Loudspeaker Fuse Placement for Audio Amplifier to Preserve A Good Bass Response

To protect the loud speaker from destructive signal, the most simple way is by placing a fast blown fuse between speaker and the amplifier output. This common solution is depicted in the figure 1 (a).

Figure 1. Fuse Placement to Preserve Good Bass Response

The fuse in the circuit has a significant resistance to generate heat, because without this the fuse couldn’t melt. The resistance affect the amplifier response in reacting to the speaker inductive load, but the worst is that this resistance varies with the temperature caused by the dynamic signal current. This resistance variation affect the linearity of the amplifier’s bass response. This situation can be solved by placing the fuse inside the amplifier’s feedback loop. Using this method, any nonlinear effect introduced by the fuse will be compensated by the amplifier via feedback mechanism. The resistor R3 is chosen to be much smaller compared to R2 but much higher compared speaker’s impedance. A value of 220? is suitable for most cases.

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