Do you have one of the first batch of ADCOM GFA-555 amps ever made? My GFA-555 MK1 boards work great in these amps, but they must be physically modified to work with the horizontal board.

Until now! I have designed new boards for these early “Vertical” 555’s.

I really like how this layout turned out. Very pleasing symmetry.

This is the original board:

One of the difficulties in this layout, was that the original RCA jacks and bridge switch are mounted on a little circuit board that sits behind the input board. The original RCA jacks are pretty crappy, so I wanted a solution that would allow people to install nice chassis-mount RCA jacks. So I decided to go with a stacked mezzanine board arrangement.

This mezzanine board mounts to the inside of the back panel, and holds the bridge switch in the original location. The hole in the center is to access the RCA jacks, which are wired to the terminals on the mezzanine board. Thermal breakers and LEDs also connect here. The main input board is stacked on top of this board and can be installed and removed without soldering!

The boards arrive from the manufacturer on Monday, and I’ll be sending them to Jon Morris, of Morris Audio, out in Wyoming to test them. I don’t happen to have one of these older 555’s in my shop right now, so he is going to validate the design for me.