Note that this is a discontinued product. You may want to visit the brand's page here to browse their newer products.
What reviewers think
Bloggers and YouTubers have tried this product—so we've summarized their strongest opinions below. Links to full reviews follow.
All
KSA i400
reviews
Manufacturer details
- Power Output: 400 Watts per Channel into 8 Ohms, 800 Watts per Channel into 4 Ohms
- Frequency Response: 20 Hz to 20 kHz, ±0.1 dB, 10 Hz to 100 kHz, ±3 dB
- Total Harmonic Distortion: < 0.05% at 1 kHz, 400W, 8 Ohms
- Signal to Noise Ratio: > 105 dB, A-weighted
- Gain: 26.5 dB
- Input Impedance: 100 kOhms (balanced XLR), 50 kOhms (single-ended RCA)
- Output Impedance: < 0.05 Ohms
- Damping Factor: > 400 (20 Hz to 20 kHz)
- Inputs: 1 x Balanced XLR, 1 x Single-ended RCA
- Power Consumption: Idle: 100W, Maximum: 2000W
- Dimensions: 19 in (483 mm) x 7.5 in (190 mm) x 21 in (533 mm)
- Weight: 100 lbs (45.4 kg)
Brand highlights
Taking a step back to look at reviewers' thoughts of the brand's entire lineup—not just this product—what stands out most is the following:
- The iBias technology allows Krell amplifiers to operate in Class A, delivering its sonic benefits, without the typical heat and power consumption drawbacks, making it suitable for modern lifestyles and versatile placement.
- Krell products often incorporate fully balanced, fully complementary circuits throughout the entire audio path, reducing noise and improving the slew rate for faster transient response.
- The power supply is robustly designed, allowing for consistent doubling of power as impedance halves down to very low ohm loads, ensuring excellent speaker control across a wide range of speaker types.
Select products
K-300i Integrated
- Positioning: Positioned as an all-in-one solution for modern audiophiles, combining amplification and digital streaming capabilities.
- Description: Delivers 150 watts per channel with advanced digital streaming capabilities, making it ideal for those who want a compact yet powerful system. Unlike the Duo XD series, which focuses on pure amplification, it offers built-in streaming services like Tidal and Spotify, making it perfect for users who prioritize convenience and digital integration. Its HDMI 2.0 inputs with 4K UHD passthrough also set it apart from the Solo XD series, catering to users with home theater setups.
Duo XD
- Positioning: Designed for high-end stereo amplification, offering models with varying power outputs to suit different needs.
- Description: Features Krell's iBias technology to deliver Class A sound quality with greater efficiency, making them suitable for audiophiles seeking high fidelity without excessive heat. Compared to the K-300i, the series focuses solely on amplification, providing more power and control for larger setups. Its advanced cooling system and protection circuitry make it more robust than the K-300i.
Solo XD
- Positioning: Krell's line of mono amplifiers, offering high power and precision for dedicated audio channels.
- Description: With high power output and Krell's CAST technology, provides excellent sound quality and system integration. Unlike the Duo XD, which is stereo-focused, the mono design allows for more precise channel separation and power delivery. Its ability to deliver 575 watts into 8 ohms makes it more powerful than the Duo XD.
KSA-i400
- Positioning: Krell's flagship stereo amplifier, offering the highest power and performance in their lineup.
- Description: The groundbreaking KSA-i400's 400 watts per channel and advanced iBias technology make it the pinnacle of Krell's amplification offerings, providing exceptional power and clarity. Compared to the Solo XD, it offers stereo amplification with even greater power. Its robust build and high-current power supply ensure it can drive any speaker with ease, setting it apart from the more integrated-focused K-300i.
