If you guys want you can send the over and I'll try to test it.

IMO the player may be a little slow. Warm, but no a lot of impact. This was with the HD600s I think. It was not horrible though, at least with the 600s. My main complain about it was the build quality for the $.

OMG, you tried to drive the HD600 SE from that thing?! 

OJ got 4ohms (apparently they don't teach precision at the Henry Samueli SoE  ) and Tyll got 3.76ohms so I think that's enough unless you really want to add a third data point.

OMG, you tried to drive the HD600 SE from that thing?! 

OJ got 4ohms (apparently they don't teach precision at the Henry Samueli SoE  ) and Tyll got 3.76ohms so I think that's enough unless you really want to add a third data point.

Rounded up for all the soc science majors out there. Most can't count past 2 decimals. Actual value was 3.86 Ohms. Chalk it up to product variance, cable and contact resistance, etc.

Thanks.  But don't you mean 3 17/20 Ohms?   

C'mon, it's obviously 193/50 

Kind of amazes me how the hi-fi designers/companies (hansen, curl et. al. from ayre, parasound, meridian) didn't even get voldemort's memo regarding headphone amp output impedance... understanding that the market, as stands, demands <=1ohm for a general use amp.

There are some explanations for this:

1. There are certain output op-amps that really aren't stable (or go boom) without the output series resistance. Not much way to get around this if you're using one of them. The unstable ones *might* be stable with less than the recommended series resistance, or *might not*--in which case, bad news. The ones without current limiting may go boom when a standard TRS headphone jack is inserted, since it shorts the output of the amp briefly. Hence, "stick a resistor in there!"

2. I wouldn't be surprised if there was a perception amongst companies that are not yet familiar with the headphone market that "a little resistance cain't hurt." It makes certain bright headphones sound a bit smoother, and, you know, TRS jacks do short the output, so whango dango, throw a resistor in there, cain't hurt!

3. In some cases (no-overall-feedback and tube- or transformer-output amps), that 0.1 ohm output impedance ain't gonna happen, no way, no how.

Well, I can think of a few larger amps that achieve <1 ohm output Z w/o a global NFB loop. Although it might depend on how we extend the definition of negative feedback.

But I'd guess that achieving such performance in such a small lower power design is more difficult. The Pono does boast a fully discrete analog stage last time I checked?