Originally Posted by Roly1650
One of the graphs you posted shows that your statement regarding all sources having non-linear output impedance is incorrect, look at the graph for the X3 again.
It probable that the frequency response of anything hooked up to the devices you've shown graphs for and of sufficiently low enough impedance, will have falling bass response anyway. So the effect will make zero audible difference, hence PDVJAM's statement that he hears no difference between DX50 and DX90 in the bass is probably correct.
The X3 shows flat FR, and the dips and peaks you see of the impedance graph is not linear to a degree(never said completely non-linear), but it's low enough that doesn't really matter. Maybe you're mixing up the FR with the impedance response barely visible at the bottom. If that measurement for the DX50 was correct(Clie has said he measured it to be not the case) and given that every headphone have different impedance characteristic, how a headphone react to output impedance is dependents on how relatively close the headphone impedance is to the output impedance. For example some iems dip as low as 10ohms in the bass region, and spec'd as 16ohms at 1k. If it was a much higher impedance phone, the difference will not be audible than if the iems were at the load. Anyway all this is mute since Clie says the measurements are wrong.
I have not seen a output impedance sweep until this one, are there others?
Originally Posted by ClieOS
The problem of quoting some guy from the internet is that he might not actually be correct in the first place. In this case, I am pretty sure the DX50 graph above is wrong on the output impedance. My own measurement puts it at 0.6ohm with a 1kHz test tone, which is more inline with iBasso's own number. Definitely not around 2.5~3ohm as the above graph suggested. That makes me wonder how accurate the rest of the graphs are.
Not really. The graph above just tells you that Calyx M has coupling caps on the output... and you don't need coupling caps on the output if your amp section doesn't have DC offset to worry about, which is the case for FiiO's DAP. It all depends on the implementation.
Yeah, when I saw the THD imbalance, I didn't have much faith in the measurements. Really?? Coupling caps at the headphone out? It's a usb DAC/Amp. Why would they add coupling caps to a headphone out? If there is indeed a cap at the output as you say, cap is still an output impedance which is affecting the FR with load. Given you say there is the cap at the output, it's probably creating a high pass filter with the resistor.
I'm curious if there are significant capacitance output by sources? Any graphs of them? I know DACs have coupling caps and the input impedance to the amp is typically very high so that shouldn't roll off to the amp, correct? Or is there a possibily for the roll-off to take place between the DAC and the amp?
Edited by SilverEars - 8/22/14 at 5:01pm