Another Electric circuit posting

[BMXTRIX]

Sounds like Radio Frequency Interference (RFI) from the dimmer. What brand dimmer, and how old are they?
Also, what type of lighting?

The dimmers are Crestron, so fairly pricey units, and prior to that they were some decent Lutron units. Once again, not the cheapies.

Most better, brand dimmers have RFI suppression circuitry. Don't go cheap, when it comes to dimmers.
Some manufacturers can supply additional filtering.

I spoke with the manufacturer, as well as with Lutron, but nobody would guarantee anything.

Off the top of my head, the first things I check are: Swap out the dimmer with a switch, just to see if the problem goes away.

The problem only exists when the lights are at a dimmed point. It does not present itself as an issue when lights are at 100% or when they are off - only partway between.

Put dimmer on a separate circuit, from the TV or audio equipment.

The AV equipment is on a dedicated circuit, has things like power conditioning, and we have lifted ground to all gear and tried it in different versions of lifting ground.

Check all the ground and neutral connections.

This would be done by an electrician, but the build is new, and I believe that it is fine.

Run dimmer wiring in its own metal conduit.

This can't happen due to the work already being done.

I really appreciate your thoughts on this. I asked at AVS and got some pretty poor responses saying "It has to be a ground loop." I'm pretty sure it's RF, but it also seems like fairly solid AV standards were used during the build including running all A/V cabling several feet from electrical.

I ended up solving this particular issue with cat-5 to HDMI converters, but I still never really figured out how to fix the issue on the electrical side of things. It doesn't seem to be straightforward even now.

 

[Rickster71]

Hi BMX,
I've always had good results from Lutron dimmers; the Maestro and Nova lines. (sounds like you've tried them)

There are lots of variables, and just trying to narrow it down between Radiated RFI and/or Conducted RFI would be a start.

If the dimmer is close to the TV or it's wiring it could be Radiated RFI.
Unfortunately they put out the most RFI when they are in the dimmed position.

Chokes can be clipped around the TV's power cord and input lines. They look like a donut shaped magnet. I've seen them at the rat shack.

If getting rid of the dimmers completely, is a option. You could switch off the lights, and have a night light circuit left on instead.

 

[BMXTRIX]

Thanks Rick, I really was able to resolve the issue by going with a HDMI to CAT-5 converter and taking the entire system to digital, but I wanted to feel like I was getting a bit of confirmation that it was RFI instead of a ground loop.

Hopefully in the future, if I run into something like this again, I can bug you a bit for some insight.

I do know that at my house I have the same issue, which I simply live with and don't argue about. It's not bad, and until I take the system to HDMI I am not really willing to make all the changes that I need to.

Just kind of weird I guess - I am using Lutron Spacer System Dimmers, which are some of their most expensive pieces, and video is run many feet from the dimmers (probably the closest is 5-6 feet), and the TV & all equipment is on a dedicated 20amp circuit AND that is using a Monster HTPS7000 power conditioner. I really can't do much else anywhere.

But, I usually turn the lights out, and I have tested with HDMI from my PS3 and have confirmed that it 100% eliminates the issue, so I will go that route in the future.

Really - thanks for your input!

 

[Rickster71]

I hoped it helped a bit.
If I see any articles, I'll send them your way.

Rick

 

[mtrycrafts]

Sounds like Radio Frequency Interference (RFI) from the dimmer. .

Why wouldn't that show up as just noise on the screen, dots all over?
Lines rolling up, as best I know, would need some 60Hz harmonic component to beat with the 60Hz sync on the vertical frame rate, no?
But, being a dimmer, a digital one that chops up the 60Hz duty cycle, perhaps that is the 60Hz component that beats and rolls up?

 

[Rickster71]

Why wouldn't that show up as just noise on the screen, dots all over?

Noise all over the screen is generally electrical interference, as you'd get from an electric motor running, like a blender, or vac.

But, being a dimmer, a digital one that chops up the 60Hz duty cycle, perhaps that is the 60Hz component that beats and rolls up?

Right, the sine wave is changed so much, it doesnt have the nice subtle curve anymore. Where the wave is chopped off, the voltage and current change, is much faster, and those fast changes cause high frequency interference going through the nearby wiring.
Those corners in the waveform consist of 60Hz plus varying amounts of other frequencies that are multiples of 60Hz.

These are a real pain to track down, worst than finding a ground loop.
When interference affects a video system, there can be so many symptoms, but the most common is a light or dark horizontal bar that moves slowly from the bottom to the top of the screen.



Dimmers emit their strongest interference at the middle position.
It depends on the frequency that's being picked up, and if it's transmitted RFI from the dimmer, or dimmer wires.
All the wiring acts as an antenna.
Dimmer noise is coupled from the power line to the internal ground of each piece of equipment, and doesn't matter if its power plug is 2- or with a ground pin. Due to the fact that, at the panel the neutral and ground are bonded.
When this noisy current flows in the shield of an unbalanced cable connecting two pieces of equipment, the noise is directly added to the signal. In general, unbalanced connections RCA connectors for audio and in this case, any composite video, S-video,etc connector for video, are far more susceptible to interference than balanced XLR.

I think it's easier prevented at the install. Otherwise it's a needle in a haystack.
I really hate typing, I have to stop now.
Rick