Well i can't exactly tell you their differences since i don't have a separate amp.
So with d1 i didn't use senns hd650 but a headset (senns pc 160).
So basically i went from d1 & headset to ST & hd650.
I'm not familiar much with the "audiophile" terms but if you want to read a noob's journey (aka wall of text) into the "head-fi" world, go on and read ahead.
Around 3 years ago my first dive into the more expensive headphone world was hd650 and a corda cantate. I bought them at the same time without ever before having a prior listen to any other high end headphones.
With that in mind i was expecting something completely "magical". Insane bass enough to shake your head, extreme soundstage, and "club feeling". (i mainly listen to trance / vocal trance but i can really appreciate everything that is good)
Can't exactly describe it with words but i was really expecting to be completely thrown away by the sound for my new expensive investment. (330 euros for the cans and 450 for the amp)
So when they both finally arrived i burned them in for around 6 days.
Boy i was disappointed. It wasn't even close to what i was expecting.
I was like "where is the bass everyone talked about that hd650 got?"
I was expecting something more dynamic. To feel the voice, the instruments, the bass, everything to be more "alive".
In corda cantate's defense, i only used it together with it's DAC which wasn't really the selling point of the amp and also i didn't change the gain of the amp. Which i think it needed another scale to drive the 650's better.
Combined with the "veiled" sound (now i see why everyone talked about that characteristic of the cans) and not testing the amp properly made me prefer the sound of my headset + audigy ls rather than my new equipment.
At least i had the sound "in my face" and it was better for games when i wanted to hear footsteps etc.
Did i dive too deep on my first contact with head-fi? Maybe, but all this led me to decide to sell both my cans and amp and maybe after some months to buy something cheaper like ad700 or dt880 and not bother much with amps and stuff.
I sold the amp but couldn't find anyone to sell the headphones. So they were stuck in their box for almost 2 years (still smell as new) without ever trying them again. (what's to try with the audigy ls anyway)
I bought a new pc and the new mobo didn't recognize my old audigy so it was time for a new card cause the onboard realtek is easily the worst piece of electronic equipment i have ever come αcrossed. Period.
Even tho i play games every day, i value music more so i decided to buy a xonar card.
I was highly satisfied by it & my headset and i promoted it to many friends and got around 4 more people to buy it.
Since it was so good for my headset i decided to give it a go with my senn 650 just for the "kicks".
While with d1 you could get high volumes with hd650's, the sound was flat and not enjoyable.
But it was enough to spark my interest again about those headphones. I knew they had much more to offer than with what i've seen so far.
Also with 3 years passed i got my hands around some more quality music so i decided to give it another go.
But this time i didn't want to spend very much on amp / dac cause my budget was very limited plus the disappointment would be lower if i wasn't satisfied again
And here i am with ST. This time around i had a more realistic idea of what headphones in general are able to achieve.
For example i knew i could never get the bass that you can get with a subwoofer ofc. Simple physics. The low frequencies need more space to travel to extend to their full etc.
I never knew my headphones could sound so "alive" and so (i don't know the english word for it so i'm gonna use google translate) "vigorously / perky".
It certainly feels more aggressive than with d1.
I can see why some might be a little annoyed from the trebles of the card with some cans especially on higher volumes but i like it. (650's aren't known to be so bright anyway)
From my little time with my previous amp i can say for sure that the cantate was a lot "warmer".
When the recording is good (and lossless) it's really a joy to listen.
But i quickly learned about the "loudness war" and it's effects.
Good recordings vs poor stuff (not in file quality) it's day and night to spot the differences.
Also i never experienced fatigue with either of those cards / cans combo and trust me when i say i listen to headphones all day. (no speakers)
And i know what fatigue is like cause when i use some old closed type philips headphones i bought many years ago when i go to my hometown, you get discomfort pretty fast from listening to them. Could be the closed design with extreme isolation and the pressure that is created. I just know i can't listen long periods with them.
Too long didn't read version: I'm satisfied with the result for the money i paid.
