@sstalwar & Rich
I don’t have a schematic for the BBAM. It’s a fairly simple circuit with capacitive filters and one AD744 op amp per signal phase. The Hovland coupling and filtering caps are easily surpassed. Replace them with best caps you can afford that fit on the PCB. I tried Mundorf SG and later switched to ClarityCap MR. You can also fit Duelund or V-Cap teflon. The stock Caddock MK-132 resistors are very good by high-end standards, but Texas Components TX2575 are more resolving and transparent. The stock AD744 is an excellent op amp. The big move is to re-power the AD744 with an external +/- 12Vdc bipolar linear supply like Hynes, Pardo, or Twisted Pear DIY kit. That means removing the stock batteries and 3-pin regulators from the PCB and running wires directly from the PCB to a panel connector. The current draw is tiny. Yes, a Hynes bipolar supply is >$1K. The others are much cheaper. IMO a well-powered op amp can rival tubes.