Overview

The SM-SX300 is a 1-bit (delta-sigma) digital power amplifier released in 2004. Manufacturer specs list 150 W per channel into 8 Ω, THD 0.05%, S/N 105 dB, and 5 Hz–100 kHz bandwidth[3]. Contemporary reports put street pricing around 17,000 USD[4]. The chassis featured premium construction such as a copper enclosure and gold-plated connectors.

Scientific Validity

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Based on manufacturer data (no comprehensive third-party lab results found), S/N at 105 dB and wide bandwidth are solid, but THD at 0.05% (1 kHz/1 W) misses typical “transparent” targets (~0.01% or below)[3][11]. By contrast, current designs at similar power commonly achieve THD+N ≈0.006% and SNR 108–110 dB[1]. As such, audible transparency is plausible in many uses, yet not at today’s best-in-class level; score set to 0.4[10][16].

Technology Level

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The 1-bit switching approach (64 fs relative to 44.1 kHz) was forward-leaning in its time[5]. However, modern GaN-based Class-D platforms have surpassed it in efficiency and linearity, and are broadly adopted. On present-day yardsticks, sophistication ranks below current industry leaders; 0.3.

Cost-Performance

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Comparator must be the cheapest equal-or-better solution[9][13]. Class D Audio Premium GaN 6.0 provides equivalent user-facing function (stereo power amplification) and equal-or-better measured performance (150 W/8 Ω, THD+N 0.006%, SNR 108–110 dB)[1], versus the SM-SX300’s 150 W/8 Ω, THD 0.05%, S/N 105 dB[3]. Using current list prices:
975 USD ÷ 17,000 USD = 0.057 → rounded to 0.1.
Because a cheaper equal-or-better option exists, CP is fixed at 0.1.

Reliability & Support

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This is a 2004 model[3]. As a discontinued, vintage unit, factory warranty/support and parts logistics are limited versus current production gear. Age-related component risk further lowers practical reliability, hence 0.2.

Rationality of Design Philosophy

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Pursuing lower distortion via short digital paths is scientifically coherent, but the product’s very high price with only moderate measured advantage versus today’s common Class-D solutions limits the rational value proposition; 0.5[6].

Advice

Unless you collect historical digital amps, a modern stereo power amp (e.g., Class D Audio Premium GaN 6.0) will deliver lower distortion/noise at a small fraction of the price[1]. If you need multi-zone plus DSP and network manageability, a distribution amp such as NAD’s CI 8-150 DSP is appropriate[2]. Both routes offer measurably superior value.

References

[1] Class D Audio, “Premium GaN 6.0 Balanced 2-Channel Amplifier 150W RMS into 8 Ω,” https://classdaudio.com/product/gan-fet-amplifiers-3/ , accessed 2025-08-15. Key specs: 150 W/8 Ω, THD+N 0.006% (1 kHz/1 W), SNR 108–110 dB.
[2] NAD Electronics, “CI 8-150 DSP Multi-Channel Amplifier,” https://nadelectronics.com/product/ci-8-150-multi-channel-amplifier/ , accessed 2025-08-15. Key specs page incl. 8×150 W@8 Ω, THD 0.02%, DSP/Web UI.
[3] HiFi Engine, “Sharp SM-SX300 Manual,” https://www.hifiengine.com/manual_library/sharp/sm-sx300.shtml , accessed 2025-08-15. Key specs: 150 W/8 Ω, THD 0.05%, S/N 105 dB, 5 Hz–100 kHz, year 2004.
[4] Gizmodo, “Sharp SM-SX300-H Amplifier,” https://gizmodo.com/sharp-sm-sx300-h-amplifier-18415 , accessed 2025-08-15. Price mention (~17,000 USD).
[5] HiFi-Wiki, “Sharp SM-SX 300,” https://hifi-wiki.com/index.php/Sharp_SM-SX_300 , accessed 2025-08-15. Note on 64 fs switching approach.
[6] NAD Electronics (product page narrative/feature list), https://nadelectronics.com/product/ci-8-150-multi-channel-amplifier/ , accessed 2025-08-15.

(2025.8.15)