ST4 DIY – VCA Board
The VCA board is the final stage in the signal path and stereo amplifies the signals, based on control voltages (0..5V). You can basically hack the CV inputs by supplying them on the 12 pin connector. TODO: connector layouts! The PCB also has a headphone amp on-board!
It’s a fully analog board, but this time it’s in SMD to save precious space. Only the connectors and phono jacks are through-hole.
The Bill Of Materials:
…and.. a Lumberg KLB-4, but that’s panel mount 😉
Start with lowest and the simplest: the passives. The 100nF bypass caps are always at the head or tail side of the IC’s. There are two 47 pFs too near the NE5532. After that just group all the resistors by value and go. Please note that R33 and R35 and 10k, the values have been overwritten by hand on the silkscreen!
Surprise, more passives at the bottom!
Solder the 1013 opamps. Look at the silkscreen of the opamps. If you look carefully you see a double silkscreen line on one side. This is the side of pin 1! The opamps have a stripe on them to denote the pin 1 side.
Now do the LM13700’s. Again, look at the double silkscreen line. Pin 1 on the IC is denoted with an embossed circle.
Idem for the bottom side.
Solder the IDC sockets. Note the silkscreen lines. These denote the side of the gap. Solder the socket for the NE5532 and mind the orientation.
Now for the finale. Push the NE5532 in the socket. Solder wiring from the headphone PCB holes (see photo below) to the Lumberg headphone socket. then solder all the Amphenol phono sockets.
