Massdrop x Eddie Current ZDT Jr. (Official Thread)

Discussion in 'Headphone Amplifiers and Combo (DAC/Amp) Units' started by Hands, Nov 15, 2017.

  1. eastboundofnowhere

    eastboundofnowhere Facebook Friend

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    just made one out of multiple layers of aluminum foil as an experiment. I could hear it from a couple of feet away with my very sensitive speakers before. Now to hear it at the same level I have to put my ear one or two inches from the speaker. Success! Still don’t know why it worked since it’s not magnetic.

    Enough derailing, just kind of cool to learn something useful from people here.
     
  2. murray

    murray Friend

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    Aluminium works in a different way, but can be quite effective when thick enough. I think it works more like a "sponge" than a true shield by transforming the EM fields into eddy currents in the aluminium which then dissipate within the material. I have successfully used 10 mm thick aluminium plate for this purpose. I suppose that many layers of foil might be similar.
     
  3. Dzerh

    Dzerh Friend

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    Photos of internal shielding I made, it is unclear why it is working, but it is working for my amp:
    [​IMG]
    [​IMG]

    Same shield between transformers was unnoticeable for my ears. 1/8in x 2in x 24in low quality steel plate was noticeable but hum reduction was low. 1/8in it is max you can fit there.

    At this point I'm satisfied with amount of residual humming in my ZDT Jr., may be latter I'll make additional shields around all 3 transformers.
     
  4. Dzerh

    Dzerh Friend

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    I checked the amp with 1/8in x 2in x 10in aluminium plate between transformers and haven't heard the difference.
    But take into account that now I have to use Monoprice 8323 as the most sensitive cans at hand. As, for example, I can't say that it is 60Hz humming with HD600 anymore. I hear something but it is hard to determine what it is in home environment.

    Also, there is an effect I haven't noticed before: when I turn on cold ZDT Jr, for first ~5 seconds there is strong humming at "before shielding" levels but it goes down then. The effect is less noticeable on the warmed amp. It is pretty hard to explain as effect from my shielding. It can be some kind of saturation involved but I doubt it.
    So I'm starting to think that it is possible my experiments just matched with end of some kind of break-in period when, for example, some electrolytics in power supply got into working specs at last.

    It would be good to remove the shield and check what is going on with humming, but I kind of reluctant to do so. First, there is another, actually measured solution from Massdrop. Second, it is not easy to remove the shield at this point as it was bent into the place - I'll need to remove all connectors from back then carefully apply force. Third, the shield may be actually helping, at least it should not make things worse, so I'll have to reinstall it.
     
  5. AudioFriend

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    Yesterday I executed some experiment too with great results. I removed the housing of the small transformers, and padded their inner sides with iron sheets. 5x0.4mm to the side that faces the main transformer, 4x0.4mm to the side towards the other small transformer:
    [​IMG]

    I also put three plates externally between the main transformer and the smll ones, and a 0.4mm extra cover to the main house.
    [​IMG]

    I know, I know... It's ugly. But who cares, if it doesn't hum anymore! :)
    I don't have the tools to measure the reduction, but I guess it's about 6-8 dB. Now the hum is barely noticable even in silence. The sound quality seems to be improved too, but it might be because of the absence of the annoyance or the fact that I fixed many poorly executed solder points.

    So the source of the hum is, without doubt, the magnetic interaction between the transformers. I believe it could have been prevented by using thicker iron for the transformer houses, because the magnetic shielding efficiency is directly proportional to the thickness of iron. Maybe Massdrop or Laconic wanted to spare on shipping and material costs. It would be interesting to know whether the pre-production units were made of thicker plates.
    Fortunately, it's relatively easy to fix. There is a lot of space between the small transformers and wall of their houses. Today I'm going to buy some 40x5mm flat steel, cut it to size and glue them inside the transfomer houses.
     
  6. Orkney

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    This is a very illuminating discussion -- many thanks to all who are contributing their knowledge and skills towards a resolution of this problem.

    Quick question to those of you who have been in touch with MD -- are there plans to release an "anti-hum" kit to those affected that can then be retrofitted to these amps? Seems like it might be a simpler and less pricy alternative to the present "return or keep as is" policy.
     
