No single best amplifier here. What decides it is what you have to drive, what you need to plug in, and how much of the system you want in one box.
| Area | Better | Why |
|---|
| Power | B | Arcam SA30 has more power - 130W against 70W into 8 ohms. That is about 2.7dB, so it plays usefully louder before it runs out and has more in hand on peaks. |
| Room size | depends | We rate Marantz Model 40n the better fit for a small room, and Arcam SA30 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 | evenly matched | Both behave much the same into 4 ohms - output increases modestly (100W and 200W). |
| Noise floor | B | Arcam SA30 is the quieter design on paper - 112dB against 106dB. Audible mainly with sensitive speakers in a quiet room. |
| Built-in DAC | B | Both decode on board, but only Arcam SA30 handles MQA. |
| Streaming | evenly matched | Only Marantz Model 40n has HEOS; only Arcam SA30 has Chromecast. Neither list is longer in a way that matters - check the one service you actually pay for. |
| Analogue inputs | B | Arcam SA30 takes more analogue sources - 4 against 3. |
| Room to grow | evenly matched | The same expansion options on both. |
| Amplifier class | depends | Marantz Model 40n is Class A/B and Arcam SA30 is Class G. Class A/B runs warm and is the long-established mainstream choice; Class G/H switches its supply rails to cut the heat a Class A/B design wastes. Modern examples of both measure well - judge by the rest of the page. |
| Shelf space | depends | Arcam SA30 takes up about 23% less shelf area (1636cm² against 2126cm²), and it is 104mm shallower, which is the measurement that decides whether a rack door shuts. |
| Price | A | Marantz Model 40n costs less - $2,499 against $3,300 at list. |
| Watts per dollar | B | Arcam SA30 is the cheaper watt - about $25 per watt against $36. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A Marantz Model 40n B Arcam SA30
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 SA30 leads across most of the measured areas for a fairly modest premium, so it is the easier pick if the budget stretches. Marantz Model 40n is the one to take if it does not. 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 SA30 has the headroom, and headroom is what stops an amplifier hardening up on peaks. At desk distance or in a small room, 70 watts is already more than most people ever use, and the extra 60 watts would be headroom you pay for and never hear - we rate Arcam SA30 poorly for near-field use for exactly that reason.
What a spec sheet cannot show: how either sounds with your speakers, how the interface feels 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.