Just finished R.G's Hum Free ABY using a pcb layout by Matt Rabe. Found a tiny error so thought I'd mention it though this appears to be an old layout so the correction is probably documented elsewhere. A tiny bit of track is missing at the output of TR1. Also. the pads for C3 appear to indicate + should be attached to the -9v rail which seemed illogical to me so I swapped it round. I made both corrections before firing up the circuit and it works fine although in my case, I had to hard wire a sleeve connection between input and ONE of the outputs - Still got separate grounds but 1 is now referenced. Without this, i could adjust hum by moving my coffee cup about the room!
Thanks R.G & Matt
Box
(http://www.stallibrass.com/images/kas/ABY.jpg)
Guts
(http://www.stallibrass.com/images/kas/ABYguts.jpg)
Layout
(http://www.stallibrass.com/images/kas/ABYcorrection.jpg)