balanced outputs hum

[rickp]

I have tried using XLRs to connect my RDC 7 to a Dreadnaught but I get hum. It goes away with RCAs. It has been suggested that the RDC uses a different ground system than the amp. I dont know much about all that grounding business but, I would like to know if it is possible, to use XLRs with this combo to some advantage.

Thanks,
Rick

[Burke Strickland]

Rick -

Sorry to hear that you are having hum problems using balanced connections between your RDC-7 and Dreadnaught power amp. Ironically, balanced connections are usually recommended because they are typically less prone to picking up noise and hum. But that doesn’t mean it can’t happen (as you know). Here are some suggestions adapted from a professional guide to PA (”public address”) installations using balanced connections http://www.epanorama.net/documents/g...pa_advice.html :

Use single power feed everywhere you can

If possible, take power only from one electrical power outlet. This will avoid the ground potential difference problem which can exist if power is taken from multiple power outlets. If the distance and electrical code permits it is a good idea to run a power extension cords from your single power feed points to all subsystems connected to your audio system.
It is best to use a dedicated power feed for your audio system. Do not connect any other equipment (such as lamps or computers) than audio equipments to this power feed. This saves you from many humming problems. It is a good idea to mark clearly which extension cords are part of your audio power feed so that you don't accidentally connect any other equipments to them (it is good idea to tape over all power outlets from this audio feed which are not used by your audio system so nobody will accidentally plug any other equipments to your audio power).
Especially avoid plugging fluorescent lights, lighting dimmers, computers and video equipment (like video projectors and TVs) to your audio power feed.

Use balanced connections everywhere you can

Balanced connections are much less sensitive to picking up interferences and humming. If you still get humming with basic balanced wiring, there are much more to do to avoid it than with unbalanced connections.
Most professional audio devices are connected via balanced cables to minimize pickup of stray electrical noise. Consumer audio devices typically use unbalanced cables and are very prone to picking up noise, especially at low signal levels. Balanced circuits have an inherent ability to only pass audio signals and reject unwanted noise.
Balanced refers to the fact that there are two symmetrical signal lines and one ground, while unbalanced uses just one signal line in reference to ground. Normally, XLR connectors are used in most balanced devices while unbalanced consumer gear normally use mini-plug or RCA connectors.

Do not ground the XLR connector shells

The recommended practice in professional audio community is not to ground the shells of XLR connectors. The reason is XLR shell can come easily in contact with metal railings or something else which is grounded to somewhere else than your audio system. If your shells are not grounded nothing harmful will happen. But if you have for some reason grounded the XLR connector shell to audio ground you will get humming in your system because all kind of ground paths/loops and sorting out those can drive you crazy. It is best to leave the shells not connected so you don't add a new, intermittent problems, to your audio system.

Good luck -

Burke

[Chris D]

Interesting... people have begun to report this same thing with the Parasound Halo equipment, when used with some very high efficient speakers, namely Klipsch. They have heard a background HISS, not hum. We've started talking about it in this thread:
http://www.htguide.com/CFBoards/inde...artRow=1&CFB=1

and there has been talk elsewhere on the net about this too. Apparently, the balanced connections add a 6dB gain with the THX standards, which has led to some hiss. Goes away with unbalanced RCA.




CHRIS
Luke: "Hey, I'm not such a bad pilot myself, you know"