Audio Engineering

322 Chapter 10

10.4.10 Class-S

Class-S, so named by Doctor Sandman,^13 uses a Class-A stage with very limited current
capability, backed up by a Class-B stage connected so as to make the load appear as a
higher resistance that is within the capability of the fi rst amplifi er.

The method used by the Technics SE-A100 amplifi er is extremely similar.^14 I hope that
that this necessarily brief catalogue is comprehensive; if anyone knows of other bona fi de
classes I would be glad to add them to the collection. This classifi cation does not allow a
completely consistent nomenclature; for example, quad-style current dumping can only

Vbias3

Vbias

2

Vbias

2

Vin

Vbias4

Re

0R1

Re

0R1

Re

0R1

Re

0R1

R 2

100R

R 3

100R

R 5

100R

R 4

100R

Q 1

Q 3

Q 5

Q 4

Q 2

Low voltage

driver

D 3

D 1

D 4 D^2

Q 7

Q 8

Low Q 6

voltage

power

device

High

voltage

power

device

High

voltage

driver

V 2 

50 V

Rload

8R

50 V

V 2 

Figure 10.4 : A Class-G shunt output stage, composed of two EF output stages with the

usual drivers. Vbias3,4 set the output level at which power is drawn from the higher rails.