![]() Low Frequency Equalizer Circuit Potentiometer SelectionĪ standard linear potentiometer should be used to control the equalizer. The component values used in the circuit will produce a cut-off frequency of 200Hz. The equation that calculates the cut-off frequency is the same as before 1 / (2 * p * R2 * C1). The circuit will pass all low frequencies up to a cut-off frequency (basically a low-pass filter). This second circuit operates as the first, but at the opposite end of the frequency range. The values called out in the equation set the frequency at 2kHz. The frequency at which the equalizer with either add gain to the signal, or attenuation to the signal is determined by the following equation: 1 / (2 * p * R2 * C1). The default gain of the amplifier is set at unity gain (1). The equalizer is configured to pass all signals with out adding or reducing gain up to a particular frequency. ![]() The first circuit uses a component placement that configures it as a high frequency equalizer. Both low and high pass equalizers are shown below. There are two types a high-pass Shelving Equalizer (which passes all frequencies above a certain frequency), and a low-pass Shelving Equalizer (which passes all frequencies below a certain frequency). The characteristic curves resemble stacked shelves. Shelving EqualizerĪ Shelving Equalizer gets its name from the frequency response curve the circuit achieves. The gain of an inverting amplifier is Rf/Ri, or in this case R2'/R2. The LM741 are configured as a unity gain amplifier, as Rf and Ri are shown as the same value. Both circuits are based on a non-inverting amplifier design. Two operational amplifier circuit schematics are provided below. In addition, no pin numbers are provided in the circuit diagrams so a single, dual or quad package Op-Amp could be used. ![]() The LM741 is just used to indicate that any general purpose operational amplifier might be used. Operational Amplifier Designīoth of the circuits below indicate that they use a LM741 operational amplifier, but like all of these Op-Amp circuits any amplifier could be used instead of the 741. ![]() In fact there isn't much difference between the two classes of circuits. The circuits are similar and use the same terms to indicate an amplification or attenuation. The actual circuit adds equalization just as the tone controls did. An audio equalizer is used to adjust the amplitude of one or more frequency bands. The follow on topics might be a 2-Band Active Tone Control, or the 3-Band Active Tone Control. This discussion continues on from the audio tone control topic, which introduced both passive and active tone controls. Definition of Engineering Phrases "A" "B", ![]()
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