Pure A/V

Discussion in 'Home Theater Projects' started by Thomas_A, Aug 19, 2005.

  1. Thomas_A

    Thomas_A Second Unit

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    I was in the market to get a subwoofer cable and thought I would try one by Belkin- Pure A/V line. It was $ cheaper then the Monster it sat next too and purchased it. What a mistake. Now I know...I could have just been the bad luck- but I hooked it up to my sub and it hummed like an S.O.B. Thought maybe I hooked it up wrong (arrows) so tried other way- no change. Well...its a sub that I had been for years running with the speaker inputs...so thought maybe something had happend to my lfe input. Pulled out my other sub- same thing! Not happy. Raided my other systems sub cable (monster 300series sub cable)...and ya know what! NO HUM:> took the bad boy back along with the other 2 packages of un-opened Pure A/V componant cables... I'm glade the Pure AV PF40 works like a charm.
     
  2. Tim Jin

    Tim Jin Supporting Actor

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    When I first got my HT setup, I went with a no name sub that I got from Ebay. It would hum and rattle, no matter what cable I used. The seller exchanged it twice and finally refunded my money. I ended up buying a sub from Velodyne with the same RCA cable that I was using with the Ebay sub and since then, I haven't encounter any problems.
     
  3. Bob McElfresh

    Bob McElfresh Producer

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    Thomas - to be honest - those cables are likely fine, just not built to prevent subwoofer hum.

    You have what is known as a "Ground Loop" problem. This is because both your reciever and subwoofer both have a 3-prong plug.

    Both of these devices "think" they represent 0.000 volts in your system. As long as you dont make a direct connection to the GROUND wires between your reciever and subwoofer, everything is fine. They dont 'fight' over who has the 0.000 volt connection.

    Your Monster cable - is actually broken. When you use it to connect your sub - only the center wire of the cable really makes contact.

    The Belken cables are 'traditional' AV cables and really contain 2 wires: one for the center pin, and one for the outer "fingers" of the RCA plug. The second wire creates a connection between the grounds and this causes the subwoofer hum.

    Hope this makes sense.
     
  4. ChristopherDAC

    ChristopherDAC Producer

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    Huh! I get a ground loop with 2-prong plugs on all of my equipment except my computer, because there's a fault in my household electrical service ground but my TV/FM antenna is well grounded [and the low impedance of the folded dipole shorts it, but that's another story]. If you're having a ground loop, it means that you have a serious problem in your household electrical wiring [which can cause a fire] and you need to call an electrician. That's what I'm going to do, now that I've tracked down the problem.
     
  5. Bob McElfresh

    Bob McElfresh Producer

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    Be carefull - a 60 hz hum can be caused by a ground-loop, or 60 hz noise brought in on the CATV line (the second-most likely cause of a hum).

    I dont believe a ground-loop means you have an electrical problem.

    Short answer: to avoid a ground-loop - you want to make sure your electronics has only 1 device with a ground-pin on the power plug.

    If you have 2 devices with ground-pins, you need to try and make sure you dont directly connect the grounds of both devices together by using an ordinary AV cable.
     
  6. ChristopherDAC

    ChristopherDAC Producer

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    Well, this is an antenna line, and I sank a ground rod for the antenna myself after I couldn't find the household service ground. The existence of something between 0.5 and 1.5 V [AC RMS] at all times between the two is indicative of leakage into the household ground and/or an undesirably high impedance in the ground circuit.
    to be blunt, the "ground" pins of all the electrical outlets in the house are supposed to be connected by solid copper conductors of gage no smaller [higher] than 12, at the electrical service box, and so they should be at the exact same potential everywhere -- that's what they're for. The presence of a "ground loop" is ipso facto indicative of a problem either with the equipment or in the household wiring, and simply using "cheater plugs" and so forth is very dangerous.
     
  7. chris_everett

    chris_everett Second Unit

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    To second what ChristopherDAC says

    Do not cut off a ground pin, or use an ungrounded cheater plug!!!!!!

    The ground is there to save your life!!

    See if the humm is still there if the subwoofer and reciver are plugged into the same outlet. If so you have an equipment problem, and if not you have a wiring problem.

    To avoid a ground loop, you want to make sure that everything is grounded to one common point, for you whole house.
     

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