Hi I am trying to build a hearing aid for my elderly father. I have run across this product and works well compared to numerous other preamps I tried.. The one I was able to purchase at the marketplace is only version 1 since I am in Taipei, I can not find the latest v2. V1 works well but I get occasional POPS and crackles. I tried a different unit and also built my own per schematic found here . All same result, so it must be the circuit design,
I was able to find the schematic here for V2, since i could not find any in the market place, I tried building my own, but can not get it to work. I have written the vendor to ask for reason for crackling and popping noise in V1, and the reason to change to V2, but they did not respond, so I have come here with my questions. Please keep in mind that I am an engineer but not electrical similar, so not very familiar with circuitry.
Questions:
1) Looking at the version 1 schematic, can someone see what causes the occasional crackling and popping, the problem goes away for a little while if powered off, and the problem always comes back very infrequently, but sporadically without reason that I can find.
2) Comparing the V1 and V2 design, I notice the diagram is similar but some resistor values have changed, and don't understand why they transposed the pin numbers on the diagram. I am able to sucessfully, build version 1, but can not repeat it for version 2. So makes me suspicious that v2 design has mistakes, but can't imagine them updating a product and making it not work. So can someone sense of what is going on?
3) I have found another similar product using LM358 with schematic here, i have successfully built this and it works, but the sound seems muffled, sounding like listening through a pillow. Anyway to alter its design to increase the crispness of sound?
Thanks all, this is the last bit to finally getting a self built hearing aid for my dad. Thanks again for your help
