Different price classes - Yamaha A-S501 costs roughly 2.8x what OSD Nero Stream ARC 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 | Yamaha A-S501 has more power - 85W against 50W into 8 ohms. That is about 2.3dB, so it plays usefully louder before it runs out and has more in hand on peaks. |
| Noise floor | B | Yamaha A-S501 is the quieter design on paper - 99dB against 95dB. Audible mainly with sensitive speakers in a quiet room. |
| Built-in DAC | evenly matched | Both have a DAC on board with much the same capability. |
| Phono stage | depends | Yamaha A-S501 has a built-in phono stage (MM) and OSD Nero Stream ARC 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. |
| Use with a TV | depends | Only OSD Nero Stream ARC has HDMI ARC, 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 | B | Only Yamaha A-S501 offers preamp outputs - which decides whether you can add a subwoofer or a power amplifier later without replacing the box. |
| Headphones | depends | Only Yamaha A-S501 has a headphone output. Worth something if you listen late, nothing if you never do. |
| Amplifier class | depends | OSD Nero Stream ARC is Class D and Yamaha A-S501 is Class A/B. Class D runs cool and draws almost nothing at idle; Class A/B runs warm and is the long-established mainstream choice. Modern examples of both measure well - judge by the rest of the page. |
| Shelf space | depends | OSD Nero Stream ARC takes up about 79% less shelf area (351cm² against 1710cm²), and it is 209mm shallower, which is the measurement that decides whether a rack door shuts. |
| Price | A | OSD Nero Stream ARC costs less - $199 against $550 at list. |
| Watts per dollar | A | OSD Nero Stream ARC is the cheaper watt - about $4 per watt against $6. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A OSD Nero Stream ARC 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?
The usual trade-off: Yamaha A-S501 measures better, OSD Nero Stream ARC costs about 64% less. With most speakers in most rooms that gap is smaller in practice than it looks here. 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 - Yamaha A-S501 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 35 watts would be headroom you pay for and never hear - we rate Yamaha A-S501 poorly for near-field use for exactly that reason. If you play records, Yamaha A-S501 saves you buying a phono stage; if you do not, ignore that row entirely.
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.