Our take on the brand
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Used
Krell
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Our summary
Product Strengths
- Very clean and noise-free output signal provides a stable soundstage with a very black background at any sound level
- Exceptional bass control and depth delivers a powerful and tight bass response that underpins the overall musical experience
- Offers flexibility with mono, stereo, and bi-amping operating modes, allowing for system upgrades and configuration changes
- Dynamic and fast, reacting instantaneously to the signal it receives and delivering power and subtlety where needed
- Continues the company's aesthetic with the massive perspex front panel covering
Product Considerations
- Speaker binding posts may not be compatible with all types of speaker cable terminations, specifically thicker spades
- The control for the illuminated 'E' on the front is located underneath the amp and may be difficult to access
- May be more 'laid-back', which some may interpret as lacking ultimate transparency or strict neutrality
- Provides only for XLR balanced inputs, though Electrocompaniet can provide appropriate high-quality adaptors for RCA connectors
Comparisons (according to reviewers)
- Brings another level of control and depth to everything, compared to Totaldac Amp 1
- The memorable blackness of bass pinged recognition, compared to Kinki Studio EX-B7 monos
Takeaway: The Electrocompaniet AW 800 M is a powerful and versatile amplifier known for its exceptional bass control, clean output, and dynamic performance. It is a great choice for audiophiles seeking a high-quality listening experience with flexibility for system configuration.
Video review
Our take on the brand
There is no mistaking the D'Agostino family styling of the second generation Progression M550 Mono Amplifier. Immediately grabbing one's attention is the new heat sink design. Drawn directly from the flagship Relentless Mono Amplifier, each heatsink is milled from a single, 48.5-pound (22-kilogram) aluminum billet slab. This highly efficient elliptical form dramatically improves the cooling ability of the design and assures that the Progression M550 Mono Amplifier runs safely and reliably even when delivering its full-rated power.
Reflected in the model name, the Progression M550 Mono Amplifier delivers 550/1,100/2,220 watts into 8/4/2 ohms. The Progression M550 includes major revisions to the input topology. Distortion, signal/noise ratio, channel separation, and bandwidth measurements have all improved. New transistors handle six times the power of the previous components and a new DC coupling circuity has improved low frequency performance and extended the bandwidth of the amplifiers.
Pairing this advanced front end to the enhanced output stage has improved the dynamic impact, detail retrieval, and spatial integrity of the amplifier's playback. The audio signal path throughout is discrete, balanced, and direct coupled. Advanced protection techniques shield the amplifier and associated components from any unexpected anomaly.
Product Strengths
- Improved high-frequency response melds lower saturation voltage with higher gain
- An upgraded output stage includes 48 power transistors and a 2000VA power supply transformer with nearly 100,000 microfarads of power supply storage capacitance
- A new and far more efficient heatsink design borrowed from the Relentless
- Can remain in class-A for up to the first 100W of their output
Product Considerations
- One of the amps wasn't working properly the entire time
- Measurements may not be stellar, even though the D'Agostino website claims that the Progression's 'distortion, signal/noise ratio, channel separation, and bandwidth measurements have all improved'
Comparisons (according to reviewers)
- The Progression M550 monoblocks replaced the original Progression monos
- Dan D'Agostino said that if he'd listened to the new Progression M550s when he designed the original Momentum monoblocks 10 or 11 years ago, he would have declared the Progression M550s better
- The Progression M550 borrowed from the Momentum
- The M550 borrowed from the Relentless
Takeaway: The Progression M550 monoblocks are a significant advance, with technological improvements resulting in a 'new amplifier' design. The M550s aim to provide both high-powered delivery when needed and sonic accuracy.
Video review
Our take on the brand
Our summary
Product Strengths
- Pleasing and natural sound at lower listening volumes, reminiscent of tube amplifiers
- Remarkable level of dynamic control over the loudspeaker load, even when pushed to high volumes, resulting in no perceived distortion, sibilance, or unpleasantness
- Warm and engaging sound stage with clarity in imaging and separation of musical elements
- Capable of handling massive dynamic shifts without compromising its panoramic soundstage—showing immense grace under pressure
- Design ensures efficient heat dissipation through convection cooling, ensuring optimal thermal management
Product Considerations
- No functionality to allow for dimming of the internal lighting, which could prove problematic in some light-sensitive home theatre configurations
Comparisons (according to reviewers)
- Vs McIntosh MC1201 monoblocks: Hard to notice a difference in their performance, even at insane listening levels, despite the McIntosh having a much higher power rating
Takeaway: The ML-50 is a visually stunning and technologically advanced amplifier that produces a lovely, subtly warm tonality whilst still sounding crystal clear. It is neutral yet detailed enough to handle any genre of music, making it a worthwhile investment for audiophiles seeking a no-compromise system.
