[raoultrifan]

I don't think output impedance is directly related to "hiss". Of course, 9-ohms headphones are usually very sensitive and some hiss might be heard, but this is mostly related to how the amp pairs with the headphones used and also internal noise provided by voltage-amplification stage and gain used and output buffer's noise too. I would suggest you to try before buy, if possible, because if we're having a look over TI's datasheet for TPA6120A (http://www.ti.com/lit/ds/symlink/tpa6120a2.pdf) then the minimum recommended headphones impedance would be 16 ohms, so theoretically neither Mojo, Air, UA-M10 etc. should not perform admirably on 9-ohms headphones (which is not quite right, of course, because TI's datasheet presents a schematic having a 10-ohms output impedance and a good designer could use low-impedance output inductors to lower any possible oscillations). So, please give it a try if possible and post your findings here.
 
A 1/8 rule between amp's impedance and headphone's impedance would be wise, of course, but mostly because the voltage that drops on internal's output resistors/inductors will be higher for amps having a higher output impedance. Most likely frequency linearity might suffer if output impedance of the amplifier is very close to headphones impedance (http://www.meier-audio.homepage.t-online.de/tipstricks.htm and http://www.innerfidelity.com/content/musings-headphone-amplifier-output-impedance#GipPCiW1utzugX1r.97 explain this very precisely!).
 
P.S.: Mojo and iDSD micro/nano have <1 ohm output impedance, so could have a slight advantage over Air when speaking of 8-ohms heapdhones, but I still think you should give it a try to each of the above DACs.

 

[Joaco]

  I don't think output impedance is directly related to "hiss". Of course, 9-ohms headphones are usually very sensitive and some hiss might be heard, but this is mostly related to how the amp pairs with the headphones used and also internal noise provided by voltage-amplification stage and gain used and output buffer's noise too. I would suggest you to try before buy, if possible, because if we're having a look over TI's datasheet for TPA6120A (http://www.ti.com/lit/ds/symlink/tpa6120a2.pdf) then the minimum recommended headphones impedance would be 16 ohms, so theoretically neither Mojo, Air, UA-M10 etc. should not perform admirably on 9-ohms headphones (which is not quite right, of course, because TI's datasheet presents a schematic having a 10-ohms output impedance and a good designer could use low-impedance output inductors to lower any possible oscillations). So, please give it a try if possible and post your findings here.
 
A 1/8 rule between amp's impedance and headphone's impedance would be wise, of course, but mostly because the voltage that drops on internal's output resistors/inductors will be higher for amps having a higher output impedance. Most likely frequency linearity might suffer if output impedance of the amplifier is very close to headphones impedance (http://www.meier-audio.homepage.t-online.de/tipstricks.htm and http://www.innerfidelity.com/content/musings-headphone-amplifier-output-impedance#GipPCiW1utzugX1r.97 explain this very precisely!).
 
P.S.: Mojo and iDSD micro/nano have <1 ohm output impedance, so could have a slight advantage over Air when speaking of 8-ohms heapdhones, but I still think you should give it a try to each of the above DACs.

I won´t get technical about hiss and amp output impedance. I´m looking for what you suggest last.
 
None of these are available at shops in my country so that is why I´m asking for other´s experience.
 
Thanks anyway!

 

[High-End-Addict]

Hello i wonder if someone experiences the same volume changes on CONDUCTOR AIR :
it happens from time to time when I touch the aluminium box : all of a sudden the volume triples ! the display don't change but the volume yes.
Supposing volume is set at 35 , all of a sudden it's like being at max 99 !
just clicking le vol- minus once makes it back to normal ; meanwhile it hurts my ears (and possibly my headphones as well)

I suspect that when I touch the box or the headphone jack i discharge some statics electricity and the volume control resets to maximum.
Very strange , noisy and annoying !.

 

[omniweltall]

Hello i wonder if someone experiences the same volume changes on CONDUCTOR AIR :
it happens from time to time when I touch the aluminium box : all of a sudden the volume triples ! the display don't change but the volume yes.
Supposing volume is set at 35 , all of a sudden it's like being at max 99 !
just clicking le vol- minus once makes it back to normal ; meanwhile it hurts my ears (and possibly my headphones as well)

I suspect that when I touch the box or the headphone jack i discharge some statics electricity and the volume control resets to maximum.
Very strange , noisy and annoying !.

That's really annoying, and not to mention, dangerous as well. Pse contact Burson for help.

 

[Wyd4]

Hello i wonder if someone experiences the same volume changes on CONDUCTOR AIR :
it happens from time to time when I touch the aluminium box : all of a sudden the volume triples ! the display don't change but the volume yes.
Supposing volume is set at 35 , all of a sudden it's like being at max 99 !
just clicking le vol- minus once makes it back to normal ; meanwhile it hurts my ears (and possibly my headphones as well)

I suspect that when I touch the box or the headphone jack i discharge some statics electricity and the volume control resets to maximum.
Very strange , noisy and annoying !.

I experienced this today.
Using iems no less. My ears are ringing, still don't know if my iems are damaged and to boot I was laying with my eyes closed on the couch so it scared the living poop out of me.

It happened to me when I changes volume via remote. Boom full volume. I unplugged the unit. It still said 11 volume. Plugged in. Tentatively pressed play and volume was still flat out. Pulled the headphones.

Now I am paranoid

 

[nicknack40]

Is Anybody using this as a Desktop Combo rather then portable this looks ideal. Anybody using this with LCD2-C May replace my Magni 3 and M/F V90 DAC for an all in one combo and the pre out is perfect for my Ruarks Actives

 

[Wyd4]

Is there any audible difference in using this powered via the 2nd usb port or is purely for OTG compatibility?