I have some PCBs to build the preamplifier. The price for one PCB (includes two channels) is now 30 Euros, including shipping.
The construction is described here:
https://audioxpress.com/article/you-can-diy-the-pr-3-a-high-quality-stereo-preamplifier
The construction is described here:
https://audioxpress.com/article/you-can-diy-the-pr-3-a-high-quality-stereo-preamplifier