I bought a cheap passive from Amazon that was xlr to try. It was the Nobsound Mini Fully-Balanced/Single-Ended Passive Preamp.
This is the circuit, for that Nobsound Fully Balanced.
For it to be proper balanced the blue pot at the front would need 4 mono alps segments not 2 as it has it would be twice as long.
https://ae01.alicdn.com/kf/HTB1vwuRam3PL1JjSZFxq6ABBVXat/Mshow-Fully-Balanced-Passive-Preamp-board-H...
Like this non encased rotary one
https://goldpt.com/sa2x_in_600d.jpg
Cheers George