Many Electronic circuit projects in simple ways of learning

Cheap & Small hearing aids circuit project

This cheap hearing aids circuit project or the small listen booster is a simple function similar to the function of the common audio amplifier.

The work starts with a preamplifier circuit, the light, and amplifier. To be the stronger. To receive audio signals from a. microphone to be larger to increase the volume up, Before it is sent to a power amplifier to power up again, To drive headphones to we hear.

Dynamic microphone amplifier for earphone

Look at the circuit below. It is a simple two-stage transistor amplifier.

All of all, a dynamic microphone gets a sound to convert into a small signal.

Then, the C2-capacitor get only AC to two 2N3053 NPN transistors have a particularly high gain.

Next, the higher signal comes out of C3 to an earphone output.Dynamic microphone Amplifier for earphones

But this circuit is not suitable for true using. So, you look at the second circuit below.

Hearing Aids circuit project

The specialty of this preamplifier circuit at The Automatic level control circuit-ALC. Which will operates at a fixed control volume automatically. This part of the circuit, the sound has been very loud, the circuit is to reduce the volume down. On the other hand, if soft the circuit is increased the volume up. Make us hear all the levels. Both lot and the less sound. Adjust the volume as needed. To set the volume to a level that is appropriate for each person.

How it works

-In the Figure 1 is a complete circuit of the cheap hearing aids project. The works of circuit will starts with the microphone MIC1, that is a condenser microphone, This MIC will be need has a voltage supply, It get a current with a battery pass through the resistor R1 – 10K.

-A sound signal from MIC will be connected through capacitor C1 value 0.1 uF, to amplify into the base pin(?B) of transistor Q1 number BC547. Which serves as a pre-amplifier audio amplifier in the first set.

-The output signal at the pin collector-C is connected through a capacitor C2 connected to the transistor Q2 acts as the second preamplifier. The circuit setting this manner a very high gain, by has the resistors R3,R5 are a load, the R4 is a feedback and bias base to the transistor Q2 works.

-The sound signal that passed the preamplifier, will be connected via the capacitor C3, and to the control volume level that acts by the transistor Q3, The Mission of the transistor Q3, the building is a voltage bias to the base of transistor Q1 to control the amplifier. By voltage that occurs from the introduction of the sound signal. from the output of the preamplifier circuit go to the rectifier to make the DC voltage by have the diode D1 work together.

-The voltage that is filtered to the stable level before moving up, by the capacitor C4 is to delay the rhythm in volume control to fast or slow. If the driver makes a slow pace before the base of transistor Q1 pass way the resistor R2.

-The MIC has been loud, will has a bias signal the transistor Q3 a lot. As a result, the voltage at collector pin-C of Q3 will decreased. As a result, the voltage across the capacitor C4 is very close from the power supply (due to resistor R7 is connected) is pulled to decrease, too.

-This control volume level voltage will send pass through the resistor R2 into the base of the transistor Q1. If the voltage is high (Low MIC) It would make have current input to the transistor Q1 makes the sound louder. And If the level volume control voltage have low level (MIC loud).

It would make current input to the transistor decreases. As a result, the audio signal will be reduced accordingly. As a result, the noise level have nearly the same all the time. Whether loud or soft.

-The sound signal through the control volume. Is sent to the power amplifier circuit to drive headphones to hear. Served by the transistor Q4 number BC337 has the potentiometer VR1 to adjust the volume. Connection signal through the capacitor C9 serves the signal feed back and bias to the transistor works in class A.

The capacitor C7 will reduce the growth rate in the high frequency range. To reduce noise and maintain the stability of circuit.

The sound signal from the collector pin is driven through headphones connected directly with the power supply. The headphones that will act as a DC voltage to the load of the amplifier circuit. It must be dynamic headphones with impedance of the power supply as well. No more, no less, in the range from 16 to 32 ohms.

Which will be the typical impedance of headphones already.A crystal earphones or a pizo ceramic headphones. Can not be used in this project. Due to the value high resistance power. Will not load current circuit to operate.

The headphone is used, can be used both headphones Mono and stereo. With the jumper JP1 is an option that will used with stereo or mono headphones. Because this project uses a stereo jack socket. The internal structure of the jack may have caused a short circuit at the jack male mono.

This jumper must be set aside to float circuit. If you intend to use with any stereo headset only. It can be Connection short jumper was not permanent.

How to makes and adjusting
PCB layout for build this circuit.

The circuit can will “throb” sound when turned on. Is typical of the output are used to current the self through headphones. Applications should be turned on before you wear headphones. And first off was to remove the ear is removed. The current flowing through the load. (Headphones or speakers) all time is not good.


