The A90D is an upgrade across the board. It’s more powerful, less distorted, and includes some great quality-of-life improvements. A front panel volume display and remote control allow you to control the A90D from the comfort of your couch. A ground loop noise terminator ensures clean output no matter how long your audio chain becomes. Output volume memorization allows you to dial in on the right level for you–and keep it there for next time. The A90 uses a standard volume potentiometer. These often suffer from channel imbalance at low volumes, which makes listening to sensitive IEMs a challenge. The A90D, on the other hand, uses an R2R volume controller. These offer massive advantages over standard potentiometers, like outstanding THD+N, SNR, and extremely well-balanced channels.