Happy Easter everyone!
You may be wondering what has been happening with the B-17B preamp. Quite a bit actually, but mostly I have been getting educated on using Cadsoft Eagle to do schematics and circuit board layouts. My first attempt was just the VU and buffer section – basically the low voltage stuff. Here is the circuit diagram and board layout from that work.
I was considering if I should send this board out to a board fabricator and get it built, but it occurred to me that if I am going to order a PC board perhaps I should try to get the entire preamp circuit on there. I knew this would be a challenge because the freeware version of Eagle is restricted to 80×100 mm board size (3.15 x 3.94 inches). I like using the Orange Drop capacitors but they are quite large and take up a lot of board space. But hey – it couldn’t hurt to try, and I was bound to learn a lot along the way.
The first challenge was learning how to create new parts in the Eagle library, since I couldn’t find existing libraries for many of the parts used in this design. So there is now an NSE Labs Eagle library where I’ve created the parts that I couldn’t find elsewhere.
Below you can see the full B-17B circuit so far. The board layout is not done, all I have done so far is place the components and they are still just connected by airwires.
This circuit does not contain the VU drivers yet. I’m debating if I should switch to a dual package for the opamp and just build the VU drivers external to this board. That would allow changing to other analog or digital VU meters in the future, for instance. The high-voltage supply is also not on this board. It wouldn’t be a big deal to keep that supply external to the PC board either. But as you can see most of the components should actually fit on the board.
That’s it for now. This is still a work in progress and I am learning a ton as I go. Stay tuned!