Krell Evolution 403 Amplifier Reviewed

Published On: March 16, 2009
Last Updated on: October 31, 2020
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Krell Evolution 403 Amplifier Reviewed

Need power? How about 400 watts of it? The Evolution 403 from Krell is a three-channel amp for the high-end audiophile. It's also beautiful enough to leave out to admire. Dr. T, Ken Taraszka, tests it out for HTR.

Krell Evolution 403 Amplifier Reviewed

By Author: Dr. Ken Taraszka

Ken Taraszka M.D. is an anesthesiologist by trade based in Tampa Bay, Florida. Ken is also a professional audiophile and home theater writer specializing in AV preamps and all facets of the audiophile market. In the past, Ken has been a staff writer and editor at He has also at times been a frequent contributor at


Krell is a legend in the audio business, especially when it comes to power amplifiers. Their new line of Evolution amplifiers are touted as their best amplifiers ever. That's a pretty big claim, but when Dan D'Agostino talks, you should listen. The new Evolution line is a follow up to the Evolution One amplifier, and heralds an entirely new way of doing things, opening up a new frontier in amplifier design. The Evolution 403 is a three-channel, 400-watts-per-channel model, selling for $22,000. The Evolution 403 is designed to be part of the highest-end home theater and multi-channel music systems on the planet. When that is your goal, don't expect things to come cheap.

The Evolution line utilizes active Cascode Topography, which eliminates global negative feedback, only allowing nested local feedback around the individual gain cells, making for a more open and liquid sound, while the massive power of these amplifiers ensures effortless audio reproduction almost regardless of your speakers' efficiency. Krell's Current Mode and CAST circuitry are employed, as well as circuit topography, which makes a huge step forward in bandwidth capability, allowing near perfect performance in the audio spectrum.

Amplifiers require good power to make good power, and the Evolution 403 uses the same power supply found in Krell's own Evolution 900 900-watts-per-channel mono-block amplifiers, supplying 6,000-volt amps of power, while both electrical and magnetic shielding keep the power supply from interfering with any of the audio circuits. The power supply itself filters RF noise, as well as correcting asymmetric power waveforms and DC current on the main AC line. All this makes for not only a large but a heavy amplifier. The Krell Evolution 403 is 17.3 inches wide, 9.8 inches tall and 26.1 inches deep, weighing 175 pounds. Krell quotes heat output as 1,270 BTU per hour in standby and a max of 7,700 BTU per hour in heavy usage; power consumption can be up to 5,000 watts.

The specs on this amp are amazing. Frequency response is 20 Hz to 20 kHz with +0 to -0.18 dB variance, with the ability to extend from 0.5 Hz to 120 kHz, with only +0 to -3 dB variance. Signal to noise is ratio is >116 dB "A" weighted at full power output, while distortion is rated at 0.15% at 20 kHz and full 400-watt output into an eight-ohm load. The output power doubles down to 800 watts per channel into four-ohm loads and 1,600 watts per channel into two-ohm loads.

When you read the specs, you know why this amplifier is so big. This is no minor piece of engineering, and the piece reflects that in every regard. The fit and finish of this amp is amazing. Mine came in a beautiful silver aluminum finish. The entire unit is machined from aluminum, and has a wonderful silvery gleam to it. The front has a thick, machined faceplate. There is a matching middle section of the Evolution 707 AV preamp and a large single button in the middle for activating the amplifier from standby mode, with the only light being a the ring around the large central power button, red for standby, blue for on.

The actual breaker switch is on the rear above the 20-amp IEC power cord receptacle. I have frequent power outages in Florida, and during one of these, the rear breaker shut off. Two 12-volt triggers and a control for the backlighting of the unit are on the rear as well. On the left of the rear are the input and outputs of the unit. Each channel is aligned vertically, with Krell CAST, single-ended and balanced connections on top and a set of seriously huge binding posts that accept spade lugs only.

The Hookup
I was thrilled to know this amplifier was coming, as I have heard so many good things about the new Evolution line and hadn't yet heard the amp in my own system. When it came, I quickly realized I would need some help. The amplifier is really heavy, but two of us were able to safely unpack it and move it to the front of my home theater. I ran the matching Evolution 707 AV preamp's front three channels to it with Transparent Reference balanced interconnects and speaker wire to the Escalante Fremonts for my left and right, with a Definitive Technology Mythos Ten center channel. I ran the 20-amp power cord to its own dedicated 20-amp line and powered it up. I later swapped in my Canton Vento 809 DC and 805 Center channel for comparison. I let the amplifier burn in for two weeks before doing any critical listening, but when I went back and listened to the same discs after another few weeks, the sound was even smoother. This didn't come as a huge surprise, as this amplifier is built with the finest components made and these can take a while to fully burn in.


