OCL Amplifier Explained

In the field of audio amplifiers OCL stands for Output Capacitor-Less Amplifier design.

In this type of amplifier topology or configuration, the power output stage is directly coupled to its preceding driver stage without coupling capacitors.

The following figure shows a typical OCL amplifier output stage, as can be seen, the VT9/VT10 power BJTs bases are directly linked with the VT7, VT8 BJT stage, and the same can be seen with the earlier stage, wherein no capacitors are involved for the indicated couplings.

ocl amplifier power stage directly coupled without capacitors.

Although there could be many versions of OCL amplifiers, mostly the push-pull type output configurations is popularly employed in OCL designs. as shown above.

The OCL configuration could become popular due to some distinct advantages it possesses, compared to the other forms of amplifier topologies. The main features can be learned from the following points:

  • Elimination of capacitor coupling enables the unit to become very sleek and compact, and also helps to make the design very cost effective.
  •  The OCL design ensures enhanced immunity to the so called "motorboat oscillations" in amplifiers. 
  •  The design also allows the unit to deliver high power outputs even at lower input audio frequencies or DC supplies.

Although OCL amplifiers come with a few great advantages, it may exhibit a couple of marked disadvantages, as given below:

  • The power devices show a tendency of dissipating significant amounts of power.
  • In amplifiers where the bias points are poorly controlled, an OCL amplifier could pass the DC content into the loudspeakers, causing heating of the loudspeaker.

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