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citraian
08-07-2012, 09:12 PM
Hi guys,

Is there any information on what is the output impedance of the headphone jack on the Xonar Phoebus? Also, does someone know how Phoebus fares against STX in regards to the headphone amp/headphone output section?

citraian
08-09-2012, 08:53 AM
Isn't anyone able to help?

thetruth1983
08-09-2012, 12:02 PM
In the Asus software, you are able to adjust the headphone gain settings. The choices are <64 ohms, 64-150 ohms, and 150-300 ohms. If you select any option other than the first one, it will reset once you restart Windows. I guess this is to avoid damaging headphones by mistake. I cannot answer the 2nd question as I have not used the STX before.

citraian
08-09-2012, 12:33 PM
Thanks for your reply. However, I was asking about the output impedance and not about the output gain. For more details about the output impedance see the following article:
http://nwavguy.blogspot.com/2011/02/headphone-amp-impedance.html

Raja@ASUS
08-09-2012, 07:28 PM
Check the TPA6120A2 datasheet, that will tell you the open loop output resistance which is stated at 13 ohms (closed loop output impedance will vary somewhat according to the applied gain). However, the minimum sustainable output load is shown as 8 ohms, while a 10 ohm series resistor is recommended to cater for load capacitance. From that I'd say that phones rated over 64 ohms will be a better overall fit. 32 ohms will work, but may show some drift. Off the top of my head, I doubt you will find any internal soundcard for gaming with an output impedance much lower than 10 ohms or so. If you really want to get into audio to that extent, then I think you may want to look towards external amplification.

citraian
08-09-2012, 08:20 PM
Thanks for the reply Raja.
I avoided looking at the datasheet since the output impedance could also depend on the implementation. For example, the Fiio E9 which uses the same TPA6120 has an output impedance of 10 on the large jack and an output impedance of 43 on the small jack.
Do you know if the Phoebus has the same 10.7 output impedance the STX had?
Also, are you saying that the output impedance depends on the selected gain? If so, can you at least aproximate the variations?

Raja@ASUS
08-09-2012, 08:42 PM
Thanks for the reply Raja.
I avoided looking at the datasheet since the output impedance could also depend on the implementation. For example, the Fiio E9 which uses the same TPA6120 has an output impedance of 10 on the large jack and an output impedance of 43 on the small jack.
Do you know if the Phoebus has the same 10.7 output impedance the STX had?
Also, are you saying that the output impedance depends on the selected gain? If so, can you at least aproximate the variations?

Don't have the circuit diagram to hand, so cant go that far for you. Likelihood is that that STX implementation is used. Not sure on the variances in impedance with gain, but I can't detect any real audible difference with my ears listening to HD800s.

BTW I wonder if the Fiio even uses the TPA6120A2 to drive both of those outputs. That change in impedance suggests the usage of a separate opamp section without the TPA in buffer configuration for the small jack.

citraian
08-11-2012, 02:24 AM
Thanks Raja.

I think the Fiio uses the TPA6120 for both outputs since I wasn't able to find any information that says otherwise.

Can you also gelp with these questions?
- Does the STX have more power since its maximum gain is 18 dB and Phoebus' maximum gain is 12 dB?
- Does the STX have better audio quality on the headphone output? If so, is it that noticeable?
- Is the audio quality on the Phoebus affected when using the Control Box output?

Have a nice weekend

Raja@ASUS
08-11-2012, 06:57 AM
Thanks Raja.

I think the Fiio uses the TPA6120 for both outputs since I wasn't able to find any information that says otherwise.

Can you also gelp with these questions?
- Does the STX have more power since its maximum gain is 18 dB and Phoebus' maximum gain is 12 dB?
- Does the STX have better audio quality on the headphone output? If so, is it that noticeable?
- Is the audio quality on the Phoebus affected when using the Control Box output?

Have a nice weekend

Hi,

Would make littel sense for those guys to change the impedance on those ports using a single output device. The impedance they are quoting is right in line with the output impedance range of some opamps, so my take is that it is using a different output device entirely.

As for your questions:

1) This very much depends on the voltage of the DAC that gain is applied to. So the volume may for all intents and purposes be exactly the same. What i can tell you is that i cannot crank the 300 ohm+ setting too far up on my HD800s, it gets too loud for my ears.

2) The STX range is egineered to be a better product. have not heard one or compared it, but it should have more clarity than the Phoebus.

3) Any time you add extra cables and juntions to the signal line there is a slight change in audio quality (cable/joint inductance and capacitance). it's not a big change. It really comes down to what is more convienient for you - as in how close do you "need" the volume control to you.

citraian
08-11-2012, 10:31 AM
Thanks Raja, your help is really appreciated.

Regarding the Fiio amp, this reviewer says that the extra 33 ohm on the small jack could have been added to prevent accidental headphone damage on lower impedance models http://nwavguy.blogspot.ro/2011/05/fiio-e9-headphone-amp.html

As for my questions:
1) So the Phoebus may well provide more voltage on the normal 0 dB setting? That could explain the gain differences..
3) Are tou saying that the control box affects sound in the same way an exterder cable will? If so, I could live with that to have better access to the headphone jack (I have multiple pairs of headphones and this would help a lot)

Raja@ASUS
08-11-2012, 05:51 PM
Hi,

1) I don't know, all I know is that the available gain is more than enough to drive all the loads I have thrown at it.
2) Yes, it's like extending a cable - same effect.

-Raja

Bojamijams
09-12-2013, 03:55 AM
Sorry for the thread necro but I just found it with google search and just want to commend Raja on how well informed he is and the great info he has provided here. Top notch work!

Glasofruix
09-13-2013, 08:55 PM
Too bad that happens waaaaaaay too rarely...

AVtemp
09-16-2013, 09:28 PM
Sorry for the thread necro but I just found it with google search and just want to commend Raja on how well informed he is and the great info he has provided here. Top notch work!

Ahaha,you must be kidding.
There is a lot of unanswered questions about Phoebus` lack of support and bugs,etc.