Active Crossover Network Jake Asmus & Steven Warren

EE 230, 3rd Design Project

Objective In this project, we are to take a single audio input and produce three separate outputs. To do this, we are going to need three active-filter circuits. One of the filters will output frequencies 300Hz and below, another between 300Hz to 5000Hz and the last one for 5000Hz or greater. With the specified corner frequencies, we are going to need a low pass (frequencies less than or equal to 300Hz), a bandpass (frequencies between 300 and 5000Hz), and a high pass (frequencies over 5000Hz). Here are the theoretical circuit diagrams of the filters:

2nd order Active Low Pass 2nd order Active High Pass 1st order Active Bandpass Photos Photo of Low Pass Filter:

High Pass on Left Side Band Pass on the Right Side

End Result of completed circuit:

Description This circuit works by having a Low Pass filter, High Pass and Band pass all in parallel and all receiving the input from our function generator. The low pass uses two op amps to get the 40 dB/decade roll off and uses two capacitors and four resistors. Two of the resistors are used for the filter and another two are used to regulate the gain. The high pass filter also goes through two op amps. The first op amp is used for the second order filter and is going through a unity gain. The second op amp controls the gain of the high pass filter and gives us the 40 dB/decade roll off. The last part of the circuit is the band pass filter. For this part, we used 2 resistors and two capacitors. We created two passive first order filters with the high pass feeding into the low pass. The band pass then was passed through a unity gain op amp to get a 20 dB/decade roll off. Each of these designs used a 660 LMC op amp. Plots High Pass Filter:

Low Pass Filter:

Band Pass Filter:

The red dot displays where the desired corner frequency should be but since we live in a real world, not everything will be ideal.

Conclusion Finding the correct values for the capacitors and resistors was the hardest part. We would calculate the theoretical values but would not get the desired cut-off. So we had to pick values in the ball park from our theoretical values until the frequency response were close to desired.