RF noise - Advice please

[DjSwirl]

I will not bore you with the full story, but I have recently purchase a Denon MC6000 which is a USB digital music controller, I get a large amount of RF noise from the PSU that’s supplied, if using a different model PSU it’s not problem, I have had a number of replacement and spent lot of time trying to find the problem, this is a video I sent to them showing the problem VIDEOIt seems that the input Art 300a is not connected to the common ground, I know other models of speakers have earth lift switches so by default are grounded.

 

Here is the question / advice, the PSU supply is such low quality and not grounded correctly that I have had to make some XLR leads with flying each lead that I can use the grounding post on the speakers which in turn is back feeding the ground to the MC6000 via the XLR lead.

 

Would you say this is expectable as a ‘professional audio company’ supplying a PSU that relies on getting its ground from the thing its outputting to, i.e. the speaker. Can this RF cause other problems?

 

Thanks in advance

 

Brian

[pete10uk]

Use a different psu if the problem is only present on one type.

 

In my experience your solution is a good fix if you're out in the field and need to get something going, but if you have an issue you can fix at a less critical place and time, do it, or it will bite you later.

[laolu]

I had the same problem with a laptop a few days ago. It made the sirring noise when the PSU was plugged in and was silent when running on battery.

 

Don't know what advise to give you, but I would try to find one with the same data - 12 V / 3A DC apparently - and see what happens. The noise comes most probably from the switched PSU, so you might even try one with an old-school transformer in it. Of course they are bigger and heavier, but might solve your problem. Pay attention to the polarity.

 

Denon should be aware of the problem, though, because I'd like to think the problem you described happens to others, too.

 

;)

[bamba]

Have you tried sticking a DI in and Groundlifting it?

Works for me when we get nasty power from laptops, etc.

[Shez]

Interesting. I acquired one of those controllers over the weekend but I can't recreate the problem you're having - mine is whisper quiet.

The sound in your video sounds like the usual laptop type PSU noise you'll hear if a ground loop is present. Could you describe exactly what is and isn't plugged in at the start of your video? The Art speaker is I presume class I; the stock Denon PSU is class II. Assuming that you're just connecting the Denon to the Art with nothing else connected to either, then something somewhere is faulty. There certainly isn't an intrinsic design flaw with the Denon.

[DjSwirl]

After many hours the problem has been found....

 

 

I am using a pair of RCF Art300A MKI, these are around 15years old and still going strong, however PIN1 on the XLR is “Chassis Ground”, not “Earth” (the correct way of doing things), over the years manufactures have adopted connecting PIN1 to both “Chassis Ground” and “Earth” due to interference being caused by cheep power supplies that give of RF interference and Hum

 

“The "Pin 1" Problem

 

Many audio manufacturers, consciously or unconsciously, connect balanced shields to audio signal ground; pin 1 for 3-pin (XLR-type) connectors, the sleeve on 1/4" (6.35mm) jacks. Any currents induced into the shield modulate the ground where the shield is terminated. This also modulates the signal referenced to that ground. Normally great pains are taken by circuit designers to ensure "clean and quiet" audio signal grounds. It is surprising that the practice of draining noisy shield currents to audio signal ground is so widespread. Amazingly enough, acceptable performance in some systems is achievable, further providing confidence for the manufacturer to continue this improper practice -- unfortunately for the unwitting user. The hum and buzz problems inherent in balanced systems with signal-grounded shields has given balanced equipment a bad reputation. This has created great confusion and apprehension among users, system designers as well as equipment designers.”

 

Denon’s PSU relying on PIN1 on the external source be connected to Earth, I have resolved the problem by making some XLR leads with a fly lead connected on PIN1 that can be connected to an earth grounding post, something that I shouldn’t have to do if I was using a well designed grounded PSU.

 

Thanks for your replies guys