Price Paid:  $1750.00 from Audiogon

Summary:
After having one MKll I decided to go mono block. This is what reference is all about. Just having one MK ll is a joy and a pleasure to listen to. Going mono block gives much more of what's there. The soundstage is breathtaking. Having so much current pushes my Mags(3.6r) with ease. I can even here Roy Ayers (Good Vibrations) walking in the backround on stage!
One of my reference recordings, Patricia Barber recording in half speed on vinyl, by the way this should be in every vinyl collection. This is truly a work of art and reveals the difference when you increase the current. There is more air between the instruments and I can hear the soft end of Patricia talking. I'm talking about each and every single word. In other words I didn't have to read the liner notes to see what she said. I was able to hear it from the break!
Then came Mycoy Tyner, Land of the Giants. This is recorded using the Sonoma DSD system. From the opening track, Serra Do Mar, it grabs you and forces you to pay attention to what's ahead. I tell you by the time I came to, I had experienced something truly special. Just to make sure that this is the real deal, I went back to vinyl. This time I went old school. Chick Correa, My Spanish Heart. Side 3 Track 0ne, Armando's Rhumba. Stanley's Bass and the handclapping can only come to life with the right juice pushing it. I listen to the same recording on CD. The CD sounded sloppy and couldn't keep up where as the vinyl version had the pace and the realism in spades!
In addition to, it absolutely necessary to have the best cable if you decide to invest and take this leap. I went from MIT Shot Gun series to VHP Pure Silver by Guerilla Audio. This made all the difference in the world.
My sessions are longer than what they use to be. In my book that's alright with me!

Strengths:
Sounstage
Tight Bass
Inner Detail
Spectacular Realism
Front to Back Nuances

Weaknesses:
I wouldn't call this a weakness per say. This amp still demands a high price on the used market. I've been lucky to have paid under 4K for both amps. Normal price for a pair of mono blocks closer to 5-5.5K.

Similar Products Used:
Krell
Ayre
Mark Levinson
Music Fidelity
Conrad Johnson
Bryston

Price Paid:  $2000.00 from Audiogon

Summary:
First I am not going to bore you with a bunch of specs or try to get intellectual about the D400MKII. What I will say, and this is from 32 years of experience with this hobby, that I truly love. That the D400MKII is by far a class A product. Even still after all these years. I had the pleasure owning one a few years ago. I didn't really appreaciate and so I got rid of it. Well now I bought another one for the same amount that I paid for, which is still a great value and now I am in Nirvana. This is what makes my Mags come to life.
I have long been a fan of Ayre gear, but it didn't do what was really need for the 3.6r.
All I can say in a nutshell. Get this amp if you can. The D400MKII outperforms power amps well over the 10k-15k range. You best believe the D400MKII will be with me for years to come.

Strengths:
Moves with Authority
Articulation
Tight Bottom
No Strain

Weaknesses:
NONE!!!

Similar Products Used:
Krell
Ayre
Conrad Johnson
Bryston

Price Paid:  $0.00 from Audiogon

Summary:
This review is for the D300,NOT the D400!
I would like to say that per the product literature, the D240 and D300 are basically the same amps,but the D400mk11 is not similiar to the D300. So one cannot
compare a D300 to a D400mk11!
First off, I am very impressed with the build quality of the amp.First rate,as with all Audio Research products.I have been listening to my D300 a ton since I bought it and I can say I am really impressed with the bottom end on this amp. I noticed a huge improvement in bass with this amp when compared to my Pass Labs Aleph 3! But the Aleph 3 is only 30wpc. The sound of the D300 is very well rounded and smooth, not at all harsh and trebly sounding like some high end amps.I think a little of the finese of the Pass Labs Aleph 3 is missing,but it more than makes up for it in the bass area. The detail is ever so present and this amp never strains to make the music clear.I am running a Audio Research SP6b tube pre-amp and I must say that Audio Research components seem to match up great together sound wise. The soundstage is huge and the highs are crisp and clear.The bass is gigantic,always present and never lacking. Great amplifier.

Strengths:
Exceptional build quality,detailed top and bottom end sound, great speaker connectors,quiet.

Weaknesses:
Well you can't lift it easily.

Similar Products Used:
Pass Labs Aleph 3,Audio Research D52b,B&K
St2140 and ST120,Linn LK100,crappy AudioSource Amp 2!

Price Paid:  $0.00

Summary:
This review is for Audio Research D-300. This model came out in the same year as D-400mkII. It've amazed me how sweet the sound is for a solid state amp. The only different between this amp and the big bother D-400mkII is the wattage. Sonically, this amp produced very tight bass, sweet mid, and very detailed high. What else can any one ask for a $4000. Audio Research build this amp like tank and the sound only gets better with time. It would outlive you any other amp. If you can find one, you've got lucky.

Strengths:
Plenty power, sounds just like its $6000 big bother D-400mkII. Built quality.

Weaknesses:
Very heavy baby, yah!

Similar Products Used:
ARC D-400mkII, Krell, Bryston.

Summary:
This review is for the original D400 (not series II)

I've used this amp since 1993 to drive my Apogee Caliper Signatures. I'm also using an Audio Research LS16 tube preamplifier. This amplifier gives me the best of both worlds. The liquid midrange and highs of tubes along with dependability, flexibility and high current capability to drive my Apogees.

I have to strongly disagree with the previous post mentioning that the D400 lacks low end detail compared to the mk II. I would describe the bass of the D400 as being very adequate and taut, however, does not have the ultimate slam as some other solid state amps. I've auditioned the D400 mk II and did find that the bass was a little tighter however the liquidity in the midrange seemed to suffer in order to get the tighter bass. I still prefer the original D400.

Strengths:
Very tubelike liquid highs and midrange with enough current to drive just about any speaker.

Weaknesses:
Does not have the ultimate bass slam.

Similar Products Used:
Threshold S300 II amp, Mark Levinson 27.5, Audio Research D400 mk II.