What, if anything, can you say about using ER4S with 02 vs Cayin C5 vs JDS C5 vs C421 with OPA2227? (I can't find a C421-AD8620 at a price I'm willing to pay)
I've got a Fiio Q1 DAC/AMP that I'm thinking about moving on from b/c the DAC doesn't seem to do much for me coming from iDevices. I use it both with a pair of over-ear cans and with ER4S. I don't need true portability - the O2's rechargeable battery is fine. But if the either C5 or C421 will sound noticeably better with ER4S, that would make the extra $$ worth it to me.
If you can shed any light, thanks! If not, thanks for all of the other knowledge you've dropped here!
Never listen to Cayin before, but C421-OPA2227 is pretty good as well, just about as good as O2 with ER4S. Neither is as good as C421-AD8620, but they are still excellent choice. Same can be said for JDS C5. These are all pretty good sounding amp with ER4S, but they don't quite have the kind of synergy as C421-AD8620. Actually you can convert a C421-OPA2227 to AD8620 by simply changing the opamp, but you need to know how to desolder / resolder SMD chip.