These are not the same size of amplifier: Arcam SA20 has roughly 3.6x the power of Arcam Solo Uno. 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 SA20 has more power - 90W against 25W 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. |
| Room size | depends | We rate Arcam Solo Uno the better fit for desk or near-field listening and a small room, and Arcam SA20 for a mid-size room, 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 | Arcam Solo Uno holds up better into a 4-ohm load: its output nearly doubles to 50W, where the other increases strongly. That matters with demanding speakers far more than the 8-ohm figure does. |
| Noise floor | A | Arcam Solo Uno is the quieter design on paper - 117dB against 106dB. Audible mainly with sensitive speakers in a quiet room. |
| Built-in DAC | A | Both decode on board, but only Arcam Solo Uno handles MQA. |
| Streaming | A | Only Arcam Solo Uno has AirPlay 2, Chromecast and Roon. |
| Analogue inputs | B | Arcam SA20 takes more analogue sources - 4 against 1. |
| Phono stage | depends | Arcam SA20 has a built-in phono stage (MM) and Arcam Solo Uno 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 Arcam SA20 has a headphone output. Worth something if you listen late, nothing if you never do. |
| Amplifier class | depends | Arcam Solo Uno is Class D and Arcam SA20 is Class G. Class D runs cool and draws almost nothing at idle; 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 Solo Uno takes up about 78% less shelf area (348cm² against 1580cm²), and it is 119mm shallower, which is the measurement that decides whether a rack door shuts. |
| Price | A | Arcam Solo Uno costs less - $769 against $1,650 at list. |
| Watts per dollar | B | Arcam SA20 is the cheaper watt - about $18 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 Solo Uno B Arcam SA20
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 Solo Uno has the edge on paper, though not by much. The rows marked "depends" are more likely to decide this than the score is. If your speakers are a difficult load - 4 ohms nominal, big woofers, or a sensitivity in the low 80s - Arcam Solo Uno 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 SA20 has the headroom, and headroom is what stops an amplifier hardening up on peaks. At desk distance or in a small room, 25 watts is already more than most people ever use, and the extra 65 watts would be headroom you pay for and never hear - we rate Arcam SA20 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.