I started off with the Alan Parsons Project I Robot (Sony) on DVD-Audio. The introduction to the title track was very open and smooth, with a vast soundstage. As the song picks up, the definition and detail were the best I have ever heard. There was openness to the sound that was unbelievable. Moving forward to "I Wouldn't Want to be Like You," I heard just how agile this monster of an amp is, as it easily handled the large dynamics and deep bass of this song while keeping plenty of separation between the instruments. The start of the bass line early on in the song was to die for and filled my room with authoritative bass to any listening level you could want. Be it quiet background levels or 100+ dB levels, it was always present.

I cued up Annie Lennox's Medusa (Arista) and was immediately impressed with the subtlety of the Evolution 403. The soft and delicate nature of "A Whiter Shade of Pale" was wonderful, being open and involving without edge to the upper end. The soundstage was huge and each minute detail was clearly portrayed. "Train in Vain" wrapped me in Annie's luscious voice and kept the bass line perfect. When I went back to this album several weeks after using the Evolution 403, I was amazed to find its reproduction of Annie's voice even more textured and appealing, with even more warmth.

For something a little edgier, I went to the Beastie Boys Paul's Boutique (Capitol) and turned it up a lot. The start off of the album comes in quietly and builds in intensity. Before I knew it, I had "To All The Girls" jammed and when "Shake your Rump" kicked in, I was surrounded by 110 dB or B-Boys, the cleanest and clearest I have ever heard them. I quickly turned it down, but never lost the energy and excitement of the album. "High Plains Drifter" floored me, as the Krell Evolution 403 would play to literally any level you wanted and sounded good at all of them.

I went to something a bit softer with Keb Mo's The Door on SACD (Sony). The smooth ease of Keb Mo's music was perfectly reproduced by the Evolution 403. The vocals were rich and clear. "Stand Up and Be Strong" is faster and livelier than some of Keb Mo's other pieces and the Evolution made the notes jump from my speakers with unaccustomed vigor. On "Mommy Can I Come Home," the quietly played guitar was perfect. Each note filled the air, while the vocals were true to life.

Three-channel amplifiers are obviously meant to integrate into multi-channel audio or home theater systems, so I had to test this on some multi-channel music, too. I put in Alice Cooper's Welcome to My Nightmare (Rhino) on DVD-Audio and I was wowed. The start of the title track showed me a huge surround field and deep bass, with each note perfectly detailed. Moving to "The Black Widow," I remembered why I liked this album so much as a child: the music is fun and twisted and the Krell Evolution 403 reproduced it with incredible detail and ease.


I watched Transporter 2 (Twentieth Century Fox Home Entertainment) on Blu-ray with its DTS HD Master Audio track and heard details I never noticed before. From the tiny tink of contacts to massive explosions, this amp reproduced it all with an ease and clarity that drew you into the film. This isn't the best film, but the Krell Evolution 403 greatly improved my enjoyment of it, thanks to the incredible detail and control of the intense dynamics of the soundtrack.

I watched the new Batman film The Dark Knight (Warner Home Video) and was amazed at how well the Krell Evolution 403 did at keeping vocals clear, while never missing a beat through the massive explosions. Minute details of the Dolby TrueHD soundtrack came through with a precision and a specificity that were amazing.

Low Points
The Krell Evolution 403 is huge, heavy and generates enough heat to have it listed in the spec sheet. During high-level listening sessions, it can serve as a small space heater, and is even pretty warm in standby mode. Once while I had this amplifier, a power outage in my neighborhood flipped the rear breaker, so you might need to have access to the rear of this amplifier if you have this problem in your area. Sonically, there is nothing to fault.

Once I fired this amplifier up, I realized I might be spoiled for life. Sure, Krell is known for exceptional bass, but this amplifier also does liquid smooth midrange and detailed but not harsh highs. There is nothing cold or sterile about this amp. It is musical and has more balls than any amplifier I have ever heard. I never had an amplifier so powerfully grab the woofers of my speakers. Not only did it give me the best bass I have ever heard, but it also showed me just how much bass my speakers were capable of reproducing, without any deficit in the quality of the rest of the audio spectrum. Subtle nuances were perfectly portrayed, while dynamics seemed limitless. Quiet passages were amazing and could be deathly silent in between massive explosions of sound. I played this amplifier to obscene listening levels and never once heard it compress or clip. It should be noted that this amplifier will take a long time to fully burn in and, after several weeks, mine continues to improve, becoming smoother and more liquid as each day passes.

Krell has put their top technology into this amplifier and it really shows. This is undoubtedly one of the best amplifiers made. The fact that it is a three-channel amp also makes it the best home theater amplifier of all time. You simply cannot go wrong with this amplifier. Give it a sturdy base to stand on, feed it plenty of power, sit back and enjoy the best you can get. Don't fret about the price - it's expensive, but it's worth it!

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