Q What do you mean by Direct coupling?

In this method the a.c. output signal is fed directly to the next stage. No reactance is included in this coupling network. Special d.c. voltage level circuits are used to match the output d.c. levels. It is used when amplification of low frequency signals is to be done. Further, coupling devices such as capacitors, transformers cannot be used at low frequencies because their size becomes very large. The amplifiers using this coupling scheme are called direct-coupled amplifiers or d.c. amplifiers.