What does the impedance curve of those phones look like? I'm just not seeing this distortion rise at all with the APx1701 driving the Superlux phones that I have on hand.
Before losing power, I performed another experiment. I connected the grado headphones to the RME and then measured THD while playing 50 Hz and alternatively blocking the back of the headphone versus not. Blocking it reduced distortion by 10 dB! So it seems that this is indeed related to back EMF energy from the driver coming into the output of the amplifier. This is what Mathias is saying is happening. What he does not address is why Benchmark is not sensitive to it, and they are.
Yes, that must be it.Superlux phones are too low end to show the difference. They are so low end not only will they not resolve distortion while listening, they won't even do it measuring with an AP unit.
That didn't take long. Already its sounding better. Had to turn the bass back down. OMG.Its going to take some time to get used to the tube not being in there. The RME dac sounds very neutral to me so I was using loudness and bass boost on it. It does sound very good, but the xduoo amp section has more watts. The distortion levels in the xduoo are higher and I can hear that also. I figure I will be switching back to the RME soon enough after it breaks in. Waiting for the massdrop/THXAAA.View attachment 12079
Before losing power, I performed another experiment. I connected the grado headphones to the RME and then measured THD while playing 50 Hz and alternatively blocking the back of the headphone versus not. Blocking it reduced distortion by 10 dB! So it seems that this is indeed related to back EMF energy from the driver coming into the output of the amplifier. This is what Mathias is saying is happening. What he does not address is why Benchmark is not sensitive to it, and they are.
Seems like a dream DAC.
I wonder:
1. If it can be stackable for doing multichannel (2 units or more) using the USB ASIO driver, the ADI-2 Pro manual hints little about this capability ("multi-interface", if I'm not confusing it) and the ADI-2 DAC hint even less. Could then be just about the best Multichannel DAC/opAMP at about $800 less than the closest contender (exaSound e38) if only 5.1ch is needed (or $1800 less for 2.2ch), with much more features and probably a better headphone AMP(s, as you get more than one unit at this price).
...
Sweetwater?
I don't but remind me in a few days and I will play around and report back.I used these settings from another forum but its not the same headphone that I have. I noticed it sounded smoother right away. But does someone have settings for the HE-400i for E.Q.?
Hifiman HE-560
B 1, G +4.0, F 120, Q 0.7, SHELF
B 2, G +6.0, F 1.90k, Q 1.2, PEAK
B 3, G -7.0, F 4.0k, Q 3.0, PEAK
B 4, G -6.0, F 10.5k, Q 3.0, PEAK
I am fairly certain I can hear a tiny bit of hiss with my Andromeda when no music is playing. I think that is to be expected even with the very good specs of the IEM out.