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Thread: mains Voltage

  1. #11
    Join Date: Feb 2008

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    Unfortunetly,these days most equipment [Still using a normal mains transformer, not switched mode] designated to be used within the EU' is supplied with a power transformer that is designed for 230v, the theory is; that it should work fine between 220v, and 240v, however, a lot of the equipment I have had in for repair, and tested needs only 220v, and sometimes less to work optimally, so in theory, it has at least 20v over what the equipment is designed for!
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  2. #12
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    Ive used a few 220v things and found 230v is fine. 240v isn't. either a regenerator or a bucking tx/variac are needed.
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  3. #13
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    Steve, you could contact Airlink, who should be able to supply a balanced mains transformer with 220v output. Be cheaper than a mains regen unit.
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  4. #14
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    Good sugestion Ali.
    A...
    Quote Originally Posted by Ali Tait View Post
    Steve, you could contact Airlink, who should be able to supply a balanced mains transformer with 220v output. Be cheaper than a mains regen unit.
    "Today scientists have substituted mathematics for experiments, and they wander off through equation after equation, and eventually build a structure which has no relation to reality"
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  5. #15
    Join Date: Oct 2016

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    You could fix the buzzing in the headphone amp by stopping its mains transformer from rattling. Basically the laminations that make up the transformer core are rattling/chattering as they are magnetised by the mains. Sometimes you can tune out the rattling by adjusting the tightness of the screws which are holding the transformer laminations together. Sometimes the transformer hasn't been potted well - maybe not all - but you can still do something about that. Transformers are dipped in varnish to pot them. You could do the same, or maybe even just drip some varnish on the top so it soaks into the laminations. Use oil-based varnish, not the modern "quick drying, low odour" water-based stuff.

    It's possible that the problem isn't so much the high mains voltage as an effective DC component on the mains.
    This explains it: http://www.isol-8.co.uk/dc_on_the_mains.html

  6. #16
    Join Date: Feb 2008

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    Yes,agree, Noise, and DC element on the mains can cause transformers to sing along with the mains, especialy toroids, and it can be worse at diffrent times of the day, this is definitely something to be considered!
    Quote Originally Posted by RothwellAudio View Post
    You could fix the buzzing in the headphone amp by stopping its mains transformer from rattling. Basically the laminations that make up the transformer core are rattling/chattering as they are magnetised by the mains. Sometimes you can tune out the rattling by adjusting the tightness of the screws which are holding the transformer laminations together. Sometimes the transformer hasn't been potted well - maybe not all - but you can still do something about that. Transformers are dipped in varnish to pot them. You could do the same, or maybe even just drip some varnish on the top so it soaks into the laminations. Use oil-based varnish, not the modern "quick drying, low odour" water-based stuff.

    It's possible that the problem isn't so much the high mains voltage as an effective DC component on the mains.
    This explains it: http://www.isol-8.co.uk/dc_on_the_mains.html
    "Today scientists have substituted mathematics for experiments, and they wander off through equation after equation, and eventually build a structure which has no relation to reality"
    Nikola Tesla


  7. #17
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    Yes indeed. Steve, if you go the Airlink route, get them to fit a DC blocker to the input.
    There are times when you canít do the sensible thing, when you canít act like a responsible adult at all; you just have to do whatever insane thing comes into your head. When bad people do it they end up murderers, when good people do it they end up heroes, and when the rest of us do it we end up looking like total idiots. But whenís that ever stopped us?

  8. #18
    Join Date: Jan 2009

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    In times past electronic gear used to be fitted with mains voltage selectors which selected the appropriate tapping on the transformer primary. This was because the transformers used were designed deliberately to be run close to saturation to improve regulation. If extra turns were wound on the primary to increase the saturation margin, the increased resistance would result in poorer regulation.

    When a transformer saturates the inductance falls and the primary current rises. Saturation can be caused either by running the primary on too high a mains voltage or by having some DC on the mains (which is effectively is similar, but only occuring each cycle, rather than every half cycle). It only takes ~100mV of DC offset to cause toroidal transformers to buzz (owing to a lack of air gap in the core, toroidals 'hard limit' when saturated).

    Early power supplies were unsophisticated, so it was important not to compromise regulation, but modern regulated power supplies can be supplied with a transformer that has a much larger saturation margin, and hence no need for a mains voltage selector.

    However regardless of the margin of saturation, if the laminations are loose they will buzz, simply due to the AC nature of the mains supply.
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  9. #19
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    Quote Originally Posted by Barry View Post
    In times past electronic gear used to be fitted with mains voltage selectors which selected the appropriate tapping on the transformer primary. This was because the transformers used were designed deliberately to be run close to saturation to improve regulation. If extra turns were wound on the primary to increase the saturation margin, the increased resistance would result in poorer regulation.

    When a transformer saturates the inductance falls and the primary current rises. Saturation can be caused either by running the primary on too high a mains voltage or by having some DC on the mains (which is effectively is similar, but only occuring each cycle, rather than every half cycle). It only takes ~100mV of DC offset to cause toroidal transformers to buzz (owing to a lack of air gap in the core, toroidals 'hard limit' when saturated).

    Early power supplies were unsophisticated, so it was important not to compromise regulation, but modern regulated power supplies can be supplied with a transformer that has a much larger saturation margin, and hence no need for a mains voltage selector.

    However regardless of the margin of saturation, if the laminations are loose they will buzz, simply due to the AC nature of the mains supply.
    "Today scientists have substituted mathematics for experiments, and they wander off through equation after equation, and eventually build a structure which has no relation to reality"
    Nikola Tesla


  10. #20
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    A lot for me to think about here folks. Many thanks.
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