Is iBasso D12 an upgrade from Xonar Essence STX?

According to Stereophile, the STX has an output impedance of 10 ohms. I suspect that the D12 & P4 would have a lower (superior) output impedance than that, and my understanding is that this may help with your relatively low impedance headpones. For example, iBasso informed me that the impedance of the D6 is a fraction of an ohm in the audio frequency range, which is very good indeed. (you'd have to enquire with them to get the spec for the D12 & P4 though)

As far as I can tell, both the D12 and P4 have significantly more power/voltage than you need for your current headphones. There is absolutely no problems with loudness with either unit. However, if you ever want to use high impedance headphones, the STX may be able to drive them louder than either of those iBasso units, because the STX has a higher output voltage than even the P4: according to this Stereophile review of the STX: http://www.stereophile.com/content/asus-xonar-essence-ststx-soundcards-measurements it can go as high as 7.03V (I assume this is an RMS figure - it normally is. I have contacted the author and asked them - no answer yet).  If the P4's specification is RMS, this means the STX could potentially be as high as 4dB more than the P4, although this is just in theory, and also, the higher output impedance of the STX would drop the level slightly. 4dB more isn't a lot - a 3dB increase sounds perceptually about 23% louder. (I don't know exactly how much louder a 4dB increase sounds - I have yet to find an actual formula - only a table)  If the STX voltage measurement is 7V peak, then the P4 and STX would be almost the same - I calculate the STX to be only 1dB higher than the P4 in that case.

I urge caution with the iBasso power specifications though, because they may be quoting peak power, instead of the more typical RMS power. For example, for the D12, it would be impossible for it to reach 110mW RMS into 32 ohms unless it has circuitry to boost the power supply,  or at least some way of extending the signal outside the range of the power supply voltage. (the Headstage Arrow amp does in fact do this, but they make a big song & dance about it, too). If it's a peak power, that means the RMS power would be half that - 55mW.  Going from 55mW up to 110mW is a 3dB increase, which is only a 23% increase in sound level, so it's not as bad as the difference in power level would suggest. 

For the P4, it would, technically, be possible for it to reach it's power spec of 600mW (RMS, if they mean RMS) into 32 ohms, but only when running from the 16V adaptor. When running from the 12.6V battery, it would not be possible.  (again, unless it makes special provisions)

If you want to compare iBasso power specifications with typical power specifications from other manufacturers, I suggest that you contact iBasso and ask them for the RMS power, just to be on the safe side.

I can't tell you what you really need to know at the moment, though - how the iBasso units sound compared to the STX. ;^)

Greg.

I've looked into this iBasso power rating issue a bit more. 

Given that headphone amp chips may have an output that covers the entire range of the power supply (i.e - a "rail to rail" voltage swing) I think that it's probably more likely that iBasso are simply giving the best case, absolute maximum power.  For example, a D12 running from a USB power supply of +5.3V (although the maximum USB voltage is supposed to be 5.25V) would, in theory, be able to achieve it's power rating.  One reason I stated that iBasso may be supplying the peak power is simply that this is what they seemed to tell me themselves, however I'm hopeful that this is simply a miscommunication. (and I think it could easily be) 

Greg

The Stereophile measurements of the STX are indeed RMS. (so it's maximum output is 7.03V RMS, when it is configured for high impedance headphones)  Their AC measurements are RMS unless stated otherwise.

Greg.

You're welcome. Just by the way, I have discovered the the FiiO E7 and E10 (and possibly others) use a DC to DC converter to create a higher power supply voltage. It's conceivable that iBasso are doing this too.  Also, in this comparison of the iBasso Dzero and the FiiO E7: http://www.head-fi.org/t/571116/review-ibasso-d-zero-with-fiio-e7-comparison the the reviewer reports that the iBasso could go louder. To me, this suggests that iBasso could well be quoting RMS power for the Dzero, which is the right way of doing it.

If they are quoting RMS power for some models, but peak power for others, that is confusing though. I am trying to get to the bottom of all this but it is very difficult due to the language barrier.

Greg.