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Thread: Power amp transformer hum

  1. #1
    Join Date: Jul 2012

    Location: Wimborne

    Posts: 701
    I'm Alex.

    Default Power amp transformer hum

    Any advice on what to do to help prevent transformer hum? I believe the first thing to try would be a DC blocker type thing but have done a bit of research and these can possibly have a bit of a negative effect on power amps. Anything else I can try?

    The amp in question is an Avondale ZAP 250 and when listening to music at anything other than very quiet the hum isn’t an issue, on the rare occasion though that I listen at quiet volumes for a bit of background music it’s annoying!

  2. #2
    Join Date: Jan 2008

    Location: Gerrards Cross

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    I'm Tony.

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    Is the noise actual transformer hum or an electrical noise through the speakers?
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  3. #3
    Join Date: Jan 2009

    Location: Essex

    Posts: 31,853
    I'm openingabottleofwine.

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    Without a source connected, is the hum electrical (i.e can be heard when listening close to the speaker), or is it mechanical (i.e. can be heard when listening close to the amplifier)?

    Is the transformer in the ampifier a toroid?
    Barry

  4. #4
    Join Date: Jul 2012

    Location: Wimborne

    Posts: 701
    I'm Alex.

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    Quote Originally Posted by RothwellAudio View Post
    Contact Avondale Audio. I'm sure they'll be very helpful.
    Sometimes just tightening a screw somewhere can be enough to reduce any vibration and quieten things down considerably.
    I keep meaning to do this! It’s the obvious starting point!

    Quote Originally Posted by Mr. C View Post
    Is the noise actual transformer hum or an electrical noise through the speakers?
    Actual transformer hum.

    Quote Originally Posted by Barry View Post
    Without a source connected, is the hum electrical (i.e can be heard when listening close to the speaker), or is it mechanical (i.e. can be heard when listening close to the amplifier)?

    Is the transformer in the ampifier a toroid?
    The amp hums with absolutely nothing connected to it, it does so when connected to different mains sockets.

    I assume it’s a toroid, I’m not certain though, I don’t even know what other types there are!?

  5. #5
    Join Date: Apr 2016

    Location: Bishops Stortford

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    I'm Chris.

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    If the hum is mechanical and if you feel,comfortable, this is what I would do.

    Put the amp on till it hums then remove the top to see if this in itself has had an effect. Then bare down on various parts of the chassis and transformer with a wooden stick. You may well find that tightening down or a new rubber washer will sort things out.

    Good luck
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  6. #6
    Join Date: Jan 2009

    Location: Essex

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    Toroidal transformers are prone to mechanical 'hum' if there is some DC present on the mains (> 100mV). But other transformer designs can vibrate mechanically at the mains frequency (and hence 'hum) if the laminations are not tighened up.

    I would suggest you contact Avondale and seek their opinion and advice.
    Barry

  7. #7
    Join Date: May 2017

    Location: West Sussex, UK

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    I'm Steve.

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    Quote Originally Posted by Barry View Post
    Toroidal transformers are prone to mechanical 'hum' if there is some DC present on the mains (> 100mV). But other transformer designs can vibrate mechanically at the mains frequency (and hence 'hum) if the laminations are not tighened up.

    I would suggest you contact Avondale and seek their opinion and advice.
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  8. #8
    Join Date: May 2018

    Location: London

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    I'm Tommy.

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    I'm using a dc blocker for my amp. And it works very well. For your use I will advise to try one out.
    The reputation is various because of various reasons. Some are also quite expensive. Actually you can get them very cheap on eBay, and they do the work.
    Actually my experience is that if you first have the hum and remove it with dc blocker, your amp will make a better sounding stage. Better dynamics and headroom ( maybe of most part because the noise flour is lower). Either way it is a plus for audio listening.

    Here is a link for what I'm using

    https://m.ebay.com/itm/DC-trap-block...e/131654666919

    Tommy

  9. #9
    Join Date: Jul 2012

    Location: Wimborne

    Posts: 701
    I'm Alex.

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    I have sent Avondale an email seeking their advice, should I not make any progress off the back of their reply I’ll have to try a DC blocker such as this.

  10. #10
    Bigman80 Guest

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    A DC blocker is unlikely to eradicate the problem. I use one and they still buzz, although it does reduce it *very little*

    I have transformers which have Mechanical buzz, which is what you have.

    The ONLY way to entirely rectify it, is to replace the TFs with audiophile quality ones. Airlink and Toriody (I like Toriody) have audiophile quality TFs but drop them an email and specify that's what they are for.

    I've used multiple cheaper Chinese alternatives and ended up throwing them out due to the noise they make

    They buzz because the laminations arent glued together 100%. Whilst this has no bearing on functionality, it does make them noisy.

    This one is in my valve phonostage, after chucking the noisy Chinese bought one. Worth every penny.

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