Just tried to put a small tube preamp between DAC and AMP. It's a FOSI Audio Tube-P1. (Same as FX-AUDIO tube 03)
Replaced OP amps with Burr Brown dual OPA627 and soldered new Wima capacitors. Changing caps made the bass cleaner and darker.
It has bass and treble controls, and I'm really enjoying sound with the stock (no foam) pads and a little added bass. (about 2 oclock).
Just sharing my experience in case anyone's interested, lol.
Replaced OP amps with Burr Brown dual OPA627 and soldered new Wima capacitors. Changing caps made the bass cleaner and darker.
It has bass and treble controls, and I'm really enjoying sound with the stock (no foam) pads and a little added bass. (about 2 oclock).
Just sharing my experience in case anyone's interested, lol.