DVD Audio available through multiple inputs?

Discussion in 'AV Receivers' started by JerryMa, May 3, 2006.

  1. JerryMa

    JerryMa Stunt Coordinator

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    I've been wrestling with speaker hum for a while and in the process of trying to alleviate the problem discovered something which I don't quite understand.

    As near as I can tell, the speaker hum (center channel) is related to the DVD player. Last night I tried moving the audio cables from the player to another, vacant input on the back of the receiver (NAD T-762). I left the player on at the time and turned the volume way down. Once I'd connected the cables to the other input ("VCR"), I started bringing the volume back up prior to switching to the appropriate input on the remote. However, even though the plugs from the DVD player were now connected to a different input on the back of the receiver, I could still hear the soundtrack of the DVD I was watching.

    I selected the "DVD" and "Satellite" inputs on the remote and the DVD was still audible. I tried the "CD" input on the remote but didn't get the sound through there (I have a CD player hooked up to the receiver). I also noticed that the speaker hum was now intermittent instead of constant.

    Anyone know what the heck is going on?? I'm thinking this goes beyond the normal issues in HT systems that can cause speaker hum. Is it possible that I might have done something strange when I assigned presets, etc.? I'm wondering if resetting everything to factory defaults might be the solution. Or is there a problem with the receiver's wiring?
     
  2. Phil A

    Phil A Producer

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    I'd guess it is the satellite box and you need to ground it.
     
  3. Phil A

    Phil A Producer

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    Here are some suggestion that came from an owner's manual of a rec'r:

    "Potential Ground Loops in a Complex A/V System

    Suggestion #1:
    To determine if a cable TV connection is responsible for the hum, first turn all components off. Disconnect the cable TV feed to your system at the first place where it connects to your components. Alternatively, disconnect the cable TV wire where it is connected at the wall outlet. Turn your system back on, and listen if the hum has disappeared. If removing
    the cable TV feed has eliminated the hum, you will need to insert a Ground Loop Isolator before reconnecting the cable TV feed, or contact your cable TV operator to see if they can better isolate your cable feed.

    Suggestion #2:
    Turn off all components in your system, and then disconnect the input cables at the amplifier. Turn the amplifier back on, and see if the hum is still present. If the hum disappears, the fault may be in the input cables used. Try replacing them with cables that have better shielding, and make certain that the input cables are not running on top of any AC power cords.
    Change the cables one at a time to determine if one, or all cables is responsive. If the hum disappears when the input cables are disconnected, but returns after the cables are changed and the system re-connected, the problem may be caused by your source device.

    Suggestion #3:
    Ground loop problems may also be caused by poor grounding of the electrical system in your home, particularly when there are multiple components with three prong, grounded, power cords. Try unplugging these components one at a time, and see if one or all of them is causing the problem. The ultimate solution to this type of problem is to re-wire your house with an isolated, star type-grounding configuration. We recognize, however, that this may be impractical and expensive. In some cases, the use of an approved AC Power Isolation Transformer of sufficient capacity may solve this problem.

    WARNING: If you suspect that the grounding system in your home’s
    electrical wiring is causing the hum problem, it is important that you do
    not make any changes to the wiring yourself. Only a licensed electrician
    should make any changes to household wiring, and they must be made in
    full compliance with all local building, safety and electrical codes.

    Suggestion #4:
    Hum may also be caused by faulty earth grounds in your home’s electrical system. In the past, cold water pipes were often used for the earth ground, so it is important to make sure that your ground connection is still valid and has not become loose or corroded. The cold water pipe method may no longer be valid in some locations due to requirements that the water meter be isolated from the water mains with a length of PVC pipe, thus interrupting the ground circuit. The safest, and most reliable, approach may be to provide your own ground. This can be accomplished by having a licensed electrician drive at least five feet of copper-jacketed steel grounding rod into the earth, and using that for your grounding connection. "

    I don't have any issues but have seen other people recommend converting the signal from 75 ohms to 300 ohms and back to 75 ohms using inexpensive stuff at places like Radio Shack. I've also seen products like the below recommended:

    http://www.zzounds.com/item--EBTHE2PKG

    http://www.cencom94.com/gpage.html8.html

    I'd try unplugging and removing connections one device at a time and try to isolate the problem as a 1st step.
     
  4. JeremyErwin

    JeremyErwin Producer

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    how are things connected? coax, toslink, rca patch cords? Are you using the multichannel inputs?

    details, please.
     
  5. JerryMa

    JerryMa Stunt Coordinator

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    Jeremy,

    I use rca cords. I route only audio through the receiver, DVD video goes straight to the TV's S-video jack, VCR is hooked up to the satellite DVR. I'm upgrading the TV shortly and will be getting new AV furniture, which will have cord management. There is currently too much clutter between audio, video and power cords, not to mention speaker wire. I'm going to try some things to separate wires until the new set up is in place.

    I have tried some other things, including resetting/clearing presets, and the hum is now intermittent, rather than constant.

    I also contacted NAD and they sent instructions on how to reset the receiver to factory defaults.

    I'm starting to think that the hum and audio being available on multiple inputs are related and a result of my not reading the manual carefully enough during on-screen set up. Stay tuned...(no pun intended!!)
     

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