Read this description of my LZ1AQ amplifier PCB build. Add a one meter loop and some CAT cable and you have a complete wideband magnetic loop that works well.
Here’s a quick run through of my LZ1AQ amplifier PCB build. With some slight modifications to the original LZ1AQ wideband loop amplifier design, I used KiCAD to design a small printed circuit board. Sized about 60 by 40 mm, this LZ1AQ Amplifier PCB build uses mostly surface mount components. Even with limited SMD experience (like me) you should find assembly quite easy.
If you want to make this amplifier, you can order the boards from OSH Park, and follow the documentation provided below.
Even if you have to order all the parts new, you can put together three of these amplifiers for under US $40, or around $12 each.
All of the resistors and capacitors are 1206 size, which is one of the larger SMD footprints. The transistors are surface mount versions of the popular 2N2222A in an SOT23 package. You may be surprised that these transistors are actually smaller than the passive components, but with only 3 leads not that hard to solder.
Your output transformer is easy to wind on an FT37-43 core. Just eight trifilar turns of magnet wire. You can either just solder the transformer directly to the board, or use a DIP socket like I did. The amplifier runs off 10-12 VDC and draws under 150 mA.
LZ1AQ Amplifier PCB Build – More Notes
The footprint for the output transformer is basically DIP spacing. Two rows of three pins are spaced 7.62 mm apart, with pin spacing of 5.08 mm. In my build, I used a DIP socket and a small mounting jig for the transformer. My jig was easy to make with a 3D printer and some pin headers. You could just solder the transformer to the socket or directly to the board.
For maximum flexibility, I used screw terminals to attach loop, output and power, as shown above.
All of the SMD components are hot air soldered but you can use a fine-tip soldering iron if you choose. Either way, you will need to use through-hole techniques for soldering the hardware.
This board uses a large ground plane for signals and power on the top layer. A power trace is used on the bottom layer with some VIAs.
Before powering up, you should check the circuit for continuity. When first powered, you can check the bias voltages on the transistors (see Chavdar’s design document) and current draw as a whole should be under 150 mA. Otherwise, plug and play!