Yamaha A-S501 Review

We have not heard this amplifier. What follows is a reading of Yamaha’s published specifications — what they promise, what they omit, and one figure that circulates widely and means something different from what people think.

The 185 watt problem

Search for this amplifier and you will find “185 W into 4 ohms” repeated everywhere. Here is what Yamaha actually publishes.

Their rated output is 85 W + 85 W into 8 Ω, measured 20 Hz–20 kHz at 0.019% THD, described as minimum RMS. That is a proper rating: a stated band, a stated distortion figure, and a stated load.

Separately, Yamaha publishes a line labeled High Dynamic Power/Channel: 130 W into 8 Ω, 150 W into 6 Ω, 185 W into 4 Ω, 220 W into 2 Ω.

Dynamic power is a short-burst IHF measurement. It describes what the amplifier can deliver for a fraction of a second before the power supply sags — a real and useful property, since music is full of transients. It is not a continuous rating, and it cannot be compared to a continuous rating. Yamaha publishes no continuous 4-ohm rating for this amplifier at all.

So the “185 W” figure being quoted as this amplifier’s 4-ohm power overstates it by roughly a factor of two. Yamaha has not claimed otherwise — the line is clearly labeled on their own spec page. The error is downstream.

What that means if your speakers dip low

It means you cannot complete the calculation. A nominally 6-ohm speaker like the Q Acoustics 3030i publishes a 4-ohm minimum; the KEF Q3 Meta is nominally 4 Ω before it dips to 3.2 Ω. To know whether this amplifier is comfortable there you would need a continuous 4-ohm rating, and there is not one.

This is not a reason to avoid the A-S501, and it is not evidence that the amplifier struggles. It is a documented gap, and the practical response is to look at the speaker first: an easy 8-ohm load with reasonable sensitivity puts you well inside what Yamaha does rate.

Compare this to the Marantz PM6007, which publishes 60 W × 2 into 4 Ω across the full band with both channels driven. Lower power, complete information — which is why it outranks the Yamaha on our vinyl-focused amplifier page even though the Yamaha wins on 8-ohm watts.

What Yamaha publishes that its rivals do not

The rest of the sheet is unusually complete, and it is worth saying so after two sections of criticism.

• Damping factor: 240.The highest figure among the integrated amplifiers we cover — Marantz publishes 100, Cambridge above 50. Damping factor is the ratio of load impedance to the amplifier’s output impedance, and a high figure means tighter control of the woofer’s motion after the signal stops.
• THD 0.019% at 50 W into 8 Ω, 20 Hz–20 kHz. Note the condition: at a real power level, across the whole band, not at 1 kHz.
• Signal-to-noise 99 dB on CD input with the input shorted, and 82 dB or more on the MM phono input.
• Phono input: MM, 3.0 mV / 47 kΩ. A published sensitivity, which Cambridge does not provide for the AXA35.
• A subwoofer output, which turns this into a 2.1 amplifier and pairs well with a small bookshelf speaker.

The digital inputs, and the missing part number

The A-S501 has optical and coaxial digital inputs, which means it contains a DAC.

Yamaha does not publish the DAC part number, and does not publish any conversion measurements for it — no THD+N, no signal-to-noise for the digital path, nothing. Compare that to any standalone DAC in our roundup, every one of which publishes both.

That is the honest argument for adding an external converter: not that Yamaha’s is bad — we have no measurements either way — but that an external one publishes its figures and this one does not.

Also worth noting: Yamaha’s specification table contains no Bluetooth row at all. If you want wireless, the Denon PMA-600NE publishes Bluetooth 5.1 with SBC and AAC.

Who should skip it

Anyone with speakers that present a genuinely difficult load. Without a continuous 4-ohm figure you are buying on faith, and the Marantz publishes what you need.

Anyone who wants Bluetooth or HDMI. There is no Bluetooth row on the spec sheet and no HDMI at all — if a television is involved, you want a receiver.

And anyone whose speakers are very sensitive in a small room. 85 watts into a 93 dB speaker at three meters is a great deal more than anyone needs, and the money would do more work somewhere else in the system.

The verdict

On published specifications this is the strongest 8-ohm amplifier in its price bracket, and the damping factor and THD conditions are both better documented than its rivals’. The gaps are specific and worth knowing: no continuous 4-ohm rating, no DAC part number, no Bluetooth.

If your speakers are an easy load and you want the most properly-specified watts for the money, this is the one. Run the arithmetic against your own speakers first — with an amplifier this powerful, the answer is usually that it is more than enough.