Threshold - S/300 Was there a Series 1 & Series 2

I agree with Rockvirgo.

I think the Series II says so on the front badge. The early S/300's, both Series I and II, say "overall feedback free" on the front. These have light grey tops and rear aprons. The later models S/300 say "optical bias" on the front, say class A/AB, and have black tops and rear aprons.

I owned a S300/2 It was a series 2 ( non Optical Bias ) ...List$ was around $2300-$2800 depending on year made.......Great amp!