I have completed a multi-room system which works absolutely fine until certain lights (halogen) are switched on, creating a hum in the background of the speakers local to that room(the others are fine).

We have double checked the speaker wires to make sure they are as far away as possible from any mains cables, transformers (every cable is at least a foot away).

From what I hear this is a fairly common problem although I have never experienced it before.
I can only presume it is a lighting transformer causing the interference as all the other zones appear fine (how is this interference caused?)

I would appreciate anyones expertise in solving this problem i.e. would shielding the transformer in a steel enclosure help?
Someone else suggested earthing the lighting transformer to a good earth such as a pipe would help.

Thanks for any help.

Shielding would help. If you try grounding you need to attach the groud to a cold water pipe. Hot water pipe have a lower ground potential or none at all. LOL

If the halogens are on a dimmer, it could be a noisy dimmer. I've fixed simillar problems by replacing switches before.

Here's a quick check for you. I've seen it twice, recently.

Check if you cable splitter at the outside of the house is grounded.

If not, ground it and it may solve the buzzing for you.

The 2 times I had noticed it, they were very strange problems, when lights are turned on, or when a sub's RCA is plugged in or when the Multiroom RCA feeds from the receiver were plugged in.

Anyway, maybe it will be that simple for you.

Jason Walter
www.electronics2you.biz

I have seen that by customers using wrong dimmers....
they were not compatible with halogen lights and it created a hum(only then I knew about the difference between dimmers)

Interference caused by electrical loads are normally found in the line level side or signal before amp. However a faulty or overloaded dimmer could emit minor noise to the high voltage side of your amp circuit. Noise could also be introduced thru your source power outlet if connected to the same phase or breaker on the electrical panel. Grounding the transformer for the dimmer control could increase the noise depending on your own equipment grounding. Your time would be better spent getting more clearance from electrical devices.
For further information refer to Cedia Code:M06 "Grounding/Interfacing for quite A/V systems".

Goodluck.

Get a Lutron electronic dimmer form home depot. I can't remember the name.. Damn.. it's on the tip of my tounge... It's really late.. I'm always happy with the way they clean up the power, noise, humming bulbs, etc.,
I wanna say around 40 bucks?? $55 for a master slave 3 way?
of course it's not always the answer.. Let me know what happens... If nothing else.. They will have a nice dimmer..

I believe they are called "Maestro"

CMO, one other thing to check: It could be the bulbs themselves creating the noise. Some halogen filaments actually "sing", or vibrate, when dimmed. See if this occurs even when the sound system is off.

Larry
www.fineelectricco.com

The cable cold water ground is really important if you have hum, but if you ground it and there is still hum, see if the hum goes away when you disconnect the cable from any and all components of the system (as at the cable entry point if necessary). If so, there are cable ground eliminators that work well with normal cable; I have no info on how they work with digital cable or cable modems.

Another thing to check if these suggestions do not work is to see if the hum goes up and down with the volume. It sorta looks from your description like it occurs with all inputs.

Anyway, if it goes up and down with the volume, the hum is coming into the preamp part of the system on a signal ground. In that case, try unplugging inputs one at a time to see if one input is totally related to the hum. If so, pursue the grounding situation with that component.

I was back at the customers today.
Interestingly it only appears to be two circuits (with dimmers) which create the interference, all the others are fine when turned on.
A third circuit located upstairs which doesn't appear to be anywhere near the system also causes interference.

The speakers on the other two zones (3 zone system) appear to be free of any type of interference whatever state the lights are in.

The difference with the problematic zone is that the speakers are running off a power amplifier connected via the multiroom controllers pre-outs.

When moving the power amps speakers back to the multiroom controllers internal amplifiers, the interference appears to go away.

Should I therefore assume as suggested above that the problem is between the pre-stage and the power amp.
Would earthing the multiroom controller and power amp together help?

At present the system is running fairly well without the additional power amp (without interference) although I would like to re-introduce the power amp as it gives a lot more control and power to the speakers.

Thanks

Just refreshing my last post to see if anyone has any ideas

I just saw your post noting that moving back to the first amp stops the hum.

Are all your amps located together, and connected to the same phase of the power line? If not, that could be a source of hum by introducing a voltage difference onto the shield of the audio leads between chassis grounds.

Do any of your components have three-wire power cords with signal ground connected to power ground? This could be its own problem.

Judging by the lack of hum when you get back to the original amp, you will lose the hum if you use transformer isolation between the multiroom output and the amp inputs. This is admitting technical defeat, and I will always pursue this problem to the end (at least I did when I worked for a corporation where the boss wanted to know WHY, no matter how long it took; these days, I just install the transformers so I can collect on the job).

There's also about 2.78 chances in hell that interconnecting the grounds of the preamp and the offending amp will lower the hum.

I will look up a GREAT hum-troubleshooting process at Jensen Transformer and provide the URL after I send this note.

Check out jensen-transformers.com

Also see the white paper on hum troubleshooting on that site,

[Link: jensen-transformers.com]

Thanks Ernie, looks an interesting article that I will read given 5 mins.

In answer to your questions:
Yes, the power amp and controller are located together.
The multiroom controller has a three pin mains while the power amp has a two pin.
I will look into your suggestion and I'm sure this will solve the problem.

This one has thrown me a little bit as you can virtually turn all the lights on in the house (dimmers and all) and there is no hum but as soon as you switch one about 3 specific circuits the hum is introduced.
Why is nothing ever simple!

This message was edited by cmo on 10/14/02 17:43.08.