Hidizs S9 Pro: power output and what it will drive

The Hidizs S9 Pro is a USB dongle at $109. It delivers 100 mW into 32Ω and 11 mW into 300Ω, which ranks it 214 of 280 for raw power among the sources in this database.

Measured at 100 dB SPL it has comfortable headroom on 478 of the 567 dynamic and planar headphones catalogued here, enough but not generous on 74, only marginal on 8 and not enough power for 7. Popular balanced dongle with plenty of power for its size.

The manufacturer publishes 100 mW into 32Ω. Everything else in the table above is worked out from those figures, and this table says which is which.

The balanced output is rated separately: 200 mW into 32Ω through the 2.5mm jack.

Derivation holds output voltage steady between and beyond the published loads rather than output power, because that is what an amplifier actually does. The full method is written up here.

The output impedance or output noise shown above did not turn up in any manufacturer document during this check. It is carried over from the material this database was first built from, and is marked unverified rather than quietly presented as sourced.

Source: hidizs.net.

Ordered from easiest to hardest to drive. Headroom is measured at 100 dB SPL, which is louder than almost anyone listens — a small negative number means the source still plays loud, just without reserve for peaks.

These figures come from each manufacturer's own sensitivity rating. A handful of planars — the HiFiMAN Susvara and the Abyss AB-1266 in particular — are widely reported to need far more than their published sensitivity implies, so treat a bare pass on those as optimistic rather than settled.

At 4 µV of output noise, here is where that noise lands in the five most revealing in-ears in the database.

That noise figure has not been traced to a document from the maker, so the levels below are as good as the number they start from.

This one hisses. With the most sensitive in-ears in the database its own noise lands around 33 dB SPL, which you will hear between tracks and in quiet passages.

At 0.3Ω output impedance this source satisfies the one-eighth rule with every headphone in the database, down to the 3Ω in-ears. Nothing here will have its frequency response shaped by the source.

That output impedance has not been traced to a document from the maker, so the count above is only as good as the number it starts from.

The rule is a rule of thumb, not physics: a source impedance below one eighth of the headphone's keeps the interaction under about 1 dB. The checker works it out for any pair.

Of the 280 sources here, 19 do everything the Hidizs S9 Pro does as a headphone output: reach 100 dB on every headphone it reaches. The cheapest of them is the FiiO KA11 at $29, against this one’s $109 — $80 less.

The cheaper one also publishes an output impedance and a noise figure, which the Hidizs S9 Pro does not — so on the paperwork it is ahead, not merely level.

This counts a headphone output and nothing else. Inputs, converters, microphone preamps, balanced outputs, the volume control, the case and the warranty are all outside it, and any of them can be the reason to buy the dearer box. What the count does say is that the three numbers a maker can be held to do not separate them.

Worked out in advance against its closest rivals: vs DUNU DTC 480 · vs FiiO KA13 · vs FiiO KA15 · vs Hidizs S9 Pro Plus · vs Hidizs SD2 · vs iBasso DC04 Pro · vs Onix Alpha XI1. Each of those pages lists the headphones that tell the two apart.

Or put any two side by side in the source comparison tool, or run your own headphones through the amplifier matcher. Or see every Hidizs source in the database, and how much of what this site says about them came from Hidizs’s own documents.