This amazing power amplifier is being sold as "used" in very good condition. Pulled from a working customer system for an upgrade. Original packaging included. Item was bought from us (When we were a Krell Dealer) and has the balance of the factory warranty, about over 2 years left. No issues, scratches, dents or other blemishes. (Retail: $10,500)
The high-efficiency Krell Duo 300 stereo power amplifier
is made for music lovers that will accept nothing less than rich, prodigious, room-filling sound that rivals what can be experienced at life-changing concerts. Capable of outputting 300 watts per channel, this cutting-edge instrument effortlessly drives and controls any pair of loudspeakers. It will fill even the largest spaces with rich, involving, dynamic sonics that are at once robust and nuanced, stentorian and clean, spirited and delicate, pure and musical. Equipped with cutting-edge iBias circuitry
, Duo 300
performs as a reference-setting Class A component but runs cool, consumes less energy, and eliminates crossover distortion all the while operating the output transistors at requisite full power. Independent complementary pre-driver and driver stages, a fully complementary and balanced signal path, 750VA toroidal transformer, and front-panel digital display come standard. When you're ready to experience studio-quality detail in every frequency range, and hear your favorite music conveyed with a realism and magnitude you only imagined a concert hall could provide, the rack-mountable Duo 300
Exuding 21st-century flexibility and convenience, Duo 300 touts network connectivity that allows users to monitor real-time performance from any smartphone, tablet, or laptop. Excessive current, output DC, fan speeds, short circuit, and overheating are constantly checked and any problems reported, with messages displayed on the front panel or reported on the Web server. Up to three email addresses can be sent notifications, so you'll always know Duo 300 is behaving as it should. Plus, a new output power device in the final gain stages that operates at a 73% higher voltage, delivers nearly 10% more current, and offers 120 watts of additional power handling compared to previous devices. This is what high-end audio is all about.
An Overview of Krell Class A iBias Technology
Audiophiles have always considered Class A technology to be the best-sounding operating state for amplifiers. However, despite Class A's unrivaled sound quality, it has fallen out of fashion because of recent demands to reduce power consumption and heat in home-electronics products. Krell took this challenge and redefined the high-performance power amplifier. The goals – unmatched performance, elegant design, and a compelling features – led to a patent-pending circuit delivering Class A operation without the excessive heat and wasted energy of conventional designs. It's all housed in a striking new form factor, with network connectivity for advanced access and monitoring. The sound is open and unconstrained in a manner that rivals live performance and the true sound of voices and instruments.
Class A designs are the most musically accurate circuit topology available. They do not suffer from the inherent distortions all Class AB amplifiers experience. In a traditional Class A design, the output transistors conduct full current at all times regardless of the actual demand from the speakers. Often, only a fraction of this power is needed to reproduce an audio signal at normal listening levels. The rest of the power is dissipated through the amplifier's heat sinks, producing large amounts of wasted heat. With Krell's iBias technology, bias is dynamically adjusted, so the output transistors receive exactly as much power – but only as much power – as they need.
Krell's iBias Class A technology allows its latest amplifiers to run in full Class A mode to full power while minimizing heat generation. Previous efforts at using a "tracking" bias only measured the incoming signal and set bias levels from this information. iBias technology significantly elevates the effectiveness of previous designs by calculating bias from the output stage. This seemingly small change in topology results in dramatic improvements in sound quality, especially midrange richness and purity. The iBias Class A circuit directly measures the output current of the amplifier and adjusts the bias to the optimum level. Because iBias Class A measures the output current, the real time demands of the specific speaker connected to the amp are directly incorporated into the circuit function. In addition, iBias Class A even reduces the bias when the signal is at very low levels, making its operation undetectable by ear and even by standard amplifier measurements.
Convenience, Drive, and Power
The power supplies of Krell iBias Class A amplifiers are optimized for use with the iBias circuit. Depending on the model, up to four toroidal transformers feed amplifier modules that include the audio circuitry, rectifier, and power supply filtering mounted to an individual heat sink. This design shortens the electrical path from the power supply to the output transistors, reducing the overall impedance and allowing the circuit to respond faster and control the speakers better and more accurately. Unlike traditional Class A amplifiers, iBias Class A amps have a compact design that allows rack-mounting, making them ideal for custom installation as well as traditional audiophile systems. The convenient form factor is made possible through thermostatically controlled ventilation fans. which are chosen for quiet operation and operate at the speed required to maintain the ideal internal temperature. They run only during periods of peak energy demand, so they are inaudible in normal use.
