Different price classes - Arcam SA45 costs roughly 1.8x what JBL SA750 75th Anniversary Edition does. Expect it to lead on paper; the question is whether you will hear the difference through the speakers you own.
| Area | Better | Why |
|---|
| Power | B | Arcam SA45 has more power - 180W against 130W into 8 ohms. That is about 1.4dB, which is a small step in loudness but real headroom on peaks. |
| Grip on hard loads | evenly matched | Both behave much the same into 4 ohms - output increases strongly (200W and 300W). |
| Noise floor | evenly matched | Much the same signal-to-noise ratio (112dB vs 110dB). |
| 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 | evenly matched | The same streaming platforms and services on both. |
| Room to grow | evenly matched | The same expansion options on both. |
| Headphones | depends | Only JBL SA750 75th Anniversary Edition has a headphone output. Worth something if you listen late, nothing if you never do. |
| Price | A | JBL SA750 75th Anniversary Edition costs less - $3,000 against $5,500 at list. |
| Watts per dollar | A | JBL SA750 75th Anniversary Edition is the cheaper watt - about $23 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 JBL SA750 75th Anniversary Edition 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?
Arcam SA45 is ahead, but on only 1 of the measured areas, and it costs about 83% more. That is a lot of money for a narrow margin - JBL SA750 75th Anniversary Edition is the sensible buy unless a specific feature above decides it for you. Think about the whole system: the roughly $2,500 saved by taking the cheaper one would buy better speakers or a subwoofer, which does more for the sound than the difference between two competent amplifiers.
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.