What’s the most underrated used Audio Research gear?

Classic 30 and the classic 60 amps.

I nominate the 100.2 solid state amp. Sounds excellent, and I wish that I had one.

Maybe not sleeper, but I always thought the “SE” versions of stock ARC components were meaningful (but pricey) upgrades and when bought used you get the upgraded versions at a very nice discount.  Kinda like when you buy used SMcAudio-upgraded McCormack amps — quite the bargain I think.

The D200 and D300 SS amplifiers still sound great even today. The SP-11 with its SS power supply was another exceptional unit.

I agree with Roxy.  Although the 100.2 was probably not underrated (try to find anything bad said about it, it’s all raves…), for the price, especially used, it’s a fantastic amplifier.  ARC should do what other companies have been doing and come out with retro products, like the 100.2 or the LS2B.  Sell them for $5000 or less to fill in that gap in their product line, they would sell like hotcakes and get more people into the line.  

The SP9 II & III were very good preamps that don't get mentioned often enough. Also the SP6 was great piece.

+1 ozzy62 

SP6 was my long time favorite.

ARC D-79B and D79 were quite good.  ARC made a lot of underachiever tube amps.

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.

SP 14, advertised as better than the sp-9, based on sp-15 technology.

Dual 76B and SP3-A-1. Much magic there. Especially when used to drive Maggie Tympani IIIs. 

17 is a great pre… the HD amplifier is a brute of a sleeper… hybrib tube / SS

One you will seldom encounter or hear about are the mono tube amps: VM220.  Magical.

I've been using an ARC LS7 that I bought used back in 1998(!) and it has consistently been an absolute champ. I have turned it off a handful of times in that period, and never changed a tube. what a demon!

I will back the Classic 60 Amp also.

Have owned mine since New, and it has been Rebuilt and Modified by Scott Frankland and Associates. He installed Bias Pots on the Back Deck & Test Probe Ports on the Side in proximity to the Bias Pots. Absolutely brilliant since all I need is my milli amp Tester (Voltmeter) with Probes and Adjust, and or Check the Bias Monthly.

Scott has also Replaced all Caps and the Amp works flawlessly.

In the time that I have owned this Amp since New, I had one Failure a number of Years ago when I tried KT90 Tubes. One Tube blew the Grid Resistor and it also took out a FET.

Recommended Tube now, even by Audio Research, is the Sovtek 6550WE which is the only type that I use. KT90 Tube experience was not pleasant. 

Months ago, I started researching:" What Amp would I replace the Classic 60 with if needed? " After many Months' reading everything I can get my hands on which includes this Forum, I do not have a Clue.

+1 @jimmy2615 

Have the 100.2. Was recommended by Marc Mickelson, a reviewer with Soundstage at the time I bought his ARC Ref3 and PH-7 through Agon (now with Audio Beat).  Love it. Has very limited negative feedback. Unfortunately I think it is now on the list of ARC gear they will not repair as some resistor is no longer available. Regret having sold my Ref3.  Warm musical darker sound signature. Currently looking for used ARC preamp, likely 5SE, but appreciate this thread and input above.