Amplifier classes

Class A-B

This is a mixture of Class A and Class B amplifiers

Class A: has a large transistor that is on all of the time. These amplifiers are linear but are not very power efficient, (can be as low as 30%) and will produce a lot of heat. That is, if you had a speaker driven at 30W power, in the worst case 70W of the amplifier power would be used WITHIN the amplifier, This energy is output as heat). Even if there is no signal then there is a significant ldling power.

Class B: has two large transistors in a push-pull setup. These are more efficient, typically 50-60%, but not as linear and produce zero-crossing distortion.

Class A-B combines these classes but keeps a more efficient power handling, typically 50-60% efficient, and adds a bias to remove the zero-crossing distortion and keep a linear signal.

In Linn amplifiers this is typically the amplifier negative is tied to ground/earth and only the positive terminal changes voltage.

In other words:

Class A: Sounds good, but uses a lot of power all of the time

Class B: Sounds OK, but doesn't uses much less power than Class-A.

Class A-B: Sounds good and but doesn't break the bank on Electricity/power bills.

Class Chakra

The Chakra amplifier design uses an array of large transistors as ‘boosters’ around a single chip integrated circuit. When the output current is less than a few amps all the power output comes from the single chip circuitry, maximising the speed and linear properties of this design. At higher output currents, the transistors provide the majority of the output current, leaving the integrated circuit to operate well within its capability and able to correct any error instantaneously.

The design is very compact, reducing the circuit area and length of the signal path and is also highly efficient, producing much less heat than traditional designs.

Linn Power Amplifier Chakra white paper

CHAKRA is a linear (continuous time) amplifier technology with a switch mode (discrete time) power supply. There are now several products on the market based on switch mode amplifier technology, commonly referred to as ‘Digital’ or ‘Class D’ amplifiers. This attempt to associate the well-known attributes of digital systems with these products is, however, at best a slightly misleading premise.

A traditional amplifier audio circuit features a continuously variable (linear) output stage generating the required output by dissipating as heat the difference between the power supply voltage and the required output voltage. A Class D amplifier uses very high-speed switches to send the entire voltage of the power supply, with minimal power loss, as a sequence of pulses to the output, where a filter averages the pulses before the loudspeaker terminals. The frequency, density and duty cycle of these pulses determine the average output voltage. This is precisely how a switch mode power supply works, except that instead of generating the system power supply, the Class D amplifier circuit is generating the final audio output.

Like SMPS, the concept of Class D amplifier audio circuit technology is not demanding; indeed Class D amplifiers have been around for 30 years, but have failed to penetrate the specialist high-fidelity sound equipment market, primarily because they lack the subtlety of well executed linear amplifier technology. However, with the ever-more widespread adoption of multichannel systems, there is pressure on the industry to develop lighter, smaller and cheaper power amplification platforms which in turn has sparked renewed interest and research effort in Class D technology. The prospect of combining Linn’s Switch Mode Power Supply technology with advanced Class D audio circuitry is an appealing one, but can only be considered when the technology is mature enough to offer a performance advantage - in other words, when it meets the standards Linn customers expect from our company.

Some Linn products included in this class are:

Majik Power Amplifiers

Akurate Power Amplifiers

Klimax Power Amplifiers

Class D

This is NOT a digital amplifier. This uses voltage pulses at a very high frequency and different pulse widths. This coupled with a inductive/capacitive load will produce a voltage. These amplifiers have an efficiency of better then 85% (e.g. 85W to speaker, 15% used in amplifier, a lot less heat than Class-A).

As the amplifier is dependant on the inductive/capative load then the usual loading of Electrostatic loudspeakers may cause poor sounding instability. Check with your speaker manufacturer for any solutions.

In Linn amplfiers using Class-D the outputs are bridged, that both speakers output terminal change voltage.

• As a precaution do NOT connect/disconnection anything from the Amplifier output terminals UNLESS the amplifier is in Standby/Sleep state
• If you plan to use a Sub-woofer amplifier that uses the power amplifier output terminals then make sure that the Sub-woofer is setup for bridged amplifiers.

Some Linn products included in this class are:

Selekt_DSM