# Construction of Collector-Emitter Feedback Bias BJT Amplifier Test with PC Oscilloscope

Here is a demonstration of how to design a collector-emitter feedback bias BJT amplifier on a breadboard and test the constructed amplifier with PC oscilloscope. A general purpose 2N3904 transistor is used for the bipolar transistor amplifier. Signal is generated using soundcard based PC oscilloscope which is sent from the PC or laptop speaker. The signal is a sine wave signal of amplitude 10mV with frequency of 1KHz. The output of the amplifier is sent back to the PC/Laptop line in(microphone) input and the input and output is displayed on the PC oscilloscope software.

The tutorial is useful to design and test BJT amplifier or other simple analog circuit. No expensive hardware and acquisition software or software is required. Here we will use the soundcard scope which you can download from the link below.

https://www.zeitnitz.eu/scms/scope_en?mid=4.01

There are also many other useful soundcard based PC oscilloscope if you are not satisfied with the one we are using here.

This is continued tutorial on building and testing BJT amplifier with PC soundcard based oscilloscope. You may want to look into other amplifier design and test where different biasing method was used.

The following picture shows the collector-emitter feedback biased BJT amplifier build on a breadboard. The DC power supply is 5V and the transistor used is the 2N3904 general purpose transistor.

The above collector-emitter feedback biased BJT amplifier was designed in our earlier tutorial How to Design Collector-Emitter Feedback biased BJT Amplifier. In that tutorial we showed with equation derivation how to calculate the resistor value and the capacitor values. The following is the circuit schematic for the amplifier.

For new design you can also use the online BJT amplifier design calculator where you can select different biasing technique.

After you have build the amplifier circuit above, you can then create a sine wave signal in the soundcard scope software as shown below.

As you can see we have created a sine wave signal of amplitude 10mV and frequency of 1KHz on channel 1 which outputs the signal on the left side of the 3.5mm audio male to male jack. We can connect the audio jack to the the speaker output of the PC. Then the left channel signal from the other side of the jack is connected to the input of the BJT amplifier on the breadboard(to the capacitor C1). The input to and output of the BJT amplifier is then connected to the another male to male audio jack left and right channel. The other end of this audio jack is connected to the line in port of the PC.

The following figure shows how the PC speaker output is connected to the BJT amplifier and the BJT output connected back to the PC line in.

The following picture shows the input 1khz signal and the amplified output signal on the PC oscilloscope.

The following video shows the constructed collector-emitter bias BJT amplifier on breadboard and how to test the designed amplifier with PC oscilloscope.