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Added an amp(P85/3) and got HUM – HELP!

Discussion in 'Arcam Owners' Forum' started by mrkeeling, Sep 12, 2004.

  1. mrkeeling

    mrkeeling
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    Just got a power amp (Arcam P85/3) and hooked it up to my receiver (Arcam AVR200) to drive my front stage. While results are quite pleasing, there is an unpleasant side effect – I got HUM! It is not terrible but it is definitely present. It is coming mostly from the LF driver in my speakers and it is constant regardless to volume control.
    Here is what I tried so far:
    - When amp is on and receiver is off – nothing but SILENCE!
    - When both amp and receiver are on but interconnects are unhooked from the receiver – nothing but SILENCE! (doh)
    - Ground lift switch on the receiver does nothing – hum is there in both positions (ground and ground lift) :(
    - Tried cheater plug on amp, receiver and both to no effect – hum is present in any and all combinations. :thumbsdow

    As I am getting nothing but silence when amp alone is powered and connected to the speakers, is it safe to assume that there is no some kind of malfunction with an amp? This is very important as I have five more days to return it for a full refund.

    Any ideas on how to get rid of that hum?
    :lease:
     
  2. mrkeeling

    mrkeeling
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    Well, I helped myself :p and found the damn humming bird! :clap:

    If was f#%!ing 12V trigger! And it was the last thing I unplugged, of course! :mad:
    All that I am left with now is a slight hiss, but I have to put my ear right on to the tweeter and then I can barely hear it. So I am a happy camper now! :thumbsup: Somewhat!

    How am I supposed to turn the amp on now? Getting up and turning it manually on? Not very satisfying! :thumbsdow

    I used mono mini plugs. Wonder if stereo would make a difference? (manual says mono or stereo)

    I am definitely going to try it as soon as I get some time to snatch another cable.

    Any other suggestions?

    Arcam people, do you have any suggestions on how to fix this?
    :lease:
     
  3. ANDY_DUTTON

    ANDY_DUTTON
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    Hi,

    The problem seems to be a ground loop through the 12V trigger. As the 12V trigger doesn't really need an independant ground return, (it can return its current down the audio interconnect) you could try just attaching the center pin of the jack plug and not the outer. Then there would be no ground loop created. (I have not tried this so can't promise it will work, but I am sure it won't hurt anything)

    Regards,
    Andrew
     
  4. mrkeeling

    mrkeeling
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    Thank you Andrew. :thumbsup:

    I am going to try it and post the results.
    :beer:
     
  5. mrkeeling

    mrkeeling
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    Andy you are a Genius! :thumbsup: :clap: :thumbsup: :clap:

    It works like a charm. :clap: :clap: :clap:

    You Arcam people are the best :thumbsup: :thumbsup: :thumbsup:

    Thanks a lot
     
  6. Icarus

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    Wot a pretty post :eek: Glad your sorted though. That Andy guy sure does know his stuff.
     
  7. mrkeeling

    mrkeeling
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    Yea, that post may be a tad over the top, :p ;) but I was (am) really happy that it fixed my problem so I can sit back and enjoy my new and improved sound. :D
    :beer:
     
  8. Limber

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    Hi,

    For a long time now I've been experiencing precisely the same problem with my AVR200 + P85 combo that mrkeeling described at the beginning of this thread. I've never been able to eliminate that hum, so I eventually just threw up my hands and contented myself with the fact that as long as I turned the thing on manually with my big toe, it worked. Now upon discovering this thread, I'd like to make another attempt, but I'm confused about Andrew's advice, and was hoping for some clarification first.

    He suggested "just attaching the center pin of the jack plug and not the outer". By "jack plug" I assume he means one end of the mono mini cable. If so, is he suggesting insulating all but the very tip of the jack plug prior to inserting it into the 12V socket on the receiver? Or am I completely mis-interpreting his instructions?

    I'd really appreciate any of you lending this non-electrically inclined soul a hand.
    Thanks
     
  9. mrkeeling

    mrkeeling
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    Most of the mini mono/stereo cables that you can buy in store have moulded miniplugs and often coaxial cable so they are quite a pain to redo.
    So here is what I did:
    I bought a pair of mono miniplugs at RadioShack, took a piece of single wire (gauge 18 I believe) and soldered it only to a centre pin of miniplugs. As you can see from my previous post – it works like a charm! :D
    :beer:
     
  10. Limber

    Limber
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    Ah, now I understand. You've made yourself the equivalent of a mono miniplug-style cable, minus the grounding wire that normally would be present. Thanks for the reply, that helped.
     
  11. Limber

    Limber
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    * 2 hours later *

    I was lucky enough to have a cable with each wire in a separate sheath, so I simply cut the grounding wire. Humming's gone, it worked!

    In addition, for over 2 years, every time I've turned the AVR200 on, the television picture has suffered from horizontal scrolling lines of interference, commonly identified as the symptom of a grounding issue. I've tried various fixes (a better outlet, using a different circuit, an isolator, and even an expensive power conditioner which I didn't keep), but nothing had any effect. Now as a very nice and unexpected bonus, this problem has disappeared as well. Frankly, I'm even happier about this than I am by the elimination of the hum, but I'm also perplexed;

    The visual interference is present when a normal, unmodified cable (with the grounding wire intact) is used between the 12V trigger sockets. It's also present without any 12V connection at all. I guess that indicates an electical flaw in there somewhere, but it's not my field.

    Well, now I'm a happy camper!
     

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