Interesting that the Pass B1 be brought up. Just today FM Tanoj dropped by with his AP speakers and DIY Pass B1 preamp. I wanted to hear his AP stand mounts with my AP combo and it was a real bonus that he brought the DIY Pass B1 along.
Folks truth be told - there was little to distinguish between the AP preamp and the DIY Pass B1. There might have been differences we might have noticed but AB comparos between the two preamps were really moot. Changing between the two were just like replacing twin brothers - those familiar with both will notice differences probably but to third party listeners they would virtually be no difference. Both were musical virtuoso in their own right.
Given that my AP Pre is about Rs 90K new plus the mods square_wave (the previous owner) has had done including new 6N2P Russian tubes. The DIY Pass B1 costs just Rs 6K! Tanoj planned upgrades on the case might add about 1.5K to the cost but that is still tremendous VFM! Serious tip of the hat to Pune DIY FMs Omishra and Sachin for their work on the DIY Pass B1.
Your observation is very true. I find the B1 so transparent and revealing. If someone has the time and energy, they must build B1 and get a good power amp (or build that too). Amazing VFM.