Krell's XD (Xtended Dynamics, Dimensionality & Detail) upgrade for iBias amps takes an already great-sounding amp and raises its performance to the next level. XD is a classic example of Krell's ongoing R&D efforts, delivering benefits across multiple product lines. During the development of the K-300i integrated amplifier we discovered substantial sonic improvements by reducing the output impedance below traditional standards. By applying this technique to our existing line of amplifiers, the improvement was so substantial that it deserved its own unique XD-designation.

It wasn't just about reducing the output impedance. This affects the amplifier's stability and transient response, so each stage before the output had to be readjusted to work optimally with the lowest output impedance. This lower output impedance exerts greater control over the speaker drivers and dampens unwanted vibration modes, allowing for a more accurate reproduction of the original signal.

Krell Class A iBias™ technology.

Krell's history is filled with breakthroughs in Class A amplifiers that have helped build Krell's legacy of offering the best sounding amplifiers available. Our revolutionary, patent-pending circuitry provides true Class A operation without the excessive heat and power waste of conventional designs.

Power Supply Highlights.

Power supply technology has always been an important factor in Krell sound. The power supplies for our Krell iBias Class A amplifiers have been optimized for use with the iBias circuit. Depending on the model, up to four toroidal transformers power amplifier modules that include the audio circuitry, rectifier, and power supply filtering mounted on a single 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 drive the speakers even better and more accurately.

Unlike traditional Class A amplifiers, iBias Class A amplifiers have a compact design that allows for rack mounting, making them ideal for custom installations as well as traditional audiophile systems. This comfortable form factor is made possible by thermostatically controlled ventilation fans. The fans used have been specifically chosen for quiet operation, and run at the speed necessary to maintain the ideal internal temperature. They work only during periods of maximum power demand - when the music is loudest - so they are inaudible in normal use.

Network connectivity.

The 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 end users. The amplifier's configuration options include screen brightness and timeout. For energy savings, the amplifiers can be programmed to turn off at a preset time of inactivity. 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 can be viewed on an Internet-connected device. Excess current, continuous output current, fan speed, short circuit and over temperature are monitored in real time. If a problem occurs, the fault is displayed on the front panel and reported on the web server interface. Emails will be automatically sent to up to three email addresses to notify the end user and/or distributor of the situation.

Circuitry highlights.

The iBias' new circuitry is built on a foundation of Krell's core circuit technologies. All signal gain is performed in the current domain using patented multi-output current mirrors with outstanding open-loop linearity. Each amplifier channel uses all of the discrete components. No generic ICs or op amps are used anywhere. The gain is distributed among several stages, which allows each of them to have a large linear operating area.

The audio signal voltages are converted to current at the input of the amplifier, and the audio signal remains in the current domain throughout the amplifier.

The current mirrors in the later gain stages use a new output power device that operates at a 73% higher voltage, supplies nearly 10% more current, and offers 120 watts of additional power handling capability compared to other devices.

With this combination, the iBias amplifiers can now deliver substantially more power using a smaller footprint. Commonly used in demanding, high-bandwidth video circuits, these transistors allow gain stages to be designed with extraordinary precision 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 insensitive to low impedance or reactive loads; it simply drives any speaker with absolute confidence, achieving the best possible sonic results.

Most amplifiers use coupling capacitors in the signal path to block DC current and prevent harmful offset voltages from reaching the speakers. Krell amplifiers are fully direct coupled, with no capacitors in the audio signal path. This design gives Krell amplifiers a lower internal impedance, allowing for tighter, more precise control of your speakers. It also provides a flatter, more extended low-frequency response, as the coupling capacitors not only block DC current, but also affect the lower low frequencies. Krell uses expensive, non-intrusive DC servos that remove DC without affecting the music signal. A) Yes,

Everything audiophiles and home theater

could want in an amplifier.

Krell iBias Class A amplifiers are the first to offer the rich musicality of Class A amplifiers combined with 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 amp is able to resolve more detail and microdynamics on even the best analog recordings; simply put, music "breathes". Whether an iBias amplifier has to reproduce the extreme dynamic range of high resolution digital files, the miniscule complexities of a 45 rpm 180 gram vinyl record, or the complexity of today's latest blockbuster action movie , it does so without altering or diminishing the music in any way.

The unparalleled ability of iBias amplifiers to bring out the finest details gives your sound incredible dimensionality, with an extraordinarily deep and wide ambient soundstage. However, despite the width of the sound, the amplifiers are capable of producing accurate stereo images if the recording requires it.

It's all the power and control that Krell has always been famous for, with a level of resolution and musicality in the mids and highs that has simply never been heard before.

In short, Krell's new patent-pending iBias Class A amplifiers offer today's audiophiles and home theater fans everything they could want in an amplifier.

Technical specifications of the Krell Duo 175 XD stereo amplifier.

175-watt amplifier with iBias™ technology from Krell.

Frequency response.

20Hz to 20kHz +0, -0.08dB.

0.5Hz to 100kHz +0, -3dB

Signal/noise ratio.

>95 dB, wideband, unweighted, referred to full power output.

>115 dB, "A" weighted.

Gain.

26.2dB

Total harmonic distortion.

<0.03% at 1 kHz, at 175 W, 8 Ω.

<0.13% at 20 kHz, at 175 W, 8 Ω.

input impedance.

Single: 100kΩ.

Balanced: 200 kΩ.

input sensitivity.

Single or balanced: 1.84 V RMS.

Output power.

175 W RMS at 8 Ω.

350 W RMS at 4 Ω.

Output voltage.

106V peak to peak.

37V RMS.

output current.

13 to peak.

Turning speed.

40V/μs.

output impedance.

<0.015Ω, 20Hz to 20kHz.

damping factor.

>530, 20 Hz to 20 kHz, referred to 8 Ω.

Krell Duo 175 XD stereo amplifier.

Energy consumption.

Standby: 1W. Idle:

73W.

Maximum: 1500W.

Heat production.

Standby: 3.42 BTU /hr. Idle

: 250 BTU

/hr. Peak: 5137 BTU/hr.

Tickets.

2 simple via RCA connector.

2 balanced via XLR connector.

Departures.

2 pairs of connection terminals.

Dimensions.

17.1 in. W x 7.65in. H x 21.10in. D.

434mm wide x 194mm high x 536mm deep.

Weight.

70 lbs., 31.8 kg (shipping).

60 lbs., 27.3 kg (unit only).