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.
What are hifi reviews useful for? (1) Identifying products you should demo in person at a dealer. (2) Learning which products reviewers unanimously praise as the best they've heard (this means they probably are legitimately great). (3) Identifying a product's attributes that satisfy your idiosyncratic needs and tastes. Beyond that, we often discount what reviewers say because they heap praise on most products—and are often apprehensive about publishing strong criticism or comparisons between products. Further, they seldom have more than a few products on-hand, often relying on their memories to compare past products. Always listen for yourself.
All
DUO 175 XD
reviews
Video Review
Manufacturer details
Features
Specifications
- Power Output: 175 watts RMS per channel at 8 ohms, 350 watts RMS per channel at 4 ohms
- Frequency Response: 20 Hz to 20 kHz +0, -0.08 dB; 0.5 Hz to 100 kHz +0, -3 dB
- Total Harmonic Distortion: <0.03% at 1 kHz, at 175 W, 8 ohms; <0.13% at 20 kHz, at 175 W, 8 ohms
- Signal-to-Noise Ratio: >95 dB, wideband, unweighted; >115 dB, "A"-weighted
- Gain: 26.2 dB
- Input Sensitivity: 1.84 V RMS
- Input Impedance: Single-ended: 100 kΩ; Balanced: 200 kΩ
- Output Voltage: 106 V peak-to-peak; 37 V RMS
- Output Current: 13 A peak
- Slew Rate: 40 V/μs
- Output Impedance: <0.015Ω, 20 Hz to 20 kHz
- Damping Factor: >530, 20 Hz to 20 kHz, referred to 8 ohms
- Power Consumption: Standby: 1 W; Idle: 73 W; Maximum: 1500 W
- Heat Output: Standby: 3.42 BTU/hr; Idle: 250 BTU/hr; Maximum: 5137 BTU/hr
- Inputs: 2 single-ended via RCA connectors; 2 balanced via XLR connectors
- Outputs: 2 pairs of binding posts
- Dimensions: 17.1 in. W x 7.65 in. H x 21.10 in. D (434 mm W x 194 mm H x 536 mm D)
- Weight: 70 lbs (31.8 kg) shipping; 60 lbs (27.3 kg) unit only
Description
The Krell DUO XD Series, including the DUO 125 XD, DUO 175 XD, and DUO 300 XD Stereo Amplifiers, embodies the pinnacle of audio performance. Designed for audiophiles and high-end audio systems, these amplifiers combine advanced circuitry, robust build quality, and Krell's innovative iBias™ Technology. This technology ensures Class A sound quality with greater efficiency, delivering unmatched musicality, dynamics, and control.
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Manufacturer Site
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.
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Select product comparisons
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.
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Avg. Product Price
$10,001-$20,000
Used For Sale
177
Available (Scroll Down)
Brand Popularity
46
of 900+
Badges
Top 50 Brand
Top 250 Brand
Products Listed
12
Founding Year
1980
Our take on the brand
Krell is a hifi brand whose amplifiers use iBias technology to operate in Class A up to full power without excessive heat, while maintaining the ability to double power output as speaker impedance halves. Their amplifiers feature XD technology for better control over speaker drivers, and modern models like the K-300i include Bluetooth, HDMI, and streaming features for contemporary audio setups.
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What are your favorite tracks for showcasing the strength of your products?
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Krell
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What if you spend more?
Balanced Audio Technology
Rex 500
25000
25000
/
5
Reviews
Balanced Audio Technology (BAT) designs all their components with fully balanced circuits and dual-mono power supplies, which deliver better channel separation and cleaner sound reproduction. BAT's signature approach includes zero global feedback and their Unistage circuit design, which amplifies the signal only once through a short signal path to preserve the original audio characteristics.
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Our summary
Product Strengths
- Powerful, able to drive any speaker at any level with ease
- Delivers a new dimension in realism at any volume level, exposing the timbre of bass instruments unlike ever heard before
- Reveals harmonic quality of instruments and voices
Product Considerations
- Heavy, weighing 140lb (63.5kg), requiring assistance for moving and unboxing
- High running temperature (55-65oC across the chassis) and draws 500W from the wall when idle
- When speaker cables are terminated with spade lugs, caution is advised as the posts are close together
- Output is floating—it should not be connected to any loudspeaker with a grounded 'black' terminal
- BAT components take a long time to "break in" (400-500 hours of use)
Takeaway: The BAT REX 500 is a very powerful amplifier that drives speakers with ease and reveals new levels of realism in familiar recordings. It is a must-audition for those seeking reference-level power amplification.
