Learning Electronics

Learning Electronics

Learn to build electronic circuits

Design Project: Sensitive microphone amplifier

Question 1:

Identify which direction each potentiometer wiper must move in this circuit to provide more volume at the headphone.
Moving each wiper to the left will increase volume.

This question simply asks students to interpret potentiometer action in the context of a negative-feedback opamp circuit. Many students seem to experience confusion on the subject of three-terminal potentiometer operation (when not used as a rheostat), so be sure to spend adequate time discussing this with them.

Question 2:

What purpose(s) do the capacitors serve in this amplifier circuit? Could we remove one or more of them and still have a working circuit?
The capacitors block DC from being amplified at any stage, which may cause the amplifier(s) to saturate. The last capacitor (C3) prevents any possible DC from getting to the headphone.

The circuit design shown is a bit conservative. That is, it should work well without all the capacitors shown. However, experience has taught me a little over-building is good when it comes to increasing circuit reliability.