Bummer... I got a hummer ??

Discussion in 'Archived Threads 2001-2004' started by JackIR, Mar 4, 2002.

  1. JackIR

    JackIR Stunt Coordinator

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    Ok here's the situation. I just replaced my B&K Ref30 with a Lexicon MC-12. The world is great except now I have a hum in my sub. My setup is a SVS sub EQ'ed by a Behringer Feedback Destroyer. The sub is powered by a Crown K1 amp. This is the exact setup I had with the Ref30. I'm using the same power outlets going into my Monster Power HTS2500. However the problem seems to be with the BFD. If I take the BFD out of the connection and have the MC-12 feeding the signal to the amp directly --- no hum! Again this is same setup I had before and I only changed processors. What gives??

    Suggestions??
     
  2. ColinM

    ColinM Cinematographer

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    Sounds like you have an unlimited budget - the BFD is the weak link. Get another higher quality PMEQ...

    If I had the ching, that's what I'd do. If it didn't fix it, just return it and try cheater plugs if you haven't.

    - Good Luck!
     
  3. LarrySkelly

    LarrySkelly Stunt Coordinator

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    You have a ground loop. There are a few solutions, which you can find on the web by searching for the phrase 'ground loop'. Thea easiest is to eiminate the ground pin on the power cord of the amp for your sub, by using a 'cheater plug' that only has two pins.

    I and many others have had the same problem on our sub amps, and the universal solution has been to eliminate the ground on the sub amp plug. I can't get cheater plugs here in Canada so I just cut off that pin and ... presto ... no more hum.

    Larry
     
  4. Glen_L

    Glen_L Stunt Coordinator

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    You may want to try unplugging your coaxial cable if you use cable TV, this removed the hum in my system (I also use a BFD). The solution in this case is to get a cable TV ground loop isolater from Rat Shack.
     
  5. Bill_D

    Bill_D Supporting Actor

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    I also developed a hum in my SVS Ultras after installing my BFD (which is currently still waiting for setup and in bypass mode). After reading another thread around here, I also realized that there was a voltage mismatch between my Onkyo and Samson. Not a big deal ... but something else to tweak. Someone in forum suggested a product called the Ebtech Line Level Shifter (LLS-2). This product helps to correct any operating voltage differences between home and pro gear and also includes a feature called "Hum Eliminator". I picked it up at Guitar Center for about $65 and it fixed both my hum and voltage mismatch. After installation, my subs are dead quiet and I had to dial down the Samson approx 25% from max with LFE output from the Onkyo at -15db. I put the LLS-2 right before the sub amp. Ebtech also has the product with the Hum Elinator feature only (HE-2). I preferred this solution because I did not have disconnect any of my grounds with those cheater plugs. Just seems ridiculous "to me" to put a .50 cheater plug on the end of non-stock power cords. Both boxes are approx 4X4X1 in size and can be easily integrated/hidden into any system.
    Link below is for info only. I have never bought a thing from them.
    http://www.allprosound.com/ecom/deta...ls-2&CAT3=20C1
     
  6. JackIR

    JackIR Stunt Coordinator

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    Thanks for the suggestions and I did some more reading on this forum and the net on ground loops. I think I have a cheater plug in my garage somewhere. Though I read that using a cheater plug is not very safe.

    But here's the part I don't understand. If I did not have a ground loop with my previous setup and all that I did was exchange one processor for another (using the same outlet on my power conditioner), how did a ground loop get created?
     
  7. JohnnyHK

    JohnnyHK Stunt Coordinator

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    You're right to be concerned. Cheater plugs are not safe. If a hot wire comes loose inside and touches the metal case, you will complete the circuit when you touch the case. Zap! Now, granted, the odds of the wire coming loose are low, but it does happen and that's why the the third prong is there.
     
  8. SanfordL

    SanfordL Stunt Coordinator

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    You might try picking up some Klein tools, and becoming an electrician too. ;-) If I had one suggestion to make (I just got done doing this to my house for the home theater, and MAN WHAT A DIFFERENCE) is to install at a minimum a 20 amp dedicated circuit, with isolated ground (they are the orange outlets you see at your local Home Repot, Lowes, Menards, etc.) outlet. To figure out the size of the circuit(s) you need, add up all of your load for the home theater, and despite what an electrician will tell you, get a circuit(s) that will handle it all because if you are like most, sooner or later you will drive it that hard.
    15 amp = 1800 volt (use at minimum 14 guage wire and you need 3+1 wire)
    20 amp = 2400 volt (... 12 guage...)
    30 amp = 3600 volt (... 10 guage...)
    The isolated ground provides 2 grounds, further isolating the very expensive equipment. You ground to your house ground (if you don't have one right now, get a book, or call an electrician) and then the second ground use the closest water pipe and an approved clamp.
    Not that this will solve your ground loop, but it's a good idea to do for anyone serious about HT.[​IMG] [​IMG]
     
  9. JackIR

    JackIR Stunt Coordinator

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    Problem solved. $.60 cheater plug on the BFD.

