hold your breath. I don't recall the 103|3.
| Ianmac wrote: | | As I upgrade my system electronics the noise floor in todays amps is below that of the KEFCUBE. |
Very unlikely, as the laws of physics have not changed recently  .
If you are experiencing noise when using the Kube it means that you are not operating it at a high enough signal level. I would suspect that you have it between the pre and power amp. This means that the full Kube output noise is always being fed to the power amp regardless of volume control setting.
Try putting the Kube in the tape monitor loop where it will normally be in circuit before the volume control. This means that the signal will be running through the Kube at a higher level and also that the signal and Kube noise will both be proportionatley attenuated by the volume control.
| Ianmac wrote: | | I would like to try and reduce the noise in the cube by using lower noise Chips and other components, and improve the powersupply. |
Changing to lower noise chips won't do a thing, as the dominant noise source is the thermal or "Johnson" noise from the resistors. To get a significant noise reduction when changing from TL072 to NE5532 opamps you would also need to scale down the impedance by lowering all the resistors and increasing all the capacitors pro rata. You would also then need to buffer the input so that the new lower impedance Kube did not excessively load your source. |
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vistisen
Intermediate Contributor 50+
Joined: 01 Sep 2006
Posts: 57
Location: Denmark
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| Posted: Mon Aug 20, 2007 4:26 pm Post subject: Re: KEF 103.3 KEFCUBE |
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| speakerguru wrote: |
If you are experiencing noise when using the Kube it means that you are not operating it at a high enough signal level. I would suspect that you have it between the pre and power amp. This means that the full Kube output noise is always being fed to the power amp regardless of volume control setting.
Try putting the Kube in the tape monitor loop where it will normally be in circuit before the volume control. This means that the signal will be running through the Kube at a higher level and also that the signal and Kube noise will both be proportionatley attenuated by the volume control.
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I tried doing this but found that some CD's were recorded at such a high level that this KUBE started popping violently, So be careful. I proved that this was the case by using a test disc, low frequency test signals at high levels, caused the popping straight away. |
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speakerguru
Über Contributor 1000+
Joined: 18 Nov 2005
Posts: 1192
Location: Green Hut, Tovil
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| Posted: Tue Aug 21, 2007 8:15 am Post subject: Re: KEF 103.3 KEFCUBE |
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| vistisen wrote: | | I tried doing this but found that some CD's were recorded at such a high level that this KUBE started popping violently, So be careful. I proved that this was the case by using a test disc, low frequency test signals at high levels, caused the popping straight away. |
In that case you would need to put attenuators in the Kube inputs or the tape monitor outputs. If you have no measuring gear then try 3dB to start with. Increase the attenuation until the popping stops.
OTOH if you decide to stick with the Kube between pre and power amp, put attenuators between the Kube and power amp. Then you can run your preamp and Kube at a higher level (relative to the Kube noise). |
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Ianmac
Junior Contributor 10+
Joined: 07 Aug 2007
Posts: 11
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| Posted: Sat Aug 25, 2007 6:02 pm Post subject: KEFCUBE 103.3 |
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Sorry for my delay in replying have been away for 2 weeks
Have already tried the various connection modes with both my integrated and separate pre amp/power amp (Cyrus) It does not cure the problem. I'm certain it is due to the signal to noise ratio of the Kube being some db's worse than a modern amplifier. I have already recieved a PM from a member who had the same problem and he replaced the NE5532 op amps in the Kube with OPA2132's and reduced the power rails. This resulted in a considerable improvement to both noise and sonic performance.
I would like to see the benefits I could gain by doing a similar excercise, I envisage a complete new build using current component and power supply technology,
( leaving my existing kube untouched )
thus my quest for a circuit diagram.
If nothing is forthcoming I will have to trace the circuit from my existing Cube
Ian |
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speakerguru
Über Contributor 1000+
Joined: 18 Nov 2005
Posts: 1192
Location: Green Hut, Tovil
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| Posted: Tue Aug 28, 2007 9:12 am Post subject: |
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Sorry, I've had a search but I can't find a schematic of the 103|3 Kube  . You'll have to trace out the existing circuit. If you send me your work I can check the topologies and help with any impedance scaling redesign, particularly the Friend biquad sections.