Video review
Our take on the brand
Balanced Audio Technology (BAT) designs all their components with fully balanced circuits and dual-mono power supplies, which deliver better channel separation and cleaner sound reproduction. BAT's signature approach includes zero global feedback and their Unistage circuit design, which amplifies the signal only once through a short signal path to preserve the original audio characteristics.
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McIntosh
MC3500 Mk II
30000
30000
/
4
Reviews
McIntosh is one of the most iconic amplifier brands in the world, recognizable for its signature blue LED displays and distinctive industrial design. With a legacy spanning decades, McIntosh is known to many, even outside the audiophile community, and is sold in both mass-market retailers and specialized hifi stores. Their amplifiers are characterized by a warm, tube-like sound that enriches the midrange and smooths out the overall tonal balance.
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Our summary
Product Strengths
- Delivers 350 watts into 2-ohm, 4-ohm, or 8-ohm loads
- The design has a purity that is quite amazing
- Effortless power
- Soundstage is big
- Transparent
Product Considerations
- Not necessarily suitable for pairing with extremely cold sounding, sterile or bright speakers
Comparisons (according to reviewers)
- MC3500 is more open and airy, with base not as hard fisted, compared to Krell KSA 250
- It compares with brands like soulution, big Audio Research, and CH Precision, but at a lower cost
Takeaway: The MC3500 is an impressive amplifier that delivers a natural and pure sound, able to drive almost any speaker. If you're in the market for a McIntosh amp, this is the one that makes music sound pure, simple and unadulterated.
Video review
Our take on the brand
McIntosh is one of the most iconic amplifier brands in the world, recognizable for its signature blue LED displays and distinctive industrial design. With a legacy spanning decades, McIntosh is known to many, even outside the audiophile community, and is sold in both mass-market retailers and specialized hifi stores. Their amplifiers are characterized by a warm, tube-like sound that enriches the midrange and smooths out the overall tonal balance.
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Electrocompaniet
AW 300 M
29000
29000
/
4
Reviews
Electrocompaniet, a nearly 50-year-old hifi brand recognized by audiophiles and major recording studios worldwide, specializes in amplifiers with unique features like Floating Transformer Technology and fully balanced operation. Their amplifiers are designed with direct-coupled high open-loop bandwidth topology and zero feedback class A operation.
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Our summary
Product Strengths
- Prodigious bass output and rich tonality, especially for a solid-state design
- Great presence, a black background, and strong resolution playing effortlessly at very high volume levels
- Offers a wide, well-defined soundstage
- Beautifully designed with a luxurious appearance, relatively compact dimensions, and attention to detail in its internal layout
- Reserves of power will comfortably drive a wide range of speakers to high levels
Product Considerations
- Attacks can be slightly soft on some material
- The soundstage, while wide and well-defined, may lack the pinpoint accuracy and layered depth of some reference amplifiers
- Requires support beneath it on carpeted floors to allow sufficient airflow
Comparisons (according to reviewers)
- Vs soulution 511, the soulution 511 was faster and more accurately conveyed bass notes, threw an image with greater accuracy, and was more open on top
Takeaway: The Electrocompaniet AW 300 M is a gutsy and poised monoblock amplifier that delivers lots of power and handles a variety of speakers, giving an excellent listening experience. Its solid build and high performance make it a great choice for those seeking high-end audio quality.
Video review
Our take on the brand
Electrocompaniet, a nearly 50-year-old hifi brand recognized by audiophiles and major recording studios worldwide, specializes in amplifiers with unique features like Floating Transformer Technology and fully balanced operation. Their amplifiers are designed with direct-coupled high open-loop bandwidth topology and zero feedback class A operation.
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MOON
861
21999
21999
/
4
Reviews
The MOON 861 is a power amplifier with the pedigree of the distinguished MOON 888 and the wholistic design philosophy of the North Collection.
MOON by Simaudio is known for their warm and natural "MOON sound," achieved through their proprietary Lynx circuit that eliminates global-feedback loop in their amplifiers. Their products feature fully balanced circuitry and customizable interfaces, with designs that minimize noise and distortion while revealing intricate audio details without harshness.
