Amplifier classes

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Class A-B

This is a mixture of Class A and Class B amplifiers
Class A: has a large transistor that is on all 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 idling 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 the time
Class B: Sounds OK, but doesn't use much less power than Class-A.
Class A-B: Sounds good and doesn't break the bank on Electricity/power bills.

Some of the Linn products included in this class are:

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
Some of the Linn products included in this class are:

Class D

This is NOT a digital amplifier. The 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 designed to have an inductive/capacitive load of a standard coil loudspeaker and have an efficiency of better than 85% (e.g. 85W to speaker, 15% used in amplifier, a lot less heat than Class-A).
As the amplifier is dependent 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 amplifiers using the Class-D amplifier, the outputs are bridged, that is, both RED and BLACK speaker output terminals 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 set up for bridged amplifiers.

The Linn products included in this class are: