New and improved power supply kits for the GFA-555!

Hi everyone, I’m really proud of this new power supply for the GFA-555! It’s been months in the works.

Hoppe’s Brain BFA-555 Smart Soft-Start

This is a whole new take on the soft-start power supply for the GFA-555 MKI and MKII. This version features:

  • An intelligent soft-start circuit that monitors a number of electrical conditions before starting the amp.
  • Easier to install than the old version
  • Remote trigger power
  • Better heatsinking of the bridge rectifiers
  • Additional bypass capacitor options
  • For the GFA-555 MKII, an option to replace back-panel fuse holders with on-board fuse holders, eliminating many inches of 16ga wire.
Hoppe’s Brain BFA-555 Smart Soft-Start

Continue reading New and improved power supply kits for the GFA-555!

Hoppe’s Brain is no longer accepting repair or refurbishing clients. Sorry! It’s only DIY Circuit Board Kits from now on.

Hi everyone,

I’ve been procrastinating writing this, as many of you will be disappointed that I can’t work on your gear. And unfortunately, I can’t even take care of the people on my waiting list, some of whom have been waiting for years! Sorry. 🙁

I’m getting old, apparently. (Never thought it would happen to me.) I am developing physical issues that make it impossible for me to keep up with repairs and refurbishings. As they say…

“Welcome to your 40’s! If you have not developed a mystery ailment, one will be assigned to you shortly.” Doctors are unsure of what’s going on with me, but I suspect it might be Polymyalgia Rhumatica.

Continue reading Hoppe’s Brain is no longer accepting repair or refurbishing clients. Sorry! It’s only DIY Circuit Board Kits from now on.

Hoppe’s Brain Coronavirus Pandemic Statement.

Remain indoors.

Hoppe’s Brain is operating more or less normally at this point! I work from home, and am getting a lot done, actually. DIY kit sales are on the rise as people want projects during their social isolation! So far I am pretty fortunate.

I am stocking up on parts, in case suppliers like Digikey and Mouser are shut down. If I start to run out of critical parts, I might have to discontinue selling certain DIY circuit board kits. In some cases, people will have their own parts they can use, or good old parts can be recycled. We can work something out.

To keep my customers safe:

I have no symptoms or any reason to believe I have C-19, but as everyone is well aware, anyone can be a carrier and not know it.

There is a small—but non-zero—risk of transmission of coronavirus via packages in the mail, and by the surfaces of products. And so I am operating on the assumption that I am a carrier of coronavirus. I am washing my hands before I go to work at the bench, and before I touch anything in the lab. While I am working, I tend to use a lot of ethanol/methanol to clean things, and so that is another preventative measure. I am also washing my hands before handling any packing material, or packing up kits and equipment.

So chow down on a protein fudge, take whatever injections are recommended in your sector, and remain indoors!

New Product: “Capacitor Hats” for large screw-terminal electrolytic capacitors.

Another new product for amp builders!

These “Capacitor Hats” provide a neat way to make connections to the tops of large, screw-terminal electrolytic capacitors, while also providing a stable platform to mount components like bypass capacitors and drain resistors.

Component pads cover most of the surface, allowing a wide variety of components to be mounted. Wire pads along the edges connect multiple wires up to 12ga. Double-sided PCB with double-thick 2oz copper. Reversible.

Shown in the example above is a 50mm diameter capacitor, with a Capacitor Hat equipped with a 47µF electrolytic capacitor, a 0.1µF polypropylene bypass capacitor, a 4.7KΩ drain resistor, an LED resistor, and LED power wire.

*Components shown are not included. Bare circuit boards only. Sold as sets of four for $25.

Get them here. Capacitor Hats for Large Aluminum Electrolytic Capacitors.

New product! Input Boards for 1985 vintage Adcom GFA-555’s

I now have input boards for the very first GFA-555’s that came out in 1985. Judging from the serial numbers I’ve seen, there are perhaps less than 8000 of these amplifiers in existence. But they deserve to be restored!

At first glance, they look just like the boards in the more common 1986 version, but they are not physically compatible. The mounting brackets are spaced wider, the RCA input jacks are different, and the bridge switch is a bit chunkier.

Continue reading New product! Input Boards for 1985 vintage Adcom GFA-555’s

Yet another variation of the Adcom GFA-555 discovered in the wild!

GFA-555 Rack Mount

CORRECTION and APOLOGY: I’ve been contacted by a friend of the original owner of Wavetrace Technologies, and was informed that the the mods I discovered in this amp are not actually a product of Wavetrace Technologies. They were done after the fact, and do not reflect on the quality of Wavetrace Technologies work. My apologies for any confusion. The article has been corrected.


A kind person called Bob contacted me out of the blue and offered me this cool old rack-mount GFA-555 for free. Of course I accepted, and I sent him a really nice custom Wisconsin cheese box as a thank-you.

The amp had been modified by Wavetrace Technologies back in 1988, and someone else did some further modifications.

It was blown out and passing DC at the speaker terminals. I didn’t want to spend a lot of time trying to repair and return it to FET operation, as I planned to install one of my input boards anyway.

I happened to have one of my replacement input boards for the GFA-555 all built up and ready to go…

But nope! The board doesn’t fit!

Continue reading Yet another variation of the Adcom GFA-555 discovered in the wild!

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!