Long time, no blog! I’ve been super busy with Adcom amp and preamp refurbishings, and obsessing over new circuit board designs.
Here are completely new versions of the GFA-565 input boards, and for the first time, I am offering fully assembled and tested boards for $380. (Please allow up to a 15-day lead time. They are hand-made, by me in my shop.) Click here to buy.
These boards are completely redesigned from scratch, and are something of a departure from the original layout, while maintaining physical compatibility. The first versions of my GFA-565 boards were essentially a clone of the original, with component placement and traces identical to the original single-sided board. This new version takes full advantage of both layers of the circuit board.
- Traces are routed on the top and bottom layers. This allows for shorter, wider traces, better spacing between conductors, and better component placement.
- Improved labeling. Lots of thought went into making component placement as confusion-free as possible. All components are labeled with their value and type of component. Inputs and outputs are labeled, as are jumpers for LEDs and thermal breakers. Populating the board goes faster, with fewer errors.
- Better thermal bonding of the input and cascode transistor pairs: Matched transistor pairs that make up the input stage should be thermally bonded with thermal paste and heat-shrink. These transistors have been located adjacent to make this easy.
- ECB, EBC, CBE confusion no more! The new boards will accommodate transistors with any pinout. The original 2SC and 2SA type transistors have leads arranged in ECB format. These are no longer available, and the modern equivalent transistors are either EBC or CBE. (KSP42/92 and BC550/560, respectively.) Previously, this meant bending the transistor legs all goofy in order to fit, and it was really easy to make a mistake. The new board has pads arranged in an ECBE format that will accommodate all three pinouts! Much less confusing.
Now available fully assembled:
Lovingly hand-assembled by me, in my little shop in Madison, WI, using high quality parts, as listed in this spreadsheet. I am a meticulous builder. The board will be assembled to the standards as seen in the photos. Testing includes probing DC operating points, checking input stage balance, DC offset, distortion, and operation of warning LEDs.
Buying a pre-assembled board is no guarantee of success. You must still possess the skills to troubleshoot a complex amplifier. Every component on the output modules should be checked before installing the input board, or the board could be damaged. Damage due to installation error is not warrantied.