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Thread: Power amp transformer hum

  1. #51
    Join Date: Nov 2015

    Location: Wolverhampton

    Posts: 6,240
    I'm Oliver.

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    This is what I wish I'd had the ability to put into words. Great post.
    Quote Originally Posted by sq225917 View Post
    1. A loosely wound transformer can vibrate/hum. If this is mechanically coupled into the chassis it will be amplified by the casework. It coupled into valves it can come out of the speakers. Refit the traffo, try soft mounts, pads, tight/loose screw mounting.
    2. DC riding on the mains. if it adjusts in sound during the day then this is likely, could be over voltage though. Get a DC blocker, get one rated to handle up to 3 volts. Soljstrom audio do a couple, they work. DC on the trafo can couple into the core and come through as noise from subsequent stages.
    3. Overvoltage, can saturate the core, cause physical hum and can come through subsequent stages. Not much you can do here other than measure it and respec new trafo's.
    4. Toroids have a gap in the winding where the wires go through, this is usually a quiet spot. If you have 100hz noise coupling into the system try rotating the traffo, if wire length allows, so you can point the quiet bit at the sensitive wires. (Honestly though, fix your ground loops, minimize your loop area and take care of circuit decoupling properly).
    Analogue: Technics SP10 MK2 > Phonomac AT-1010 MK5 tonearm > Ortofon Kontrapunkt b > Bigbottle Jfet MC Valve Phonostage (Telefunken & Tesla Valves)
    Digital: NONE
    Amplification: Nelson Pass DCB1 & Monarchy Audio SM-70 Class A Amplifier
    Cables: Fisual S-Flex Speaker Cable & SPOTFIRE IC Cables & NEW SPOTFIRE Tonearm cable
    Speakers: Pioneer CS-77A

  2. #52
    Join Date: Aug 2012

    Location: Hartlepool UK

    Posts: 1,383
    I'm Alan.

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    I've had a few torroidal transformers from Terry at Canterbury Winding's and they have all been quiet and excellent quality
    My mains varies between 240 -250 so I always ask him for 240V primary, Goss band and electrostatic screen
    http://www.canterburywindings.co.uk/standard_range.html
    Those Torroidy ones look very well made may try some of them on my next amp build

    Alan
    Turntable - Garrard 401/Jelco 750L/Ortofon Kontrapunkt B, Pioneer PLC 590, SME 3009/2 , Denon DL103R - DIY Paradise Phono stage - Reel 2 Reel Studer A810, Otari MX55,Tascam BR20 - Digital HTPC / Young Dac - Preamp - DIY B4, 821, Power Amp's DIY Voyager Mono Block, Speakers Tannoy precision 6.4 / Wilmslow Kit Volt BM220.8 / Scanspeak D2905/9500

  3. #53
    Join Date: Aug 2011

    Location: Coventry, England UK

    Posts: 503
    I'm Simon.

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    Quote Originally Posted by RothwellAudio View Post
    I think you're barking up the wrong tree there. Yes, electricity meters can make a noise, but there's no reason why that should necessarily cause the speakers to buzz. The problem lies elsewhere imo.
    Could be, I just find it strange that 1 amp doesn't let it through but the others do. I can only think it has something in the circuit to filter/clean it. Going by my sample is that a buzz or hum? Should it be coming through both tweeter and woofer?

  4. #54
    Join Date: Oct 2016

    Location: Bolton, England

    Posts: 1,380
    I'm Andrew.

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    Quote Originally Posted by Simon_LDT View Post
    Could be, I just find it strange that 1 amp doesn't let it through but the others do. I can only think it has something in the circuit to filter/clean it. Going by my sample is that a buzz or hum? Should it be coming through both tweeter and woofer?
    I would class that as buzzing rather than humming. I don't think it's a case of some amps "letting the noise through" and one amp blocking the noise. Rather it's a case of one amp having a very low noise floor and the others not. The fact that the noise sounds similar to what you hear from the electricity meter doesn't mean the noise is being "let through". It's just at the same frequency because it has the same origin - 50Hz AC mains.

  5. #55
    Join Date: Jan 2008

    Location: Gerrards Cross

    Posts: 2,112
    I'm Tony.

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    Over the last few years we have come across more TX's actually buzzing through the speakers, rather than a mechanical hum,

    Electrically generated noise seems to be the common bugbear currently, usually the TX just needs be swung to find its happy point.
    As Simon covered all of the basics for you guys should help you in the future deal with any untoward TX related issues you may come across.

    We are fortunate enough to have in house TX facilities, however when we have used outside contractors Air-link have always delivered what was asked, though if you do opt for this route, at the very least have a screen on the primary winding's that taken to ground.
    Coherent Systems
    Real high end sound with musicality not hifi

  6. #56
    Join Date: Jan 2009

    Location: Sheffield - UK

    Posts: 6,072
    I'm Mark.

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    You need one of these:




    100% Analogue

  7. #57
    Join Date: Aug 2011

    Location: Coventry, England UK

    Posts: 503
    I'm Simon.

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    What's that Mark?

  8. #58
    Join Date: Apr 2018

    Location: Cornwall

    Posts: 134
    I'm Dominic.

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    Mains DC blocker?
    CD player = Vincent
    Pre amp = Rotel RA03
    Power amp = Lyngdorf SDA 2175
    Speaks = Quadral Chromium Style 6

  9. #59
    Join Date: Jan 2009

    Location: Sheffield - UK

    Posts: 6,072
    I'm Mark.

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    Yep, mains DC blocker - made it yesterday .

    100% Analogue

  10. #60
    Join Date: Aug 2011

    Location: Coventry, England UK

    Posts: 503
    I'm Simon.

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    Already have one and it doesn't get rid of the buzzing.

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