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Thread: Help needed from Electronic Experts

  1. #1
    Senior Member Guido's Avatar
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    Help needed from Electronic Experts

    I need some help from our electronic experts.
    Found the attached schematic of the input terminal from my main amps. These caps seem to be something like a subsonic filter. Problem is that they are electrolytic and carry the signal. Weird is that they are reversly polarized.

    Do i need them?
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    Senior Member LE15-Thumper's Avatar
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    Quote Originally Posted by Guido
    I need some help from our electronic experts.
    Found the attached schematic of the input terminal from my main amps. These caps seem to be something like a subsonic filter. Problem is that they are electrolytic and carry the signal. Weird is that they are reversly polarized.

    Do i need them?
    Do you need them ? Yes and no. It depends on whether or not there is a DC offset on the other side of them and/or a dc offset from your pre-amp. It is usually always a good idea to have coupling caps on the input of an amplifier. You don't know the condition of the signal is coming in.
    Being in series, you have an effective value of half the total. I would try a high quality 10uf@50V in place of one cap in each channel and put a jumper in each channel where the second cap is.
    Worst case is your bass output will suffer. You will then have to bump up the value of this cap untill you are happy with the sound. Usually 1uf and up is plenty for input coupling but it depends on the input impedance of the circuit following the cap.
    LE15-Thumper
    "Give me JBL, or give me death"

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    Senior Member LE15-Thumper's Avatar
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    Also, forgot to mention. They are back-to-back in that polarity to effectivley give you a non-polarized cap. Being that music is an ac voltage it is best to always use a nice fat value non-polar cap with a small .1uf bypass as well (connected in parallel) Say, like a 10uf polycarb with a .1uf film foil bypass.

    There are a lot of combinations you can try. Different values and different types of caps can really affect sound quality. Have some fun, fool around with it. Almost anything will sound better than Electrolytics. Some guys even try tanatlums with film-foil bypass.
    LE15-Thumper
    "Give me JBL, or give me death"

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    Senior Member Guido's Avatar
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    Thanks for help!

    I'll mess around with it

  5. #5
    Senior Member Ian Mackenzie's Avatar
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    Quote Originally Posted by Guido
    I need some help from our electronic experts.
    Found the attached schematic of the input terminal from my main amps. These caps seem to be something like a subsonic filter. Problem is that they are electrolytic and carry the signal. Weird is that they are reversly polarized.

    Do i need them?
    I would leave them in there and bypass with one 0.047 film foil across both electros.

    The 220uf is large enough to prevent any phase shift in the passband which is important, the natural rise in esr is the only issue but that is a subjective matter.

    The Doctor

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    Senior Member Guido's Avatar
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    Quote Originally Posted by Ian Mackenzie
    I would leave them in there and bypass with one 0.047 film foil across both electros.

    The 220uf is large enough to prevent any phase shift in the passband which is important, the natural rise in esr is the only issue but that is a subjective matter.

    The Doctor
    Thanks for that Ian.
    But why exactly a 0.047 uF? I have some nice 0.01 uF Wima film foil. Not good?

  7. #7
    Senior Member Ian Mackenzie's Avatar
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    Guido.

    0.01 will be fine

    The Doctor - Who

    Quote Originally Posted by Guido
    Thanks for that Ian.
    But why exactly a 0.047 uF? I have some nice 0.01 uF Wima film foil. Not good?

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