Price range: $80.00 through $440.00
ADCOM GFA-555 MK2 Input Board
Description
Improved input board for the Adcom GFA-555 Mark 2.
**Not for currently produced GFA-555 “SE” or “MS” models. MK2 amps are labeled “model GFA-555 II” above the power switch. MK1 amps are labeled “model GFA-555” can be identified by the lack of a “Thermal Protection” LED on the front panel. MK1 board is available here.
Legend has it that the “GFA” in GFA-555 stands for “Good effing amplifier”. Ahem… With this improved board, model BFA-555 II, you will have a “Better effing amplifier”. See what I did there?
Features:
- NEW: Includes new bias transistor cable assembles.
- Two-layer circuit board allows for shorter, wider traces, better spacing between conductors, and better component placement. A ground plane covers the entire top surface.
- Clear component 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 terminals for LEDs and thermal breakers.
- Heatsinks are fitted to the TO-126 driver transistors. This addresses an occasional failure point for the GFA-555. These transistors run pretty hot, and broken solder joints can develop due to heat cycling. The heatsinks keep the transistors quite comfortable, and the plated through-hole board is much less prone to heat-cracked solder joints.
- Local power supply bypass capacitors built in. These added capacitors reduce noise on the power rails, and deliver fast, high-frequency currents to the input board than cannot be provided by the main power supply capacitors, which reside at the end of long supply wires.
- Top-shelf parts from On Semi, Vishay/Dale, TE, Kemet, Panasonic, WIMA and Cornell Dubilier.
- 0.1% tolerance resistors are used in the signal path anywhere they would affect gain. Channel matching is within 0.01db.
- The complete kit also includes two pairs of matched input transistors. For best thermal tracking, these transistors are thermally bonded with copper foil tape and heat-shrink. They are positioned face-to-face to make this easy.
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.
DOCUMENTATION:
Hoppe’s Brain BFA-555 MK2 Assembly Notes
ADCOM BOMs – Parts upgrades and substitutions for the rest of the amplifier.
Also recommended reading:Â Another Tour of a Hoppe’s Brain GFA-555 Restoration, 5 years later, with better technology. This article contains detailed documentation on every aspect of a 555 restoration. Article refers to a MK1, but many aspects are the same.
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.
I cannot repair or troubleshoot customer-assembled boards. This is a “pack your own parachute” type situation.
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.)
Additional information
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Can any of the Adcoms drive the 1 ohm load of Apogee Scintillas ?
Wasn’t there a mod to do it?
I wouldn’t recommend the GFA-555 for this task. It would probably survive, but the it’s just not designed for this kind of load. The power supply would sag like crazy. Better to have a lower voltage amp with more current, for the same power rating.
The GFA-565 might fit the bill though! I had a customer who had a pair of Eminent Technology LFT-6’s, and these are also transformerless planars, with some crazy low-impedance dips, though not as extreme as the Scintilla’s. This customer hadn’t found an amp that could drive them decently until this pair of GFA-565’s I built. The 565 is totally unbothered by a 1 ohm impedance dip. There’s 20 Output transistors!
I have and ADCOM 555 MKII driving a pair of APOGEE Centaur minor, without problem, but scintillas are lower impedance
Running a mk2 with a aircom-t10 driving RP-8000F’s. This is a wonderful way to remove stuff from the walls with ease.
I want this board just for spite!