[klh]

OK, so I got my new JVC ILA-RS1 over the weekend (wonderful) but I got the dreaded hum after I pluged it in. All the equimpent except for the RS1 is plugged into a surge protector coming off one outlet in the front of the room. When done that way, the noise floor is very low. When the RS1 is plugged in at the back of the room, the hum starts. It's not bad (I've had much worse in appartments), but it's annoying since it wasn't there before. I tried plugging the PJ into 3 different duplex outlets, and the hum is present and equal every time. The question is, what should I do? I could get a heavy duty extension cord and plug it into the front outlet... that should eliminate the hum... but it may affect the image. The room has it's own 15 amp circuit... since the hum is equal at 3 different outlets, I get the impression the problem may be at or near the fuse box (Murphy's Law). What do you guys recommend?

[klh]

BTW, I'm not about to use a cheater plug with my RS1!!!

[klh]

One thing I forgot to mention is a hum was also introduced when I brought my computer up to use REW to calibrate the BFD for the subwoofer. I tried plugging it into two outlets in the back of the room and the hum was present. When I used an extension cord and plugged the computer into the front outlet, the hum went away. So, it really seems to be a product of the electrical system in the house and not the components. I don't necessarily like the idea of running the HDMI cable next to a heavy duty extension cord but it may be a necessary evil. Besides hiring an electrician, is there any way I could test for proper grounding? Is it likely I had grounding problems with both the computer and the projector and not the house?

[klh]

Just got this...

http://www.musiciansfriend.com/product/Ebtech-Hum-X-Hum-Exterminator?sku=150452

Thanks for the help! j/k

Somebody mentioned it more quickly on another forum. Anybody have experience with it?

[Wayner]

You probably do have a "ground loop". If your equipment has a 3-prong plug, then it's grounded. Then you send and audio signal to another part of the room, plugged into a different outlet (perhaps on a different circuit, and breaker) and you get hum. The outer shield of the audio cable is also a ground connector, so there is your "ground loop". To eliminate it, you must break the circuit. Either remove the ground from the main equipment, remove the ground from the remote equipment, sever the ground on your audio cable, or plug the remote equipment to the common ground the rest of the system is on.

W

[klh]

Gotcha! That's the best explanation I've heard yet. Thank you . The interesting thing is the circuit sent to the room is supposed to go to all duplex outlets in that room but no others in the house. If that is in fact how the wiring was done, then, according to your explanation, I shouldn't have a hum (provided the PJ itself isn't the source). Hmm. Something's not right. I wonder if they wired it incorrectly. That wouldn't be surprizing... the house is part of a planned development.

[Gordy]

Unfortunately, there is no standardization when it comes to grounding in audio equipment, everyone has their own way of interpreting what is best    Using a cheater plug / removing the ground pin on the power cords will certainly work but, it will also toast your fire insurance when the fire or insurance inspector finds it. The safe and effective thing to do is use a line level isolation transformer like the Jensen... Markertek
Cinemag makes an excellent (and less expensive) one as well I believe, can't seem to find it at the moment... Cinemag

[samplesj]

The interesting thing is the circuit sent to the room is supposed to go to all duplex outlets in that room but no others in the house.

Easy enough to test.  Just go drop the breaker and see if any of the outlets still work.  If you don't know which breaker there are tools you can get that will sound it out for you.

If that is in fact how the wiring was done, then, according to your explanation, I shouldn't have a hum (provided the PJ itself isn't the source).

There was another way to introduce a ground loop that wasn't mentioned before.  This is a video system so you probably are connected to cable or sat right?  Make sure they properly grounded their cable.  Often the cable/sat input on a cable/sat box isn't isolated from the outputs.  This means any voltage on the cable ground is also going to leak onto the output grounds.  If its properly grounded and you still get a humm, check out they routed the wires.  My cable entry is right beside my main service panel and for a long time I had a ground hum with cable EVEN though it was clearly grounded right.  One day I had to make some wiring changes so I moved them around and now I don't get the hum anymore.

