Can bipolar capacitors be used instead of polar capacitors?

Discussion in 'DIY' started by birchoak, Jun 21, 2018.

  1. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    All those changes would very likely have been made at the factory and other changes would probably also have been made to accommodate them. Sometimes the designers make a mistake and/or a circuit behaves differently to their calculations so these kinds of changes are made, to achieve a performance, function, or stability goal. The changes above are definitely NOT applicable to other situations in this equipment, or in any other equipment.

    In my opinion using a bipolar electrolytic instead of a polar electrolytic is a bad idea, but a solution nevertheless. (if the reason is that you just don't have a polar one available). Film capacitor replacements for polar or bipolar electrolytics is always a good idea, space permitting.
     
    Last edited: Jul 6, 2018

     

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  2. birchoak

    birchoak Hi-Fi Nut Subscriber

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    Could you clarify? Also, does your handle refer to the Hyperion series written by Dan Simmons? If so, one of the greatest modern sci-fi series, an absolute joy.
     
  3. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    To clarify
    If there are other positions where (for example) a ceramic 0.47uF 50V cap is installed - then it is NOT ok to change them for 10uF 16V bipolar electrolytic capacitors. Just in case you might have thought that to be the case, there is a lot of talk about capacitor substitutions in this thread. ;)
    It would be nice to be associated with such a sci-fi series - but I heard the name somewhere and liked it - nothing more significant than that. :)
     
  4. birchoak

    birchoak Hi-Fi Nut Subscriber

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    Thank you for the clarification. If it's gear I really care about, I tend to be very, very careful about uF values (I've heard no more than 10% +/- deviation) and never go below the V although I do go above it if it will physically fit on the PCB.
     
    Hyperion likes this.
  5. Powertech

    Powertech Active Member

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    I think that the answer to the OP is ………. It all depends on the situation.
    Particular caps are normally used for a specific reason, sometimes through a designers habit (they worked in previous designs, so I will use them again) but sometimes particular caps are used purely because they were available with a good deal on a bulk purchase. But if changing types and values, you need to fully understand the application.
    Example:-
    In my NAD C320 (which I use purely as a preamp in an active system) the original preamp modules had 10uF/50V polarised electrolytic caps in the output lines. These are there because these discrete class A modules exhibit a standing voltage of about 0.4 volts at their output. I have replaced these modules with differential OPamp based circuits using OPA2143 OPamps, the ones with high impedance jFET front ends. The in-line caps at the outputs of the circuits have been removed because there is now no DC voltage standing on the line. Had I used NE5532 Opamps I would have retained the caps but made them 1uF film caps as the NE5532 does leave a very small offset voltage at it's output. The caps are there in the first place because a standing voltage applied to a following volume pot will make it go scratchy over time. There is still a small cap at the preamp output (2uF film type), but that is there in combination with a resistor to counter any HF oscillation from reactive inductance effects from connecting leads and to act as a high pass filter set around 3Hz.

    So you can see that I have changed, deleted or replaced capacitors, but only after fully analysing their purpose and changes to the specific application. When dealing with like for like replacement, you have to consider a number of factors. Firstly, why is a capacitor there in the first place - what is it's intended function. Secondly, consider the age of the equipment - this may sound daft, but ideas change over time. Remember that a lot of the early solid state designers had grown up with valve based equipment and that these require a different mindset due to the voltages involved. Also, component availability has changed over the years. So you can see that there are so many factors to consider, that no one can really give a generalised answer to your original question - It all depends!
     
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