These are not the same size of amplifier: Arcam SA45 has roughly 3.6x the power of Arcam A5+. That is about 5.6dB, 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 | Arcam SA45 has more power - 180W against 50W into 8 ohms. That is about 5.6dB - a different class of amplifier rather than a bigger version of the same one, and far more than most rooms will ever ask for. |
| Grip on hard loads | B | Arcam SA45 holds up better into a 4-ohm load: its output increases strongly to 300W, where the other increases strongly. That matters with demanding speakers far more than the 8-ohm figure does. |
| Noise floor | B | Arcam SA45 is the quieter design on paper - 110dB against 106dB. Audible mainly with sensitive speakers in a quiet room. |
| Built-in DAC | B | Both decode on board. Arcam SA45 goes higher - 384kHz against 192kHz. Very few recordings exist above 192kHz, so treat this as headroom, not as sound quality. |
| Streaming | B | Only Arcam SA45 has AirPlay 2, Chromecast and Roon. |
| Use with a TV | depends | Only Arcam SA45 has HDMI, so the television can drive it directly and one remote controls the volume. If the system is for music only, this changes nothing. |
| Room to grow | evenly matched | The same expansion options on both. |
| Headphones | depends | Only Arcam A5+ has a headphone output. Worth something if you listen late, nothing if you never do. |
| Amplifier class | depends | Arcam A5+ is Class A/B and Arcam SA45 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 A5+ takes up about 17% less shelf area (1483cm² against 1796cm²), and it is 70mm shallower, which is the measurement that decides whether a rack door shuts. |
| Price | A | Arcam A5+ costs less - $1,200 against $5,500 at list. |
| Watts per dollar | A | Arcam A5+ is the cheaper watt - about $24 per watt against $31. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A Arcam A5+ B Arcam SA45
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 SA45 measures better, Arcam A5+ costs about 78% 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 SA45 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 - Arcam SA45 has the headroom, and headroom is what stops an amplifier hardening up on peaks. At desk distance or in a small room, 50 watts is already more than most people ever use, and the extra 130 watts would be headroom you pay for and never hear.
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.