This is also easy enough to test.  Just disconnect the cable from the cable/sat box and see if it goes away.

If its cable related there are several ways to skin that cat.  There are a couple of parts from radio shack you can buy and string together to isolate that ground as a quick fix, but long term you'd want to buy a real cable isolator (works better).  Just be careful if you have HD feeds or other interactive features in that system the isolator will reduce your signal strength some.  When I ran one I had bad break up on the HD channels so I had to add a booster in the basement where the line entered the house to make up the losses.

[Bob Reynolds]

Gotcha! That's the best explanation I've heard yet. Thank you . The interesting thing is the circuit sent to the room is supposed to go to all duplex outlets in that room but no others in the house. If that is in fact how the wiring was done, then, according to your explanation, I shouldn't have a hum (provided the PJ itself isn't the source). Hmm. Something's not right. I wonder if they wired it incorrectly. That wouldn't be surprizing... the house is part of a planned development.

Even if every duplex outlet is on the same circuit, each one (as the outlets are daisy chained together) has a chance of injecting a high resistance which raises the ground potential between the outlets which allows current to flow and causes the hum. Thus, if you connect one piece of gear to the first outlet in the circuit and another piece to the last outlet in the same circuit, you increase the chance of a ground loop.

You could visit each outlet and make sure the ground connection is tight. You might find a less than perfect connection that you could fix and save the cost of an isolation transformer.

[boead]

I’ve had this happen often, it’s from your cable TV, right?
If you disconnect the CTV from the system the hum goes away?

I use this; Jensen VRD-1FF Cable TV RF Isolator
http://www.markertek.com/Product.asp?baseItem=JEN%2DVRD1FF&cat=VIDEOEQUIP&subcat=VIDPROCESS&prodClass=VIDEOHUM&mfg=Jensen+Transformers&search=0&off=

works with on-demand and HiDef.

[Wayner]

I don't have cable (high def though Antenna), but have heard bad stories about ground induction. If that is the source, I'd hit up the cable provider for a soulution to the problem (at their expense).

w

[klh]

Thanks for all the input guys. The cable service is not the cause as the hum is present and stable with and without the coax cable hooked up. Moreover, it's only present when more than one outlet in the room is used. I'll take Jeremy's advice and flip the breaker and see if any of the outlets still work. Then I'll take Bob's advice and check the grounds on each outlet to see if they are tight (while the breaker is still off ). Hopefully there is a simple answer. If the room has an isolated circuit (as it's supposed to) then the signal should be more or less unaffected by other electrical draws in the house... especially since it's on the opposite end of the house from the waher/dryer/fridge, etc. The other nice thing is the circuit breaker is on the first floor directly below the home theater. I'll get back after I do a little discovery .

[klh]

Another point that complicates this is the only thing connecting the bulk of the components (all working off one outlet) from the other is an HDMI cable. The weird thing is the hum was only present the other day when the projector and DVD player were turned on (the HDMI cable goes directly between the two) but it was also present regardless of whether the integrated amp was on or off. Last night, that wasn't the case; the hum was only present when all three were on and I swear it wasn't as loud as before. It's really strange. BTW, I was the only one home both nights and no other lights or real draws were on in the house either time. It's interesting that this was happening each time at a time when electrical use is supposed to be less (and thus the electrical supply is supposed to be better). I don't know what to make of it all.

[boead]

Thanks for all the input guys. The cable service is not the cause as the hum is present and stable with and without the coax cable hooked up. Moreover, it's only present when more than one outlet in the room is used.

Yup, have had that happen too. Different circuit, you can fix it with dedicated grounds to earth but it’s a big waste of time and money. Just keep everything on one breaker.


In one system I had to use an optical digital cable from my computer to my DAC to avoid the ground leak. It was the CTV connected to my computers TV Tuner that was causing the hum yet again! The optical cable isolated the computer from the system.