  7. Orkney

    Orkney Acquaintance

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    Quick update: I've installed a (very basic) rectangle of sheet steel between the transformers and the case, as per the pix in post #503. It ain't pretty, but the him is no longer audible on my 800s, 650 or 701s, and only faintly audible on my IEMS. Will run it today and check in later.
     
  8. atomicbob

    atomicbob dScope Yoda

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    Aluminum and copper plate will NOT work to reduce magnetic flux lines. Copper and, to a lesser degree, aluminum affect the E field. This is an M field issue. Material needs to be high permeability steel or mu-metal. Mu-metal is more effective for moderate flux densities but will saturate before steel.
     
  9. Dzerh

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    I just checked as I have suitable plate, @murray's post above provoked me.
     
  10. atomicbob

    atomicbob dScope Yoda

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    Ahh, I missed @murray post above.

    I should make comparison measurements of steel, mu-metal, aluminum and copper plate both residual hum and direct flux field measurement with a gauss meter. Another 'round tuit project.
     
  11. Ringingears

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    I tried to find some 3M mu-metal online but they only offered it in large quantities. :(
     
  12. atomicbob

    atomicbob dScope Yoda

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  13. msommers

    msommers High on Epipens

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    While this seems to be an interesting science experiment, pretty limited on the sound quality feedback. I mean if this was any other brand, it’d be ChiFi garbage by now.
     
  14. atomicbob

    atomicbob dScope Yoda

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    My impressions skills aren't as capable as others on this forum, but this amp has a sound reminiscent of my Zana Deux making it worthy of such efforts to reduce the residual hum. The tone is both balanced and lovely fitting my personal preferences quite well. For me, this is a keeper.
     
  15. Dzerh

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    For me it was worth keeping even with the amount of humming I got it. Decreasing/removing humming it is more for my peace of mind than anything else.
     
    Last edited: Sep 4, 2018
  16. e.schell

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    I got lucky enough to pick one up second hand finally, on it's way should be here friday. Planning on ordering some 3m mu-metal mention above.... should i get enough to do in the inside of all 3 housings or just the one for the power? I'd rather do a little more work and buy more mu-metal than i need and overkill it as opposed to not doing enough... could someone with an amp in hand measure the housings and give me an estimate of how much i should order pretty please? Looks like it comes it 2inx8in sheets?
     
  17. Ringingears

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    I have made the same mods as @atomicbob with excellent results. This amp is definitely not chi-fi garbage. I own an Eddie Current Black Widow and have heard all of the other Eddie Current amps on more than one occasion. This amp has a sound that fits right in with the other Eddie Current amps. I agree with @atomicbob. The sound is closest to the Zana Deux. I’m loving the sound. Smooth, great mids and non- fatiguing. Great synergy with HD600/800. Was up late this weekend listening to my favorite music. My unit now has the sound that the loaner unit had. The reason I ordered it in the first place. IMHO, this is a great deal at this price point.
     
  18. Dzerh

    Dzerh Friend

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    Keep in mind that mu-metal is easy saturated so I'd not use it for power transformer without measuring magnetic field we have there. Also, I believe we have enough space and weight restrictions for shields to be good enough just with iron.
    If you insists on using mu-metal I'd used it inside output transformer housings sandwiched between 2 steel sheets.
     
  19. e.schell

    e.schell Friend

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    I will do some more research and reread the last few pages myself, but in the end am not set on using any one thing yet and will use which ever material atomicbob and those knowledgeable agree is the best to use and where to use it.
     
  20. atomicbob

    atomicbob dScope Yoda

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    Experimenters should take to heart what @Dzerh said. Steel first, mu-metal second, for power supply transformers.

    My plan is the Massdrop proposed solution of high permeability steel band around the power supply toroid transformer first, followed by additional high-u sheet in appropriate locations as determined experimentally. The only reason I am pursuing addional shielding is due to my exceptionally low ambient sound level of 21.1 dBA, my high sensitivity and extreme dislike for hum. The Massdrop proposed solution is more than adequate for 99.99% of everyone.

    Experimenters might find the following useful:
    https://www.amazon.com/dp/B0754VVW4W
     

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