Amp Hum

Discussion in 'Hi-Fi and General Audio' started by James_1D, Apr 1, 2011.

  1. James_1D

    James_1D

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    Folks, I've had some amp hum for a while now...and recently it's been annoying me, so I tried the amp in other rooms....hum still present...I have a cheaper older amp that does not hum, so thought it was a dodgy unit....however I recently took it back to hi-fi shop and they tested it as normal....and last night to the old boys house and no hum...Soooo that leaves my electricity supply...perhaps more DC sneeking in I dunno....so I am getting a loan from hi-fi shop a conditioner that allows AC, but kills DC dead....and I'm sure this will indeed resolve the issue...my problem is it's £500.....and therefore do I live with Hum

    You can't hear the hum when playing music...so if it will not get worse, the amp's life will not be reduced and it defo does not affect the sound qaulity, then I'd live with it...

    Thoughts
     
    James_1D, Apr 1, 2011
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  2. James_1D

    Tenson Moderator

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    Does the hum reduce when the amp is nice and warm? Sometimes the coils of wire in the transformer need to expand just that tiny bit.

    It shouldn't cause a problem to sound quality or the life of the amp, assuming everything works correctly as the shop tested it.
     
    Tenson, Apr 1, 2011
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  3. James_1D

    James_1D

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    No it ossilates with variation in pitch. Hi Fi dealer...thinks I'm getting a little too much DC, so the power block I'm going to borrow, allows AC, but blocks DC...apparantly Naim are bad for Hum.

    I've just stuck a £40 tacima mains power block in just now, but it does not block DC, and thus still getting hum...so this does leave DC as a possible culprit !

    I mean it's not loud loud....and when listening to music I can't hear it, even at low volume...so if it's not going to get worse or shorten life of amp...then I may well just live with it...£500 is a lot of money for what I'd be gaining.
     
    James_1D, Apr 1, 2011
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  4. James_1D

    RobHolt Moderator

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    Does the problem vary at different times of the day?

    If constant, you could have an earth loop if you have a ground link established through a connected unit via the interconnect, plus the mains ground.
     
    RobHolt, Apr 1, 2011
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  5. James_1D

    Tenson Moderator

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    Oh, I assume the hum is directly from the amp itself, not from the speakers?
     
    Tenson, Apr 1, 2011
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  6. James_1D

    James_1D

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    Thanks guys, it's not constant, and does not seem to follow a pattern...I even tried things like ensuring dimmer lights were all off....

    Fact that it does not hum at my Dad's or mates house...tells me it's not the amp itself...which is a good thing !

    And no, nothing through speakers.....
     
    James_1D, Apr 1, 2011
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  7. James_1D

    zanash

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    do you have dimmer switches ?.....

    these will often cause amps to hum
     
    zanash, Apr 2, 2011
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  8. James_1D

    James_1D

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    Well I have borrowed a PowerLine Axis from local dealer...and this device only allows AC and blocks DC....and guess what....hum gone and system sounding better....amazing....so mains can indeed affect your hi-fi....
     
    James_1D, Apr 2, 2011
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  9. James_1D

    zanash

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    oh dear........thats going to upset a few people on here!
     
    zanash, Apr 2, 2011
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  10. James_1D

    RobHolt Moderator

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    Not at all - its a DC blocker and the effects are well understood.
     
    RobHolt, Apr 2, 2011
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  11. James_1D

    James_1D

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    Indeed, a fix to a specific issue...so it's not a solution for everyone.
     
    James_1D, Apr 2, 2011
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  12. James_1D

    RobHolt Moderator

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    Glad you got it sorted James.
    If you have the details of the unit please post them as it might help others with a similar problem.
     
    RobHolt, Apr 3, 2011
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  13. James_1D

    James_1D

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    Sure, this is a review of the device - http://www.techradar.com/reviews/au...cessories/isol-8-powerline-axis-695285/review

    I was getting a hum from the amp that varied in pitch, which did not come through speakers. With music on even at low volume I was not able to hear the hum. I tried a few power points around the house to determine if it was the socket and a poor earth (remember I'm not technical, so it was just a first thought before I rang hi-fi shop)...hummed away in any or my rooms. Spoke to my hi-fi dealer who have been in business for many years and have had their fair share of problems like this....and from my description of the issue, they suggested taking the amp to a friends...and see if it still makes the same pitch change....so I took to Dad's....no hum at all...so at least I knew it was not the amp itself.

    Back to dealer, and they deduced that it was likely I was getting some excessive DC, that can cause the transformer to vibrate more, and hum is the result. If it is excessive DC, then one thing to try to rule it in or out was this block...it is not a mains conditioner as such, all it does is allows AC through, the stuff you want...and blocks DC, the stuff you don't want....soon as I plugged it in, I noticed the system sounded much better, and the hum is gone....I did not want to make a snap call on it...so have had is running for 2 days now...and so far so good....no hum, and system does sound better than before it's use.

    This might not solve every amp hum issue, for some, it's things like dimmer lights and sky tv boxes....but if your hum changes in pitch, it is likely that it's excessive DC.
     
    James_1D, Apr 3, 2011
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  14. James_1D

    Tenson Moderator

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    Good you got it sorted.

    Shame about the cost!

    Having done a little reading just now it seems like the insides are likely to consist of a diode bridge and a pair of caps. You could make this for £5, or £25 with a nice case.

    Zanash, I'm not sure it will upset anyone, there was obviously something going on to upset the amp since the transformer was making sounds it didn't do at another location. I don't think it translates to an improvement being made in a case where equipment is already operating correctly.
     
    Tenson, Apr 3, 2011
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  15. James_1D

    Tenson Moderator

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    This is what Bryston put inside their amps after the IEC socket and before the transformers. The components are put in the neutral line to keep them near ground voltages. You don't need to touch the live connection at all in this.

    You get a bridge rectifier and connect the + and - terminals together. Then you feed the neutral line into one of the ~AC terminals and out the other ~AC terminal. A pair of electrolytic caps are placed across the bridge rectifier, note the polarity. Because the voltages on the neutral line are small you only need 16V caps max.

    I want to make it very clear that even if you are only putting these parts in the neutral line, you are messing with the mains supply to the equipment here and these voltages are seriously dangerous. This post is made as a guide only, and AudioSmile or myself take no responsibility for what you do with it. If you don't know what you are doing, get someone who does.

    [​IMG]
     
    Tenson, Apr 3, 2011
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  16. James_1D

    Tenson Moderator

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    Tenson, Apr 3, 2011
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