The board assembled with the higher quality components that are available.
In the construction are used 2x OPA637BP for 2 channels and high quality metal-film 1% resistors (Dale mil).
Electrolytic capacitors are made from Panasonic (LX series 105°C), film capacitors are MKT (Siemens).The test circuit supplied from 2x 9V batteries.
The PCB in postscript and pdf format.
A close-up view of the capsule's wiring. The 3rd tab is less than 1mm wide and needs a very small soldering tip. The capsule has 6mm diameter.