“Let our rigorous testing and reviews be your guidelines to A/V equipment – not marketing slogans”
Facebook Youtube Twitter instagram pinterest

Krell Introduces new iBias Class A Amplifier Line Preview

by January 16, 2014
Krell: Making amps you cant afford since forever

Krell: Making amps you can't afford since forever

Krell announced their new iBias technology at CES 2014 to be integrated into their amplifier line. Many audiophiles (and people that care about sound if you feel "audiophile" is a dirty word) believe that Class A amplifiers are best for audio reproduction. Unlike other amplifier typologies, Class A amps are always on. As such, they tend to be very inefficient (losing 75% of their power to heat is considered a pretty efficient Class A design) and run very hot. 

iBias seeks to fix this while maintaining the dynamics of a traditional Class A design.

Most of the alternatives to Class A designs suffer from crossover distortion. This distortion occurs when the audio signal shifts from positive to negative polarity. Though for conventional Class AB designs, this is easily resolved by introducing a slight Class A bias to overcome the distortion.  Traditional Class A amps operate the output transistors at full power at all times, eliminating this distortion. Any additional energy not required to drive the speakers is dissipated through the amp's heat sinks. 

Yeah, that's why they run so hot.

iBias, on the other hand, has a circuit which continuously measures the current flow through the amp's output transistors and instantly adjusts the power (or bias) to suit. While the output transistors are never shut "off", when not needed, the iBias circuitry sends very little power to them. This allows them to run more efficiently, cooler, and be much more compact as they don't need the large heat sinks. To us, this sounds an awful lot like a Class A/B or sliding bias design but Krell is refusing to label it as such. As previously stated, Class AB can suffer from crossover distortion but it’s mitigated with a slight bias into Class A operation at low power levels - exactly what Krell is saying its iBias circuitry does. We won't know for sure until the reviews start coming in.


This is the back of the Monoblock - the bigger amps have many more fans

Krell likens the iBias technology to an engine that might shut off some of its cylinders when not needed. Others might liken it to those hybrid cars that shut down their engines when at rest and run completely off their batteries. Either way, the effect is the same - energy retention in general while huge reserves available when needed. 

The new line includes seven models, each one built into a 3U-high (5.25 inch) chassis with removable rack-mount ears. The model numbers of the amplifiers indicate their power in watts RMS per channel into an 8-ohm load. The line includes two monoblocks, the Solo 550 and Solo 375; two stereo amps, the Duo 175 and Duo 275; the three-channel Trio 275; the five-channel Chorus 5200 (five channels, 200 watts per) and the seven-channel Chorus 7200.

While the new amps might be smaller than traditional Class A amps and more efficient, they still sport fans. Krell promises ultra-quiet operation though we're betting audiophiles willing to shell out the money for Krell amps are not going to chance the fans disrupting their sonic bliss. The rack-mountable ears make placing them in a different room a breeze.

Custom installers will like that Krell has included Ethernet connections with each of the iBias amps. Once connected to the local network, the iBias amps can be accessed via a web browser on a dedicated web page. Installers (or owners) can view heat sink temp, fan speed, and monitor alerts such as overheating, fan failure, or shorting of the output terminals.

All of the iBias amplifiers have begun shipping or will ship later this month. Here are the prices:


Model - Description - Price (each)

  • Duo 175 - 175 wpc stereo - $7,500
  • Duo 300 - 300 wpc stereo - $9,500
  • Chorus 5200 - 200 wpc 5-channel - $7,500
  • Chorus 7200 - 200 wpc 7-channel - $9,500
  • Solo 375 - 375 watt monoblock - $8,750
  • Solo 575 - 575 watt monoblock - $11,250
  • Trio 300 - 300 wpc 3-channel - $11,500

For more information, please visit www.krellonline.com.

About the author:
author portrait

As Associate Editor at Audioholics, Tom promises to the best of his ability to give each review the same amount of attention, consideration, and thoughtfulness as possible and keep his writings free from undue bias and preconceptions. Any indication, either internally or from another, that bias has entered into his review will be immediately investigated. Substantiation of mistakes or bias will be immediately corrected regardless of personal stake, feelings, or ego.

View full profile