Weird Mixer

This article is about a transistor

mixer circuit that I made:

Step 1: Design the Circuit

I have drawn the circuit via

PSpice Simulation software student edition:

The circuit requires adjustment.

When both LEDs are OFF you can connect the music source to the mixer.

Alternatively you can use the 1 Meg variable resistor for clipping sound affects.

 

Calculate the steady state Vc value:

Vc = Vs - Ic * Rc

Vc = Vs - Beta * Ib * Rc

 = Vs - Beta * (Vs - Vbe) / (Rb1 + Rb2) * Rc

 = 3 V - 100 * (3 V - 0.7 V) / (140 kohm + 10 kohm) * 1,000 ohms

 = 3 V - 100 * (3 V - 0.7 V) / 150,000 ohm * 1,000 ohms

= 3 V - 1.53333333 V

= 1.46666666667

Step 2: Simulations

Simulations show that my circuit has a high gain.

This might not be true for practice.

Transient:

Frequency Domain:

Step 3: Make the Circuit

I implemented the circuit with the heat sink:

 

Step 4: Testing

Distortion Adjustment Video:

I used Instrustar USB Oscilloscope for testing.

 

20 Hz Input:

 

1 kHz Input:

 

20 kHz Input:

100 Hz and 1 kHz Sine Wave Inputs:

 

100 Hz Triangle and 1 kHz Sine Wave Inputs:

 

Testing showed that output signal needs to be small to

maintain the mixer output linearity because of the connected LEDs.

 

Conclusion

You can implement the circuit with only one LED. This LED would be LED1 in the circuit diagram.