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Toroidal power supply transformer noisier or quieter than EI?

Discussion in 'Shock Brother's DIY Amps' started by LetItGrowTone, Nov 30, 2020.

  1. LetItGrowTone

    LetItGrowTone Tele-Meister

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    I have a large tube bass amp that's a little noisy for several reasons. A large toroidal power supply transformer might be just one of the reasons. Outside diameter of the windings is almost 6", mounted half in half out of the chassis, and chassis is full of circuit boards and ribbon cables.

    My understanding was that a toroid is better at containing flux instead of leaking it. But I think I am asking about noise radiating from it into surrounding circuitry.

    (As part of a bigger project that I could talk about in another thread), I will consider blocking the hole and mounting an EI transformer on the *outside*.
     
  2. LightningPhil

    LightningPhil Tele-Meister

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    Toroidal is pretty good for keeping the field in. Though if you get too close with something too sensitive, hum will result.

    As the coils are on top of each other, there can be a sizeable capacitance coupling mains noise into the circuit - unless it has an electrostatic screen.

    What does the noise you have sound like?
     
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  3. LetItGrowTone

    LetItGrowTone Tele-Meister

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    Thank you.
    The usual hum and buzz, just a lot more than I think it should have.

    I have another tube amp that I assembled myself using a little coax and careful grounding, that is silent enough. So I think I could do better by rebuilding this one.

    It has circuit boards, ribbon cables, and 1/4W resistors that I can't see, so I might rebuild it using the older methods.
     
  4. LightningPhil

    LightningPhil Tele-Meister

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    Are there snubber caps across the rectifier diodes?
     
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  5. LetItGrowTone

    LetItGrowTone Tele-Meister

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    No.
    I did think of that. Researched what size to use. Haven't tried it yet.

    Did get tangled up looking into RC snubbers across the secondary too.
    Truth is I can't do the math or theory anymore.

    In the past I had great results with a choke in the B+ (after the first filter capacitors but *before* the plates), in a 2xEL34 circuit. Could do that here. Plenty of room to mount it on the outside of the chassis and wouldn't cost much.

    The choke above was 2H 200mA, and conveniently fit where the usual Fender choke for the screens was mounted. Same screw holes.
     
    Last edited: Nov 30, 2020
  6. printer2

    printer2 Poster Extraordinaire

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    Snubbers would do nothing for hum, buzz yes, or maybe.
     
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  7. tubelectron

    tubelectron Tele-Afflicted

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    In my Serial Tone Killer guitar amp, I started with a, Audio / Hi-Fi (Copland-made) Toroïdal transformer at first :

    [​IMG]

    I even added a sheilding shell bottom closed :

    [​IMG]

    No way : unbearable hum radiation induced to the circuits, impossible to eradicate completely.

    I finally replaced it with a good EI transformer with aluminium shield screens :

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]

    Perfect : No hum, no buzzz, no noise - total quietness. Merci, au revoir.

    I'm now suspicious about Toroïds... I used them in the past with success, that's true, but I don't think I'll start again.

    -tbln.
     
    Last edited: Dec 1, 2020
  8. LetItGrowTone

    LetItGrowTone Tele-Meister

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    I thank you very much for your post.
    I'll collate it with everything else I've read, but I tend to believe it.

    Have you verified that the aluminum shield makes a good difference?
     
  9. LetItGrowTone

    LetItGrowTone Tele-Meister

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    I am NOT criticizing the manufacturer (because they don't claim traditional construction methods), and because my complaint about it is mild - I haven't heard other reviewers complaining. It's a good company and a very good amp.

    I just want to show you what I'm looking at. Several ribbon cables (and the functionality that they enable) are omitted already:
    20201201_121812.jpg 20201201_121951.jpg
     
  10. tubelectron

    tubelectron Tele-Afflicted

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    For sure ! I duly checked it, of course. :)

    The 2 "C" screens that I put around the EI transformer are efficient : they really cut the magnetic radiated field from the transformer laminations.

    That said, the screen thickness must be at least 3-4mm. I used 4mm here. The thicker, the better.

    If I could have made a closed pot of 4mm aluminium for the Toroïd, it would have certainly have done the same, I guess. But arrived there, it wouldn't had presented advantages over the EI design.

    Another good point to do on a EI trafo : putting a flux band. It will help greatly to cut the electric radiated field from the transformer windings

    [​IMG]

    -tbln.
     
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  11. KirbyBarba

    KirbyBarba TDPRI Member

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    I had an odd experience with my Audio Research LS-25 HiFi preamp. It produced hum that was audible from the speakers and the chassis. I replaced the 4 6922 tubes and it became dead quiet again. I never thought tubes could cause the transformer to hum.
     
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  12. LetItGrowTone

    LetItGrowTone Tele-Meister

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    I see, thank you. But is that really a continuous "turn" around the transformer?
     
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  13. printer2

    printer2 Poster Extraordinaire

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    Just to mention, aluminum, copper and any other non-ferrous materials are generally transparent to a magnetic field.
     
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  14. El Famoso

    El Famoso Tele-Meister

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    R core transformers are very quiet. Not much stray flux and the construction and copper shield keep the electrical noise very low. 02A340A6-039A-411B-A8F2-D24C5EA9C057.jpeg
     
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  15. tubelectron

    tubelectron Tele-Afflicted

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    Yes it is, but it passes over the laminations, not in the windings window, just like shown on my picture above. Otherwise, it would act as a short-circuit.

    Well, aluminium seems not to be : I primarily made the test and it is clearly conclusive. Otherwise, I wouldn't hassle making those screens... ;)

    [​IMG]
    [​IMG]

    My pals at ALSTOM told me about that property of aluminium, and I was doubtful, but they were right : Aluminium proves to be an efficient barrier against magnetic radiation... :cool:

    That said, maybe not all aluminiums or alloys are equivalent. o_O

    I did not have copper to compare, but I have lead in 3mm thick : no efficiency at all. 2mm Steel was the worse material : it acted as a spreader...:eek:

    I even tested 0.1mm Mumetal foil all around the laminations : a pest to work, costy to buy, and totally useless ! :mad:

    [​IMG]
    [​IMG]
    [​IMG]

    Finally, aluminium screens proved to be the best, against all odds... :confused::cool:

    -tbln.
     
    Last edited: Dec 1, 2020
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  16. LetItGrowTone

    LetItGrowTone Tele-Meister

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    Ah, I see! Thank you again. :)
     
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  17. LetItGrowTone

    LetItGrowTone Tele-Meister

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    I've heard of them, that's all. What brand do you use?
     
  18. aging_rocker

    aging_rocker Tele-Afflicted

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    @tubelectron - just wanted to say that Serial Tone Killer amp is a (hum-free) thing of beauty.
     
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  19. tubelectron

    tubelectron Tele-Afflicted

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    Thanks @aging_rocker ! :)

    [​IMG]

    But yes, I really had a hard time :mad: because of that power Toroïdal transformer... A very bad surprise that now stops me from using them anymore - in favour of the EI design.

    -tbln.
     
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  20. LetItGrowTone

    LetItGrowTone Tele-Meister

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    And where did you buy the one in your photo?
     
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