Overview

Fosi Audio’s ZA3 is a palm-sized Class-D power amplifier based on TI’s TPA3255. Notable features at this price include a balanced combo input (XLR/¼” TRS), stereo/mono PBTL switch, 12V trigger-in, active subwoofer out, and five DIP8 op-amp sockets for rolling. With the 48V/5A PSU, the maker specifies 155 W×2 @4Ω (stereo) or 235 W×1 @4Ω (mono), SINAD 89 dB, SNR ≥106 dB, THD <0.006%, and FR 20 Hz–20 kHz (±0.1 dB). Independent measurements confirm generally low distortion/noise but report protection at sustained high power into 4Ω with both channels driven and that the sub-out does not high-pass the mains. [1][2]

Scientific Validity

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Manufacturer specs (with 48V/5A PSU): SINAD 89 dB, SNR ≥106 dB, THD <0.006%, FR 20 Hz–20 kHz (±0.1 dB), noise floor ≈150 μV; power 155 W×2 (4Ω, stereo) / 235 W×1 (4Ω, mono). [1]
Third-party results: Erin’s Audio Corner shows load-dependent behavior; in 4Ω stereo sustained testing the amp goes into protect, while shorter “burst” windows yield higher numbers. The main speaker outputs are full-range even when sub-out is engaged (mains not high-passed; sub LPF ≈120 Hz, −3 dB). Test rig: QA402, 22.4 kHz BW, 4/8 Ω loads, both channels loaded; reactive loads also evaluated. [2]
Interpretation: Distortion/noise are well below audibility in typical use. Treat 155 W×2 as an upper bound rather than continuous 4Ω two-channel sine capability. [1][2]

Technology Level

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TPA3255 platforms are common, but the ZA3’s balanced combo input, PBTL mono, 12V trigger, and five socketed op-amps in a compact chassis remain uncommon under 200 USD. The design refines thermal layout (side vents, chassis heatsinking) and modularity without exotic or proprietary silicon. [1][2]

Cost-Performance

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ZA3 current price (with 48V/5A PSU): 149.99 USD. [1]
Cheapest equal-or-better comparator (balanced input, comparable “transparent-class” measured behavior): AIYIMA A70 — 199 USD. [3]
At this time the ZA3 is the world’s cheapest product meeting the required balanced I/O + stereo/mono + measured transparency set among reputable brands; therefore CP = 1.0 by rule. [1][2][3]

Reliability & Support

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Two-year warranty and broad distribution; simple Class-D topology and quality passives (NCC/ELNA, WIMA, Sumida) are positives. Op-amp rolling is supported but must be done carefully to avoid instability or damage. [1][2]

Rationality of Design Philosophy

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Function-first feature set (balanced, PBTL, trigger, sub-out) at low cost aligns with transparent-performance goals. The no-HPF mains with sub-out is a design compromise; otherwise, engineering choices are pragmatic for measurement-first users. [1][2]

Advice

Great value when you need balanced input, plan for mono bridging someday, or want a compact power stage for desks/small-to-mid rooms. For 2.1 systems, implement bass management upstream (DAC/pre-DSP) since mains are full-range. If you routinely drive 4Ω speakers loudly for long durations, consider dual ZA3 in mono or a higher-current alternative. [1][2][3]

References

[1] Fosi Audio — “Fosi Audio ZA3 Balanced Stereo Amplifier (Stereo/Mono, XLR/TRS, 12V Trigger, specs & variants).” https://fosiaudio.com/products/fosi-audio-za3-balanced-dual-mode-class-d-amplifier (accessed Aug 26, 2025). Key specs: 48V/5A rated power 155 W×2 (stereo) / 235 W×1 (mono); SINAD 89 dB; SNR ≥106 dB; THD <0.006%; FR ±0.1 dB; five DIP8 op-amps; price options incl. 149.99 USD with 48V/5A PSU.
[2] Erin’s Audio Corner — “Fosi Audio ZA3 Balanced Stereo Amplifier Review.” https://erinsaudiocorner.com/electronics/fosi_za3/ (published Mar 16, 2024; accessed Aug 26, 2025). QA402, both channels loaded; 4 Ω & 8 Ω; 22.4 kHz BW; burst vs sustained; sub-out does not high-pass mains; protection at sustained 4 Ω stereo.
[3] AIYIMA — “A70” (balanced XLR/TRS, PFFB, price). https://www.aiyima.com/products/aiyima-a70 (accessed Aug 26, 2025). 199 USD.
[4] Amazon US — “Fosi Audio ZA3 listing: balanced combo input & 12V trigger text.” https://www.amazon.com/dp/B0CLP4T5L7 (accessed Aug 26, 2025).
[5] Audio Science Review — “Fosi Audio ZA3 Amplifier Review.” https://www.audiosciencereview.com/forum/index.php?threads/fosi-audio-za3-amplifier-review.52139/ (published Feb 10, 2024; accessed Aug 26, 2025).

(2025.9.15)