Summary:
I had a Krell KSA 250 driving Apogee DIVA.

I had the chance to find a second pair of Krell MDA500. The MDA500s are to the KSA250 what the MDA300 is to the KSA150.

I am now biamping the DIVA. The KSA250 is in charge of the bass and the MDA500s are driving the upper frequency ways.
I chose not to put the most powerful amps in the bass because :

mono blocks are leading to a better channel separation
transients ask for more energy

Anyway, the sensitivity of the amps keeps it consistent.

Great great amps. A bargain due to trade in.

Strengths:
Power, soundstage, bass, treble, midrange

Weaknesses:
electricity consumption, heat

Similar Products Used:
Krell KSA 250

Price Paid:  $4000.00 from Acquaintance

Summary:
I use these monoblocks to power my Martin-Logans Requests, which are, in my opinion, a brilliantly designed loudspeaker. I purchased these guys (MDA-300s)used at a very reasonable cost. They are phenomenal in every respect. For those of you who can not mentally place this model, it is an early 90's KSA 150 in a pseudo-bridged mode. The other review listed under this heading provides excellent information, but severely under rates these units. I have looked long and hard to find perfect sound for well over 12 years of my life (I'm 37) and never found anything that convinced me fork over retail amounts of dollars. This included being a broker of used high end equipment and representing up-and-coming product lines. I chanced upon these things in a real round about way, along with a KRC-2 preamplifier. In my years I have had many systems only to sell them within a year out of disgust. One simply can not trust most audio dealers and the opinions on audiophile publications because these people have alterior motives that motivate them to say what they say. As indicated, I have bought/owned/brokered all kinds of equipment, but was only able to warm up to Krell, Pass, and Classe designs.

I hooked these things in my system, and was joyously enthralled. If I don't comment on all the normal particulars, it is because everything sounds so downright correct, I honestly can not pick these things apart in the form of a critique. I just lay in my Stressless chair and relax with the music! I have never been able to do this-ever! In my humble opinion, these amplifiers have produced the best sound I have yet to hear, and my sense of hearing is reputed to be better than that of a Juno-winning recording engineer (Several people witnessed it). So, I am left speechless, and very content. If you can find a pair on the used market, jump over them as soon as you see them. They are that good. I know they are a class a design and run much warmer and consume more energy than other designs, but who really cares? At this level, you need to be comfortable with the design compromises made by the amplifier designer. In the case of the MDA-300s, there are none. The high operating temperature and increased energy use are a small price to pay for a perfect performance.

My less than enjoyable quest for good sound has come to end, and I can close the book on this chapter of my life. I never thought it would end! I have spoken my peace, because my ears, psyche, and soul now know it.

Regards,

David Zolyak, CSP, PE

Strengths:
Tremendous power, an amazing grace with the musical signal, never seems to be working hard, leaves no sonic signature, rock-solid image.

Weaknesses:
None that I aware of at this time.

Similar Products Used:
Classe CA-300, Bryston (Brightstown!)4B-ST, Mark Levinson 23.5

Summary:
I first heard about this product when Apogee used four pairs of these powerhouses to demonstrate their reference Grand loudspeakers at the 1992 Summer CES. It was also impressive to see the list of reviews/owners of these amps, including Tony Cordesman and Glenn Hammett of TAS, Ken Kessler and Martin Colloms of HFNRR, Lewis Lipnick of Stereophile, and Bill Brassington ("Brass Ear"). I owned a Krell KSA-150 at the time and it did a fine job driving my Thiel CS3.6's. But my dealer contacted me in 1993 that he had a pair of MDA-300 demos for sale. These were monoblock versions of the KSA-150, but did not use conventional channel bridging. Instead, the amp circuit has two separate hemispheres to amplify the normal and inverted version of the signal in a differential manner, not referenced to ground. Bias current was increased over the KSA-150 to enrich class A operation and global feedback was eliminated. The result is a 90 lb. (net), 32 output transistor, 1.8 kVA transformer-equipped monaural powerhouse with Stygian bass power and control. I listened to these first at my dealer's driving the big B&W 800 system. After hearing this system reproduce large orchestral works with ease, I decided to try them at home. These amps had a warmer sound than most solid-state, with a sweet, relatively grainless top end. Dynamics were effortless, soundstaging was wider and more upfront than the KSA-150 when the material lacked depth (the midrange and presence region of the KSA-150 is depressed, giving extra depth which can be a euphonic effect). Above all, however, was the bass slam and authority, which set the standard for its price class. [Currently I own the FPB600 and it is a superior amp except in two ways: the MDA-300's have a wider soundstage (probably a result of true dual mono operation) and their bottom end is the equal of the FPB600.] I was surprised to admit that the MDA-300's justified the doubled cost over the KSA-150; and this made me wonder if the $32,500 KAS was three times better than the MDA-300. They are big, each generates 400 watts of heat at idle, do best hooked up to dedicated 20 amp AC circuits for each amp, and can be operated well in both single-ended and balanced mode. And if you've got a difficult load, especially in the low frequencies, these amps can deliver the goods.