In this instructable i am going to show you how you can build a simple hearing aid with an op amp. The device can amplify the sound up to 5 times.

The making of the hearing aid is also very simple and would not take more than an hour.

The output of the device is a little cracky due to the crude op amp used but for the cost it is made (that is less than 1$) the device is very appreciable.


The materials you will require are very easy to source and inexpensive .

The materials are

1.An op amp (any would work but i am using the 741)

2. Audio jack

3. 0.1uf caps x2

4. ~4.7k ohms resistor x3

5.~1k ohm resistor x1

6. 2.2 mega ohm or higher value resistor (i used 10 megs)

7. Earphones (any would work)

8. Purf board (about 20x15 holes)

9. An electret mic (best is from a phone )

The tools you would be requiring are

1. Soldering iron


3.Wire cutters and strippers (you can always use a pair of scissor)


The schematics in the picture above may seem very complex to beginners but is actually very simple , if you are not able to read the schematics I recommend you to go to this site reading schematics which will help you read it.

Also I will give you an overview so you can go on with me. You may be ready with your breadboard and some wires and the materials and then

1.place the 741 ic in the center socket with the notch pointing away from you

2.the first pin is not connected

3.connect the positive end of the electrit mic to vcc (positive end is the one that is not connected to the body of the mic, you can find this out by testing with a multimeter or just see the traces that follow to the body. ofcourse the other one is negetive.)

4. the other end of the mic connects to the 4k7 resistor

5.the 4k7 's other end is grounded.

6. the point at where the mic and resistor meet is connected to the 1k resistor

7.the1k resistor is then connected to a 0.1uf cap

8. the 0.1uf is connected to pin 2 of the 741

9. the pin 2 of the 741 also connects to the pin 6 through a 1m ohm or higher value resistor

10. a voltage divider of 2 4k7 resistor is connected to the pin 3 of the ic

11. pin 4 is grounded

12. pin 5 is not connected

13.pin 6 earlier connected to the 1m ohm resistor is connected to the headphone through the 0.1 uf capacitor

14. pin 7 is connected to vcc

15. pin 8 is not connected

After doing this ,plug in your headphones and give power to the circuit.


Before going on to the working, I would like to tell you that since this is a sound related project i can't guarantee that the project will work for all of you. But don't get discouraged it is very easy to make it work. Here are some tips and tricks that will help you troubleshoot and get it right -

1. NOT SURE IF YOUR DEVICE IS WORKING-try speaking into the mic if you don't hear any sound then try blowing on it .We will learn later why blowing has better results.

2.THE SOUND OUT OF THE EARPHONES IS TOO NOISY - try increasing the value of the capacitor between the output and the earphones.

3. WHICH MIC SHOULD I GET?-the best mic would be out of a mobile phone but you can always buy a mic from an electronics store. Also remember not to peel off the filter even if it is tempting as it affects the sound quality tremendously.

4.IMPROVE SOUND QUALITY-this works with some mics, you can attach a capacitor between the leads of the mic this way the sound will become more boxy that is the time delay between the pulses of the sound will increase. In simple words the sound becomes more square wavy

5. INVERT THE VOLTAGE DIVIDER- if the sound on your device is faint then connect the positive end to the mic and the ground to the 4k7 resistor. Or else if the sound is loud enough then no need. But keep in mind this will reduce the sound quality.



The working is simple it is

-firstly, the mic consists of two plates situated very close to each other. when a sound is produced then the disturbances in air cause the distance between the plates to change which produces a very minute voltage of about 0.002 volts.

-then this voltage is amplified by the op amp to about 2 or so volts which goes to the headphones.

-to learn about op amps go to op amps

-the basis is very simple and can be understood easily. If any doubts please ask me in the comments.


Plug in power and audio and you should hear sound in the earphones.

if any queries please post in the comments and I will reply to them

Also just to tell you the sound from the hearing aid will be a little cracky but for the cost with which it is made it is very efficient. This device was made by spending only one dollar. so please appreciate it rather than saying negative in the comments

What is the voltage of vcc
<p>can you explain the circuit thanks :D </p>
Hey, were trying to make this for our science fair project and were having a diffculty on where to find the materials. Could you possibly tell us where you found them
depending on where you live. but you can get everything online also. just that it would take a while to ship depending on where you live
<p>hi.. i read your whole circuit mr. omnivent. i have one question? where to ocnnect speaker on your circuit? </p>
<p style="color: black;">Hi,</p><p style="color: black;">Not trying to be negative here, but I'm not sure you know how to set the gain?</p><p style="color: black;">You talk about a gain of five, then about amplifying 2mV to 2V (a gain of 1,000) and your 10M resistor assumes a gain of 10,000 - gotta make up your mind ;)</p><p style="color: black;">While the poor 741 can handle a gain of 5, trying to push it so immensely beyond its limits and then blaming it for being &quot;cracky&quot; doesn't sound fair to me. And it's not just the gain that you need to sort out...</p><p style="color: black;">Your -3dB bandwidth is as little as 108Hz (!) from 352Hz to 460Hz, You have a 180&deg; Phase reversal right in your pass band (@ 422Hz) and the peak gain is almost 80dB, but falling fast at either side of your pass band. Further, your THD is too high for me to measure, but as you can see in the attached pictures, it's not a hearing aid for the hard of hearing, it's a noise maker ;)</p><p style="color: black;">To really help a hearing impaired person, you have to first measure their hearing loss over a range of frequencies and then tailor the gain to make up for the loss. For most people with age related hearing loss, it's a fair bet to gain them up from say 2kHz to 5..6kHz tops, with a steep filter above that - that will still not give them the &quot;f&quot; and &quot;s&quot; sounds, but it will be extremely noisy if you try to add extreme gain here.</p><p style="color: black;">I've added a schematic and you are free to use it however you like. It has got a more moderate gain of 11, THD below 0.001% and -3dB bandwidth from ~17Hz to 16.3kHz, so will amplify all vocal sounds equally (including &quot;f&quot; and &quot;s&quot;). While such a simple circuit isn't perfect in any way, there's no phase reversal and hence no tendency to oscillate.</p><p style="color: black;">Hope you'll use this to learn some more about op-amps. Datasheets are a good source for further self education.</p><p style="color: black;">Have a nice day :)</p>
<p>hi could u explain your circuit</p>
<p>Sure, what are your questions, or which part don't you understand?</p><p>School assignment?</p>
<p>the part around capacitor 3 C3</p>
<p>can we text ,am thinking about doing it for my IC project</p>
<p>Texting internationally cost a bunch and isn't faster, so let's keep it here or to PM's.</p>
contact t me with email or give me your number<br>also where do you live
<p>It's just showing the cap over the supply. All labels with the same name is connected, so the two marked &quot;+9V&quot; should be physically connected, just like all &quot;GND&quot; must be connected.</p><p>Where it says &quot;To Battery&quot; is where you connect the battery (obviously), perhaps through a switch, to make it easy to turn on/off.</p><p>Do you have <strong>any</strong> op-amp but the 741?</p>
<p>my facebook name is sathya cristo</p>
<p>and am gonna do it in a breadboard</p>
<p>Very nice!</p>

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