DIFFICULTIES WITH SINGLE-SIDED AMPLIFIERS 



to eradicate altogether, but is likely to be particularly bad in a single-sided 

 amplifier design. 



LOAD POLARIZATION 



In single-sided power stages directly coupled to a load such as a penwriter, 

 or transformer coupled to a device such as a loudspeaker, there is in both 

 cases a steady component of current which produces a steady magnetic bias 

 in the iron of the penwriter or transformer. It is clear from Figure 10.6 that 

 this is a bad thing. The curves represent the hysteresis curve of the iron. 

 When there is no bias the working point is at O and the input can have the 

 value shown in Figure 10.6a. When bias is present the working point is 



Flux 

 produced 



Flux 



wave 



produced 



Magneto-motive 

 force i — •- 



Max possible alternating- 

 input swing 



Flux 

 produced 



Flux 



wave 



produced 



Max possible 

 alternating- 

 input swing 



Figure 10.6 



Magneto-motive 

 force 



(b) 



some such as P in Figure 10.6b and saturation occurs if the input exceeds 

 the level shown. The implication is that the power-handling capacity of a 

 given penwriter or transformer is reduced, and that to achieve the same power- 

 handling capacity the cross-section of iron in the magnetic circuit must be 



162 