Video review
Our take on the brand
The Momentum S250 MxV stereo amplifier delivers the extraordinary sound quality of the Momentum M400 MxV monoblock in a more affordable stereo design. The circuit topology and construction of the stereo amplifier mirror those of the monoblock, using the same ultra-efficient copper heat sinks with venturi cooling, the same 1% metal-film resistors, the same 69 MHz output transistors and the same fully complementary balanced configuration. The result is audio fidelity equaled by no other amplifier—except, of course, the Momentum M400 MxV monoblock itself.
The leading compliment to the Momentum S250 MxV Stereo is the Momentum HD Preamplifier, creating a harmony worthy of any aficionado.
The Momentum S250 MxV models feature techniques and topologies initially developed and implemented in the Relentless Mono Amplifier. This fullest expression of the Momentum circuitry is reflected in the new model name, MxV. Those with a physics background will recognize that MxV or Mass times Velocity is the equation for Momentum.
Our summary
Product Strengths
- Incredibly resolving, with plenty of detail
- Perfectly controlled, 'wide' sound in terms of dynamics and panorama
- A quieter background brings forward a level of detail
- A clearly structured form, with symmetrical divisions and repetitions
- Inspired by the Relentless Epic amplifier series
Product Considerations
- Speaker jacks accept only spades and bare wires, and connecting spades from the top bends the cable significantly
- Components on the rear panel are placed close to each other and not particularly convenient to use
Takeaway: The Momentum S250 MxV amplifier delivers an immersive and detailed listening experience, making it great for those who enjoy actively listening to music. It brings out the best in loudspeakers, offering tremendous dynamics and a wide soundstage.
Video review
Our take on the brand
What competes at this price?
Our Summary
Product Strengths
- Ample power with minimal distortion
- Audionet's ULA (Ultra-Linear-Amplifier) technology, originally developed for medical engineering
- Impressive dynamic prowess and the ability to plumb the hidden depths of CDs and LPs
- Subtle musical and instrumental details come through cleanly and coherently, without compromising life-likeness of tone colors and harmonic expression
- Exceptional bass reproduction, with a rich, detailed, and uniform low end
Product Considerations
- Positive and negative speaker terminals are close together, requiring caution when connecting speaker cables
- Balanced input use involves an op-amp, which some believe impacts sound quality, single-ended inputs are preferred by some
- A preamp should be used to get the best sound from these amplifiers
- Display text changes locations randomly, which some may find distracting
Comparisons (according to reviewers)
- The Burmester sounded cleaner, airier, and more revealing, but could not quite compete with the AMP II MAX in authority over the bass frequencies and in blackness of the background
- The Pass Labs was tonally rich and pleasurably soft, plus the amp gave an extraordinarily punchy presentation, in that it bettered the performance of the AMP II MAXes, on the other hand, it was rather general in the organization of the soundstage and the background wasn't quite as black as with the AMP II MAXes
- Plinius shone in resolution, as well as delivered exceptionally dimensional soundstage and very neutral overall sound, especially in Class A mode, however, it did not have the same punch as the AMP II MAXes, and the sound wasn't equally gentle
- The McIntosh MC-501 delivered a richer and warmer sound, but with less power and extension than the AMP II MAX
Takeaway: The Audionet Max monoblocks offer a powerful and refined listening experience, making music sound engaging and detailed. Their ability to control speakers and reveal nuances in recordings makes them a great choice for serious audiophiles.
Video review
Our take on the brand
Our Summary
Product Strengths
- Neutral and grain-free sound, not like typical solid-state or tube amplifiers.
- Powerful and articulate bass, seamless and smooth mids, and extended, non-harsh highs.
- Exceptional build quality and a luxurious feel with immaculate laser-cut detailing and silver anodizing.
