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hummmmming toroidal transformers

Discussion in 'd.i.y.' started by firestorm, May 11, 2021.

  1. John Phillips

    John Phillips pfm Member

    I guess that's right. A humming transformer is probably not a safety failure in kit designed for the entire "230 V" region (as was the 1995 free market objective). So we are left with having to fix something that isn't considered a "real" problem. The last time I designed and built a power amplifier was in the early 1980s and IIRC a good transformer was a simpler task to select then.
     
  2. bugbear

    bugbear pfm Member

    Linguistic aside: the conventional word is "nominal"; 2x4s don't measure 2 inches by 4 inches, 35mm film is not quite 35mm and so on.

    https://en.wikipedia.org/wiki/Real_versus_nominal_value

    BugBear
     
    laverda likes this.
  3. CJ14

    CJ14 Retired

    Naim and many other companies have trouble with humming transformer. I built two of these monster test units for Naim one stayed in the UK the other I took from Scotland via Dover to Prague to there custom transformer manufactures by car.
    It looked for vibration and listenen to Hum, you could adjust input voltage and waveform and the DC offset.
    It looked for harmonics in the vibration, so you could be certain it was lams or wire or just crap that was singing to the mains.
    [​IMG]
     
    nobeone, MJS, mega lord and 5 others like this.
  4. say it as it is

    say it as it is pfm Member


    Well not questioning naim efforts to reduce hum but like many owners or past owners like myself did suffer excessive hum that Naim classed as a characteristic yet other amps seem to fair better
     
    CJ14 likes this.
  5. firestorm

    firestorm pfm Member

    CJ14 - impressive looking test rig.
    What's inside it? Variac?
    Signal generator with a big AF amp to generate the AC?
    Some sort of transducer setup on the platform with cascaded low-pass filters, comparator circuits?
     
  6. CJ14

    CJ14 Retired

    In side was a 10KW amp, with a random generator, a pulse generator and a DC add on isolated from the amp.
    Narrow band filter that had microphone and hall effect detection in as you say a bunch of comparator, it was so interesting in Prague it could detect trucks and from the harmonic you tell if it was Volvo or a dust cart.
    It also was very delicate as it's test platform was suspended on PTFE and magnetic floaters. It took 8wk each to make and calibrate, a bloody nightmare to be honest. But all analogue nice, and very heavy at 60Kgs.
    It would find unglued lams and joined lams and lose vibrating wires, and check saturation of the core as the signal flat toped.
    I think I still have the circuit I will check. Catch XXII became Tellurium Q when Geoff joined me to sell some IP stuff I had under the name of I.P.I Technology Ltd https://find-and-update.company-information.service.gov.uk/company/06383382
     
    firestorm and mega lord like this.
  7. CJ14

    CJ14 Retired

  8. Gervais Cote

    Gervais Cote Predator

    Nice machine but it seems Naim forgot to use it on my NAP 250.2...............
     
  9. CJ14

    CJ14 Retired

    That is a shame, how old is it?
     
  10. Gervais Cote

    Gervais Cote Predator

    From 2009 IIRC
    Fully recapped in 2020, tantalum and electrolytics.
     
    CJ14 likes this.
  11. MJS

    MJS Technical Tinkerer

    Interesting stuff.
    I was at Naim when they were measuring stray fields and noise and trying to find the best way to wire and select those Nuvotem transformers. I saw the massive pile of rejects. I don't understand why they persist with a manufacturer when there are plenty of others that know how to do it. I mean Holden and Fisher could do it properly half a century ago.

    I suspect that their choice of low, flat, boxes necessitates a pancake design for their transformers and this probably has a influence on how tightly the windings can be made or how big the core can be. This is just my opinion. When I designed my amps I went for a more square design that lent itself to a more optimized transformer shape.
     
  12. say it as it is

    say it as it is pfm Member

    Not knocking Naim great that they went to such lengths to try and cure the issues, but yes seems their choice of supplier is the issue as the H&F does seem quieter.
     
  13. Gervais Cote

    Gervais Cote Predator

    The quiet H&F transformers are one of the reasons why I prefer my chrome bumper kit to my classic 2009/2011 Naim gears.
     
  14. 337alant

    337alant Negatively Biased

    I think the height restriction in the Naim case and possibly coinciding with the EU harmonisation of standards for the 230VAC is probably the reason for the uncanny rise in customers complaining about humming transformers, particularly in the UK as we haven't actually changed from the 240VAC +- 10%
    Anyway I am really surprised for the price of their amplifiers that they haven't done more for their customer service (ISO 9001 QMS) than just saying its an artefact, like if you want our amplifiers you have to accept our humming transformers on our power amp and our excessive hiss from our pre amps LOL

    Alan
     
    Garrard 401, CJ14 and MJS like this.
  15. CJ14

    CJ14 Retired

    In the Claymore the transformer part no was 916, we chatted with Peter Harris at the time at Airlink and managed to get the vibration down by adding 20% more turn on the primary and pre dipping the core in a soft resin.
    Then by loading the MC/MM input we turned the transformer to reduce the hum pick up, caused by the cable exit from the toroidal, fun day .
    Oh at the time UK mains was supposed to be 240VAC, but we saw all over the UK anything from 196VAC - 262VAC oh lovely. And some place were there was lots of power demand from factories we had as much as 10VDC on top of the AC and sometime flat topping in the day time.
    Let all go solar and do night shift, so we can listen to music in the sunshine.
     
    mega lord likes this.
  16. 40imp

    40imp Member

    I think that a lot of this humming with toroidal transformers is due to them being run at too a high a flux density for purely cost reasons. The 20% increase in primary winding turns is a clue. That will reduce flux density so they knew what they were doing. Otherwise its a larger core. Canterbury Windings make a point of this.
     
    CJ14 likes this.
  17. CJ14

    CJ14 Retired

    S.P.O. If you worked for Plessey you will get this if not, 337alant dead right a common mistake made by many transformer companies not using the right material that should be based on the spec of there calculations.
     
  18. firestorm

    firestorm pfm Member

    Quick update
    I've ordered the following from Tiger Toroids:
    • Designed for low noise
    • Multi-tap primary which allows for 220,230,240,250V (In reality 0, 10V, 230V, 250V taps)
    • 2 x 18-0-18
    • Rated for 450VA on an oversize core allowing for more primary winding
    • GOSS band
    • Electrostatic screen
    • Centre-potted
    • Varnished windings

    Should get it in a couple of weeks.
    Really looking forward to it.

    I'll probably use it on the 240V tap. My amp is running on the VARIAC (set to 230V out) and sounding very sweet.
    Runs cooler and consumes less energy, about 240W instead of 262W straight on the mains.
     
  19. firestorm

    firestorm pfm Member

    Trivia
    Steve @ Tiger Toroids provided Terry (?) at Canterbury Windings with some of the winding gear.
    Tiger Toroids also supply Rega with trafos.
     
  20. say it as it is

    say it as it is pfm Member

    yes when I spoke to Stephen he certainly knew his stuff and was happy to help and not just sell stuff, yes told me thy have been supplying Rega for a long time, that for me was big plus
     

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