Can output impedance be different for the same 3.5mm port if it's a combo HP/Line-out?

[companyja]

Heyo, posted this on Reddit but this might be the more appropriate place. I'm temporarily using my Fiio X3 III as a DAC connected to my desktop since I sold my desktop dacamp, and because it has rather bad crosstalk figures and a high noise floor with sensitive IEMs, I tried putting it on line-out which has adjustable volume levels, so effectively a pre-out. I listened to my AKG K712 on the X3 III from time to time on headphone out and it always sounded the same as my desktop K5 Pro, but now that I put it in line-out, man it just sounds delicious. I don't know if I'm psyching myself out but I swear it catches me off-guard how nice the low-end is and it always feels a bit extra. At the loudest I'd ever listen I cap out at 116/120 on the pre-amp. I tried lowering and increasing the volume as well cause I know how much uneven matching makes an impact.

My question is, can the same output port have different impedances depending on whether the signal is going straight DAC to output or if it's going though the additional pair of OPA1622 inside the X3 III? The only figures I've found is the headphone out on RAA, which is 1 ohm so it doesn't affect anything I'm plugging it into. I'm thinking maybe this is affecting the low-end, if it's outputting something like 20ohm or above as line-out?

By the way, really fascinating player, I don't think I've seen a dual burr-brown DAC anywhere else. Currently the most annoying thing is the audio latency in DAC mode which is only tolerable if I run it at 192khz.

 

[twsecrest]

I'm guessing the FiiO X3 III combo headphone/line-out jack, that when set to line-output, it increase the output impedance of the jack, which I'm guessing is effecting the damping control of the K712, causing a bloated (louder, less detailed) bass, and you like a lot of bass?
The 62-Ohm AKG K700 series headphones are considered more power hungry, then my 250-Ohm Beyer headphones.
Maybe the FiiO X3 III jack, set to line-output, feeds the K712 what it needs, which could be more voltage or more current.

 

[solderdude]

The K712 does not react to a higher output R 0.2 Ohm, 120 Ohm

As long as there is no relay 'clicking' inside chances are the same output stage (imp) is being used and perhaps they do something with output levels only.

 

[companyja]

Hmm, very interesting. I don't hear clicking but the output pauses for a split second while switching from line out and hp out (it is also a coax digital out on the same port). I know that with my sensitive IEMs which otherwise have some background noise on headphone out due to solely digital volume control, when I switch to line-out, the noise completely disappears and the volume gets a lot lower (when using variable line-out volume from the dac chips). It also measures differently according to RAA, with lower distortion but most notably super low crosstalk, like a line-out would. So there is definitely a difference between them in some regards, I was just wondering about the difference in actual tonality I think I'm hearing.

I didn't know that about damping control, I imagine it wouldn't apply since the K712 doesn't measure differently under higher resistance? I had a K240 before and that definitely did sound different to me from my dacamp and from my old soundcard, which I imagine might have a bit of resistance on the output. All in all it works for me, the K712 are not extremely bassy as is and this doesn't really bloat the bass audibly, it still sounds rather fast.

The reason I'm skeptical about the power being the difference is that I used it with a K5 Pro before and that could definitely power the K712 with ease, I wouldn't go past 1 o clock on the medium gain for the loudest of listening

 

[twsecrest]

The guideline is you want the Ohm (impedance) of the headphones, to be at least 8 to 10 times the output impedance of headphone jack.
For the 62-Ohm AKG K712, you want the headphone jack to have an output impedance of around 6-Ohms or less (for best damping control).
The FiiO X3 III headphone jack has an output impedance of <1.4-Ohms
The FiiO K5 Pro's output impedance is 1.2.

 

[solderdude]

Hmm, very interesting. I don't hear clicking but the output pauses for a split second while switching from line out and hp out (it is also a coax digital out on the same port). I know that with my sensitive IEMs which otherwise have some background noise on headphone out due to solely digital volume control, when I switch to line-out, the noise completely disappears and the volume gets a lot lower (when using variable line-out volume from the dac chips). It also measures differently according to RAA, with lower distortion but most notably super low crosstalk, like a line-out would. So there is definitely a difference between them in some regards, I was just wondering about the difference in actual tonality I think I'm hearing.