Product Considerations
- The glitzy appearance might be divisive.
- High-quality source components and speakers are required to perform at its best.
- The unit is large (almost 50cm wide) and very heavy (32kg), requiring a sturdy rack and careful handling during setup.
Takeaway: The Burmester 911 mk.3 provides exceptionally intricate, powerful, and dynamic sound, making it a very refined amplifier that is a treat for your ears. It is a top-performing amplifier made with great craftsmanship and build quality.
Video review
Our take on the brand
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Our Summary
Product Strengths
- Incredibly nimble, with every detail highlighted, providing an extra layer of resolution
- Delivers all of the detail and clarity without the traditional fatigue
- The balanced input transformer properly sums the positive and negative legs of the balanced signal, and in so doing retains much of the benefits that you normally achieve with fully balanced amps—noise rejection
- The distortion numbers are exceptional for a tube amplifier
- Compatibility with nearly every commercially available speaker, due to the support of three impedances (4 ohms, 8 ohms, and 16 ohms), and output power exceeding 60 watts with KT88s, and 80 watts with KT150s
Product Considerations
- There are no modern reproductions of the 12BY7A, requiring matched pairs to run the amplifiers
- The bias is fixed—it's selectable between settings, but dialing in the distortion could not be simplified further
- Heavy at nearly 100 lbs each, as there's a lot of iron in both the transformers and the chassis work
- A hint of tube noise was present in one channel when no music was playing, likely specific to the tubes used
- Not a wise choice to any planer but complex crossovers and difficult loads have not compressed the amp in testing
Comparisons (according to reviewers)
- Vs ampsandsound Zion Monos: The Arch Monos are more neutral, faster, and provide an extra layer of resolution, compared to the richer and more harmonic sound of the Zions
- Vs TAD: The Arch is clean, powerful, and has many characteristics of very good solid-state amp, though the TAD approach was similarly neutral in many ways, albeit with a lightning quickness that the Arch did not have
Takeaway: The ampsandsound Arch Monoblock amplifiers are a technically proficient and beautifully built amplifier that delivers exceptional detail and clarity without fatigue. If one wants a vintage but modern sound, the Arch Monoblocks could be a good choice.
Video review
Our take on the brand
Our Summary
Product Strengths
- Completely balanced and DC-coupled
- Uses the Class A 'X-Amp' input stage technology from the 159
- Has a high damping factor over the entire frequency range and a very wide, distortion-free Class-A range
- The thermal concept uses 'universal heat pipes' to keep temperatures constant and low, increasing the lifespan of the amplifier
- Signal processing reaches the input signal unaltered via silver cables
Product Considerations
- The Burmester visual aesthetic will not please everyone
- Power needs are consistently overestimated, and this amp has 100Wpc continuous into 8 ohms
- The single-ended RCA inputs are not available on the back panel, unbalanced input requires an adapter
Comparisons (according to reviewers)
- Vs Burmester 911 Mk 3: The 216 adds extra depth, precision, control, and ability to 'wig out' bass, also more reactive and dynamically dynamic
- Vs Burmester 911 Mk 3: The 216 is the more liquid sounding of the two, is more dynamic, has better bass definition and control, a more even sounding treble, a more open midrange, a keener sense of rhythm
Takeaway: The Burmester 216 is a musical chameleon that is carefully and meticulously crafted, it will bring the best out of any genre. Its utter lack of electronic character is a huge plus, making it a worthwhile consideration for any audiophile.
Video review
Our take on the brand
Our Summary
Product Strengths
- Sound is better lit than previous Grandioso series, with more color and brilliance
- More natural and realistic sound
- Smooth, captivating midrange that produces no listening fatigue
- Fine detail is exposed due to its somewhat laid-back presentation
- Incredible bass
Product Considerations
- Takes days to warm-up and sound its best
Takeaway: The Esoteric Grandioso M1X is a monoblock amplifier that delivers a burnished sound effortlessly, making it good for audiophiles. It offers a natural sound with impressive bass and a smooth midrange.
Video review
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