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Thread: Power amp transformer hum

  1. #1
    Join Date: Jul 2012

    Location: Benson, Oxfordshire

    Posts: 490
    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 isnít an issue, on the rare occasion though that I listen at quiet volumes for a bit of background music itís 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: Oct 2016

    Location: Bolton, England

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    I'm Andrew.

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    Quote Originally Posted by alcarmichael View Post
    Any advice on what to do to help prevent transformer hum?...
    The amp in question is an Avondale ZAP 250 ...
    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.

  4. #4
    Join Date: Jan 2009

    Location: Essex

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    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?
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  5. #5
    Join Date: Jul 2012

    Location: Benson, Oxfordshire

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    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!?

  6. #6
    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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  7. #7
    Join Date: Jan 2009

    Location: Essex

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    I'm openingabottleofwine.

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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.
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  8. #8
    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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  9. #9
    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

  10. #10
    Join Date: Jul 2012

    Location: Benson, Oxfordshire

    Posts: 490
    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 Iíll have to try a DC blocker such as this.

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