Overview

The Topping PA5 II is a compact desktop Class-D power amplifier specified at 100 W ×2 into 4 Ω (at 1 % THD) with both TRS balanced and RCA inputs in a 16.6 × 12.9 × 4.1 cm chassis. It provides a 12 V trigger, ships with a 38 V/3 A supply, and targets transparent, load-invariant behavior from a balanced signal path. [2][3][4]

Scientific Validity

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Manufacturer-published specs (PA5 II): THD+N as low as 0.0004 % @ 4 Ω, 5 W (balanced), and 0.0003 % @ 8 Ω, 5 W; frequency response 20 Hz–40 kHz (±0.3 dB); dynamic range/SNR 121 dB (A-wt @1 kHz); crosstalk −90 dB @1 kHz; noise <15 µVrms (A-wt). These comfortably clear transparency thresholds (THD+N ≤0.01 %, DR/SNR ≥105 dB). [2][3]

Third-party evidence (closely related PA5 II Plus): Independent measurements report ~600 kHz switching with well-attenuated ultrasonic content and damping factor >100 across the band (very low output impedance). Power testing shows ≈102 W/4 Ω (both channels) at 0.1 % THD+N for the Plus model, consistent with Topping’s 100 W/4 Ω theme for the non-Plus at stricter distortion limits than brochure 1 %. [4][1]

Technology Level

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Balanced desktop Class-D implementation with sensible features (balanced/TRS input, 12 V trigger) executed to a high measured standard. The design follows well-understood TI-based Class-D practices rather than introducing novel topologies or proprietary control schemes. Solid engineering, modest innovation. [2][4]

Cost-Performance

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Market price (denominator): 199 USD. We surveyed balanced desktop power amps with equal-or-better functions and measured performance. None cheaper than PA5 II met or exceeded its key specs (e.g., THD+N ≈0.0004 % @5 W/4 Ω and SNR ≈121 dB). Examples of excluded (inferior) candidates: SMSL AO200 MKII (THD+N 0.004 %, SNR 106 dB) [6]; AIYIMA A70 (THD+N 0.0015 % @1 W, SNR ≥116 dB) [7]; Sabaj A20a 2022 (THD+N 0.004 %, SNR 103 dB) [8]. Therefore, no cheaper equal-or-better option exists → CP = 1.0. [2][3][6][7][8]

Reliability & Support

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Topping’s desktop line has wide distribution and typical warranty coverage. The PA5 II series addresses prior-generation concerns with a refreshed platform and higher damping-factor behavior observed in independent tests of the Plus variant. Still, warranty length and service differentiation are average. [4]

Rationality of Design Philosophy

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Prioritizing measurable transparency (very low THD+N, high DR, low output impedance) in a compact, balanced form is rational and aligns with fidelity-first goals. The approach focuses on audible performance rather than cosmetic or myth-driven features. [2][3][4]

Advice

Choose PA5 II if you specifically want a compact balanced desktop power amp with verified transparent-class specs and a tidy trigger-friendly stack. If you only need “audibly transparent” at the lowest price and can accept inferior measured margins, options like Fosi ZA3 are cheaper but do not meet or exceed PA5 II’s measurement levels; they are therefore excluded from CP. [5][6][7][8]

References

[1] Archimago’s Musings, “Part II: Topping PA5 Mk II Plus (PA5II+) Class D amplifier review,” Oct 28, 2023. Power at 0.1 % THD; both channels; 4/8 Ω loads; Cosmos ADC. https://archimago.blogspot.com/2023/10/part-ii-topping-pa5-mk-ii-plus-pa5ii.html
[2] Apos Audio, “TOPPING PA5 II / PA5 II Plus – Specs,” accessed Aug 20, 2025. THD+N @5 W (4/8 Ω), dimensions, inputs. https://apos.audio/products/topping-pa5ii-plus-amplifier
[3] Audiophonics, “TOPPING PA5 II Class D Amplifier Balanced 2×100 W 4 Ω,” accessed Aug 20, 2025. DR/SNR 121 dB, FR ±0.3 dB, crosstalk −90 dB, noise <15 µV, power specs. https://www.audiophonics.fr/en/integrated-amplifiers/topping-pa5-ii-class-d-amplifier-balanced-2x100w-4-ohm-silver-p-18003.html
[4] Archimago’s Musings, “Part I: Topping PA5 Mk II Plus (PA5II+)…,” Oct 21, 2023. ~600 kHz switching, damping factor >100, input/gain notes. https://archimago.blogspot.com/2023/10/part-i-topping-pa5-mk-ii-plus-pa5ii.html
[5] Erin’s Audio Corner, “Fosi Audio ZA3 Balanced Stereo Amplifier – Measurements,” Mar 16, 2024. https://erinsaudiocorner.com/electronics/fosi_za3/
[6] Linsoul, “SMSL AO200 MKII – Technical Details,” accessed Aug 20, 2025. THD+N 0.004 %, SNR 106 dB. https://www.linsoul.com/products/smsl-ao200-mkii
[7] AIYIMA, “A70 – Product Page / Specs,” accessed Aug 20, 2025. THD 0.0015 % (@1 W), SNR ≥116 dB. https://www.aiyima.com/products/aiyima-a70
[8] Audiophonics, “Sabaj A20a 2022 – Specs,” accessed Aug 20, 2025. THD+N 0.004 %, SNR 103 dB. https://www.audiophonics.fr/en/hifi-devices/sabaj-a20a-2022-amplifier-stereo-class-d-infineon-ma5332m-bluetooth-50-2x170w-1x350w-4-ohm-p-17037.html

(2025.8.20)