Grace Design m900: power output and what it will drive

The Grace Design m900 is a desktop amplifier at $660. It delivers 1.0 W into 32Ω and 115 mW into 300Ω, which ranks it 55 of 156 for raw power among the sources in this database.

Measured at 100 dB SPL it has comfortable headroom on 396 of the 396 dynamic and planar headphones catalogued here.

The manufacturer publishes 1.9 W into 16Ω, 1.0 W into 32Ω, 680 mW into 50Ω, 115 mW into 300Ω, 57 mW into 600Ω. Everything else in the table above is worked out from those figures, and this table says which is which.

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.

Source: gracedesign.com.

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 HE-6se 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 5.01 µV of output noise, here is where that noise lands in the five most revealing in-ears in the database.

This one hisses. With the most sensitive in-ears in the database its own noise lands around 28 dB SPL, which you will hear between tracks and in quiet passages.

At 0.08 Ω output impedance this source satisfies the one-eighth rule with every headphone in the database, down to the 5Ω in-ears. Nothing here will have its frequency response shaped by the source.

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.

Or put any two side by side in the source comparison tool, or run your own headphones through the amplifier matcher.