is this 5 band EQ schematic correct?

Papabravo

Joined Feb 24, 2006
19,570
Without having some definition of what you mean by "correct", it would be difficult to give you a definitive answer. It might be a "toy", or it might perform "some" function, or it might be an innovative design. Tell us something about your expectations.

Is there some reason why you attached 3 identical copies of this guys thesis?

I did note that:
The BOM calls for 2 LM833 dual opamps for a total of 4 amplifiers. The schematic shows seven amplifiers for a total of 4 dual amplifier packages. There is no evidence of a printed circuit board layout so I'm assuming this was constructed using breadboard techniques. If I can find one error with a cursory examination how many more errors might there be.

I'll reserve further judgement until I understand more about your expectations.
 
Last edited:

Thread Starter

MaxMichaels

Joined Nov 30, 2021
28
The objective of this project is to build a five-band equalizer. The equalizer is a hardware filter intended to adjust the volume of specific frequencies of an audio signal. The adjustment works on the audio supply by either increasing or cutting off certain frequency ranges. The purpose of an equalizer is to make the sound louder or softer by varying the notes, or it can keep the same sound of the original.


Operate on frequencies from 0 – 16 kHz
- Filter audio output
- Boost or cut the frequency ranges defined in each band
- Drive a pair of headphones or a set of speakers

The project goal is to design a five-band equalizer. In the first stage, the equalizer has an audio input, which goes through filtering circuits, and each band of the filter has an output that can cut or boost the high and low ranges. In the second stage, the result of summing the signals comes to the output jack, which is connected to a pair of speakers or headphones. To have a more professional and customizable sound, the equalizer provides control of 5 bands to accommodate for the wide range of human hearing spectrum.
 

Papabravo

Joined Feb 24, 2006
19,570
The objective of this project is to build a five-band equalizer. The equalizer is a hardware filter intended to adjust the volume of specific frequencies of an audio signal. The adjustment works on the audio supply by either increasing or cutting off certain frequency ranges. The purpose of an equalizer is to make the sound louder or softer by varying the notes, or it can keep the same sound of the original.


Operate on frequencies from 0 – 16 kHz
- Filter audio output
- Boost or cut the frequency ranges defined in each band
- Drive a pair of headphones or a set of speakers

The project goal is to design a five-band equalizer. In the first stage, the equalizer has an audio input, which goes through filtering circuits, and each band of the filter has an output that can cut or boost the high and low ranges. In the second stage, the result of summing the signals comes to the output jack, which is connected to a pair of speakers or headphones. To have a more professional and customizable sound, the equalizer provides control of 5 bands to accommodate for the wide range of human hearing spectrum.
I know what the guy wrote in the introduction for his thesis. Plagiarizing what he wrote is just plain insulting. He probably got a passing grade on it. I asked you to tell me about your expectations for "correct". Since you won't do what I asked I'll just tell you what I think. You asked if the schematic was correct, and it probably is because the schematic was drawn in LTspice, and the simulation ran. He also constructed one and was satisfied with the result.

Would I construct this design for my audio system? No. It is basic, rudimentary, and constructed on a breadboard. I would not expect the same results as would be available in a commercial product. Take the $30.00 parts cost and some estimate of what your time is worth and you can buy this device cheaper than you can take an existing design and fabricate it.
 

Ian0

Joined Aug 7, 2020
6,677
Where are the potentiometers in the final circuit?
There's something very weird about the virtual earth mixer on the output. Firstly, what is C27 for?
Secondly, 500Ω is a very low value for the input resistor to that circuit. The LM833 will struggle to drive that low an impedance.
The use of MFB bandpass filters is not exactly conventional. The usual circuit uses series LC filters (often with the L implemented as a gyrator). Difficult to see how the MFB bandpass filter can do the "cut" part of the circuit.
Professional audio would rarely use a single supply, it would almost always use ±12V or ±15V supplies.
I wonder why he thinks resistors can reduce noise. Has he not heard of √4kTfR ?

Don't forget that this circuit was designed by a 3rd-year university student, not an applications engineer at a major semiconductor manufacturer!

Have a look at this one instead
https://www.ti.com/lit/an/slyt134/slyt134.pdf
It's the circuit everyone uses!
There's a reference to Eliot sound products at the end
1. Elliott Sound Products, Projects 28 and 64, http://sound.au.com
That's the same circuit.

