Unfortunately, in my measurements, "the most any output transformer" is worse than capacitor except some very expensive output transformers.
Most transformers cannot have over 30 kHz frequency and phase response, but capacitor can easily pass 100 kHz with good linearity. Some very expensive transformers can reach 80 kHz at small signal level, but not linear when signal level changes.
This design has the flat frequency response up to 200 kHz with only -1dB, if memory tells me right there is no transformer can do so. I will share my figure later.
There are many "mythology" on audio related stuffs on internet. Please provide the scientific measurement data to prove your opinion. Otherwise, you are telling your own stories.
Well sure - if you want to design a headphone amplifier that responds all the way to 200 kHz, then your strategy is just fine. If you want to design a headphone amplifier that responds best to
what you can hear, then you're missing the boat. As a device in the signal path, electrolytics are high in odd-order distortion. Moreover, they "cloud" the entire output. Even run-of-the-mill output transformers are more transparent than an electrolytic capacitor on the output. The difference is not really subtle. It's immediately obvious in direct comparisons.
The problem is that you're over-designing when the result is that your C14 capacitor will dictate most of the sound quality of the entire circuit. If you don't want output transformers, fine. I think that's your loss to close off that possibility, but it's a design choice that's yours to make. I just think if you're going on about the rest of the circuit, you would be better off designing some way to get rid of the circuit's biggest fault: C14. Maybe investigate the use of a DC servo if you don't want an output transformer. Right now, C14 is a band-aid over the entire circuit.
I'm not going to provide you with "scientific measurement data." The internet is full of references about electrolytic capacitor distortion and lack of transparency. Suffice to say there's ample evidence simply in the market for electrolytic capacitors: it's the reason they invented
audio-quality electrolytic capacitors in the first place (Black Gates, Elna Cerafines, Elna RFS Silmics, Muse ES, Muse FG, Muse KZ, etc.,etc., etc.). They improve upon the problem; they don't solve it.