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I've come across a video on a popular and well-respected electronics channel on Youtube where they say that even bipolar capacitors have a preferred orientation in a circuit that minimizes hum and interference etc. They describe an oscilloscope based method to determine that orientation of the capacitor that is easy enough to implement.

I wonder, however, once that capacitor polarity is determined, how to find out which way to put the cap into the PCB .. without knowing too much about the circuit or the schematics. Is there a multimeter or oscilloscope based measurement that could be carried out? The capacitor is supposed to go into the board so that one side goes in direction of lower impedance and the other in direction of higher impedance. Positions of electrolytic caps are labeled + and -, but PCBs are not typically labeled that way for bipolar caps, and schematics of circuits are not always available.

I understand that most people would consider this overkill on most circuits, but I'm interested if it's technically possible to carry out the corresponding measurement on the PCB side of things. Thanks!

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    \$\begingroup\$ As I understand it, this applies to conventional capacitors in a "can." That is, capacitors with a metal housing. If you connect the leg of the capacitor that is the outside of the can to the ground of the circuit, then you will have less hum in your audio. So, look for capacitors which have one side grounded. Other than that, figuring out which connection on the board has lower impedance is tricky and probably not worth doing. \$\endgroup\$
    – JRE
    Commented Mar 17, 2019 at 19:13
  • \$\begingroup\$ Thanks for your reply. They specifically test newer Mica caps which I thought have no metal housing? \$\endgroup\$
    – bs448c
    Commented Mar 17, 2019 at 19:32
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    \$\begingroup\$ Also would apply to layered capacitors that have the top and bottom layers attached to the same pin (or end of the SMD part.) \$\endgroup\$
    – JRE
    Commented Mar 17, 2019 at 19:42
  • \$\begingroup\$ What you say about different ends going to the sides with lower and higher impedance sounds fishy at first glance (although what @JRE said about the can being on the ground side, makes sense). Maybe you could post the Youtube link? Also, are you talking about bipolar electrolytic capacitors, or non-electrolytic capacitors (which are, technically, bipolar, but aren't called out as such)? \$\endgroup\$
    – Eamon
    Commented Apr 27, 2019 at 1:37

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If you have a capacitance meter, you can wrap the capacitor in aluminum foil and measure the capacitance between each lead and the foil. The lead connected to the outer wrapper (or can) will have a slightly higher capacitance; you may be able to detect this. If your capacitance meter has a 'guard' terminal, connect this to the unused capacitor lead -- this will create a more significant change between measurements of each lead.

Note the capacitance you may measure will be quite small -- few pF, and you will need a stable and repeatable setup.

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