For those of you who prefer a more original looking GFA-565 board, I still sell this older version, the BFA-565. It works great. I prefer the new version, the EBFA-565; It has many subtle improvements, is easier to build, easier to install, and even shows a measurable improvement in performance.
Every circuit board I sell need to be thoroughly tested, and measurements taken that should agree with expected values. Tests are chosen to show up any errors I might have made in the board’s assembly.
Gain. I use 0.1% tolerance resistors in key parts of the circuit, so gain should match within 0.01db from one board to another.
DC operating points, such as the drive voltage to the output sections, DC offset, DC servo output, and bias voltages
Distortion; it should match measurements from other boards, all the way up to full-scale output.
Current running through various branches of the circuit.
Functionality of indicator LEDs
Here’s how I build my test jigs.
Long story short: Printed circuit board+Pogo pins=Test jig.
Check out these serial number tags! So cool. They’re made of 1mm thick FR4 PCB material, with the text in ENIG gold finish. I use an engraver pen to fill in the date for the serial number. Held in place with a little JB Weld epoxy.
Launching a new product is a lot of work! I’ve been working on these new boards for the Adcom GFA-565 for about six months now. (Now available here.)
This is the last step before I consider it fit for sale—design validation. It has to perform at least as good as the previous version, and it has to deliver on the usability improvements. I need to install it into an amp, and not only test its electrical operation, but the user experience of installing it.
Big news! I have completely re-designed circuit boards for the Adcom GFA-565. Based on customer feedback, I’ve made many improvements. These new boards are easier to install, harder to screw up, and they even perform a little better!
So I’ve been sitting on this new design for a GFA-565 power supply for two years, because I haven’t found the time to test and validate the design before I start offering them for sale. I needed to install it in an actual amplifier and test its performance. Recently I found the time to build myself a GFA-565!
One of the key features of this new power supply, is the relocation of the bridge rectifier to the tops of the capacitors, which eliminates about 20 inches of 14ga hookup wire that normally runs from the bridge rectifier mounted on the floor on the left side of the amp, to the capacitors on the right side. In my design, the bridge rectifier is made up of four discrete diodes in TO-220 packages, mounted to a circuit board on top of the capacitors.
My design goal is that the heat dissipation for the bridge rectifier needs at least as good as—or better than—the OEM arrangement, with the bridge rectifier mounted to a heatsink on the floor of the chassis.
As I’m about to find out, this heatsink arrangement isn’t enough.
So I’ve started taking on new refurb customers, at a much slower pace, and for a lot more money. 😸 I realized, like many small business owners, I have been under-charging for my work. The following is what you get when you drop some coin with me.
The TI BUF634A adds a fast and powerful output stage to any op-amp. It is inserted into the feedback loop, essentially becoming a part of the op-amp itself.
Here’s one installed in a phono preamp I built for a friend. This particular design benefited greatly from the BUF634A, as the output drives a 464 ohm load on its feedback loop, which is a heavy load for most op-amps, but a breeze for the BUF634A.