These are not the same size of amplifier: NAD C 399 has roughly 2x the power of Yamaha A-S1200. That is about 3dB, so it is a question of room size and how hard your speakers are to drive, not of one being the better amplifier.
| Area | Better | Why |
|---|
| Power | B | NAD C 399 has more power - 180W against 90W into 8 ohms. That is about 3dB, so it plays usefully louder before it runs out and has more in hand on peaks. |
| Room size | depends | We rate Yamaha A-S1200 the better fit for desk or near-field listening, a small room and a mid-size room, and NAD C 399 for a large room and a very large room. Match the amplifier to the room you actually have, not the one you want. |
| Grip on hard loads | A | Yamaha A-S1200 holds up better into a 4-ohm load: its output increases strongly to 150W, where the other barely increases. That matters with demanding speakers far more than the 8-ohm figure does. |
| Noise floor | A | Yamaha A-S1200 is the quieter design on paper - 110dB against 95dB. Audible mainly with sensitive speakers in a quiet room. |
| Built-in DAC | B | NAD C 399 has a DAC on board; the other needs an external one, which is another box, another power lead and another purchase. |
| Analogue inputs | A | Yamaha A-S1200 takes more analogue sources - 6 against 2. |
| Room to grow | evenly matched | The same expansion options on both. |
| Amplifier class | depends | Yamaha A-S1200 is Class A/B and NAD C 399 is Class D. Class A/B runs warm and is the long-established mainstream choice; Class D runs cool and draws almost nothing at idle. Modern examples of both measure well - judge by the rest of the page. |
| Shelf space | depends | NAD C 399 takes up about 14% less shelf area (1818cm² against 2123cm²), and it is 70mm shallower, which is the measurement that decides whether a rack door shuts. |
| Price | B | NAD C 399 costs less - $1,999 against $3,000 at list. |
| Watts per dollar | B | NAD C 399 is the cheaper watt - about $11 per watt against $33. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A Yamaha A-S1200 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?
Neither runs away with it - they trade advantages. Let the "depends" rows and the speakers you already own settle it. If your speakers are a difficult load - 4 ohms nominal, big woofers, or a sensitivity in the low 80s - Yamaha A-S1200 is the safer partner, because how an amplifier behaves when the impedance drops matters more than its 8-ohm rating. Start with the room. In a large or open-plan room, or with speakers that are hard to drive - low sensitivity, or an impedance that dips - NAD C 399 has the headroom, and headroom is what stops an amplifier hardening up on peaks. At desk distance or in a small room, 90 watts is already more than most people ever use, and the extra 90 watts would be headroom you pay for and never hear - we rate NAD C 399 poorly for near-field use for exactly that reason.
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.