Just a note of caution for folks thinking about adding an onboard effects loop to a guitar without using the unity gain buffer ... I recently acquired a lefty preowned Scott Walker Santa Cruz. Scott originally built the guitar with the customized Jangletone buffer that included a separate volume boost. The original owner had Scott remove the buffer and just wire in a blaster, that's how the guitar came to me.
When I plugged in a Q-Tron to try out the effects loop before making the guitar available for sale, I was greeted with an ear-splitting feedback screech when the envelope was triggered with a hard attack on the note. It kept doing that, and exhibited the same behavior with a Boss OD-2r pedal, although, curiously, only when a single pickup was used, it wouldn't do it with both pickups on.
After a little back and forth with Scott, Brad and Waldo, it seemed there was some crosstalk involved that was causing the screeching. Both recommended trying a buffer in there to see.
I had my friend Ned come over last night with his soldering iron and we installed a buffer into the guitar, and, presto, the effects loop works perfectly. We also put in Scott's latest version of the blaster with a separate boost volume control that he's been working on with Steve Kimock, and it is awesome, you can dial in a small boost to a big boost to really get the overdrive happening with a flip of the toggle. Highly recommended.
Hope that might be helpful to some of you builders out there ...
And a big thanks to Ned, Scott, Brad and Waldo for their input and assistance.