Amplifier classes

Class A-B

This is a mixture of Class A and Class B amplifiers

Class A: Where there is a large transistor that is on all of the time. The issue with Class A is that it is not power efficient this 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 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: This are two large transistors in a push-pull setup. In this case there is only one transistor is on at time, one for postive sections of the waveforms and one for the negative sections of the waveform. However, in this configuration there is distortion as there is a gap between one power transistor switching off and the other transisitor switching on when the incoming signal goes from the positve section to the negative section. This is called 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 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

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.