Input transformers

Discussion in 'DIY' started by Cspirou, Sep 28, 2015.

  1. Cspirou

    Cspirou They call me Sparky

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    I have been looking at schematics for a bunch of tube amps. Most of them are couple with a capacitor or just a resistor. However a few of them have input transformers. I assumed that transformers in the signal path added distortion and was undesirable.

    So does anyone know why I would want an input transformer?
     
  2. OJneg

    OJneg The Most Insufferable

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    • Convert balanced, differential signal for a single-ended input stage. Gets you best CMRR
    • Use a slight step up. Sometimes 1:2 or 1:4. This gets you some extra gain obviously. Must ensure the preceding stage has reasonably low Zout.
    • Isolation. Both primary inputs are essentially floating. Ensures no ground loops.
     
  3. shipsupt

    shipsupt Admin

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  4. dBel84

    dBel84 Friend

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    The quality of the transformer as well as the design of the amp will impact the effect on the sound. (profound I know)

    ..dB
     
  5. Steve Eddy

    Steve Eddy Acquaintance

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    A good quality input transformer will be audibly transparent.

    se
     
  6. dBel84

    dBel84 Friend

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    its impact is conspicuously absent by its presence ... such magical devices

    ..dB
     
  7. Steve Eddy

    Steve Eddy Acquaintance

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    Not quite sure how to interpret that.

    se
     
  8. OJneg

    OJneg The Most Insufferable

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    I'm curious to test input transformers for phono and mic pre applications. I'm going to try to find some cheapies to prototype first.
     

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