In the case of a high-watt power amplifier. Because it can cause have current to flow through lot headphones. In the earphones and the wire burn. But in this case, the power supply is 1.5V. The circuit use low current consumption 26-27mA (Use stereo headphones Impedance 16Ω)

The headphone jack is not less than 1mA current during the power flow headphones have a 7-8mA per watt is equivalent to approximately 1-1.3mW per side, which is still in the safe range. It is not fair.

Related Posts

JLCPCB - Only $2 for PCB Protytpe(Any Color)

With 600,000+ Customers Worldwide, 10,000+ PCB Orders Per Day

Up to $20 shipping discount on first order now:

This Post Has 38 Comments

  1. This sounds like a great project and it will be extremely effective in many ways. Keep up the great work. Thanks for sharing! – Hearing Aids Colorado

  2. Thank for sharing this interesting project.
    A question… What are the technical specifications of the mic? Voltage, etc…
    (Sorry but english is not my first language)
    Thanks in advance

  3. @Nicole Renee
    Thanks for your encouragement.
    I was very happy. You like this project.

  4. @Jose M
    You welcome.
    My English is poor,too.
    We same English not well.
    But we love hobby electronic like you.

    Thanks a lot.

  5. Nice project.

    I was wondering if i could replace the MIC with an input audio jack for an mp3 player so that i can have fix volume from varying mp3s volume?

  6. thank u sir,, v nice project,, almost i have done it…. (y)

  7. So, the voltage supply is just 1.5V, not 3V? Because I see 2 “1.5V” in the schematic but in figure 2 the battery is just 1.5V.

    ..just verifying, thank you~ (^^,)

  8. do you have a block biagram of ths? just asking :))

  9. can you show the connection in the bo J1 ie the jack connection box.please help me with a quick reply??

  10. Will this work? the headphone connection block diagram please?

  11. Hello 😀
    I’ve finished it for my projeeeect~
    Thsnk you for posting this :))
    I would've wanted to leave a picture of the final thing with packaging but oh well….

    again, THANKS!!

  12. I’ve finished it for my projeeeect~
    Thsnk you for posting this :))
    I would've wanted to leave a picture of the final thing with packaging but oh well….

    again, THANKS!!

  13. hey Aethel. can you please help me in the connection of jackbox.please help

  14. what is operating frequency this circuit?
    please help me with quick reply.

  15. thanks for sharing this kind of project,i try to make this for myself,more power!

  16. Hi,mel
    Thanks a lot for your feedback.

  17. Plz someone help me in connection of this circuit on pcb……..plz

  18. Pls some help in the connections of pcb!! Immediately….

  19. Pls guide us to connect jumper and jack sacket …….

  20. Plz help me…..

    In the connection of d ckt on pcb.plz……immediatly

  21. spear detail want immigeat

  22. to detail

  23. please send me the schematic and pcb board,i want to build it as a gift to my father,,,pls reply if possible immediate


  24. Hi spyru,
    Thanks for your feedback.
    I cannot send you schematic and PCB board.
    GOOD job for your father.

  25. Hi,
    what software you are using in drawing of schematic,pcb and the 2D view

  26. Hi Spyru,
    Thanks for your feedback.
    Long time ago, I use illustrator and corel draw
    Now I use the Inkscape and the gimp.

  27. wow,you have great work,,,

  28. good job

  29. anyway,i have been design the circuit in cadsoft eagle…

  30. can u plzz give me the design of the circuit.

  31. This is a super project. I built one for my Dad for his birthday. Most of the parts you can get in the USA from RadioShack. The transistors I got on eBay.

  32. on a project hearing aid device

  33. help out circuit please

  34. For the science fair in our school, we are trying to make a hearing aid which could work with an app that would control the volume, is there a way for that to happen? We have not yet built it but the hearing aid seems simple to acomplish. Great job!

  35. hy its so good…..keep the fire burning

  36. Hello,
    I tried your circuit and it works on the breadboard,
    But when i transfered it into PCB i can only hear static and noise ,i all the connections are ok and i already replace the mic with a new one ,what do you think is the problem im missing?
    Thank you

  37. Hello.
    First of all thanks fo the circuit. I had done the circuit in a breadboard n had got output also. But the problem is that the audio output is very faint as if no amplification takes place. I had replaced 1.5v source with 9v battery and i had replaced 1uf capacitor with 0.1uf capacitor(the one in between two bc547-middle part). Could point out what might be the mistake.
    Thanks in advance.

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Close Menu