Today in this article we are going to show you the circuit diagram and description of 5 Band Audio Equalizer Circuit using LM833.
At first let’s talk about what equalizer is?
Equalizer circuits are those circuits that are responsible to maintain balance between the frequency components. These circuits divide the audio spectrum into multiple frequency bands. The gain control of each band can be adjusted as per requirement separately. A separate IC4 is used to mix the outputs signals obtained from each frequency band and the mixed output is then fed as input to the audio power amplifier. The output might be disrupted due to overlapping of signals obtained from different sources and to avoid that a suitable quality factor (Q) must be selected. Doing so introduces coloration into the audio signal.
The band graphic equaliser circuit is constructed using two cheap and good quality operational amplifiers which are readily available in the market. These op-amps feed on a single voltage supply which is another advantage to the user. However, the operational amplifiers must meet certain requirement standard, they should have a noise density of less than 24nV/ VHz, slew rate of more than 5V/µs and gain-bandwidth product greater than 3 MHz. If available, you can use op-amps NE5532 or LM833 which fulfill our requirements to a greater extent.
Components Values for 5-Band Equaliser
|Centre frequency f0 (in Hz)||Capacitor value (in uF)||Resistors Ra value (in K)||Resistors Rb value (in K)||Resistors Rc value (in K)||Gain (A)||Quality (Q)|
|60||C4 = C5 = 0.1||R9 = 11||R11 = 27||R10 = 91||4.1||1.7|
|250||C7 = C8 = 0.1||R14 = 2.7||R15 = 6.3||R13 = 22||4.1||1.7|
|1000||C10 = C11 = 0.047||R18 = 1.5||R19 = 3.3||R17 = 11||3.7||1.6|
|4000||C13 = C14 = 0.0022||R22 = 7.5||R23 = 18||R21 = 63||4.2||1.7|
|16000||C16 = C17 = 0.0022||R26 = 2||R27 = 4.3||R25 = 15||4.2||1.7|
For the development of band graphic equalizer circuit, we have utilized the multiple-feedback bandpass filter topology, the figure of which is given in the left-most corner at the bottom of the figure. The figure includes a prototype for a single-channel bandpass filter. If you decide to use the capacitors of the same value as we have listed in the project, it will be easier to make rough calculations in the project. You are familiar with these formula, I think. They help us to choose our components accordingly for the desired effect in the final result. Here are those formula:
Using these basic formulae, other formulae are also generated to find component values for remaining.
On the basis of capacitor value used in the circuit, select different values of resistors used in the project. So, the first step is choosing capacitor value. Choose a capacitor with high capacitance of about 0.1F and resistor with resistance as small as fit. Capacitance is inversely proportional to the resistance value and thus a high capacitance results in smaller resistance values for all three resistors used in the project. There are multiple factors that might affect the performance of the project, and hence the areas where circuit failure is likely must be taken care of. In the input buffer op-amp, there might be chances of overloading, the overall capacitance of the circuit can be possibly reduced by the stray capacitance generated through the board. It will reduce the resistance to much lower value. However, resistance Rb doesn’t influence the bandwidth and gain of the circuit and thus is used to alter the mid-frequency of the circuit.
The mid-frequencies are standards used in band graphic equalizers. The value of these frequencies varies according to different parameters like the octave division, application and manufacturers’ preference, since most of the devices include same octave rules, the center frequency is fixed at 1000 Hz.
Referring to the project title; equalizer, one must monitor the balance between the filters used and their bandwidth. We can compromise at some situations with the number of filters. With a wide range of bandwidth, we can use less filters and more filters with a narrow bandwidth. With the increase in quality factor(Q) of the filters, the complexity of the circuit also increases and thus using filter with a narrow bandwidth less than 1/3 octave is rare and not wise as well. Doing so, adds to the cost and limited applications of the circuit.
National semiconductor has defined a standard, to build a 10-band graphic equalizer circuit, the range of mid-frequencies which can be used are: 32, 64, 125, 250, 500, 1k, 2k, 4k, 8k and 16k. Similarly, a quality factor of 1.7 is desired.
For a particular center frequency of the circuit, component values are listed in the table. The gain factor (A) of 4 is preferred.
Circuit Description of 5 Band Audio Equalizer using LM833
The band graphic equalizer circuit provides five bands control, the project circuit is centered around the IC1 (A) LM833 as the buffer stage. This IC has a gain factor of 2 and is a non-inverting amplifier. Two resistors R3 and R4 form up the resistive network and this network divides the input signal by 2. For this reason, the amplifier has a net gain factor of unit value. Resistors R1 and R2, each of 100k value build up the voltage divider section and the voltage obtained at the junction of these two resistors is fed to its positive input terminal through another resistor R6. The power possessed by the voltage divider circuit is adequate enough to operate the op-amps used in the project if needed. Another resistor; Ro (R8=R12=R16=R20=R24=R28=R30=100W) is included in the project that serve dual purpose of reducing noise effects and task concerning resistive isolation of capacitive load. The value of resistor can be adjusted in between the values of the range 50-150 ohms as per the noise in the circuit.
Five potentiometers are also included in the circuit; VR1 through VR5 along the signal path, high quality potmeter are preferred. The potmeter must be wrapped with bare copper wire around the body and the other end of the wire must be soldered to the ground. The metal-film type resistors and polyester type capacitors must be used in the project with sensitive filters.
The op-amp stages must be capacitively coupled with each other so as to avoid any chances of DC signa being propagated or amplified. A coupling capacitor of value greater than 1 µF is suitable for a low frequency response. In between the op-amp stages, a 10µF, 16V capacitor is used to avoid output failure.
To power the entire circuit and its components, a regulated 12V DC supply is used. To avoid the noise effect, connect a 0.1 µF ceramic disk capacitor in between the Vcc pin of each op-amp and the ground.
PARTS LISRT OF 5 Band Audio Equalizer Circuit using LM833
|Resistors (all ¼-watt, ± 5% Carbon)|
|R1, R2 = 100 KΩ
R3 – R7 = 47 KΩ
R8, R12, R16, R20, R24, R28, R30 = 100 Ω
R9, R17 = 11 KΩ
R10 = 91 KΩ
R11 = 27 KΩ
R13 = 22 KΩ
R14 = 2.7 KΩ
R15 = 6.3 KΩ
R18 = 1.8 KΩ
R19 = 3.3 KΩ
R21 = 63 KΩ
R22 = 7.5 KΩ
R23 = 18 KΩ
R25 = 25 KΩ
R26 = 2 KΩ
R27 = 43 KΩ
R29 = 10 KΩ
VR1 – VR4 = 4.7 KΩ
|C1, C3, C6, C9, C`12, C15, C18, C19 = 10 µF
C2 = 100 µF
C4. C5, C7, C8, C20 – C23 = 0.1 µF
C10, C11 = 0.047 µF
C13, C14, C16, C17 = 0.0022 µF
|IC1 – IC4 = LM833|