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Transformer for NCC220

Discussion in 'd.i.y.' started by say it as it is, Apr 17, 2021.

  1. JimmyB

    JimmyB pfm Member

    That's a nice price and I could do with those extra windings. Are they centre potted (assuming toroids?) or any options for that?
     
  2. grahamdocman

    grahamdocman pfm Member

    Ah now a can of worms is just what you need for a good earth! :D I wouldn't take S-man and me trolling each other about mains transformers too seriously... It's just a stereo ... (but I'm right of course:p)...


    A philosophical question:
    While we're all trolling around searching the earth amongst the worms, does a toroidal TF give a different hum on a metal detector to an R or C core TF or do only bees hum. :rolleyes::)
     
    Mike Hanson likes this.
  3. muchtoofast

    muchtoofast pfm Member

    ...and where are all the bees ;)
     
  4. a.palfreyman

    a.palfreyman pfm Member

    LMAO?: Lick my an4l orif1ce / laugh my ar5e 0ff / like melons and oranges.... etc?
    One sez 'I hear it', one sez 'not possible'.
    How do we prove it one way or the other (serious question, please Jez, don't beat me :eek:)? I certainly know that psu impedance can affect the 'sound' of the circuit being supplied.
     
  5. muchtoofast

    muchtoofast pfm Member

    Well, changing the transformer in the PSU to the pre-amp would be quite interesting.

    I replaced a FlatCap with a HiCap, and then a cheap LM317 reg board of my own with an R core 100VA.

    Everything sounded different in some way, but probably more to do with wiring layout and the regulators.

    The 100VA R core was most definately thinner sounding with less 'life', but as stated, this was also coupled with an inferior reg board.

    I didn't want to destroy the HiCap to this degree at the time by replacing just the transformer.

    Maybe someone has done this?

    As for Power Amps, maybe too far down the line of amplification to make much of a difference? To me, as long as it's got enough welly to push those cones in and out properly and in an idle state, doesn't sound like its about to take off, I'm happy.
     
  6. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    Impedance can have huge effects yes. Dynamic impedance is set almost entirely by the smoothing caps and if a regulated supply is used then it's entirely in the hands of the regulators. Remember that the transformer is only even connected around the peaks of half cycles. So long as it can provide enough current to keep the smoothing caps charged without over heating then its done its job.
     
  7. a.palfreyman

    a.palfreyman pfm Member

    Cheers Jez, I think I understand where you are coming from. However I do wonder if the separate transformer windings (for + and - supplies) interact, particularly with class AB where essentially (if I understand correctly) the amp acts as two half-amplifiers. The positive output swings fed from the + supply to centre-tap couple with the negative supply via the windings due to dynamic loading; whilst the negative output swings fed from the - supply to centre-tap couple with the positive supply via the windings, again due to dynamic loading. Presumably though, this would only occur during the charging phase as the diodes isolate the windings when not conducting? I remember reading some time ago about transformers on ESP and the 'mess' that ensues during charging. Wouldn't surprise me if there were notable interactions that were more audible in class AB amps than class A as these are essentially a reasonably constant current drain in comparison, again IIUC.
     
  8. S-Man

    S-Man Kinkless Tetrode Admirer


    I have done a lot of experiments with transformers, rectifiers, caps and regs.
    IME for low current supplies an EI transfomer is often markedly preferable to toroids irrespective of what is downstream.
    For power amps the distinction is less clear cut. Low impedance seems to be the most beneficial attribute of a power transformer for power amps.

    Before Bollox-Meister shouts me down, maybe it's worth considering the imperfections of transformers and the possible effects these could have:
    https://www.nutsvolts.com/magazine/article/a-transformer-tutorial
    (This does not include the capacitive effects and noise coupling etc.)

    The interaction of the leakage reactance with the rectifier characeristics and ESL of smoothing caps is rather complex. Yes, it's only "connected" for a short period during charging, but consider that many tens of amps with much HF content can flow during this period and that it happens 100 times per second!

    I would recommend doing your own experiments to find out for yourself.
     
    Last edited: Apr 29, 2021
  9. DaveMc64

    DaveMc64 pfm Member

    Snubbing capacitors, if present, are effectively coupling HFs over the entire cycle if just mounted across the diodes. Diodes also have an intrinsic variable capacitance dependant on the reverse voltage which also couples ouside the conduction period although the capacitance drops off quite rapidly as the reverse voltage increases.
     
  10. a.palfreyman

    a.palfreyman pfm Member

    Yes, if you say a typical charging period of about 3.3ms, that is 1 full wave at 300Hz or thereabouts.
    Might have to try something along the lines of setting up a transformer with +/ct/-, load both halves with a resistive load and then modulate one side with say 1kHz (via a capacitor) and see if anything happens on the other rail. Problem is I suppose that the load presented by the power supply will require a power-amp to drive such a low impedance....
    and of course you are feeding a triangular wave into the output of the amp.
    Only other method I can think of is to play a 'snippet' that sounds different and record this at the speaker terminal with soundcard/computer then repeat after the transformer change. Then compare (invert one and add?) to see what the differences are?
     
    Mike Hanson likes this.
  11. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    ...or you could simply simulate it... it comes into its own when you need to see what happens when you push a 100A waveform through a 0.001R resistance into some load and all without smoke...

    FWIW I consider the whole shebang of transformers, rectifiers, snubbers, mains noise, smoothing capacitor brand irrelevant to sound quality.
     
  12. James Evans

    James Evans Bedroom Bodger

    Out of interest, what diameter and height did they quote?
     
  13. say it as it is

    say it as it is pfm Member

    sorry cant remember the height, am sure they quoted 125mm diameter

    when they arrive I will measure them up and put up some pics, mine are being made on 400VA spindles as I have requested extra windings for my mains voltage so regular ones might be smaller again
     
  14. James Evans

    James Evans Bedroom Bodger

  15. say it as it is

    say it as it is pfm Member

    as mine have the extra winding to operate at 250v they measure 130mm dia by 55mm high
    look well made and fact they are the supplier to Rega, yet happy to custom build at sensible cost appealed to me.
    Added bonus is the option of 240 or 250 primary means if I ever move or sell them on be fine.
    once I power them up will check for hum but Stephen at Tiger seemed very confident they will be silent when made to my voltage and fully screened

    [​IMG]IMG_20210509_234222017[1]
     
  16. bugbear

    bugbear pfm Member

    Tiger Toroids? How interesting. They're (very!) local to me.

    BugBear
     
    muchtoofast likes this.
  17. Marra

    Marra pfm Member

    If it's like the one they made for me it will be nice and quiet.
     
  18. muchtoofast

    muchtoofast pfm Member

    Looks very cool! Wonder if they do them in green :p
     
  19. say it as it is

    say it as it is pfm Member

    no idea the colour was not a concern, when Stephen talked to me on the phone it was clear he knew his stuff and fully understood what I was looking for being familiar with the industry and quickly put me at ease that I had found a good supplier.
     
  20. muchtoofast

    muchtoofast pfm Member

    Yours looks like a sparkling tiger colour to me:). Tempted now to try a 500VA HiCap clone toroid from them :D
     

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