This is an implementation of a hearing aid circuit as presented on radiofun232’s YouTube channel.

The goal is an inexpensive, open source, battery powered amplifier that takes a signal from a condenser microphone and drives an earphone to help people who are having trouble hearing. This board is designed to be worn around the neck with an earphone connected to the 3.5mm barrel jack.

Part list:
B1, B2 - AA battery holder - Digikey p/n BCAAPC-ND
M1 - Condenser microphone - Digikey p/n 102-1721-ND
J1 - 3.5mm Barrel jack - Digikey p/n CP1-3523N-ND
LED1 - 5mm Green LED - Digikey p/n 754-1263-ND
S1 - Slide switch - Digikey p/n EG1916-ND
C1 - 0.1uF capacitor - Digikey p/n 399-4329-ND
C2 - 0.22uF capacitor - Digikey p/n 478-4863-ND
C3 - 0.047uF capacitor - Digikey p/n 399-4371-ND
C4 - 47uF capacitor - Digikey p/n 399-6610-ND
Q1 - BC557 pnp transistor - Digikey p/n BC557BTACT-ND
Q2, Q3, Q4 - BC547 npn transistor - Digikey p/n BC547BTACT-ND
Q5 - BC237B npn transistor - Digikey p/n BC237BGOS-ND
R1, R2, R3 - 1k Ohm resistor - Digikey p/n CF14JT1K00CT-ND
R4 - 66.5k Ohm resistor - Digikey p/n 66.5KXBK-ND
R5 - 100 Ohm resistor - Digikey p/n CF14JT100RCT-ND
R6 - 1M Ohm resistor - Digikey p/n CF14JT1M00CT-ND
R7 - 470k Ohm resistor - Digikey p/n CF14JT470KCT-ND
R8 - 220k Ohm resistor - Digikey p/n CF14JT220KCT-ND
R9 - 10k Ohm resistor - Digikey p/n CF14JT10K0CT-ND
R10 - 27 Ohm resistor - Digikey p/n CF14JT27R0CT-ND
R11 - 470 Ohm resistor - Digikey p/n CF14JT470RCT-ND
32 Ohm Headphone - link or equivalent

This circuit has not been tested yet, and it will almost certainly have some tweaks after assembling the board. So stay tuned for the final version. :-)