All GFA-565 and GFA-555 MK2 board kits now include new cable assemblies

One issue that vintage Adcom amplifiers occasionally suffer from, is corrosion on the snap-in board headers and plugs that connect the bias compensation transistors to the input board on models GFA-565/585 and GFA-555 MK2. The corrosion can be caused by high humidity, salty sea air, or in the case of the GFA-565, leaked capacitor electrolyte. Failure of this connection can cause a DC offset to to appear at the output.

New bias comp cables

Continue reading All GFA-565 and GFA-555 MK2 board kits now include new cable assemblies

ADCOM GFA-555 MK1 “Vertical” circuit boards are here!

Some early models of the GFA-555 MK1 used these vertically-mounted input boards. My existing horizontal board kits could be adapted to work with these amps, but it required fabricating brackets, drilling holes, and adapting the wiring. It was kind of a pain and a bit confusing.

The biggest design challenge for the vertical board model, is the way the original bridge switch is mounted to a small circuit board that is held in place by the RCA jacks. These are not great RCA jacks, and most people will want to swap them for nice chassis-mount types. So I came up with this “Mezzanine board” arrangement with two PCBs stacked together. The first board holds the bridge switch in place, and houses connections for the RCA jacks, LEDs and thermal breakers. Then the input board stacks on top of the mezzanine board, and uses WAGO cage-clamp terminal blocks to connect to the output modules. The input board can be removed and serviced without soldering!

Buy one here!

GFA-555 MK1 “VERTICAL” boards coming soon!

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:

Continue reading GFA-555 MK1 “VERTICAL” boards coming soon!

The nicest GFA-555 MK1 I’ve ever built, $1600

Dang, I kinda want to keep this one, but here it is for sale!
Hoppe’s Brain Refurbished ADCOM GFA-555 MK1
This particular GFA-555 came to me as a customer trade-in, and was very well loved and cared for, so I thought it deserved a new life.

I went all-out on this one. It’s got all the options, including an entirely new input circuit board, and a soft-start power supply with (4) 27,000uF capacitors.

Continue reading The nicest GFA-555 MK1 I’ve ever built, $1600

Because I’m terrible at self-promotion, here’s a video I should have posted last month!

YouTube blogger XRayTonyB did a three-part video series on repairing a GFA-585 using my boards!

As usual, he goes into great detail on the restoration process, and gives all kinds of generally helpful electronics troubleshooting advice along the way. Tony’s channel is loaded with videos about restoring some really interesting gear like vintage receivers, amplifiers, test gear, etc.

This was not a paid promotion, and there is no commercial affiliation. Tony just bought boards from me like any other customer.

A Tour of a Hoppe’s Brain Adcom GFA-585 Restoration

Hi everyone,

This is perhaps the nicest amplifier I’ve ever restored! A GFA-585; The first of its kind with newly designed replacement input boards. (To fix the infamous leaking capacitor issue.) And I can’t believe I’m saying this, but…

It’s for sale. $1800. Update: SOLD to previous customer, Bill.

Also, I wanted to share what I know about restoring a GFA-585. I hope this is useful to others who are tweaking their GFA-585’s, or installing a set of my replacement circuit boards.


Continue reading A Tour of a Hoppe’s Brain Adcom GFA-585 Restoration