10 Band Graphic Equalizer

The proposed 10 band graphic equalizer circuit can be used in conjunction with any existing home theater system to get an enhanced 10 stage audio processing.

The Circuit Concept


The unit is quite simple to use. Al one has to do is feed the TV or PC audio input to this circuit and hook the output with the existing home theater amplifier.

Next, it would be just a matter of adjusting the given 10 band controls and enjoying the vastly improved sound quality.

You would be able to tailor the sound as per your preferred tastes.As an example, the midrange controls of the equalizer can be adjusted to highlight dialogue or in order to reduce the harshness over a particular range of voice audio.

Or perhaps you can roll off the high pitched even to further extents in case you wished, or simply heightened the bas boost to your liking.

Typically the controls would be able to provide upto 10dB of boost or cut at nominal center frequencies of 150Hz, 500Hz, 1kHz, 2kHz, 5kHz, 7kHz, 10kHz, 13kHz, 15kHz, 18kHz.

The circuit also includes a fixed 10kHz low pass filter stage for cancelling out unwanted noise such as hiss or other high frequencies disturbances.

How the 10 band graphic equalizer circuit functions


Referring to the given circuit diagram we can see that the associated opamps form the main active component responsible for the required optimizations.

You will notice that all the 10 stages are identical, it's the difference in the values of the incuded capacitors and the pot which effectively varies the processing leves across the various stages.

For analyzing the operation we may consider any one of the opamp stages since all of them are identical.

Here the opamps act as "gyrators" which refers to an opamp circuit which effectively converts a capacitive response to an inductance response.

Consider an AC voltage source Vi connected to the opamp stage. This pushes a current Ic via the capacitor (C1, C2, C3 etc), which constitutes a proportional voltage across the connected ground resistance (R11, R12, R13 etc).

This voltage across the ground resistance is conveyed at the ouput of the opamp.

Due to this the voltage across the feedback resistor (R1, R2, R3 etc) becomes equal to the difference between Vin and Vout which causes current to flow via the feedback resistor and back into the input voltage source!

A careful assessment of the phases of the above developed current would show that as Ic leads the voltage Vin (as it can expected for any capacitive circuit) the net input current that may be the vector sum of Ic and Io in fact trails the voltage Vi.

Using Capacitors as Tuned Inductors


Therefore this implies that in effect, the capacitor C has gotten transformed into a virtual inductor due to the actions of the opamp.

This transformed "inductance" may be expressed by the following equation:

L = R1xR2xC

where R1 = ground resistance, R2 = feedback resistance while C = associated capacitors.
Here C would be in Farads and the resistances in Ohms.

The pots effectively vary the input current to the opamps which results in a change in the value of the above explained "inductance", which in turn results in the required music enhancement in the form of treble cuts or bass boosts.

Circuit Diagram




 

Response Curve for the above 10 band graphic equalizer design


 



 

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Comments

Ruizhe Shang said…
hmm, what's the supply voltage you give to the IC, it seems we don't need to use negative voltage here, right? :)
Swagatam said…
yes it needs a single supply, can be anywhere between 5 and 24V,

IC is LM324
jose said…
What components are conected to inversor inputs?
Swagatam said…
please click the diagram to enlarge and see the details.
Garry Gutierrez said…
where is the + and - supply?
Swagatam said…
for LM324 IC, pin4 is the positive and pin11 is the negative....
Julie Himaya said…
Hi there. Nice circuit. Good for anyone who has the enthutiast in electronic. Is there a ready made pcb lay out for this project? Planning to build it. Thanks
Swagatam said…
I am sorry, PCB is not available at the moment, but I may surely try to update it in near future
Swagatam said…
Hi, you can probably try the formulas explained in the following article:

https://homemade-circuits.com/2016/01/design-high-pass-filter-circuit-quickly.html
Dual OpAmps that work: 1458's & 4558's. The latter has Lower Noise if I remember correctly.
Anthony Wolf said…
hi my name is anthony and im fairly new to audio circuts and circuts in general, im just a kid but i got into makeing cool audio circuts and i wanna make this equalizer but i have two questions :/ i hope you can help, on the 250k pot there is a wire that kinda goes off into nothing, is that conected to anything, im asuming ground but i just wanted to check, and there is a circle on the wire going from the 250k pot to the 10k resistor :/ i know this is probobly a dumb question but if anything what does it mean??? i really hope you can help im getting a bunch of money for my birthday on the 18th os september(on sunday) and i wanna build a nice equalizer for my room and electronics projects and this is the best one ive seen so far, i hope you can help and im sorry if these are dumb questions im just learning. thanks :)
Swagatam said…
Hi, the lower end of the 250K goes nowhere meaning this terminal should be kept unused....to be precise the center lead of this pot needs to be connected with R24, and one of the outer leads to C22 while the other outer lead may be left unused, please ignore the circle you can replace it with a wire link.

Wish you all the best with this project and a Happy Birthday in Advance
Guillermo said…
Hi Swagatam, thanks for the circuit. I was wondering, in each filter the feedback is done througth the inverting terminal or the non inverging one?
Swag said…
Hi Guillermo, I have updated the design with signs, please check it out, you can use TL074 for the ICs, or even LM324, or RC4136 will work
Berner said…
Thanks for the circuit!

I recently bought a home theater system and found out it had a terrible software. the equilizer is simply awfull, hard to cut the bass and with a poor digital-only interface.

So I'm planning to build my own equilizer to improve it. the point is: it has 5 speakers + a sub.

If I wanted to equilize every single channel, how would you suggest me to do it? Maybe those multi-channel pots to equilize them together without mixing the outputs?
Swag said…
My pleasure!

for controlling tone individually and with maximum effectiveness and range, you can probably try any of the following concepts:

makingcircuits(dot)com/?s=bass

and build 5 of these modules together to get five separate equalizing options....you can also play with the values of the caps around the relevant pots to tailor the response levels.
Jack said…
can I make use of ic LM339 ?hope it will not affect d response output? I have interest in this cct I hv been looking for such pretty small smart Unique cct.sir If adding like another 5 freq to it or more,what will be d output status? I want to build it an use it for m church
Jack said…
15band eq
Swag said…
LM339 might not work correctly, only an opamo is recommended such as LM324, or other similar....you can add as many stages as you like by suitably modifying the capacitor/resistor values

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