I didn't know that about damping control, I imagine it wouldn't apply since the K712 doesn't measure differently under higher resistance? I had a K240 before and that definitely did sound different to me from my dacamp and from my old soundcard, which I imagine might have a bit of resistance on the output. All in all it works for me, the K712 are not extremely bassy as is and this doesn't really bloat the bass audibly, it still sounds rather fast.

The reason I'm skeptical about the power being the difference is that I used it with a K5 Pro before and that could definitely power the K712 with ease, I wouldn't go past 1 o clock on the medium gain for the loudest of listening

There is a way you can check if output resistance increases in line-out mode.
The fact that the same pins can also put out coax makes it likely different analog output circuits can also be switched.

Connect the output to the K5.
switch between line-out and HP out and set the volume so they sound equally loud when listening to the K5.

Then remove the K5 and switch between HP out and line-out but with the K712 connected.
When in one setting the volume is lower it has a higher output resistance.

 

[companyja]

Ah, I don't have the K5 Pro anymore, I just sold it! That's why I'm using the X3 as a DAC. It's actually a way better experience than I thought - if you don't start it manually and it cold-boots when the USB gets inserted, it will shut itself down completely as soon as there's no power anymore (when I shut my PC off) and it will start up again as soon as I boot my PC up, so it's acting exactly like a soundcard. From the very obscure info I've been able to find, the X3 III does not use the battery at all when plugged in and charged, so I'm hopefully not reducing its lifespan that way either. The only annoyance is still that latency when I set to anything lower than 192khz (96 is also okay but still slightly noticeable). I guess it has a larger buffer for resampling since its SoC is so old and whatnot, I really have no idea but it seems to be a thing on all Fiio X series players.

I can probably try it via my old soundcard, might report back when I'm bored enough to do it

 

[companyja]

Right! So this is what I did - I connected the line-out of the X3 III to the line-in on my soundcard and recorded a 1khz sine, then disconnected, switched to headphone out, hooked it up to the line-in and adjusted the headphone level to roughly match the line-out at max/no preamp as seen here:

(the levels are low cause the line-in volume in windows was set to a lower value than 100% by default for some reason, didn't feel the need to mess with it)

I couldn't get it exactly but I got it as close as I can with the 120 volume steps available on the player (I didn't change any volume settings on the line-in).

This gave me 106/120 on the headphone out to be equivalent to 120/120 on the line-out (and those last steps are fucking brutal, I don't think it's a linear step so 120 is quite a bit louder than 106).

I then used only the player to see whether one was louder, and the headphone out on 106/120 (on the right) is indeed quite a bit louder than the line-out at 120/120 (on the left) with the K712 plugged in. Does this indicate that the output impedance is indeed higher with the line-out?

(Also ow, it's way too loud at this volume, I should've set the pre-out to something lower so that my ears wouldn't hate me for the few seconds that I did try it)

 

[twsecrest]

Ah, I don't have the K5 Pro anymore, I just sold it! That's why I'm using the X3 as a DAC. It's actually a way better experience than I thought - if you don't start it manually and it cold-boots when the USB gets inserted, it will shut itself down completely as soon as there's no power anymore (when I shut my PC off) and it will start up again as soon as I boot my PC up, so it's acting exactly like a soundcard. From the very obscure info I've been able to find, the X3 III does not use the battery at all when plugged in and charged, so I'm hopefully not reducing its lifespan that way either. The only annoyance is still that latency when I set to anything lower than 192khz (96 is also okay but still slightly noticeable). I guess it has a larger buffer for resampling since its SoC is so old and whatnot, I really have no idea but it seems to be a thing on all Fiio X series players.

I can probably try it via my old soundcard, might report back when I'm bored enough to do it

So what happens when you set it for 16-bit/48K?

 

[companyja]

There is a noticable latency in audio, to the degree that the audio is noticably out of sync when watching videos. If I had to estimate by seeing how much time it takes for sound to play after plessing play in a player, in 192khz it's not noticable at all, it feels like there's no delay, but in anything below 96 it takes a good let's say 0.7 seconds. A bit more than half a second in any case, I'd say. It's a common experience with a lot of DAPs in DAC mode, certainly with Fiio X series ones. It's whatever, I doubt I can hear the difference. I set the SoX resampler to 192khz in foobar to get verifiably good resampling at least, why not