[MikuLover]

"excellent match to colder and more neutral IEM like ER4S in a subtle way"
 
Won't the 3x gain be a bit too loud? Will channel imbalance be present at low volumes? I am planning to get T1 or the JDS O2 amp currently.

 

[ClieOS]

Whether 3X gain is too much will depend on both the source and the headphone in question. With a full 2Vrms signal, it probably will be a lot for many highly sensitive headphone; but if it is iPod level 0.55Vrms line-out, they will most likely be fine.
 
I don't remember any noticeable channel imbalance with the T1, but I can't confirm it doesn't have any either. The review unit is a loaner and there is no way I can check for it, but I'll assume there should be some channel imbalance on the lower range (7~8 o'clock) simply because of the type of volume pot it used.

 

[MikuLover]

I am so sorry not to mention that my source is a fiio x3 and I am currently using the er4s. Any idea on how many V the line out on the fiio x3 is? ( around 1.7V I think??) I am currently looking for a serious amp for my er4s but can't really find anything that would really fit my budget other than the CMOY2.03, JDS O2, Fiio E17, JDS C5, IBasso D4, and the T1 of course. 

 

[ClieOS]

X3 should be more than enough to drive ER4S by itself, but if you are planning to stick to ER4S for awhile and have no plan of upgrading any time soon, you can try to find yourself a 2nd hand JDS Labs C421 with AD8620. It has some of the best synergy with ER4S than all other portable amps I have heard.