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Product Strengths
- Great build quality that feels solid and built to last
- Impressive control, speed, and transparency in sound reproduction, resulting in a highly satisfying and natural sound
- Excellent bass grip, with precisely layered and insightful basslines
- Each instrument is distinct within the orchestra
Product Considerations
- Speaker cable terminals are a bit tight, especially with larger spades
- Software may need updates to ensure devices connect seamlessly
- Setup may be crucial to get the best sound
- According to one commenter, the treble can be hard and tiring
Comparisons (according to reviewers)
- The 861 exceeds the Moon 860A v2 in performance due to improvements in isolation, mechanical damping, and power supply
- The 861 has less pronounced colors than Burmester 218 amplifiers
- The 861 has more weight and oomph than Octave MRE 220 SE
Takeaway: The Moon 861 is a powerful and well-built amplifier that delivers a natural and detailed sound, with excellent control and dynamics. With its power and balanced sound, listeners may find themselves enjoying music even more.
Video review
Our take on the brand
MOON by Simaudio is known for their warm and natural "MOON sound," achieved through their proprietary Lynx circuit that eliminates global-feedback loop in their amplifiers. Their products feature fully balanced circuitry and customizable interfaces, with designs that minimize noise and distortion while revealing intricate audio details without harshness.
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What competes at this price?
Krell
Solo 575 XD
14300
/
Released
The Krell Industries Solo 375 XD and Solo 575 XD Mono Amplifiers are designed for audiophiles seeking unparalleled power and precision. Featuring Krell's innovative iBias™ Technology, these amplifiers ensure superior sound quality with enhanced efficiency. Both models provide exceptional performance, making them ideal for high-end audio systems.
Krell is a hifi brand whose amplifiers use iBias technology to operate in Class A up to full power without excessive heat, while maintaining the ability to double power output as speaker impedance halves. Their amplifiers feature XD technology for better control over speaker drivers, and modern models like the K-300i include Bluetooth, HDMI, and streaming features for contemporary audio setups.
Expand Details
Our Summary
Product Strengths
- Superior grip on woofers
- Muscular, well-textured bottom end
- Unusually powerful for a class-A amp, outputting a claimed 575W RMS into 8 ohms or 900W into 4 ohms, yet weighing only 70 lbs and having no external heatsinks
- Weight and power were undeniable
- Transient slam and grip on the Wilson Audio woofers took it to another level of excitement
Product Considerations
- Aesthetic design uses a thin, U-shaped cover which is more common for home-theater receivers and processors, suggesting it saves on cost compared to milled-aluminum cases
- LCD screen has a somewhat dated look
- Initial impressions were negative, sounding 'broken: glazed and spatially flat, with weak bass,'—but this was resolved
Comparisons (according to reviewers)
- Vs darTZeel NHB-458 monoblocks, the Solo 575 exerted a superior grip on the woofers of the reviewer's Wilson Audio Specialties Alexandria XLF speakers
- Vs Bel Canto Design's Black amplification system, the Krells had a bottom-end whomp that reminded the reviewer of the Bel Canto system
Takeaway: The Krell Solo 575 is a powerful amplifier that delivers impressive bass control and a muscular sound. It could be a great choice for audiophiles looking for a class-A amp with high power output without the need for massive heatsinks.
Video review
Our take on the brand
Krell is a hifi brand whose amplifiers use iBias technology to operate in Class A up to full power without excessive heat, while maintaining the ability to double power output as speaker impedance halves. Their amplifiers feature XD technology for better control over speaker drivers, and modern models like the K-300i include Bluetooth, HDMI, and streaming features for contemporary audio setups.
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Krell
Solo 375 XD
14002
/
Released
The Krell Industries Solo 375 XD and Solo 575 XD Mono Amplifiers are designed for audiophiles seeking unparalleled power and precision. Featuring Krell's innovative iBias™ Technology, these amplifiers ensure superior sound quality with enhanced efficiency. Both models provide exceptional performance, making them ideal for high-end audio systems.
Krell is a hifi brand whose amplifiers use iBias technology to operate in Class A up to full power without excessive heat, while maintaining the ability to double power output as speaker impedance halves. Their amplifiers feature XD technology for better control over speaker drivers, and modern models like the K-300i include Bluetooth, HDMI, and streaming features for contemporary audio setups.
