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ALOT of Coupling Transformers?

Discussion in 'Electronic Design' started by Barry Reise, Dec 9, 2011.

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  1. Barry Reise

    Barry Reise Guest

    Can anyone suggest a supplier that stocks ALOT of audio coupling
    transformers?

    I am looking for something outside of the standard values.

    In particular 16R primary, with secondary somewhere in the range of
    50R-100R.

    I am using the low end of the band, so these resistances would be more
    like at DC (via DMM) than the usual 1KHz.

    Thanks for any pointers.

    Or ... if I need to wind my own, what type of core is suitable for a
    manual hand winder, and available through the usual outlets?

    Barry Reise
     
  2. Phil Allison

    Phil Allison Guest

    "Barry Reise"
    ** You post makes very little sense.

    You must specify the frequencies and power level involved and if you need
    isolation between the input and output.

    Or better still, say what you are trying to do.


    .... Phil
     
  3. Phil Allison

    Phil Allison Guest

    "Robert Macy"

    The 'gotcha' is going ot be that low cutoff frequency. 10Hz not so
    bad, but even going down to 1 Hz,


    ** The OP asked for an "audio" transformer - so the lowest frequency is
    20Hz.

    Let him say if it is otherwise in his app.



    .... Phil
     
  4. Barry Reise

    Barry Reise Guest

    Thank you for your reply.

    The "DC" referred to measurement of the winding resistance via DMM,
    not an impedance meter. IOW it was not the lower freq limit.

    Some "audio" transformer will do 10Hz, but 20Hz would be OK. Top end
    2KHz. 10W power rating. Apart form the 16R pri and 50/100R sec, that's
    all that matters.

    I am really looking for a supplier who has a wide range these things
    off-the-shelf. If not, I would need to source a type of core I can
    wind myself without industrial equipment.

    The suggestion to use the secondary of a mains transformer is
    something I had looked into. But a center-tap is not going to provide
    complete isolation. And completely split secondary windings are
    usually equal resistance, ie 12-0-12V. This does not provide the
    desired ratio.

    Barry
     
  5. Phil Allison

    Phil Allison Guest

    "Barry Reise"

    ** The 953-0398 toroidal tranny from Element 14 is all you need.

    Twin 115 volt primaries and twin 25 volt secondaries with a 50VA rating at
    50 Hz - wire the primaries in parallel and the secondaries in series to
    get 115V to 50V.

    Scale that down to 20 Hz and the relevant voltages change to 46V to 20V.

    For 10 watts at 16 ohms you need 12.6 volts - so 20 gives a nice margin.

    A cheaper alternative is the similar E core 178-0860 - this will be less
    good at high frequencies and draw far more magnetising current.

    You pays your money and takes your choice ....



    .... Phil
     
  6. Phil Allison

    Phil Allison Guest

    "Robert Macy"


    Keyword is 'might work', because many of those AC mains transformers
    have their performance peak at 50/60Hz and purposely reduce higher
    frequencies.

    ** Most are good to a few kHz and toroidal types work well out to 50kHz or
    more.


    Worse, they're usually higher coercivity material [since
    with AC mains the 'signal' is always there] which means that if used
    for audio the transformer disappears at low signal levels,


    ** Absurd nonsense.



    .... Phil
     
  7. Guest

  8. Phil Allison

    Phil Allison Guest

    "Robert Macy"

    What is the EXACT URL for "...953-0398 toroidal tranny from Element
    14..." ?

    ** It's Farnell under a new name.

    http://au.element14.com/



    .... Phil
     
  9. Barry Reise

    Barry Reise Guest

    OK, they're on my Christmas list.

    And why did they ever change their name from Far--nell to
    El--e--ment--four--teen? I thought electronics guys were smart.

    Barry
     
  10. Phil Allison

    Phil Allison Guest

    "Robert Macy"
    "Phil Allison"
    "Robert Macy"
    Why do you say "** Absurd nonsense." ??


    ** Because no such effect exists.

    Consider that the laminated cores used in the vast majority of AC power
    transformers and audio output transformers the same - ie silicon steel,
    grain oriented or possibly not.

    Toroidal AC power transformers all use grain oriented silicon steel, the
    exact same cores are used for audio applications.

    You need to test some REAL transformers if you still think everyone is
    wrong.


    .... Phil
     
  11. Tim Williams

    Tim Williams Guest

    Only if you're operating in the low frequency limit where inductance is
    critical. Generally, where mu_r is over a thousand under all conditions,
    it's high enough not to notice.

    To be precise, coercivity isn't the property that produces this effect,
    because coercivity is measured with a fully saturating waveform. Small
    signal effects occur in their own (very small) hysteresis loops. However,
    the physical mechanism ("sticky" magnetic domains) is the same.

    As for frequency response, Phil is correct about toroidials -- they are
    good enough to have been used in some fairly involved tube amplifiers.
    The leakage is small enough that lots of NFB can be used (cathode
    feedback, global, etc.) while maintaining the high bandwidth (~50kHz).

    Tim
     
  12. Phil Allison

    Phil Allison Guest

    "Tim Williams"

    ** The OP will of course complain that those are specially made
    ransformers - just like E-Core types used in tube amplifiers are specially
    designed with many layers of winding sandwiched together to reduce leakage
    inductance.

    OTOH - my comment was about regular, off the shelf AC power transformers.
    I have tested any number of them and at least in the step down role,
    bandwidth is around 100kHz.

    Another plus is the extremely low magnetising current - right up until
    saturation begins. Means distortion products will be completely negligible
    long as the saturation limit is not reached.

    The only drawback is sensitivity it DC current in the windings, so tube
    balance in push-pull output stages is critical.



    .... Phil
     
  13. John Doe

    John Doe Guest

    Do your really think so, Philly?
    --
     
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