Just how much more powerful is the HA-1 for 300 Ohm headphones than some popular heavyweights?

For 150 Ohm loads, Tyll Hertsens' measurements of the Burson Soloist show that THD%+N remains below 0.1% all the way to an Output Voltage of 9.3Vrms, as seen in this chart:

Some research has taught me that the HA-1 isn't the only amp designed to limit current into lower impedance loads and unlike the HA-1, some amps have output impedances nowhere near 0%, and thus, it's not safe to assume that the same output voltage can be achieved with a lower impedance load as a measured output voltage for a given higher impedance. We can, however, safely assume that the same or higher output voltage can be achieved with higher impedance loads than the voltages measured at lower impedances.

You might have to read that a few times, but all I'm saying is that if you measure 2V rms into a 150 Ohm load, for example, it's safe to assume you'll get at least 2V rms into a 300 Ohm load, but measuring 2V into a 300 Ohm load, you

*cannot* assume that you'll get as much as 2V into a 150 Ohm load - due to the possibility of the amp limiting current at lower impedances and/or the amp's output impedance not being less than or equal to 1/8th the headphone impedance.

Thus, with Tyll having measured 9.3V rms into a 150 Ohm load (at 0.1% THD+N), it's safe to assume the Burson Soloist delivers at least 9.3V rms output into a 300 Ohm load (but this is likely lower than the actual Vrms into 300 Ohms). Given that the Vrms into 300 Ohm is at least equal to that for 150 Ohm, using the following formula, we can calculate the Watts Rms into 300 Ohm as being at least...

Burson Soloist Watts rms into 300 Ohm at 0.1% THD+N = (v*V)/Impedance = (9.3*9.3)/300 = 0.2883

... so, at least 288.3 mW into 300 Ohm.

We can get closer to the truth by plotting the measured Vrms at 0.1% THD+N for 16, 32, and 150 Ohm, and extrapolating the Vrms for 300 Ohm via a (best-fitting) polynomial trendline, as shown here:

... then, rearranging the polynomial equation to solve for Volts instead of Ohms, getting...

Volts = (2 (sqrt(334250 Ohms-2223381)+24163))/6685 = 10.192 Vrms into 300-Ohms at 0.1% THD+N

**Just looking at Tyll's chart, an output of 10.192 Vrms into 300 Ohm "feels" about right, given the measured values of**** 6.7Vrms for 16 Ohm,**** 8.1Vrms for 32 Ohm, and**** 9.3 Vrms for 150 Ohm** **impedances.**
Going back to the previous formula, we get...

Burson Soloist Watts rms into 300 Ohm at 0.1% THD+N = (v*V)/Impedance = (10.192*10.192)/300 = 0.3463 or 346.3mW rms

If the OPPO HA-1 really can deliver 1084 mW rms (as I calculated previously) into 300 Ohm at 0.1% THD+N,

**the HA-1 is a whopping 3.13 times more powerful than the Burson Solist, into the HD800 for example.**
Schiit's specifications for the Lyr2 show it delivering 660 mW rms into 300 Ohm (at an unspecified %THD+N, but that's still less than my interpolated estimate for the OPPO HA-1). Even the solid state Mjolnir, specifies 850 mW rms into 300 Ohm (at an unspecified %THD+N) vs. my calculated 1084 mW rms for the OPPO HA-1 into 300 Ohm, at less than 0.0018% THD+N (and that's at rated power output, not at the oft'-used 1W figure.)

Please consider all of this to be speculation until we can see Tyll's measurements for the HA-1 (if indeed he plans to take them) and keep in mind that Burson Soloist specs show 4.0 Watts rms into 16 Ohm (at an unspecified %THD+N), with Tyll having measured only 2.8 Watts [(6.7V*6.7V)/16 Ohm] at 0.1% THD+N. We need measurements that would allow comparison of power output at the same %THD+N, into the same load.