DIY neckloop help

Assistive Listening Devices
#1

I need help understanding some components in the schematic in the following link: Silicon Chip Online - Microphone To Neck Loop Coupler For Hearing Aids
I know it might be outdated, suggestions for newer devices welcome. I’m going the DIY route just out of curiously and it being cost effective.

I’m confused about two components:

  1. I don’t understand what component ZD1 is assuming it’s some kind of diode. I’m hoping to find some exact diodes to use for ZD1 or some suggestions would help.
  2. In the picture of the assembled schematic, some capacitors look like ceramic disk capacitors but others look like rectangular boxes. What kind of capacitors are those? Does it matter which kind I use? Also curious about why if you know.

Thanks!

#2

Hi,

ZD1 is a 4.7V Zener diode. Here’s a Digikey part number for a typical device: 568-5914-3-ND

I didn’t see the picture you referred to, but the non-polarized capacitors would probably be ceramic for good high frequency response. I’d suggest tantalum for those capacitors marked with a polarity.

Let us know how this works out, if you build it.

-Doug