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How much hum is too much?

Discussion in 'classic' started by Cool_jeeves, Sep 10, 2019.

  1. Cool_jeeves

    Cool_jeeves pfm Member

    I moved around things a bit today. Things seem to have moved more than I wanted.

    I have a habit of turning up the volume to max before connecting my amp to the speakers. The amp has VU meters (Accuphase), so I can detect hum by watching the needles. Sure enough, if the needles move, and I connect the speakers and again slowly turn the volume up, I can hear the hum.

    My normal listening position is 9' o clock. Arond 10' o clock at times. At this level, the needles don't move. More than this drags the needle up to -40db, then -30 and at max volume, around -25db.

    If I connect the speakers and listen, I can detect the hum at -40 itself, and there is no need to take the volume beyond 12' o clock.

    If I keep the volume at the usual level and listen, then the sound seems quite OK. The TT is a Garrard 301, arm is SMEV, phono is a DIY (which till now did not hum, and all this is since I moved stuff around).

    The question is - does a properly set up deck have hum beginning sligtly about normal listening positions?
     
  2. Vinny

    Vinny pfm Member

    Maybe talking slightly different things here, but my current system has all but no hum at any volume - you have to concentrate hard to make it out.

    Why have you pitched the question with regards the deck, or do you mean a vinyl system in total? I would be very hard-pressed to say that my PT1 or LP12 ever produced any hum themselves, no matter what they have been hitched-up to.

    Reading again, is this not mains hum? If so, a cable, probably an IC, is now picking up the hum because it has been moved.
     
  3. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    Phono stage probably been moved too close to another item with a mains transformer in it.
     
    Darren L, Snufkin and Mike P like this.
  4. Dougie2404

    Dougie2404 pfm Member

    As Arkless says, I had horrendous hum with a phono stage and a stepup because they were too close. Move things around again.
     
  5. Mike P

    Mike P pfm Member

    I think Jez has it already but also worth asking if you're running any non-shielded interconnects?
     
  6. sq225917

    sq225917 situation engineer

    Cordless phones?

    I have no noise in my system from any source, my phonostage is in an acrylic case, and neither my tonearm or phono to pre cables are shielded. Dac and pre onwards are all balanced, and screened.

    Good earthing and tidy cable practice pays dividends
     
  7. Cool_jeeves

    Cool_jeeves pfm Member

    Hmm. thanks a lot, especially Vinny for pointing our that there is no hum at ANY volume...I think i have to solve this over the weekend. I am not using an un-shielded IC from the tonearm - but will change that around also. I can also try to disconnect the Garrard and plug in only the phono stage and see if the hum is still there. So a few things to try...
     
  8. Mike P

    Mike P pfm Member

    As Jez says above, physical distance between the phonostage and anything with mains transformer can often be the key thing.

    Let us know how you get on.
     
  9. MikeMA

    MikeMA pfm Member

    Yes most likely this.

    Another thing to look out for is power cables too close/parallel to interconnects, especially if you've moved stuff around. Try to keep them well apart/crossed at 90 degrees or thereabouts.
     
  10. sq225917

    sq225917 situation engineer

    I've never had noise induced via interconnects, mine run alongside power cables, side by side.
     
  11. Vinny

    Vinny pfm Member

    Always used screened interconnects? If not, you are, by a very long way, the luckiest person alive. Although transformers are probably many, many times the problem of mains cables.

    It was night v. day when I changed to screened.
     
  12. MikeMA

    MikeMA pfm Member

    Lucky you! I have, particularly with valve phono stages.
     
  13. david ellwood

    david ellwood Kirabosi Kognoscente

    My issues with hum are related to mechanical transformer noise rather than what comes out of the speakers.

    I would say if you can hear it from the listening position with no music coming through then its too loud.
     
    Darren L, cctaylor and Wolfmancatsup like this.
  14. sq225917

    sq225917 situation engineer

    I had ear 509s that hummed, binned em off.
     
  15. Nagraboy

    Nagraboy pfm Member

    Used to have hum when I used my Leben amp with Tannoys Kensingtons but due to the lower sensitivity of my subsequent Spendor and Harbeth speakers, the hum became undetectable at the listening position.

    In my current house things are a lot quieter. Could be equipment positioning as Jez says. Certainly moving around SUTs helps reduce hum.
     
  16. Cool_jeeves

    Cool_jeeves pfm Member

    Occam's Razor principle mixed with a bit of recklessness => i removed the ground wire - voila! Hum gone - don't ask me how. and just to be sure, if I put it back, the hum comes back. I will enjoy the music first and ask questions later.
     
  17. Julf

    Julf Evil brother of Mark V Shaney

    Classic demonstration of ground loop :)
     
    Arkless Electronics likes this.

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