Basic electrical questions.

Sorry to rain on the parade, but I have been unable to find any evidence of RFI interference with my audio system. I do live in a rural area where the RF energy is probably lower than in cities. However, I have tried activating cordless phones and cell phones within inches of the equipment, with no effect.

Has anyone else done this experiment?

Just to follow up… as I said above and as another has said here… dedicated ckts merely limit the immediate impact of untowards interference from other household appliances, various lighting t-formers, cell phone chargers, etc. They don’t ultimately prevent this interaction… it is more a subdued, or less impactful contact.

BTW… cheater plugs work on thihngs other than audio and video gear, ie., dishwasher,., fridge, phone, faxz, etc. that’s where I put mine… not on my audio gear… and only if those items were also possessing non conductive surfaces.

Dedicated lines and or cheater plugs will not prevent nor eliminate ground loops. To eliminate the ground loop issue find the cause. Generally it comes from your telephone, cable, or satellite equipment… or some other porrly isolated or grounded item. A simple inductor can dispel this issue and why so many simply use transformers of one sort or another.

A minor difference of potential at one ground point, if several or more than one is used, can also cause such an event.

One point of interest here is what was said about the actual length of the ckts themselves. I read somewhere there is a formula for figuring out the db per feet in loss. I don’t recall it now, but I know it happens. This effect occurs using dedicated lines as an added benefit, though it’s seldom if ever expressed as such.

Another item is the cost to benefit ratio… or in other words “overkill”.

Unless we’re talking new construction implementing numerous single serve power lines just isn’t financially feasible for the majority of folks. A few sources, a preamp, mono blocks, and say a sub or two means 8 separate lines…. Which are all tied together at the breaker box anyways, seems of and by itself as overkill to me.

Rather the digital issues should be addressed, if any, at the device… or by a wholly separate and individual power supply and line (s).

As dedicated power lines aren’t prevention measures, and only limit initial impact of other on site problems, look to power conditioning, power isolation, and other grounding measures to further aid the supplied items… and there are still some precautions to be taken doing those tasks… and or find and eliminate, exchange, or replace the culprit causing them.

Cellphones and cordless phones emit far higher frequencies than the frequency components of the digital hash, other component-induced noise, and power line noise that we have been speaking of. I believe cellphones operate in the range of 800 to 1900 MHz or so, while cordless phones are around 2400 MHz. Audio equipment seems unlikely to have any detectable sensitivity to frequencies above perhaps a few ten's of MHz, and perhaps much less than that.

Also, as you appear to realize, these kinds of issues are likely to be dependent on location, house wiring, system components, system interconnections and setup, and listener.

Regards,
-- Al

In my own system, I have installed an isolation transformer feeding the subpanel, with separate dedicated lines to each component. To address the issue above, I have put a second isolation transformer on the CD dedicated line to keep its digital hash from contaminating the other components.

This has proved very effective for me, as there is now no difference in the background noise level between the CD player while off, and the CD player playing while muted. If you are contemplating multiple dedicated lines off a single subpanel, I suggest you consider this approach.
12-10-08: Zargon

Zargon,
I was burning the midnight oil last night when I responded to your post. I forgot to address your comments in regards to the use of good isolation transformers.

The application of iso xfmrs as you have is a great way to go. Especially using iso xfmrs on your digital equipment.

Al,

You are correct about ground loops - usually ground and neutral are connected at the electrical panel. If you have different equipment plugged in to different locations and then chained together for audio purposes there is indeed a greater risk of a ground loop. Provided house wiring is correct then the major culprits are high impedance shields on interconnects, imbalanced RCA consumer gear and power supply leakage from components.

The digital issue is I believe related to the use of switched mode power supplies - which is common these days as they are cheap. These can create noise on AC power which can affect some equipment with less than perfectly designed power supplies. I have not seen any proof of this but my experience suggests that PC's are particularly nasty/noisy - they also vary in demand as a function of processor requirements - simply look at a Playstation - how hot it runs and the tiny size for all the current it takes....

As for RF/EMI - never been a problem for me - so I'd agree with Eldartford that this is a much rarer problem.

Here is a useful resource. Enjoy! BTW - it is great to see some well thought out posts on these subjects - I read your thoughtful posts with interest.