XLR to RCA to XLR

Assuming that the KUBE is connected between the processor and the amp, and if it has a 3-prong AC power plug, chances are that the noise is being caused by a ground loop between the KUBE and one or both of the other two components.

To verify that, temporarily isolate the AC safety ground pin on the KUBE's power plug by connecting it via a 3-prong to 2-prong adapter (a "cheater" plug), with the adapter's ground lug or ground wire left unconnected.

That will break any ground loops between the KUBE and the components it is connected to. If that eliminates the noise, remove the adapter from the KUBE's plug and use it on the plugs of each of the other two components, one at a time. That will enable you to determine which interconnection is causing the problematic ground loop (although the answer might be both).

Post back your results, and also see the following references:

http://www.jensen-transformers.com/an/an003.pdf.

http://www.jensen-transformers.com/an/an004.pdf.

Also, if you are connecting the KUBE to the power amp by means of an unbalanced RCA cable followed by an RCA-female to XLR-male adapter at the amp's input, you may be able to improve the noise by instead using an RCA-male to XLR-male adapter at the KUBE's output followed by a balanced XLR cable. That would be electrically equivalent to the approach shown in Figure 2.1 of the first reference. Although as indicated in the reference that approach is less ideal than a well implemented transformer-based approach.

Regards,
-- Al

Al,

The KUBE has a 2-prong AC plug.

I used a female XLR to male RCA adapter into the KUBE from the XLR line out of a Cary 11a and a male RCA to male XLR adapter to the line into a Proceed Amp 3.

Turns out I was using a KUBE designed for the KEF 102.2s I have in another system that has short lines between a Proceed PAV.PDSD and Amp 2, so unbalanced is no problem. But I'm negotiating the purchase of a pair of KEF 107.2s to replace the 104.2s, and a 107.2 KUBE is recommended by KEF.

Hi Dbphd

Thanks for posting this thread. I may be facing a similar issue soon. I'm have a pair of KEF 104/2s and was able to score the 104/2 Kube for them. Nothing is hooked up at the moment due to renovations being done in my house. My amp and preamp combo have XLR inputs and outputs. I was going to put the Kube in the signal path between preamp and amp and use XLR adapters for at the preamp and amp sides. I hooked up a temporary system with the KEF Kube in place and heard a faint hum from my speakers. It was only when I was close to them though. I don't think the issue is you having a KEF Kube 102/2 with your 104/2s. It may just be the KEF Kube itself. I routed the AC Adapter and it cords as far away as I could from the unbalanced cables but there was still a hum.

Al. Many thanks for your contribution as well. Always very sage advice.

Would ferrite choke cores on the plug and umbilical cord ends help reduce the hum? I was thinking about putting choke cores near where the wires meet AC adapters as well where the umbilical cord plugs in along with where the 2 prong plug is.

Here are some pics of the KEF Kube. It looks the same for the 104/2, 102/2 and 103/3 speakers.

KEF Kube rear
http://img.2dehands.be/f/normal/120814494_3-kef-104-2-kube-inbegrepen.jpg

KEF Kube front
http://img.2dehands.be/f/normal/120814494_2-kef-104-2-kube-inbegrepen.jpg

KEF Kube AC Adapter
http://p2.la-img.com/236/423/197124_1_l.jpg

If the hum still persists I may just sell the KEF Kube.

Jedinite,

As I understand it, and my understanding may be incorrect, the use of a KUBE with the 104.2s is optional -- it only extends LF. In some applications, e.g. 107.2, the KUBE also tailors audio above the usual sub crossover. Thus, if you use a sub with your 104.2s, you may not need a KUBE.

The KEF museum is a treasure trove of information where you can download the installation instructions for the 104.2 as well as a nifty brochure that shows a cutaway of the speaker.

I have KEF 102s, 102.2s, 104.2s, and plan to buy 107.2s, so I've done lots of downloading and reading.

db