Dimmer induced noise in audio system

Recently I have noticed a very pronounced buzz coming through my hifi speakers whenever certain CBUS dimmer loads are on. The buzz is very noticeable with the pre-amplifier volume control turned down, and as the volume control is turned up the loudness of the buzz remains unchanged, but it becomes less noticeable at higher volumes (due to the buzzing noise being drowned out my other sounds).

Now there have been no changes in either CBUS or my hifi equipment to account for this buzzing. The hifi is on its own discrete power circuit with comprehensive power conditioning (all power cables are shielded), and the CBUS dimmers are on a lighting circuit. There is ample distance separation between the dimmer modules and transformers and all the hifi gear. And as I said earlier there have been no changes to account for this, the CBUS dimmers have been in my home for many years without issue. This noise has presented recently, reason unknown.

The buzzing is very annoying, whenever a bedroom or office light is turned on I get the loud buzzing in my theater room. It needs to be fixed, but where to go from here? The only common denominator is a particular 4ch CBUS dimmer, when any of its loads are other than OFF, I get noise in my hifi. Are there any known issues with CBUS dimmers changing over time, inso far as them generating EMI or electrical noise that pollutes other devices connected to other circuits in the home?

 

From memory the dimmer in question is an L5504D1A. I also have 2 L5508D1A and these have no adverse effect on my hifi. Anyway. The L5504D1A is functioning normally in every way, except for this loud buzzing noise which is breaking through in all channels of my Hifi system. The only change I have made to my CBUS is repositioning the 2 CBUS PCI's in my Hifi rack (co-incidently after changing the position of the PCI's in the rack the buzzing noise in the speakers has become evident, but I doubt very much this is the cause as there are no CBUS output mains loads routed through the rack, only the CBUS Cat5 cable). The CBUS Cat5 was also re-routed and now resides in the same bundle as my pre-amplifier output cables, but all my audio cables are of the 3-conductor balanced type so again there shouldn't be a cross-talk issue there. I've had 5 years of trouble free service from my CBUS dimmers, only now when this particular 4 channel dimmer is controlling any of the 4 connected loads I get the buzzing in my speakers.

 

Yes, the obvious is to undo what was done...it's just that it was such a big job doing it in the first place, undoing all that work I'm feeling a little stuck between a rock and a hard place here: wife grizzles about the buzzing in the speakers; wife grizzles whenever I'm working on my electrical stuff. Rewire it it is.

 

A small troubleshooting step

It could be that your noise is actually travelling on the CBUS network (Cat 5 wire). You mentioned that you put this wire in with your pre-amp cables (in parallel I'm assuming). Before you go undoing all your nice wire work, I'd try temporarily disconnecting the CBUS cables to your PCI. Make sure you disconnect it at the dimmer panel (or at least near the line voltage source). My thought is that the Cat 5 is picking up some EMC from the line voltage lines and transferring it to your pre-amp cables. I'm probably way off but it's worth a try before you pull apart your wire bundles.

 

Bump.

I've been forced to investigate this noise problem again, the dimmer noise is driving me crazy!

I have undone everything that was done prior and noise is still there. Separated the CBUS cat5 from other cables, noise still there.

Plugged my home theater system into a different power point via extension lead, noise gone! complete silence, oh joy! So now I'm thinking WTF? I've got a dedicated 15A power circuit powering my home theater and there is nothing else connected to this circuit. Noise is getting off a CBUS dimmer on a lighting circuit and polluting my dedicated home theater power circuit. But dimmer noise is not getting onto any other power circuits in the home.

I just don't understand this. The home theater power circuit comes from the front meter box on a shielded cable (shield drain wire connected to earth on upstream side), and that cable doesn't go anywhere near any other power or lighting cable (the meter box is directly on the other side of the wall, only 3m away).

I don't want to run an extension lead from the kitchen to the home theater as the solution, I want to solve this problem. I'm thinking next step take out the offending dimmer module and replace it with another one. If that solves the problem then I know for sure it's a faulty dimmer.

But first, has anyone on the forum got an alternative for me to try?

 

I've had a similar issue where all the monitors connected to an AV Multiroom System displayed patterning interference when dimming was active, and worse the more scenes I switched on. It was to do with an earth loop and an earth potential difference between boards. This is a difficult problem to overcome, but we made good headway by strapping all the earth's together with an 11mm conductor. Also check that all the neutrals in your CBUS board are very tight.

If it's a 3 phase installation check variances between phases.

You could also use a good quality mains filter on the Theatre.

Not sure if this will help, but hope it gives some clues...

R

 

Nope, only single. I got a quote to have 3-phase installed years ago and I almost fell over when I saw the price.

I am. I'm using a uber-high end filter followed by an AC regenerator to power my home theater, but these don't stop noise getting through the grounds (and they don't trap any DC offset on the AC line either which can cause transformers to hum).

So given it looks like there is a grounding problem of some sort here, (and this is a question for any electricians, don't know if this suggestion complies with the code). So if I run an earth line between the earth on the home theater power circuit, and the earth on the dimmer lighting circuit, then they should be at the exact same potential and the buzz will go away?

What to try first, this, or replace the offending dimmer module?

 

The shield on the home theater supply cable is connected to earth only on the upstream side. My equipment will remain properly earthed, hence I won't be messing around with properly wiring stuff up (the shield is not being used as an earth point for the remainder of the system).

But I'm still lost for any reason why this has happened all of a sudden when prior everything was OK. I keep coming back to suspecting something untoward with the CBUS dimmer - I'll swap it out for another one and see what happens. Although I do understand this is unlikely as the dimmer is dimming normally.

 

Just a small, seemingly innocuos suggestion, have you tried disconnecting the shield? Also, have you tried swapping the ends at which the cable is earthed. As Ashleigh said, welcome to the world of the counter-intuitive.

 

Or maybe the earth's magnetic field moved just a smidgen on you, or there is an electromagnetic storm brewing at the moment due to a sun spot

 

Dear Merge,

I am facing almost same kind of problem. There is a video wall and same thing is happening...Patterns of interference appears when the Dimmer L5508D1A is active and they become worse when scenes are working....i.e. Lights are more dimmed.
Could you or anyone please guide...
Apparently Grounding and Earthing has been checked by electricians,,,,Can u please guide how can I cross check their Readings ? (Electricians's readings whether they are telling the truth)
Secondly what improvement can i Make in this scenario...Should I replace dimmer or what ?
Note that all system is of an Auditorium and every equipment including CBus are being powered up with same UPS.

Will appreciate your early response !
Regards;

Hamza Shamim Siddiqui