If the sound quality on the bipolar amplifier was poor, it sure was not due to the MRF455 transistors it used. More than likly it was being overdriven because those transistors, have much more gain than the switch mode MOSFET's and require less drive power.The Palomar ERF9530 is what the Rocketbox website says is used. IDK for sure but Whatever they are they work quite well & have very low amperage draw. The amp pictured above has been through Hell & back for the past year & still works as well as the first time I hooked it up. The Sound Quality is much better than the bipolar two pill mrf455 amp it replaced.