Readers: If you'd like to build the project featured in today's post, please go to PCBWAY's Community pages--gerber file; KiCAD 9 project/pcb/schematic/library files, a B.O.M., and more are here.
You can also help out this site immensely by checking out PCBWAY using the link here. Thanks!
============
At my day job I'm up to my knees in Artificial Intelligence. Thank goodness I can do something simple and stupid for AudioDiWHY and get away from AI for a bit.
How about a 3x BNC to mono 3.5" adapter PCB? BNC's can be found on most of my bench test gear, and 3.5" jacks are common on anything DiWHY.
Sure, I could buy or make BNC to 3.5mm mono adapters/adapter cables, but what fun is that?
THE BOARD
 |
| In addition to the 3x breakout the PCB has signal and ground brought to wirepads. |
For the audio jacks I used my favorite horizontal 3.5" switching mono jack, the Switchcraft 35RAPCVAV.
KICAD 9 doesn't provide a footprint for this connector, so I made my own. Get it from Github, here (a library with all my custom KICAD footprints is here).
For the BNC's I had a lot of choices, but, in the spirit of this blog, I chose cheap Chinese BNC's sourced from Amazon: "Superbat":
I had to make a custom a Kicad footprint for this component as well, get it here.....and, assuming the link still works--you can buy the connectors here.
THIS BLOG'S SPONSOR
Once again helping with my DiWHY addiction is this blog's humble sponsor, PCBWAY. They do all sorts of great fabrication, CNC/3D printing, assembly, and much more.
Please help out this blog and check them out--use the link here.
DESIGN AND BUILD
Designing the PCB was easy. I used Kicad 9 and made the board less than 100x100 mm to lock in PCBWAY's ridiculously low price of $5USD for 10 boards.
 |
| Happiness is new boards from PCBWAY! |
 |
SE HABLA TARIFFS?
For the first time I had to pay a tariff for these PCB's. It was surprisingly tricky to figure out how to do that.
Here is the process (for DHL Express; other shippers will differ):
- Print DHL's POA form (download it here). As of 6-8-25: You have to complete this form, and have DHL sign off, to get shipments from China to the U.S.A. using DHL.
- Go to page 2 and figure out who/what you are.
- I am an "individual" so I had to fill out the boxes listed in that form on pages 3 and 4. Yes, I had to provide my social security number.
- Sign the form.
- Scan the completed form and email it to DHLExpressUSA.POA@dhl.com
- They emailed me back quickly--one business day--to acknowledge they got the form and it was OK.
- After my order shipped from PCBWAY, DHL sent me an email telling me how much additional USD I had to pay them before I could take delivery of the goods.
- For me, it was about half the cost of the boards and another $18 USD for handling fees.
- Yes, this raised the price of the boards, but they were still a lot less expensive than any PCB fabrication houses I could find in the US, even with the tariff in place.
With that out of the way, I got building!
USELESS BUILD PHOTOS
 |
 |
| The BNC's are pretty chunky; I had to increase my solder temp to about 750 degrees F to get their leads hot enough to fuse with the solder. |
 |
| It was hard getting the BNC's perfectly aligned but everything works--good enough. |
USE CASE?
If I ever get time I will use this adapter board next time I fire up my QuantAsylum Audio QA403 test rig; right now, with all the adapters and jumper cables needed to hook A to B and B to C and C to D my bench quickly becomes covered in spaghetti. Hopefully this simple BNC to 3.5mm adapter board helps sort this a bit.
I also might build a few of these to make the BNC's behind my test gear--like the trigger input to my Siglent SDG1025--easier to patch.
Beyond that? Who knows. Adapter boards are great fun and soldering connectors on a simple PCB is satisfying.