Connectivity Prepared to Handle 21st Century Demands
Krell's new amplifiers include RJ 45 Ethernet connectivity and an internal Web page accessible from any smartphone, tablet, or laptop. Network connectivity brings convenience, monitoring, and reporting to users. Amplifier configuration options include display brightness and timeout. For energy conservation, the amplifiers can be programmed to power off at a preset time of inactivity. In addition, individual channels can be muted and firmware updates can be initiated from the web server. Once the amplifier is connected to a network router with Internet access, the amplifier's advanced protection systems are viewable on an Internet-connected device. Excessive current, output DC, fan speeds, short circuit, and overheating are monitored in real time. If an issue occurs, the fault is displayed on the front panel and reported on the Web server interface. Emails will automatically be sent to as many as three email addresses to notify the user and/or the dealer of the condition.
Why iBias Circuitry is Better
iBias circuitry is built on a foundation of core Krell circuit technologies. All signal gain is realized in the current domain using proprietary multiple-output current mirrors with extraordinary open loop linearity. Each amplifier channel uses all discrete components. Gain is distributed among several stages, allowing each to have a large linear operating area. Audio signal voltages are converted to current at the amplifier input, and the audio signal remains in the current domain throughout the entire amplifier. Current mirrors in the final gain stages use a new output power device that operates at a 73% higher voltage, delivers almost 10% more current, and offers 120 watts of additional power handling capability as compared to other devices.
With this combination, iBias amplifiers deliver substantially more power while using a smaller footprint. Normally used in demanding, high-bandwidth video circuits, these transistors allow for the design of gain stages with superb accuracy and very low distortion. The signal path is fully complementary and fully balanced from input to output. Independent complementary pre driver and driver stages for the positive and negative output transistors make the output stages extremely fast and linear. This unique circuit is impervious to low-impedance or reactive loads. It simply drives any loudspeaker with absolute confidence, achieving the outstanding sonic results.
Most amplifiers use coupling capacitors in the signal path to block DC and prevent damaging offset voltages from reaching your speakers. Krell amplifiers are fully direct-coupled, with no capacitors in the audio signal path. This design gives Krell amplifiers lower internal impedance, which allows firmer, more precise control of your speakers. It also provides flatter, more extended low-frequency response, because coupling capacitors not only block DC but also affect the lowest bass frequencies. Krell employs expensive, non intrusive DC servos that remove DC without impacting the musical signal.
Best of All Worlds: Musicality, Dynamics, and Efficiency
Krell iBias Class A amplifiers are the first to deliver the rich musicality of Class A amplifiers, the uncompromising dynamics of classic Krell amplifiers, and the efficiency and low power consumption of Class G and H amplifiers. Because the iBias circuit eliminates crossover distortion, the amplifier is able to resolve more of the detail and microdynamics in even the best analog recordings. Simply put, the music breathes. Whether an iBias amplifier is called on to reproduce the extreme dynamic range of high-resolution digital files, the minute intricacies of a 45RPM 180-gram vinyl record, or the complexity of today's latest blockbuster action film, it does so without altering or abating the music in any way. iBias amplifiers' wowing ability to retrieve the subtlest details gives their sound an incredible dimensionality, with an ambient, broad, and extraordinarily deep soundstage.
3 Channel Power Amplifier
300 Watt Amplifier Featuring Krell iBias Technology Specifications
20 Hz to 20 kHz +0, –0.13 dB
<0.5 Hz to 100 kHz +0, –3 dB
>98 dB, wideband, unweighted, referred to full power output
>116 dB, “A”-weighted
Gain 26.2 dB
Total harmonic distortion
<0.045% at 1 kHz, at 300 W, 8 Ω
<0.17% at 20 kHz, at 300 W, 8 Ω
Single-ended: 100 kΩ
Balanced: 200 kΩ
Single-ended or balanced: 2.4 V RMS
Output power 300 W RMS at 8 Ω
540 W RMS at 4 Ω
138 V peak-to-peak
49 V RMS
16 A peak
<0.017 W, 20 Hz to 20 kHz
>470, 20 Hz to 20 kHz, referred to 8W
Standby: 4 W
Idle: 200 W
Maximum: 2160 W
Heat output< Standby: 13.7 BTU/hr.
Idle: 800 BTU/hr.
Maximum: 7387 BTU/hr.
3 single-ended via RCA connector
3 balanced via XLR connector
3 pairs 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
100lbs., 45.4 kg (shipping)
85 lbs., 38.6 kg (unit only)
Sale is ONLY for Krell Trio 300 (One) - Includes Power Cord
*We have an Original box for the Krell Trio 300
*Any warranty claims will be handled thru Krell (Other than shipping issues - Handled by Us)
*Please feel free to contact us with any questions or additional information.