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Thread: Power amp transformer hum

  1. #31
    Bigman80 Guest

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    Quote Originally Posted by alcarmichael View Post
    OK, so after a bit of trial and error tightening down the transformers really quite firmly and then loosening them; I’ve made an improvement and reduced the hum. I’ve done so rather crudely with a couple of pieces of speaker wire between the chassis and the transformers, the nuts aren’t really providing any clamping pressure on to the transformers now:



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    If you can get some silicone/rubber "O" rings, the round ones used for plumbing, you can use those instead of your speaker wire. That will help.

  2. #32
    Join Date: Aug 2011

    Location: Coventry, England UK

    Posts: 534
    I'm Simon.

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    Apologies for hijacking slightly... What can cause hum to come through the speakers? It's buzzing through both tweeter and woofer also so no idea of the frequency. It's not a ground loop as I do have an amp which doesn't transmit it at all but 3-4 other amps I've tried all do it.

    Don't know if it's DC or just dodgy mains. I'm using a dc blocker but it's not doing owt. Thing also is that all my gear with toroids in do have this mains noise but it's very quiet and can only be heard when ear pressed against the case and the room is silent. Even the hum from the speakers is low enough that it can't be heard from about 3ft away so It's not audible at the listening position. It just bugs me that it's there though.

    When I stick my head under the stairs cupboard I hear the same noise/hum which makes me think it's dodgy mains... Maybe the 1 amp that doesn't transmit it has something in the circuit blocking it somehow?

  3. #33
    Join Date: Jul 2012

    Location: Wimborne

    Posts: 701
    I'm Alex.

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    Quote Originally Posted by Bigman80 View Post
    If you can get some silicone/rubber "O" rings, the round ones used for plumbing, you can use those instead of your speaker wire. That will help.
    Is that the ideal? I was thinking about getting some sorbothane to take the place of the speaker wire.


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  4. #34
    Bigman80 Guest

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    Quote Originally Posted by alcarmichael View Post
    Is that the ideal? I was thinking about getting some sorbothane to take the place of the speaker wire.


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    The ideal is to go for a purpose made audio TF.

    Everything else is "bodge"

  5. #35
    Bigman80 Guest

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    Thanks for that. I'll give that a go!
    Quote Originally Posted by RothwellAudio View Post
    Use some kind of rubbery stuff to hold the PCB instead of screwing it down tightly. I use large holes in the PCB and fit a grommet. Then I use some rubber sleaving over the screw which passes through the grommet. The screws are rigid but the PCB is loosely fitted to the screws.

    There are many ways in which noise can appear through the speakers. It's useful to differentiate between hum and buzz. They're two different sounds and suggest different causes. The transformer could be absolutely perfect but you could still have a hum or buzz through the speakers. One possible cause is incorrect track routing on the PCB which allows spikes of current into the power supply to pollute the audio signal. Unfortunately, there's not much that you as a consumer can do about it - it's a design fault.

  6. #36
    Join Date: Aug 2011

    Location: Coventry, England UK

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    I'm Simon.

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    Just stuck my head under the cupboard with all the incoming mains and sounds like this noise is coming from a particular box (I'm no expert but it doesn't look to be the main incoming, looks like something attached after, maybe it's polluting the mains). I've tried to capture it the best I can with the crap mic on my phone.

    https://drive.google.com/file/d/1hh6...w?usp=drivesdk

    Hope the link works ok.

  7. #37
    Join Date: Jan 2008

    Location: Gerrards Cross

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    I'm Tony.

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    I would also try turning the transformer as well, find that null point and things will improve
    Coherent Systems
    Real high end sound with musicality not hifi

  8. #38
    Join Date: Jul 2012

    Location: Wimborne

    Posts: 701
    I'm Alex.

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    Quote Originally Posted by Mr. C View Post
    I would also try turning the transformer as well, find that null point and things will improve
    Ah, I think I know what you mean now. Rotate them on the stud as if I’m trying to find a balance or equilibrium point?

    Would this be a painstaking trial and error job? I’m assuming it’s unwise to handle the transformers while connected to mains power!?


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  9. #39
    Join Date: May 2018

    Location: London

    Posts: 17
    I'm Tommy.

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    Noratel is a good brand.
    However also they can have the hum problem.
    Special the older ones.
    The newer Noratel is made better. Dc on the electricity net is more normal now then 10 years or even 5 years ago.
    Now the Noratel take that in the consideration.
    The Norwegian high End brand Musical Innovation made by Roar Malmin have always used the Noratel trafo. They are known to be very quiet.
    A lot of people here in Norway did change to Noratel trafos because of the quality.
    Quote Originally Posted by alcarmichael View Post
    So, these are my transformers:

    I have no idea how they rank quality wise...?


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    Tommy

  10. #40
    Join Date: Apr 2016

    Location: Bishops Stortford

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    I'm Chris.

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    Quote Originally Posted by RothwellAudio View Post
    I think there's a whole load of different stuff getting all mixed-up here. Firstly, a transformer can vibrate and make a noise - but that doesn't mean the cause is necessarily DC on the mains. If it isn't, a DC blocker won't do any good. And anyway, according to this quite comprehensive analysis mains DC, the problem only occurs which toroidal transformers of about 300VA and above:
    http://sound.whsites.net/articles/xfmr-dc.htm

    EI transformers can be noisy because the laminations rattle. Tightening them and potting them will cure that.

    The above is mechanical noise coming straight off the transformer. Electrical noise is something else completely. The magnetic field radiated from the transformer can cause nearby circuits to hum, and rotating the transformer (particularly an EI type) can redirect the magnetic field away from circuit and reduce hum. However, it won't have any impact on mechanical buzzing.
    I'm guessing by the term 'electrical noise' you mean the noise that ends up coming from the speaker. I believe there are some simple measuring devices to detect magnetic field.
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