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I am trying to output PWM from an MCU, filter it with a LPF to form an analog signal, cascade an audio volume control that allows for smooth control between silence and a somewhat amplified signal, and output the result to headphones (Z ~ 32Ω).

How can I cascade the stages so that the audio volume control circuit (which would use a digital potentiometer) doesn't impact the impedance of the LFP and mess with the cut off frequency?

I would also like to minimize the impact of the external load (from the headphones) on the cut off frequency of the LPF.

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  • \$\begingroup\$ Please add a schematic of your current circuit if you could. Without additional information adding an op amp buffer would probably be sufficient. \$\endgroup\$ – Captainj2001 Nov 26 '19 at 16:39
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For audio work, op amps are inexpensive and nearly ideal in their response. So, either use an active filter for your low pass, or add an op amp buffer between stages for isolation.

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