PFFB (Post-Filter Feedback)
PFFB (Post-Filter Feedback) is a circuit technique that dramatically reduces distortion in Class-D amps under real-world speaker loads. Amps with proper PFFB (like the 3e Audio A7) measure and sound noticeably cleaner than plain TPA3255 designs.
PFFB (Post-Filter Feedback) is a circuit technique where the amplifier feedback loop is taken from AFTER the output low-pass filter, not before it (which is the traditional approach). This seemingly small change dramatically improves how a Class-D amp behaves when connected to a real speaker.
Why it matters
Traditional Class-D amps have a problem: their frequency response and distortion depend heavily on the speaker impedance. Connect a 4Ω speaker and the treble drops. Connect an 8Ω speaker and it stays flat. Not ideal.
PFFB fixes this by making the amp’s output insensitive to load. Frequency response stays flat with any speaker. THD drops noticeably. The result is a Class-D amp that behaves more like a well-designed Class-AB amp.
Where you’ll find it
Not all TPA3255-based amps implement PFFB properly. The ones that do include: AIYIMA A80, 3e Audio A7 (“Enhanced PFFB” — one of the best implementations in budget hi-fi), Fosi ZA3.
Common myths & realities
PFFB is marketing fluff
Independent ASR measurements show measurable improvements in load-independent frequency response and lower THD.
Sources & further reading
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