These are not the same size of amplifier: Arcam SA45 has roughly 2.3x the power of Naim Uniti Nova. That is about 3.5dB, 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 | A | Arcam SA45 has more power - 180W against 80W into 8 ohms. That is about 3.5dB, so it plays usefully louder before it runs out and has more in hand on peaks. |
| Built-in DAC | B | Both decode on board, but only Naim Uniti Nova handles DSD. |
| Streaming | evenly matched | The same streaming platforms and services on both. |
| Phono stage | depends | Arcam SA45 has a built-in phono stage and Naim Uniti Nova does not. Decisive if you own a turntable, completely irrelevant if you do not - and an outboard phono stage is easy to add later either way. |
| Room to grow | evenly matched | The same expansion options on both. |
| Headphones | depends | Only Naim Uniti Nova has a headphone output. Worth something if you listen late, nothing if you never do. |
| Amplifier class | depends | Arcam SA45 is Class G and Naim Uniti Nova is Class A/B. Class G/H switches its supply rails to cut the heat a Class A/B design wastes; Class A/B runs warm and is the long-established mainstream choice. Modern examples of both measure well - judge by the rest of the page. |
| Shelf space | depends | Naim Uniti Nova takes up about 24% less shelf area (1371cm² against 1796cm²), and it is 98mm shallower, which is the measurement that decides whether a rack door shuts. |
| Price | A | Arcam SA45 costs less - $5,500 against $6,899 at list. |
| Watts per dollar | A | Arcam SA45 is the cheaper watt - about $31 per watt against $86. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A Arcam SA45 B Naim Uniti Nova
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?
Arcam SA45 has the edge on paper, though not by much. The rows marked "depends" are more likely to decide this than the score is. 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 - Arcam SA45 has the headroom, and headroom is what stops an amplifier hardening up on peaks. At desk distance or in a small room, 80 watts is already more than most people ever use, and the extra 100 watts would be headroom you pay for and never hear. If you play records, Arcam SA45 saves you buying a phono stage; if you do not, ignore that row entirely.
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.