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Improving transformer hum

Discussion in 'd.i.y.' started by IWC Doppel, Jan 3, 2010.

  1. IWC Doppel

    IWC Doppel pfm Member

    Are there any tricks to improve mild transformer hum as I sit close to 4 Naims 135's and 2 250's ?

    I wondered about something like thin felt or sorbothane between the transformer and case ?
     
  2. 337alant

    337alant Negatively Biased

    Jesus thats some nice welly you have there:eek:, you must have some electricity bill :D bet that sound good though ;).

    Yes I always mount a transformer on a thick rubber pad, if it has a big washer on the top I put a rubber washer in there as well, the sorbothane would probably be better than plain rubber.
    Just make sure that putting something under the tranny doesen't make the through bold touch the top cover plate of your amp :eek: or it will short it out.
    Experiment with the tightness of the clamping as well.

    Alan
     
  3. IWC Doppel

    IWC Doppel pfm Member

    Thanks, I'll experiment ;)

    Hoping it will be 6 x 135's and 1 x 250 shortly :)
     
  4. sq225917

    sq225917 situation engineer

    Currently fiddling with two nap 140 traffos in the same case, I'll let you know, Sorbothane is on its way, soft foam and rubber already tried, not that useful. I think not bolting them but gluing them to a bottom pad might work best. Maybe even velcro onto Sorbothane...
     
  5. simeon

    simeon No fixed engagements

    I tightened up the bolt on my amp just a smidgen a few weeks ago while I had the lid off and induced hum. Backing it off cured it completely. My most cost-effective bodge yet :rolleyes:
     
  6. sam_cat

    sam_cat ᶜ ᶦˢ ᶠᵒʳ ᶜᵒᵒᵏᶦᵉ


    Not exactly a bodge, as loosening/tightening the bolt is an accepted method of managing the hum.
    A bodge would be using duct-tape to hold it down instead of a bolt....

    Sam
     
  7. simeon

    simeon No fixed engagements

    I'll give it a go.
     
  8. sam_cat

    sam_cat ᶜ ᶦˢ ᶠᵒʳ ᶜᵒᵒᵏᶦᵉ

    Not the duct-tape I hope ;)
     
  9. croak

    croak Registered User

    hi

    What causes the buzz?
    Having had my share of buzzing transformers I have done my bits of clamping and padding.
    Here in Johannesburg there were/are a few areas notorious for having buzzing transformers that are dead quiet elsewhere on a different grid.
    I now believe this to be a result of a small DC component riding on the mains...
    Clamps and pads are bandaids imo. Rather install a DC blocker in the amplifier. Bryston fits them standard on all their amps.

    You can use a bridge rectifier with the two ac terminals tied and the two dc terminals tied in series with live or neutral, across this you place a large set of electrolytics back to back. 16volt is even fine as the bridge sets the voltage (1.2v).
    back to back diodes or a low voltage transorb can be used in place of the bridge too.
    I woukd recommend this is fitted inside the amp and after the mains fuse else a fuse should be included. please note that the aluminium cans of the caps now do have mains running on them so I would insulate with some shrink tube or simillar.

    In the case of my buzzing Theta dac transformers they became dead silent and the sound improved.

    4700 mfd is ok for sources but the more current drawn the bigger the cap should be. I would use 10 000 mfd on a power amp as a minimum.

    You could rig up a test circuit (fused) in a box with some Iec male and female fly leads to test to see if it will solve the problem..
     
  10. mikesnowdon

    mikesnowdon resU deretsigeR

    Sounds interesting croak.

    To aid my understanding of how this is done could you post a simple schematic please?

    I have a pair of buzzing trafos in my DIY integrated so Im keen to try this.
     
  11. croak

    croak Registered User

  12. mikesnowdon

    mikesnowdon resU deretsigeR

    I'll insert the image for others to see. Thanks :)

    [​IMG]
     
  13. croak

    croak Registered User

    if you put the diodes in paralel but opposing directions you can just connect the series caps across the diodes too.

    http://www.lcaudio.com/index.php?page=316

    This uses a transorb but a bridge rctifier with tied legs is fine too and it is assumed that a typical cap can handle a fraction of its rating in reverse.
     
  14. mikesnowdon

    mikesnowdon resU deretsigeR

    I like this idea.

    If Martin Clark is reading - Could you share your opinion on this please Martin?
     
  15. mikesnowdon

    mikesnowdon resU deretsigeR

    Just bumping up this thread.

    Im curious if the DC blocking circuit will harm the sound in any way, such as suppressing dynamics?
     
  16. Joe

    Joe pfm Member

    Shipping seems a little excessive?


    Amount
    Mains DC Filter - Stop Transformer Noise! 1000 VA € 26,81
    Freight € 30,28
    Total amount ex. VAT € 57,09
    VAT 25% € 6,70
    Total Amount € 63,80
    Shipment Weight kg. 0,28
     
  17. mikesnowdon

    mikesnowdon resU deretsigeR

    OMFG is the shipping that much!!!! How can it cost more than the actual product??

    Still, it wouldn't cost much to build something like this point 2 point with plenty of heat-shrink for safety. Im still not sure how this will effect the sound though. In general mains filters are reported to squash dynamic range.....But this could be different.

    Wheres Martin Clark?
     
  18. croak

    croak Registered User

    IMO if it hurts, the caps are too low in value.

    I have however predominantly used this on source components.
     
  19. martin clark

    martin clark pinko bodger

    Here you go Mike ;)

    http://sound.westhost.com/articles/xfmr-dc.htm

    The most comprehensive write-up I've seen on the subject - esp. read the conclusion carefully : it's the cap that blocks DC, not the diodes - and the diodes protect the caps.

    Not tried it myself and frankly I'm a bit wary about recommending this whole approach. It's mains voltage and inevitably uses low-voltage electrolytic caps passing currents with a high crest factor - longevity will be limited (including your own if you get it wrong!)
     
  20. PigletsDad

    PigletsDad pfm Member

    Yes, but the as the circuit is on the primary side, currents are low - 5A DC from a supply fed by a 32Vrms secondary might easily involve secondary spikes up to say 50A. On a 240V primary, "average" current is 0.66A, with spikes up to 6(ish)A. This is well within the ripple current capacity of even small size cans, so I think part life should be pretty good.

    But the warning about this circuit remains - it is DIRECTLY CONNECTED.

    BE VERY CAREFUL. You must know what you are doing for safety, not just think you know.
     

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