    Thanks for the help guys.
     
  10. jeff lam

    jeff lam Screenwriter

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    Bill,

    How many dB gain did you get with the LLS2? I just won a LLS2 on ebay for $45 and will get it soon. I have a Yamaha Receiver and crown CE1000.

    What were your before and after settings on sub level and amp gain?
     
  11. Bill_D

    Bill_D Supporting Actor

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    Jeff:

    Before LLS-2: Onkyo 898(+5db) ..... S1000 100% Gain

    After LLS-2: Onkyo 898(-15db) ..... S1000 ~65% Gain

    BFD in the loop in both cases but in bypass mode
     
  12. jeff lam

    jeff lam Screenwriter

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    Bill,

    WOW, that's great. I should get my LLS2 today so I'm pretty excited. Anyway, how much variance does the onkyo have in the sub output? I thought most receivers only had 20 notches in the sub output level. My yamaha goes from -20 to 0, and denons go from -10 to +10 right? What does your onkyo do?

    Also, where in the chain did you put the LLS2, between the BFD and S1000?
     
  13. Bill_D

    Bill_D Supporting Actor

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    I haven't explored the top end of the Onkyo's sub output beyond the pre-LLS2 setting of +5db. But, the bottom is -15db which is where it is set now. I would assume that the gain would mirror the cut ... but I am not sure.

    The LLS is in between the BFD and the S1000 since the BFD was introducing the hum. I didn't bother to try it anywhere else since it does the trick in its initial placement.

    I am sure the settings will change once again once I get around to putting the BFD to its intended use.
     
  14. jeff lam

    jeff lam Screenwriter

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    Bill,

    Once you flatten out the response, you'll probably have to bring up the sub level or amp gain a little. For me it was about 7db. After the cut's with the BFD, I needed an extra 7dB to get back to calibration levels. It will vary with every room depending on how much you have to cut or boost to get it flat. Sounds like you are all set.

    Good luck with the BFD, once you get familliar with it, it's really not complicated at all. At least, thats what think.
     
  15. jeff lam

    jeff lam Screenwriter

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    Bill,

    I got my LLS last night, hooked it up and found it didn't boost the gain at all. I don't know what's going on???

    BTW, Do you happen to know what the voltage level and impedance output of your Onkyo is?

    My Yamaha Sub output is 4V @ 1.2K ohms I believe. I found it in the mannual specs.

    Could it be possible that the LLS does not function with an output impedance this high?
     
  16. Bill_D

    Bill_D Supporting Actor

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    I know your have probably already done this but check your setup. The LLS-2 inputs/outputs are in pairs and not grouped.

    Looking at the manual, the sub pre-out voltage is 1V @ 470 Ohms. If I am correct, your output is better/higher/stronger (pick the appropriate term).

    The LLS-2 is not an amp, although the results of this box would have you to believe otherwise when used in the proper setup. I do not think that the LLS-2 will "shift" voltages beyond the ones that are common fro Pro equipment.

    The Yammy's output must be in Pro range.
     
  17. DeanQ

    DeanQ Stunt Coordinator

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    Ok I still dont understand what a "cheater plug" is? Is that just a thing I plug into my samson amp's 3 prong power outlet that converts it to a 2 prong power outlet that I plug into the wall?? Someone help me.

    I have a yamaha reciever and the samson amp 700 and a svs 25-31cs that Im getting a humming sound as soon as I hooked up the RCA mini-amp. If I take the mini-amp out of the loop the humm is gone. So this cheater plug would I plug this into the samson amp power plug?
     
  18. JackIR

    JackIR Stunt Coordinator

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    DeanQ,

    Yes you are correct. the cheater plug converts a 3 prong to 2. Use on your miniamp. No more humm!
     
  19. DeanQ

    DeanQ Stunt Coordinator

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    Ok I think my little mini-amp is already a 2-prong plug. Its a little small box. So would I use the cheater plug on my samson amp instead?? Thats a 3 prong plug?
     
  20. jeff lam

    jeff lam Screenwriter

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    Bill,

    After picking up another 1/4" patch cable and pitting the LLS between the BFD and CE1000 it worked and gave me 7dB gain(a little less than I expected but still a help). Why it wasn't working without the BFD in the loop I have no clue. However, It didn't eliminate the hum. I'm actually getting a louder hum than before but it's not loud enough to be an issue.

    My Yamaha is [email protected] ohms so in actuality after the voltage drop across the 1.2K ohms, the voltage is quite low. I think the LLS2 actually uses components to better match impedance rather than voltage. My Yamaha is nowhere near pro levels I'll tell you that much!
     

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