Expand Details
Our Summary
Product Strengths
- Combines a smooth, un-solid-state sound with loads of power and dynamics
- Has a practical and versatile design suitable for different placements
- Delivers a warm and involving sound
- Is a reviewer's 'favorite Krell ever' in part due to its relatively lighter weight—60 pounds—compared to older models
- Can be accessed via a web page that shows current operating temperature, fan speed, and overload conditions when wired to an Ethernet network
Product Considerations
- The top end is smooth and not very detailed, which may not appeal to audiophiles seeking highly detailed treble
- Despite iBias technology, the unit generates some wasted heat, indicated by the presence of cooling fans
- Some Krell enthusiasts may not like the lighter weight compared to older, heavier Krell amplifiers
Comparisons (according to reviewers)
- Vs Classé Audio CA-2300: The Solo 375 has better spaciousness, but the CA-2300 has more detailed and delicate treble
- Vs Pass Labs X350.5: The Solo 375 has smoother treble than the X350.5, but the X350.5 has greater spaciousness
Takeaway: The Solo 375 is a powerful amplifier that has a warm, smooth sound. It is versatile enough to be used in different setups, so it's a great choice for audiophiles.
Video review
Our take on the brand
Krell is a hifi brand whose amplifiers use iBias technology to operate in Class A up to full power without excessive heat, while maintaining the ability to double power output as speaker impedance halves. Their amplifiers feature XD technology for better control over speaker drivers, and modern models like the K-300i include Bluetooth, HDMI, and streaming features for contemporary audio setups.
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Chord Electronics
Ultima
15375
/
Released
2023
The ULTIMA mono power amplifiers have been conceived for the very finest high-end audio systems, those which by their very nature, tend to have the most demanding and most difficult-to-drive large loudspeakers. They deliver unsurpassed power and are capable of effortlessly driving any speaker.
Chord Electronics designs and manufactures all their products in Great Britain, setting themselves apart by using proprietary FPGA technology instead of off-the-shelf DAC chips found in most competitors' products. Their DACs and portable audio devices, featuring distinctive color-changing buttons and portholes, deliver studio-grade performance through unique technologies like the Watts Transient Aligned filter, which provides more natural and detailed sound reproduction.
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Our Summary
Product Strengths
- Offers a remarkably smooth, unforced, and natural presentation with a touch of warmth
- Excels in detail retrieval and textured presentation of instruments and vocals, making the music feel alive
- Presents a wide and holographic soundstage, especially when paired with speakers that are already strong in this area
- Demonstrates agility, precision, and clarity, combined with a naturalness that eluded earlier generations of Chord amplifiers
- Scales dynamically and has the ability to punch hard when required
Product Considerations
- Has a minimalist design with just four line-level inputs, lacking features like phono stages, tone controls, headphone outputs, or DAC modules
- Some may find its sonic signature prioritizes articulation over qualities such as richness and authority, potentially sounding thin if partnered poorly
- Balance control has no center indent or marked position
- The polychromatic lighting may be an issue for the color-blind
- Remote operation can be affected by direct sunlight
Comparisons (according to reviewers)
- Vs Rega Elex-R Mk3, the Chord Ultima Integrated delivers undeniably elevated sound in all respects, with greater dimensionality and smoother vocals
- Vs Bryston 7B 3 monoblocks, the Chord Ultima Integrated offers a weightier and more thunderous delivery, especially in the midrange and vocals, with more inner warmth in tone
- Vs Benchmark AHB2, the Chord Ultima Integrated provides a more energetic and fun listening experience, with Thor-like bass impact and overall superior dynamics
- Vs Accuphase E-270, the Chord Ultima Integrated is warmer, rounder, more powerful, and refined, with a more fluid and emotionally engaging performance
Takeaway: The Chord Ultima Integrated is a unique and well-built amplifier that combines a visually pleasing design with a captivating sound, full of detail and dynamic precision. It brings music to life with an engaging and immersive experience, making it a worthy addition to any audiophile's setup.
Video review
Our take on the brand
Chord Electronics designs and manufactures all their products in Great Britain, setting themselves apart by using proprietary FPGA technology instead of off-the-shelf DAC chips found in most competitors' products. Their DACs and portable audio devices, featuring distinctive color-changing buttons and portholes, deliver studio-grade performance through unique technologies like the Watts Transient Aligned filter, which provides more natural and detailed sound reproduction.
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AGD
Duet
11500
/
Released
2024
AGD Productions uses GaN (Gallium Nitride) technology in their amplifiers, which are housed in glass tubes reminiscent of classic vacuum tubes, delivering high power from a compact size with near-perfect square waves. The amplifiers are designed to be upgradeable as technology advances, with GaN modules that can be replaced, while handling complex impedance loads similar to high-end Class-A or SET tube amps.
