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Thread: Changing a Quad 405-2 transformer that has a buzz/hum

  1. #11
    Join Date: Feb 2008

    Location: Middlesex, UK

    Posts: 4,282
    I'm Alex.

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    It was fairly early on in production that this mechanical noise was reported, I think Quad soon got to grips with it. I was disappointed with mine as it was the first brand new piece of Quad equipment that I bought, and it was not cheap. I am very happy with it now though!
    Spendorman

  2. #12
    Join Date: May 2013

    Location: Milton Keynes

    Posts: 362
    I'm Martin.

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    Quote Originally Posted by high.spirits View Post
    Let me dig out the paperwork tomorrow and I will see if I can find the original photos showing connections to the existing transformer wiring. A picture paints a thousand words!
    Just had a look to see what I had done and I have connected the following wires to the existing transformer wires. If you have the Quad wiring diagram the transformer terminals are numbered. This has illiminated the voltage switching so permantly 240v.

    Torodial Orange & Black to Quad xformer green wire (terminal 7A linked 6A, 7B, 6B on xformer)
    Torodial Yellow to Quad yellow (outer terminal 5B linked to 8A)
    Torodial Red to Quad yellow ( inner 8B linked to 5A)

    I hope that helps.
    GyroDec 2M Black, Amplification: Luxman 505ux.
    Loudspeakers: Harbeth HL-K6

    Quad 99 CD, Amplifier: Teac A H 500i, Loudspeakers: SCM11

    Receiver: Teac CR H500, Loudspeakers: B&W CDM 1NT

  3. #13
    Join Date: Jan 2009

    Location: Essex

    Posts: 23,806
    I'm openingabottleofwine.

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    Thanks, that confirms what I wrote in post 10.
    Barry

  4. #14
    Join Date: May 2020

    Location: NorthWest

    Posts: 42
    I'm Philip.

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    Martin, thank you for checking. The way you describe your wiring is different to how Barry describes in post 10. Or is that essentially the same thing? His description is how I would have thought best to do it - Red and Orange to Rectifier. Black and Yellow form centre tap to ground.

    I've just spoken to Quad and double checked the price of a replacement transformer. It's not as much as I seemed to remember, coming in at 90 inc vat. The torodial that we are discussing comes in at 86 (plus a little to have a mounting plate made) so I'm currently mulling over my options. The torodial would be the better transformer in theory, but the original style may be a safer bet in terms of fit, and possible re-sale (though I have zero plans to sell my 405's).

    I've got four 405's and really love them as amplifiers. They sound great with my speakers and are a joy to tinker with or work on. I would be interested to know if anyone has noticed an audible difference with a torodial?
    Never underestimate the power of stupid people in large numbers...

  5. #15
    Join Date: Feb 2008

    Location: Middlesex, UK

    Posts: 4,282
    I'm Alex.

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    That Quad price for a replacement transformer seems pretty good, I'd go for that, but others probably will have different views.
    Spendorman

  6. #16
    Join Date: Jan 2009

    Location: Essex

    Posts: 23,806
    I'm openingabottleofwine.

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    Quote Originally Posted by HarryCrumb View Post
    Martin, thank you for checking. The way you describe your wiring is different to how Barry describes in post 10. Or is that essentially the same thing? His description is how I would have thought best to do it - Red and Orange to Rectifier. Black and Yellow form centre tap to ground.

    I've just spoken to Quad and double checked the price of a replacement transformer. It's not as much as I seemed to remember, coming in at 90 inc vat. The torodial that we are discussing comes in at 86 (plus a little to have a mounting plate made) so I'm currently mulling over my options. The torodial would be the better transformer in theory, but the original style may be a safer bet in terms of fit, and possible re-sale (though I have zero plans to sell my 405's).

    I've got four 405's and really love them as amplifiers. They sound great with my speakers and are a joy to tinker with or work on. I would be interested to know if anyone has noticed an audible difference with a torodial?
    I think Martin and I are saying the same: Black and Yellow joined together to form a centre tap to the 0V rail (green wire on the Quad transformer), with the Red and Orange wires going to the bridge rectifier and replacing the yellow wires on the Quad transformer.

    I have three stereo 405s (with various levels of upgrade and improvement) and two of which have been 'monoblocked' (i.e. converted to single channel amplifiers) and extensively modified. However, in all of them the potted Quad transformer has been retained (and all are mechanically silent).

    If it was up to me - I would replace your buzzing transformer with a Quad replacement. The cost is virtually the same, the new transformer is guaranteed to fit, and more importantly the resale value of your amp would be preserved.
    Barry

  7. #17
    Join Date: May 2020

    Location: NorthWest

    Posts: 42
    I'm Philip.

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    Thanks for everyones comments. I was in the neighbourhood on Monday...sort of.... So I called in at IAG House and picked one up. Not quite as new and shiny as the torodial may have been, and I will forever wonder how it would have looked, but there you go. I agree that a guaranteed fit and re-sale value are important enough.

    I'm going to bypass the voltage selector as I don't see any benefit of having it wired in, and I'm going to hard-wire it for 240v as per the later Quad 405-2. Diagram below;

    Never underestimate the power of stupid people in large numbers...

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