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Coupling caps

Discussion in 'Solid State' started by The Fuxtor, Sep 17, 2018.

  1. The Fuxtor

    The Fuxtor AK Subscriber Subscriber

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    Is it acceptable to use 2 polar caps tied together at negative and again at the positive to create a bi-polar cap for a capacitor coupled application? I would just order a bipolar, but getting them in larger uf seems hard to find?
     

     

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  2. stoutblock

    stoutblock If it sounds good, it is good... Subscriber

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    Lordy!

    Ah no...

    Get a film cap.
     
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  3. The Fuxtor

    The Fuxtor AK Subscriber Subscriber

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    Well this is for a Sansui 3000a, not a tube amp. The originals are 2 - 1000uf bipolar. Wish to increase them to 3000uf....
     
  4. ivandezande

    ivandezande Super Member

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    Yes, it's fine, except the value is 1/3 the combined I believe so they would have to be pretty large.
     
  5. The Fuxtor

    The Fuxtor AK Subscriber Subscriber

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    Easy to find large uf values in a package half the size of what's in this guy already! I'm sure I could easily fit 2 new caps in the same clamp. As long as it's gonna do the job properly....
     
  6. Bob

    Bob AK Subscriber Subscriber

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    yes, you can tie polar caps together at either the negative side or the positive side to form
    a non-polar. not optimal since it's not a designed-that-way cap but useable if necessity
    calls for it.

    it halves the individual value and may or may not affect the frequency signatures
    you may be able to hear.
     
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  7. The Fuxtor

    The Fuxtor AK Subscriber Subscriber

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    Well, this is essentially what I am wondering, would doing this be ok in this application?
     
  8. Bob

    Bob AK Subscriber Subscriber

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    could you post the portion of the schematic that uses one? two? 1000uf bipolar cap
    and what voltage (on cap, and in schematic?)

    1000 seems too large for coupling say driver to output stage, maybe as cathode bypass
    but not an absolute need for bipolar, PS? BP not needed there.

    a picture of the cap would also help.

    in general I'd say maybe-to-yes. with schematic I could go to just yes.
     
  9. Retrovert

    Retrovert AK Subscriber Subscriber

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    Electrolytic capacitors in the signal path create harmonic distortion because of the rectification effects of the dielectric, higher ESR, and dielectric absorption.

    For a coupling capacitor film is always the superior choice.

    But when film cannot be used, because of issues with the larger physical size or greater cost, building a portion of the capacitor from film can help reduce the ESR (like parallel resistors), and it can help with the higher frequency response because the charge moves and redistributes faster in a film capacitor than in an electrolytic. Bypass capacitor is the phrase for searching.
     
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  10. Bob

    Bob AK Subscriber Subscriber

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    we need to see the schematic - coupling is too general since coupling always applies where
    one end is attached to something different than the other end.

    1000uf is pretty large for a pure "coupling cap" even if its less than 10v in circuit.

    and if the original is electrolytic, and cost/availability/size/etc is an issue then improving
    the SQ is last on the list.

    although I routinely replace electrolytics and tantalums with films, and cheap low
    value ceramics with film and in certain cases, micas.
     
  11. Retrovert

    Retrovert AK Subscriber Subscriber

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    Large values are often used for output stages to avoid placing DC voltages on the speakers.
    1,000 uF = 19 Hz
     

     

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  12. Pio1980

    Pio1980 AK Member Subscriber

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    This may not be necessary for larger capacity elyticaps operating in biased charge coupled mode.
    Bypassing with a smaller film cap would be good practice.
     
  13. The Fuxtor

    The Fuxtor AK Subscriber Subscriber

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    This is the application! The Sansui 3000a originally never used these caps , but a service bulletin was released to address an issue , which was speakers catching fire! The mod included more components, but the nasty DC was meant to be filtered by these 2 bipolar 1000uf caps!
    http://audiokarma.org/forums/index.php?threads/3000a-mod-question.509180/
    This post includes a schematic
     
  14. Retrovert

    Retrovert AK Subscriber Subscriber

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    That's what happens when speakers don't pay protection money.

    Be a terrible shame if ya speakers was ta, ya know, catch fyah.
     
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  15. The Fuxtor

    The Fuxtor AK Subscriber Subscriber

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    Nice one!
     
  16. Pio1980

    Pio1980 AK Member Subscriber

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    Thnx, that's what I was afraid I'd see. Balanced power rails, so no charge coupled mode here, and no polar caps allowed.
    I remember this problem and the kits, but never did the upgrade mods myself. If only there were film caps in that value range, what has a Web search shown?
     

     

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  17. Bob

    Bob AK Subscriber Subscriber

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    if the electrical specs allow, use a nichicon ES muse which is bipolar. it is limited to 35v
    and about 1000uf. there are others if these limits are exceeded.
     
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  18. Pio1980

    Pio1980 AK Member Subscriber

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    Is there space to parallel two or three of these?
    Three may be overkill.
     
  19. The Fuxtor

    The Fuxtor AK Subscriber Subscriber

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    The old caps are huge .... I'm quite sure I could parallel 2 nichicon muse.....
    Seems the biggest bipolar I can find is 1000uf. Maybe my thinking is wrong, but I figured more capacitance here would help this ol girl out....
     
  20. Pio1980

    Pio1980 AK Member Subscriber

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    It is a fairly modest power rated amp by later standards, a larger value would extend bottom end into a lower impedance load, Sansui apparently considered the recommended value adequate.
     
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