What’s the most underrated used Audio Research gear?

100.2. Owned one and should have kept her. Wonderful amp.

@bpoletti - you hit the nail on the head.  PLUS once you upgrade them, they improve tremendously!  

The SP9 II & III ARE very good preamps.

I never understood the the criticism that they were or are lean. If they are then a warmer tube and or warmer cables will help if not cure. I have no problem the lowest of lows to come out of it let alone the mid bass.The soundstage to me is expansive and deep with well placed imaging, Especially with small room or close recorded material.Clarity, Dynamics are both exceptional IMHO. Nothing exaggerated even with the levels are turned up, no hardness or glare. i can only imagine the sound of the sp-11 ,sp-10. And for the price.

Still have a SP9 mkll, but wish I’d kept the SP3a.

sp11 a very good ARC tube pre-amp value IMHO,   Enjoyed one for many years.