Make it with a ±15V supply and NE5532 op-amps which cost buttons these days.
 

Thread Starter

MaxMichaels

Joined Nov 30, 2021
28
I know what the guy wrote in the introduction for his thesis. Plagiarizing what he wrote is just plain insulting. He probably got a passing grade on it. I asked you to tell me about your expectations for "correct". Since you won't do what I asked I'll just tell you what I think. You asked if the schematic was correct, and it probably is because the schematic was drawn in LTspice, and the simulation ran. He also constructed one and was satisfied with the result.

Would I construct this design for my audio system? No. It is basic, rudimentary, and constructed on a breadboard. I would not expect the same results as would be available in a commercial product. Take the $30.00 parts cost and some estimate of what your time is worth and you can buy this device cheaper than you can take an existing design and fabricate it.
Plagiarizing? I clearly stated I “found” this schematic. So if I told you I “found” it, what would make you think I’m plagiarizing? Because I assumed you wanted to hear what I found from the thesis? I came to you to “clarify” what I found. Accusing me of plagiarizing is insulting. This is not a test, or quiz. This is a forum. You really need a better life sir. Because you are too occupied with internet patrolling.
 

Thread Starter

MaxMichaels

Joined Nov 30, 2021
28
Where are the potentiometers in the final circuit?
There's something very weird about the virtual earth mixer on the output. Firstly, what is C27 for?
Secondly, 500Ω is a very low value for the input resistor to that circuit. The LM833 will struggle to drive that low an impedance.
The use of MFB bandpass filters is not exactly conventional. The usual circuit uses series LC filters (often with the L implemented as a gyrator). Difficult to see how the MFB bandpass filter can do the "cut" part of the circuit.
Professional audio would rarely use a single supply, it would almost always use ±12V or ±15V supplies.
I wonder why he thinks resistors can reduce noise. Has he not heard of √4kTfR ?

Don't forget that this circuit was designed by a 3rd-year university student, not an applications engineer at a major semiconductor manufacturer!

Have a look at this one instead
https://www.ti.com/lit/an/slyt134/slyt134.pdf
It's the circuit everyone uses!
There's a reference to Eliot sound products at the end
1. Elliott Sound Products, Projects 28 and 64, http://sound.au.com
That's the same circuit.

Make it with a ±15V supply and NE5532 op-amps which cost buttons these days.
Thanks a lot. I found this schematic on the internet and it did seem a bit off. I am trying to create my own 5-band EQ but the potentiometer symbol was off and I’m a novice in engineering, but I picked up on that very quick. Thank you very much for your feedback. I’ll check the link and contact you.
 

Thread Starter

MaxMichaels

Joined Nov 30, 2021
28
Thanks a lot. I found this schematic on the internet and it did seem a bit off. I am trying to create my own 5-band EQ but the potentiometer symbol was off and I’m a novice in engineering, but I picked up on that very quick. Thank you very much for your feedback. I’ll check the link and contact you.
also, do you have the link to part 1 & 2 of "An Audio Circuit collection". as i was reading the introduction, i noticed that part 1 concentrated on lowpass filters, and i would need help on that as well. thanks
 

Papabravo

Joined Feb 24, 2006
19,570
Plagiarizing? I clearly stated I “found” this schematic. So if I told you I “found” it, what would make you think I’m plagiarizing? Because I assumed you wanted to hear what I found from the thesis? I came to you to “clarify” what I found. Accusing me of plagiarizing is insulting. This is not a test, or quiz. This is a forum. You really need a better life sir. Because you are too occupied with internet patrolling.
In post #3 you copied the introduction to the paper you found on the internet. Those were not you`re own words, that's copying and pasting. What would you call it?
 

Audioguru again

Joined Oct 21, 2019
5,413
Guess what? Exactly the same circuit was also plagiarized at the university of Nepal with much of the same text. Some of its schematic was corrected: https://bestengineeringprojects.com/5-band-audio-equalizer-circuit-using-lm833/

The circuit in this thread has serious errors and will not work because the first opamp has its DC output saturated as high as it can go.
I see no boost-cut pots in the schematic.
The frequency response is very lumpy since the wrong kind of filters (MFB) do not add and subtract together at +3dB or -3dB.
 