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Our Summary
Product Strengths
- Compact size, lightweight, and runs cool compared to traditional high-end amplifiers
- Exceptionally quiet operation, with reviewers noting a complete absence of hum or buzz
- Delivers a clean, crisp, and neutral sound signature without added coloration
- Upgradeable design, allowing users to update the amplifier with new GaN modules as technology evolves
- Produces a Single Ended Triode-like midrange and top end
Product Considerations
- The polished finish is a fingerprint magnet, requiring the use of gloves for handling
Comparisons (according to reviewers)
- Vs AGD Audion MKIII: The Duets offer a cleaner and more refined sound with improved bass and greater immediacy and snap compared to the Audion MKIII
- Vs Daniel Hertz Maria: The AGD Duets seem to have a little more inner resolution
- Vs Pass Labs X250.8: The AGD Duets performed to a higher level
- Vs Peachtree GaN 1/VTV GaN amps: AGD amps seem to be on another level in regards to design, and the sound is more refined and beautiful
- Vs Aavik U-150, Luxman 595, Yamaha A-S 3200, Axxess Forte 1, Line Magnetic 219ia: The AGD Duets performed to a higher level
Takeaway: The AGD Duet amplifiers offer a blend of cutting-edge technology, exceptional sound quality, and user-friendly design. They are a great option for those seeking a high-end audio experience in a compact and energy-efficient package.
Video review
Our take on the brand
AGD Productions uses GaN (Gallium Nitride) technology in their amplifiers, which are housed in glass tubes reminiscent of classic vacuum tubes, delivering high power from a compact size with near-perfect square waves. The amplifiers are designed to be upgradeable as technology advances, with GaN modules that can be replaced, while handling complex impedance loads similar to high-end Class-A or SET tube amps.
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ASR
Emitter II
18750
/
Released
The Emitter II models are considered by true music connoisseurs and uncompromising audiophiles as the ultimate in amplifier construction. Through word of mouth alone, a music-addicted and steadily growing global fanbase has developed, who have realized their desire for a concert hall in their home environment. Powered by two separate power supplies, the most demanding speakers and elaborately built dynamic transducers are driven to peak sonic performance.
ASR Audio's Emitter II Exclusive amplifier creates a vast, tube-like soundstage and three-dimensional presentation without tube colorations, while maintaining exceptional transparency and a low noise floor. The brand stands out for its emphasis on measurements and scientific analysis in audio equipment evaluation, often sparking debates between measurement-focused and subjective listening-focused audiophiles.
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Our Summary
Product Strengths
- Known for combining the musicality of tube amplifiers with the precision and power of solid-state amplifiers.
- It provides a transparent sound with steel control, without the electronic 'shine' associated with transistor amplifiers.
- Exceptional bass performance, described as deep, explosive, and completely controlled.
- Homogeneous frequency range, offering a very high degree of transparency and control.
- Offers an ability to resolve even the finest musically significant details.
Product Considerations
- Requires a substantial amount of space due to its multi-component design.
- The sound offered might be 'too beautiful' for some listeners, as it is not 'brutal' or 'terse' enough.
- Requires care in using its switches to avoid shutdowns.
- Some reviewers note it was 'dark sounding' on the highs, though it did not lack information.
Comparisons (according to reviewers)
- Compared to Quad ESL loudspeakers, it surpasses the musicality and clarity achieved with many tube amps, rivaling even high-end options like Lamm Industries ML2.2 and Miyajima Laboratory 2010.
- The ASR has better bass and is more transparent than MBL, however, it lacks the grace that MBL offers.
- Compared to Rogue 180W monoblocks, the ASR Emitter II delivers better bass.
- The ASR Emitter II has slightly better bass control than Manley Neoclassic 500, but the Neoclassic 500 has a more marvelous style of fiddling.
- Compared to Edge and Audio Research, the ASR is darker sounding.
Takeaway: The ASR Emitter II Exclusive offers a combination of tube-like warmth and solid-state precision, making the listening experience a very involving one. It provides exceptional control and detail across the entire frequency range, making it a great choice for audiophiles.
Video review
Our take on the brand
ASR Audio's Emitter II Exclusive amplifier creates a vast, tube-like soundstage and three-dimensional presentation without tube colorations, while maintaining exceptional transparency and a low noise floor. The brand stands out for its emphasis on measurements and scientific analysis in audio equipment evaluation, often sparking debates between measurement-focused and subjective listening-focused audiophiles.
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