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.
Replacement circuit board for Adcom GFA-565. (Original model)
This is the cure for leaky capacitors and DC offset problems in the original Adcom GFA-565! Nearly every GFA-565 ever made was affected by a bad batch of leaky capacitors that cause speaker-blowing DC offset to appear on the output. You can try to clean up the original board, but the DC offset issue often persists. The electrolyte actually soaks into the fiberglass, making it ever-so-slightly conductive. This affects the balance of the high-impedance circuitry around the input stage and DC servo. Amps that seem fixed can actually develop DC offset later on, as the electrolyte continues to spread through the fiberglass. It’s a frustrating problem to work on.
My solution is a new board! Due to the availability of high-quality 2-layer PCBs for a reasonable manufacturing cost, a number of improvements can be made.
- 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 transistors 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.
- STABISTORS: These components are rare and getting rarer, so the board supports three types of stabistors.
- OEM through-hole KB262 and KB362. (Little epoxy blobs) You may re-use them if their leads are not corroded. Caution: Anode is marked with black stripe instead of cathode as you would expect. Double-check with multimeter diode-check function.
- Some 565’s came with unknown, unlabeled stabistors that look like 1N4148’s, but will show 1.2V and 1.8V drop on diode check. (2 and 3 junctions) These are legit and can be re-used.
- CMXSTB400 SOT-6 SMD – EOL.
- Nexperia BAS17,215 Discontinued in 2025 but may still be available. Single-diode SOT23 package, and you need 10 diodes for a board. Fortunately SOT23 is pretty easy to solder for SMD.
- ECB, EBC, CBE confusion no more! The boards accommodate original or new 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 replacement 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 either! Much less confusing.
New transistor footprints accept any transistor pinout, ECB, EBC or CBE.
Read more here at my original blog post.
How to Fix Leaking Capacitors in the Adcom GFA-565 for good!
Skills Required:
Support:
This is an advanced electronics project. You should have some experience repairing audio amplifiers. Please read through the documentation before ordering.
30 minutes free tech support is included with every purchase. Time beyond 30 minutes is billed at $75/hour. This includes time spent researching your issue, writing emails and talking on the phone.
I am happy to provide technical support, but please anticipate paying for for my time as part of the cost of your project. Tech support time is always billed, whether the issue is yours, mine or one of my suppliers.
Alternately, consider asking your question on a forum such as DIYAUDIO.COM. Send me a link and I may comment on the thread.
Parts:
Most parts are available from Mouser, Digikey and other suppliers. Some parts are end-of-life and out of stock. Here is the BFA-565 parts list. That’s absolutely everything you’ll need, not just for the input board, but for a thorough refurbishing of the whole amplifier, including higher-voltage driver transistors, parts for the soft-start board, power switch, etc. Likely, you can re-use many original parts to save money.
I also sell matched sets of input transistors, along with their cascodes, 8 matched transistors in total for $40. (When you buy a board.) Matching these devices is a significant project in itself, so I sell matched sets. I use a test jig to sort and match transistors, based on this discussion at diyaudio.com. You can use the original transistors if they are good, but they often have electrolyte goo on their leads, so if you do re-use the originals, make sure you clean them really, really well, and that the leads are not corroded too much.
Documentation:
Hoppe’s Brain Do-Over policy
Has this happened to you? You’re installing or testing a Hoppe’s Brain PCB and the magic smoke gets out somehow? It happens to every tech, including me, see below. (Backwards transistor, oops.)
This is a bummer, and a lot of work to fix, and even if this PCB was repaired, it wouldn’t look very nice. I want my customer’s projects to look and work nice! I don’t make the boards so pretty just for people to have scorch marks on them.
If your board is smoked, and you want a do-over, here is my “Do-Over” policy. I’ve been doing this for people for years, but haven’t defined it officially until now.
It’s no secret that quality PCB’s have become cheap to manufacture. The PCB itself is not where the value lies in buying a Hoppe’s Brain board. The value is in their design, and the support I provide. The actual board is a tiny percentage of my own costs. (Parts, however are increasingly expensive and I don’t mark them up much.)
So, if you have well and truly smoked your board and want a new one, I can offer you that at close to free.
My boards come in three flavors; Board-Only, Board with Parts, and Fully Assembled.
If you bought:
- Board-Only: A new board for free, plus shipping, about $10 continental US.
- Board with parts: A new board for free, plus shipping, but I cannot sell individual repair parts. All parts are available at reputable vendors like Mouser and Digikey. Part numbers are in my ADCOM BOMs document linked here.
- Fully Assembled:
- A new bare board for free, plus shipping, and you perform your own repair, with your own parts. ~or~
- Send it to me for repair at a rate of $75/hr, capped at $200 maximum. No parts charge. If I cannot re-work the board to work perfectly, and look decent, I will just replace it entirely. If I wouldn’t use it, I won’t send it to you.
Proof of Destruction:
I don’t need your board back, but before I can send you a new board, I need proof you have destroyed the original.
Just drill a big hole through it and send me the picture! (Harvest the parts you want to keep first.)
