In the circuit below:

enter image description here

I often see capacitors like C4 added in the feedback path of a non-inverting audio amplifier, and often times I heard that it acts like a high-pass filter.


At low frequencies, C4 is open, and at high frequencies, C4 is a short circuit.

But R1 isn't changed. And there is no "DC blocking capacitor" shown by default. So does placing a capacitor in series with the "low-side feedback resistor" (R2 in the circuit) make the amplifier a high pass filter or a high shelf filter?

  • 2
    \$\begingroup\$ I would say high shelf. At low frequencies, the gain is unity, and at high frequencies, the gain is 12. \$\endgroup\$ – BeB00 Jun 19 '18 at 17:31
  • \$\begingroup\$ Thanks! Everyone keeps saying that it's a "high pass" and I believed it until I saw that there was no blocking capacitor, so yeah, it must be high shelf, not high pass. You'd need another capacitor and resistor ahead of the amp to do that. \$\endgroup\$ – El Ectric Jun 19 '18 at 17:43
  • 1
    \$\begingroup\$ Try read this electronics.stackexchange.com/questions/374867/… and this electronics.stackexchange.com/questions/377355/… \$\endgroup\$ – G36 Jun 19 '18 at 17:54
  • \$\begingroup\$ When in doubt, try only the equivalent passive filter, sometimes it provides a clearer answer. \$\endgroup\$ – a concerned citizen Jun 19 '18 at 18:27

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