Dimmer induced noise in audio system

Discussion in 'C-Bus Wired Hardware' started by brodricj, Jul 15, 2009.

  1. brodricj

    brodricj

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    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?
     
    brodricj, Jul 15, 2009
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  2. brodricj

    ashleigh Moderator

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    Is this a 4 ch universal dimmer, or a 4 ch LE dimmer? Quoting the model number would be very helpful.

    The two dimmers have quite a different technology used in them, the 4 ch LE dimmer uses some inductors to shape the switching waveform for EMC compliance, and there is not much can go wrong with them. They either work, or they are open circuit. The universal dimmer is a different beast entirely and uses a different method of switching, and a different method of controlling emissions. But if anything there breaks, it won't dim.

    For either type of dimmer, this leads me to the next question: have you changed any of the loads on that dimmer? New lamps, even replacing a bulb? Its a very long shot but it might be that the load type has an effect on the dimmer performance.
     
    ashleigh, Jul 16, 2009
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  3. brodricj

    brodricj

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    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.
     
    brodricj, Jul 16, 2009
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  4. brodricj

    ashleigh Moderator

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    Can you please do the obvious...

    Those things you re-routed. Can you move / separate them. It does not have to be a complete pull-it-down-and-rip-it-apart. Just try and move the cbus cables out of the bundle. Move the PCIs. Quick and dirty.

    You want to see if moving the equipment and/or cables makes a difference. If it does, it tells you that you need to do more of the same (basically undo some or all of the change you made). If it makes no difference, then there needs to be a look somewhere else.

    Given that its an L5504D series dimmer, if it dims, it aint broke.

    This does sound a lot like EMC coupling, and even with a balanced pre-amp cable, signals can (and do) get in.

    So try moving those cbus cables as far away from the audio cables as you can. If that makes a difference, you have a pointer to the way ahead. If it does not, see if you can move the PCI's.
     
    ashleigh, Jul 16, 2009
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  5. brodricj

    brodricj

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    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.
     
    brodricj, Jul 16, 2009
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  6. brodricj

    NickD Moderator

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    Rather than "rewire".. try changing things/disconnecting the PCIs etc... temporarily... change one thing at a time and note which if any has an effect.

    We don't want you to rewire the whole thing only to find it makes no difference!

    Nick
     
    NickD, Jul 16, 2009
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  7. brodricj

    gotliebk

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    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.
     
    gotliebk, Jul 16, 2009
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  8. brodricj

    brodricj

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    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?
     
    brodricj, Aug 25, 2009
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  9. brodricj

    Merge

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    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
     
    Merge, Aug 25, 2009
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  10. brodricj

    brodricj

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    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?
     
    brodricj, Aug 26, 2009
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  11. brodricj

    ashleigh Moderator

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    Ooooooooooooooooh Earth loops.

    Welcome to the wonderful world of the counter-intuitive.

    This one is going to be hard to sort out.

    You say you have a SHIELDED mains cable running from the DB to the home theatre system. Is that shield connected to local earths at BOTH ends?

    (Warning warning. We are getting into very difficult territory here. You much have grounds in your mains. MUST MUST MUST. But SHIELDS are in the territory of the Dark Arts, and only Lord Voldemort knows the full ins-n-outs of shields. But for wild generalisation, connecting a shield to ground at both ends can be very bad because it leads to circulating currents. Shields ARE NOT a substitute for a ground wire in the mains wiring.)
     
    ashleigh, Aug 26, 2009
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  12. brodricj

    brodricj

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    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.
     
    brodricj, Aug 26, 2009
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  13. brodricj

    CC&C

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    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.
     
    CC&C, Aug 26, 2009
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  14. brodricj

    ashleigh Moderator

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    Yeah. Strangely enough, connecting the shield to earth at the AV end may make a difference. So may disconnecting it completely. Or it might be the dimmer. Or it might be where the cable is located. Or some other fault as yet undiscovered.
     
    ashleigh, Aug 26, 2009
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  15. brodricj

    Darpa

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    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 :p
     
    Darpa, Aug 26, 2009
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  16. brodricj

    Hamza Shamim Siddiqui

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    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
     
    Hamza Shamim Siddiqui, Feb 1, 2018
    #16
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