The Amazing Semiconductor-Part 5 | Building Our First Amplifier

๐Ÿ“– Foundation

Psalm 128:1โ€“2 (KJV)

1. Blessed is every one that feareth the LORD; that walketh in his ways.

2. For thou shalt eat the labour of thine hands: happy shalt thou be, and it shall be well with thee.

๐Ÿš€ WHOO Buddy!! Welcome Back!

In this episode of The Amazing Semiconductor, we finally build our first transistor amplifier.

Instead of starting with a lot of math, this lesson focuses on the hands-on build. We assemble the circuit, bias the transistor, apply a small input signal, observe the output on the oscilloscope, and then see what happens when we add an emitter bypass capacitor.

The math behind the resistor values and biasing will be covered in the next video.

๐ŸŽฅ Watch the Video

๐Ÿ”ง What We Build

In this lesson, we build a simple Class A common-emitter transistor amplifier using a 2N3904 NPN transistor.

This circuit is designed to take a small AC signal and amplify it into a larger signal.

A Class A amplifier is biased so the transistor is always turned on. That makes it useful for small-signal amplification, but it also means it continuously draws current.

โšก Main Ideas Covered

In this video, we look at:

  • Building a common-emitter amplifier

  • Using a voltage divider to bias the transistor

  • Setting the collector voltage near the middle of the supply

  • Understanding the Q-point

  • Watching for clipping on the oscilloscope

  • Using coupling capacitors to pass AC and block DC

  • Seeing how the emitter resistor provides negative feedback

  • Adding an emitter bypass capacitor to increase gain

  • Measuring input and output voltage

  • Calculating voltage gain from real oscilloscope measurements

๐ŸŽฏ The Q-Point

Since the circuit uses a 5V supply, we want the collector voltage to sit near the middle:

VC โ‰ˆ 2.5V

This gives the output signal room to swing upward and downward without clipping.

If the signal is driven too hard, it can hit the limits of the supply rails. When that happens, the waveform gets clipped and distorted.

๐Ÿงฐ Parts Used

  • 2N3904 NPN transistor

  • 10kฮฉ resistor

  • 1kฮฉ resistor

  • 470ฮฉ emitter resistor

  • 10kฮฉ potentiometer

  • Electrolytic capacitors

  • Breadboard

  • Jumper wires

  • 5V breadboard power supply

  • Function generator

  • DSO138 oscilloscope

๐Ÿงช Building the Circuit in Stages

The circuit is built piece by piece.

First, we build the voltage divider network using the 10kฮฉ resistor, 1kฮฉ resistor, and potentiometer. This lets us adjust the base bias voltage.

Next, we add the 2N3904 transistor, the collector resistor, and the emitter resistor.

Then we adjust the circuit until the collector voltage is close to 2.5V.

Once the bias point is set, we add the coupling capacitor and connect the function generator and oscilloscope.

๐Ÿ“‰ Input and Output Signal

The function generator signal is first measured on the oscilloscope. The original signal is too large for the higher-gain amplifier setup, so the input is attenuated using the potentiometer.

After adjustment, the input signal is reduced to about:

50mV peak-to-peak

The amplified output signal is about:

2V peak-to-peak

That gives a voltage gain of:

Gain = 2V / 0.05V = 40

So this small transistor amplifier achieved a gain of approximately:

40ร—

๐Ÿ”‹ What the Emitter Bypass Capacitor Does

Without the emitter bypass capacitor, the emitter resistor provides negative feedback. This makes the amplifier more stable, but it also reduces gain.

When the emitter bypass capacitor is added, the AC signal is partially bypassed around the emitter resistor. The DC bias stays stable, but the AC gain increases dramatically.

In the video, adding the capacitor causes the output signal to jump much higher. Then the input signal must be reduced to prevent clipping.

๐Ÿ“Œ Why This Circuit Matters

This amplifier is not meant to directly drive a speaker by itself. Instead, it is a small-signal voltage amplifier.

It could be used as an early stage in a larger signal chain, such as:

Microphone or sensor signal
โ†’ transistor preamplifier
โ†’ another amplifier stage
โ†’ power amplifier
โ†’ speaker or output device

This is why amplifier stages are so important in electronics.

โœ… Final Result

By the end of the video, we have a working transistor amplifier that takes a tiny input signal and produces a much larger output signal.

We also see how biasing, clipping, input attenuation, and the emitter bypass capacitor affect amplifier performance.

This is a big step in learning how transistors can be used for more than just switching.

๐Ÿ”œ Coming Next

In the next lesson, we will slow down and look at the math behind the circuit.

We will talk about:

  • Why we chose the resistor values

  • How to calculate the Q-point

  • How the base, emitter, and collector voltages are related

  • How current flows through the amplifier

  • How gain is affected by RC, RE, and the bypass capacitor

๐Ÿ‘ Thanks for Watching

Thanks for spending time with me on The Amazing Semiconductor โ€“ Part 5: Building Our First Amplifier.

If this lesson helped you, please like the video, subscribe to the channel, and share it with someone learning electronics.

WHOO Buddy!! ๐Ÿš€โšก๐ŸŽฅ

My Notes:
Video Notes

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