I would like to add that these measurements were made with a simple multimeter, without being able to analyse the waveforms, at least with the naked eye. Now, I have a small oscilloscope, how does this improve the measurements? Well, I can't analyse the THD, but you can see if the waveforms are pure or deformed or saturated. That can give you an idea: if the wave is clean there is no visible distortion, the THD will be lower.
I can make a small measurement now, to see if I have a similar impedance...
Edit:
Well, I had some time and did a quick measurement of the Sonata HD Pro with my little oscilloscope and some 33 Ohms and 48 Ohms resistors (33 + 15 Ohms) and these are the results:
33 Ohms: As expected, the oscilloscope shows a drop in voltage, which the multimeter is unable to detect. Anyway, almost 1.5V RMS at 33 Ohms is a good figure.
48 Ohms: With this impedance, you can almost use the device, at full volume, giving a voltage of almost 1.9V RMS over the entire range. I think that's pretty good for an SE output in a fairly inexpensive device.
It should be understood that the volume has been set to the maximum that allows the waveform to be seen without visible distortion, in 0.5dB steps, using pure waveforms, amplitude 1, in FLAC 96000 Hz format. For playback I have used the Foobar2000 connected to my Windows 10 PC, under the ASIO driver provided by Tempotec.
To get the maximum power that the HD Pro can give, I used the trick of the 3.5mm male-to-female angled converter, connected to the output (no load) when plugged into the PC. This "tricks" the Sonata into pretending it has a very high load connected and automatically sets itself to high gain.
By the way @baskingshark, thank you for your thoughtful words. I think you think highly of my reviews, but I think you're exaggerating ...
Finally, I think that when the Sonata HD Pro is set to low gain, I don't think it will give less than 1V. This gives 117dB for the Etymotic Research ER4XR. I think that's already a pretty high volume.
And at high gain you can push this headphone to the maximum of its supported power.
Thanks for the great info!
Anyways, can any folks here help @Jitu13 with some queries here (posted from another thread), I think the problem is that the ER4SR etymotic gets no sound with the Tempotec Sonata HD Pro. It shouldn't be a drivability issue as the etymotics aren't the toughest IEM to drive.
I'm not very technical so any advise for us is much appreciated!
I got my sonata hd pro (amp+dac, around $50 ish in us) and neoteck ntk059(just pure amp, $30 ish) yesterday. First the neoteck has lots of problem with hissing! Especially if your iem is not high impedance (16 ohm iem has lot of bg noise! Especially in high gain, the low gain mode suppresses a lot of noise). Even my er4sr suffer from hiss(small but noticeable) for high gain. There is also hissing when you charge, when you are near refrigerator, movement in the 3.5mm jack (I guess you git the drill) . But the saving grace is when you are hearing music, I never heard them. Sonata hd pro on the other hand, has no hissing issue. The only problem I face with it till now is that it doesn't play well with my smartphone! For example it doesn't drive my er4sr at all from my galaxy s10e! It does drive other low impedance iem though. I will try the trick of using a 3.5mm to 3.5mm jack to drive it to highest voltage to see if it solves the issue with my smartphone.
Initial impression: both of them makes the sound from my er4sr sharper. They also retrieves more details. Not sure which one retrieves more. Once I hear them enough maybe I will have a definitive answer. Neoteck also colors the sound a bit (warmer, with more bass). On the other hand, sonata hd pro doesn't color the sound to my ear.
So as was pointed out above, maybe sonata hd pro is your best bet.
Well I use Spotify for music, is there any way to force it? Also as I was testing it with er4sr, I thought it would use the full power, no?
*Update* It can play my edx from my galaxy s10e. Also the sound is quite good and has high volume. On the other hand, there is no sound when I use my er4sr! Is this a hardware issue?