One is a streaming all-in-one and the other is an amplifier. Judge them on how many boxes you want and what you already own, not on the spec sheet alone.
| Area | Better | Why |
|---|
| Power | B | NAD C 399 has more power - 180W against 130W into 8 ohms. That is about 1.4dB, which is a small step in loudness but real headroom on peaks. |
| Room size | depends | We rate Arcam SA30 the better fit for desk or near-field listening, a small room and a mid-size room, and NAD C 399 for a very large room. Match the amplifier to the room you actually have, not the one you want. |
| Grip on hard loads | A | Arcam SA30 holds up better into a 4-ohm load: its output increases strongly to 200W, where the other barely increases. That matters with demanding speakers far more than the 8-ohm figure does. |
| Noise floor | A | Arcam SA30 is the quieter design on paper - 112dB against 95dB. Audible mainly with sensitive speakers in a quiet room. |
| Built-in DAC | B | Both decode on board. NAD C 399 goes higher - 384kHz against 192kHz. Very few recordings exist above 192kHz, so treat this as headroom, not as sound quality. |
| Streaming | A | Only Arcam SA30 has AirPlay 2, Chromecast and Roon. |
| Analogue inputs | A | Arcam SA30 takes more analogue sources - 4 against 2. |
| Room to grow | evenly matched | The same expansion options on both. |
| Amplifier class | depends | Arcam SA30 is Class G and NAD C 399 is Class D. Class G/H switches its supply rails to cut the heat a Class A/B design wastes; Class D runs cool and draws almost nothing at idle. Modern examples of both measure well - judge by the rest of the page. |
| Price | B | NAD C 399 costs less - $2,899 against $3,300 at list. |
| Watts per dollar | B | NAD C 399 is the cheaper watt - about $16 per watt against $25. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A Arcam SA30 B NAD C 399
depends neither is better in the abstract - it turns on your room, your system or how you will use them. Only specs published for both amplifiers are judged; anything missing on either side is left out rather than guessed.
Which should you choose?
The usual trade-off: Arcam SA30 measures better, NAD C 399 costs about 12% less. With most speakers in most rooms that gap is smaller in practice than it looks here. If your speakers are a difficult load - 4 ohms nominal, big woofers, or a sensitivity in the low 80s - Arcam SA30 is the safer partner, because how an amplifier behaves when the impedance drops matters more than its 8-ohm rating.
What a spec sheet cannot show: how either sounds with your speakers, how the controls feel day to day, and what the app is like to live with - which is where most all-in-one amplifiers are actually won or lost. Power figures are the manufacturers' own and are not measured to a common standard, so treat small differences as noise. If you can hear both, that will tell you more than any row above.