I'm designing a PCB where I could use one layer as massive groundplane and shield. Do I have to make some form of shield for THT part pins, or are they small enough to not pickup a lot of electromagnetic interference? (Device works in audio range, so mostly I seek to eliminate the mains hum)

Edit 30/12/2023: Okay since I see this went very in-depth: the problem I am dealing with is guitar tone control panel/ pickup mounting spots which I even try to make into PCB just because of pcb rigidity and the fact that one could really make the most of cheap pcb assembly more than any practical concern about hum, I was just considering whether to go THT - which exposes at the very least the tips of components mounted on the other side or to go SMD route which makes the ground plane whole.

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    \$\begingroup\$ Mains hum is quite low and low frequencies are not the easiest things to shield. I would say that if 60Hz hum is your concern, there are more important things to worry about than the anti-pads in the ground plane. \$\endgroup\$
    – DKNguyen
    Nov 28, 2023 at 3:33

1 Answer 1


Ground plane will have the most benefit at high frequencies, which is still of concern for audio circuitry as RFI can become detected (rectified) by semiconductor junctions, whether discrete (transistors) or in ICs.

This is the origin of the occasionally-familiar beeping and popping sounds heard when a GSM cellphone sits near poor-quality audio equipment.

Good mitigation for which, might include ferrite beads at the input wires, a small ceramic capacitor to ground, and a ground plane around the circuit.

Mains hum essentially flows on DC current paths, for any size of circuit we care about. Electrostatic coupling is avoided by using low circuit node impedances (typically audio circuits use ballpark 10kΩ or lower, which is fine) and shielding (ground plane also helps greatly with this), while ground loop is avoided by using differential inputs.

Note that unbalanced connectors, like RCA jacks, can still be treated differentially for purposes of breaking ground loop. A key insight, perhaps, is that impedances attached to the two terminals need not be balanced. I don't have the slightest clue why this is so uncommon in audio equipment; it's not hard to do, and can be done in a way that respects both RF immunity and audio fidelity.

  • \$\begingroup\$ Hi, you can see the edited question, but just to answer to your comment, it's connected to the rest of circuit with 2 wire audio jack so I don't know if there is real potential for differential input unless I modify it to somehow also accept 3 wire jacks and make it fit both regular amplifier and the one with differential input. \$\endgroup\$ Dec 30, 2023 at 19:54
  • \$\begingroup\$ Having a ground plane fill most of the board area, solves most issues with electrostatic coupling. I doubt your application is sensitive enough to need more, or care about THT vs SMT. But if you find it's better with a shield, that's something you can always add anyway. \$\endgroup\$ Dec 30, 2023 at 20:30

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