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Thread Starter

MaxMichaels

Joined Nov 30, 2021
28
In post #3 you copied the introduction to the paper you found on the internet. Those were not you`re own words, that's copying and pasting. What would you call it?
Well being that i stated i got it off the internet, why would you think that those are my own words? I’m a little confused.
 

Thread Starter

MaxMichaels

Joined Nov 30, 2021
28
Guess what? Exactly the same circuit was also plagiarized at the university of Nepal with much of the same text. Some of its schematic was corrected: https://bestengineeringprojects.com/5-band-audio-equalizer-circuit-using-lm833/

The circuit in this thread has serious errors and will not work because the first opamp has its DC output saturated as high as it can go.
I see no boost-cut pots in the schematic.
The frequency response is very lumpy since the wrong kind of filters (MFB) do not add and subtract together at +3dB or -3dB.
Yes. That is the only reason I posted it. I noticed some errors but I wasn’t sure where the error was. I’m not in school and I’m not handing this in to anyone so I’m not sure how I fell into a plagiarizing category. Lol. I just want some help with reading this
 

Audioguru again

Joined Oct 21, 2019
5,413
CORRECTION: R14 was used instead of adding a capacitor in series with R12 but the 47k value of R14 is wrong and causes the output of the first opamp to clip the tops of the waveform because the bias voltage of the opamp is too high (4V instead of 3V) when it has the DC gain of 2.
 

Thread Starter

MaxMichaels

Joined Nov 30, 2021
28
Guess what? Exactly the same circuit was also plagiarized at the university of Nepal with much of the same text. Some of its schematic was corrected: https://bestengineeringprojects.com/5-band-audio-equalizer-circuit-using-lm833/

The circuit in this thread has serious errors and will not work because the first opamp has its DC output saturated as high as it can go.
I see no boost-cut pots in the schematic.
The frequency response is very lumpy since the wrong kind of filters (MFB) do not add and subtract together at +3dB or -3dB.
this is the boost cut diagram that was also included.
 

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Thread Starter

MaxMichaels

Joined Nov 30, 2021
28
CORRECTION: R14 was used instead of adding a capacitor in series with R12 but the 47k value of R14 is wrong and causes the output of the first opamp to clip the tops of the waveform because the bias voltage of the opamp is too high (4V instead of 3V) when it has the DC gain of 2.
so what must i do to get the proper value for R14?
 

Thread Starter

MaxMichaels

Joined Nov 30, 2021
28
Guess what? Exactly the same circuit was also plagiarized at the university of Nepal with much of the same text. Some of its schematic was corrected: https://bestengineeringprojects.com/5-band-audio-equalizer-circuit-using-lm833/

The circuit in this thread has serious errors and will not work because the first opamp has its DC output saturated as high as it can go.
I see no boost-cut pots in the schematic.
The frequency response is very lumpy since the wrong kind of filters (MFB) do not add and subtract together at +3dB or -3dB.
im reading the article you just sent me. are the component values on the chart, listed that you sent me, more accurate than the previous chart?
 

Papabravo

Joined Feb 24, 2006
19,570
Well being that i stated i got it off the internet, why would you think that those are my own words? I’m a little confused.
You don't get it do you? I asked you to tell me in your own words what you meant by "correct". You chose to take words from the paper, found the internet, and copy them into a post as an answer to my question. On top of that, it did NOT answer the question.

I'm all for education and learning, but when I ask a question I expect a thoughtful and meaningful answer, not a pile of word salad copied from another source.
 

Audioguru again

Joined Oct 21, 2019
5,413
so what must i do to get the proper value for R14?
Simply look at the datasheet of the LM833 to see that its maximum output swing is symmetrical then since it has a DC gain of 2 times you use simple arithmetic to calculate a value of R14 so that the voltage feeding the + input of the opamp is 1/4 of the supply voltage. You might not need R14 parallel to R12 so that only a single resistor can do it.

Why do the professors allow the assignment to be posted on the internet when it is completely wrong??
 

Thread Starter

MaxMichaels

Joined Nov 30, 2021
28
no. you do not get it. check your threads. this is the FIRST time you've ACTUALLY asked me to express it in my own words. i get you are all for education, but i am all for clarity. you get that?
 
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