Report The Headcase Stax thread in Headphones Posted December 31, 2020 On 12/29/2020 at 9:33 PM, Spychedelic Whale said: It was a silver one recently ordered from Japan and the serial number SZ2, wasn't suppose the new ones to be SZ3 ? SZ2 are current production. Also amps... I think I posted someone's FR graph here a year or so ago recording no difference from 252 on up to 717 at very high amplitudes with an 007a. This suggests to me that Stax amplifier differences lie in the ultrasonic region. On the other hand I haven't heard any amp other than 323S, and this puts me in contrast a little bit with others here.