Siblings in Yamaha's A-S range, so they share a design and a house sound. It comes down to power, features and price.
| Area | Better | Why |
|---|
| Power | evenly matched | Effectively the same output - 100W against 85W into 8 ohms is under 1dB, which is not an audible difference in loudness. |
| Room size | depends | We rate Yamaha A-S801 the better fit for a large room and a very large room, and Yamaha A-S501 for a small room. Match the amplifier to the room you actually have, not the one you want. |
| Noise floor | evenly matched | Much the same signal-to-noise ratio (99dB vs 99dB). |
| Built-in DAC | A | Both decode on board. Yamaha A-S801 goes higher - 384kHz against 192kHz. Very few recordings exist above 192kHz, so treat this as headroom, not as sound quality. |
| Analogue inputs | evenly matched | The same number of line-level inputs (6). |
| Room to grow | evenly matched | The same expansion options on both. |
| Price | B | Yamaha A-S501 costs less - $550 against $900 at list. |
| Watts per dollar | B | Yamaha A-S501 is the cheaper watt - about $6 per watt against $9. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A Yamaha A-S801 B Yamaha A-S501
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?
Neither runs away with it - they trade advantages. Let the "depends" rows and the speakers you already own settle it. Think about the whole system: the roughly $350 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.