Introduction: Hearing Aid Amplifier Four Transistors (good Quality and Low Cost)
Hi from France
Here is a small amp with 4 transistors which improves listening for person are obliged to turn up
the volume of the TV and that hinder their families they hear very well.
Is a Canadian "Cousin" named Gary Pechon who is behind this arrangement.
Assembly is supplied with a 1.5 volt AA battery and the sound quality is good and is very low cost.
I built everything with KiCad ( the zip is attached with all the project files at the end of this instructable)
I 've build it with the free Kicad electronic software but you can easily convert to Eagle
here is link to dowload Kicad:
here is the link for various component libraries submitted by the community:
Step 1: COMPONENTS:
3 x 100nF
2 x 1 uF
1 x 10uF tantalum
1 x 470uF chemical
1 x 100R
1 x 1.5 K
1 x 3.9K
1 x 4.7 K
2 x 10K
2 x 100K
1 x 1M
Potentiometer: 1 x Miniature 22K
Diode: 1 x 1N4848
3 x BC54B7 or BC547C
1 x BC337 25 or BC337 40
1 x 3.5 stereo jack socket for PCB
1 x mini On / Off switch
1 x AA battery or AAA
1 x battery holder with welding wire out
1 x Micro HiFi quality electret (20 to 20,000 Hz)
1 x Mini stereo headphones for walkman
1x Presensitized copper plate 50 x 100 mm
Welding clamp, forests 0.8 and 1 mm
Step 2: Schema and PCB View
This small amplifier operates with 4 transistors the first 2 amplifies the microphone, the third acts as automatic gain control which allows a constant listening level, are automatically weakened Strong sound are automatically weakened and low sounds are amplified a volume control potentiometer for the determination of sound before amplification through the fourth transistor.
for listening you can use headphones or Walkman or whatever, it just requires that each listener have an impedance of 32 Ohms, in fact mounting requires impedance 64 Ohms for its operation but as the ground is not connected PCB, this means connecting two headphones connected in series e 64 Ohms.
I have not tried it on a bakelite plate prototype but I tried on a solderless prototype breadboard before building the assembly and there was feedback (possibly because of connections too long)
So I advise the PCB for a good listener choose a good quality electret microphone (bandwidth 20 to 16,000 Hz , for example) the connection to the microphone should be as short as possible and for good directivity and isolate unwanted noise I surrounded the microphone in a little thin foam and have set into a piece of ballpoint pen 1 cm in length.