Unless you have a rare ProKube, your Kube will have TL072 opamps, so anything you've been told about changing NE5532s is not really relevant, is it?  . Assuming you don't have a circuit simulator I am willing to run designs through one for you so you'll be able to assess if any worthwhile noise reductions are possible.
BTW, the noise for both NE5532 and OPA2132 is 8nV/rtHz, so the only increase in signal to noise you can get by using OPA2132s is by increasing (you said decrease in your post; that's wrong) the supply volts and running them at a higher signal level. The NE5532s will run on +/-22V supplies and the OPAs will run on +/-36V, so there is a potential 4dB improvement there, if, and only if, you reduce the resistor noise by scaling the circuit impedances and you run the Kubes at a higher signal level (and then attenuate both signal and noise before the power amp). |
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Ianmac
Junior Contributor 10+
Joined: 07 Aug 2007
Posts: 11
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| Posted: Wed Aug 29, 2007 1:55 pm Post subject: Kef 103.3 Cube |
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Many thanks. I still have a few feelers out trying to get a circuit. If these turn up blanks I will try to trace it from the PCB.
Ian |
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speakerguru
Über Contributor 1000+
Joined: 18 Nov 2005
Posts: 1192
Location: Green Hut, Tovil
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| Posted: Thu Aug 30, 2007 11:24 am Post subject: |
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| What is the SP number of the 103|3 Kube? |
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Ianmac
Junior Contributor 10+
Joined: 07 Aug 2007
Posts: 11
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| Posted: Thu Aug 30, 2007 4:17 pm Post subject: Kef 103.3 Kefcube |
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Cube No SP2080BA S/N 3930
Spkrs S/N 002925A and B
Ian |
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speakerguru
Über Contributor 1000+
Joined: 18 Nov 2005
Posts: 1192
Location: Green Hut, Tovil
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| Posted: Tue Sep 18, 2007 8:46 am Post subject: |
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Well, well, well, who's a lucky boy then  Ianmac.
I have managed to get a copy of a set of 103|3 Kube drawings. Don't ask.
Send me a pm with your email and I will send you a zip file. |
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Ianmac
Junior Contributor 10+
Joined: 07 Aug 2007
Posts: 11
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| Posted: Wed Sep 19, 2007 8:06 pm Post subject: 103.3 cube |
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Many thanks for the diagrams. have sent a PM
Ianmac  |
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erik_bjorge@hotmail.com
Introductory Contributor
Joined: 04 Aug 2016
Posts: 3
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| Posted: Fri Aug 05, 2016 6:43 pm Post subject: Schematics kube 103/3 |
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Hi
Im looking for schematics to my kube 103/3 - sp 2115 - no 001355
Can somebody help me.......
Erik |
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speakerguru
Über Contributor 1000+
Joined: 18 Nov 2005
Posts: 1192
Location: Green Hut, Tovil
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| Posted: Sun Aug 14, 2016 3:36 pm Post subject: |
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| I've not found them. Can you help, Ianmac? |
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SprungNickel
Introductory Contributor
Joined: 31 Oct 2022
Posts: 6
Location: Hamptons NY USA
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| Posted: Fri Nov 04, 2022 10:51 pm Post subject: |
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| speakerguru wrote: | | I've not found them. Can you help, Ianmac? |
I recently joined to undertake a revival of My father's KEF 103.3.
I connected with a KEF Customer service rep in NJ USA who provided me with 103.3 crossover schematics and KUBE SP2122 Schematics. I exchanged pictures of my gear. I'd like to share these for the Forum archives.
How might I do that?
_________________
Restoring my Father's KEF 103/3 Reference Speakers.
Other KEF C15 with C200SW
Yamaha RX-V2095
NAD 7175PE
Flickr album with photos inside 103.3
Schematics of crossover and KUBE |
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