Hey internet, I just finished refurbishing this GFA-555, and the customer opted to go without the BFA-555 Smart Soft-Start Power Supply, so if you’re wondering what you get without this option, here it is! I do install some Capacitor Hats to replace the crusty originals. The original power supply capacitors were replaced with Kemet ALS30, 22,000uF, which is about as big as you can go without a soft-start. (Or the switch will spark too much and the fuse may blow due to the in-rush current.)

Invoice on this one was $1210, which includes new Kemet power supply capacitors. Without the capacitors this is a $930 job.

Dust is attracted to electric fields, and sticks to a board in a way that reveals the shape of the electric field in one plane. Dramatically illustrated here on the underside of an Adcom GFA-555. These dusty traces are at only 83V potential, but that’s enough to make them dustier than surrounding traces at lower voltages. Check out how there is a bunch of dust between the grounded mounting bracket and the adjacent trace at 83VDC.

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.

But the original board is still available if you want it! Here.

Printed circuit board+Pogo pins=Test jig.

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. This close gain matching is in-audible, but helps to expose potential issues with a board.
• 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.

Continue reading How to build a Test Jig, or Test Fixture, for your Printed Circuit Boards

Good news! I have tested and validated the performance of the new heat sinks for the BFA-565 power supply board. They work great, and the boards will be ready for purchase later this week.

Continue reading Heatsink WIN! New BFA-565 power boards are go. 👍

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.

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!

Buy them here. Hoppe’s Brain EBFA-565.

Continue reading Introducing the EBFA-565; the Even Better F–cking Amplifier (New version Adcom GFA-565 Circuit Boards)

EBFA-565 Assembly and installation guide

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.

Continue reading Heatsink FAIL delays release of my new power supply for the GFA-565. :^/