Sorry, Hoppe’s Brain is temporarily not accepting new clients for equipment refurbishing or repairs. Circuit boards will continue to be available. (Power supply kits for GFA-535, 545, and 555, GFA-565 input boards, and a few others.)

I am fully booked, with more than a year’s worth of clients lined up for amp and preamp refurbishing and repairs. I’m declaring a temporary hiatus so I can concentrate on my existing customers.

Information below is for reference only.


Hoppe’s Brain offers flat rates on complete audiophile upgrade packages to classic Adcom amplifiers and preamplifiers, as well as repairs and customization at $60/hr.

My audiophile restoration upgrade packages are very thorough; much more than just a “re-capping”. The unit is completely dismantled and rebuilt, using better parts than original wherever appropriate. Hand-matched parts are installed. All known reliability issues are addressed.


Repair simply means making the equipment work again, as original, or performing specific work such as capacitor upgrades and other components. There is a 1-hour minimum, plus shipping. I will provide an estimate before proceeding beyond an hour.

Full audiophile restorations are offered at a flat-rate for specific Adcom models. Flat-rate assumes the unit is basically functioning. Minor repairs are included in the flat-rate, but expensive items like power output transistors and transformers are extra, and I will provide an estimate before proceeding.

If you have Adcom equipment, you probably love it, but you know it’s approaching 30 years old now…

I really like Adcom stuff too, and believe it is very much worth keeping in top running condition! A re-capped and refurbished amplifier or preamplifier, with carefully upgraded components in key areas, makes for even better sound and performance than a new one!

When I refurbish a piece of equipment, my intent is to make it last another 30 years or more.

A little history behind the brand… ADCOM made a huge splash in the 80s, offering truly high-performance amplifiers and preamplifiers at a price previously impossible. (Semiconductor technology was accelerating along with fabrication technology.) The value proposition was simple; You get a no-frills, minimalist design using high-quality parts throughout for a reasonable price.

The abbreviation “GFA” was rumored to stand for “Good effing amp”, ahem, and they are very effing good indeed! The GFA-535, 545 and 555 were all variations on a circuit designed for Adcom by the renowned Nelson Pass. There is nothing unusual about the circuit itself. It’s a distillation of many of the best ideas in transistor amps at the time. Minimalist in design, and beautifully executed.

Sales surged along with rave magazine reviews, such as this review of the 200WPC GFA-555 in Stereophile magazine, comparing the sound favorably with much more expensive amplifiers.

So this wonderful gear gets old just the same as anything electronic. Most worryingly, electrolytic capacitors dry out and lose their effectiveness, causing problems ranging from loss of performance or sound quality to complete failure.

FULL refurbishments including re-capping and circuit improvements.

What I do is much more than just a simple re-capping! I’ve been working on Adcom amplifiers for many years, and have identified some key areas that I target for improvement. Every amplifier is carefully obsessed over until I am satisfied it is running better than new, and that it will last a long, long time.


(Details vary depending on the model.)

All electrolytic capacitors are replaced, optionally including the large power supply filters. Audio-grade capacitors like Nichicon FG are used in signal applications, and low-esr types like Panasonic FC for supply bypassing and the like. Polypropylene film caps from Panasonic, Kemet or Wima are used for signal coupling. (If you have a favorite brand or type of capacitor I am happy to use them, provided they are appropriate for the application.)

Soft-start power supply board being installed in a GFA-555 MKI. This is a $375 option, and recommended if your large filter capacitors are old or have high hours on them. More here.

I replace most polyester caps with polypropylene, and for many of the other small capacitors, Adcom chose very high quality parts, so I leave them be. Those nice polycarbonate film caps are hard to improve on. Even those gross-looking little brown blobby ones are actually very nice and expensive silver-micas. I understand you may have a preference for a particular type or brand of capacitor, so I am happy to install these for cost plus any additional labor, as long as the part is appropriate.

Transistors in the critical input stage are replaced with a carefully matched pairs. This step is important to assure low DC offset at the output, and low distortion. The stock transistors are rarely well-matched, especially on later models. I buy hundreds of transistors at a time, and using a custom jig to simulate the operating conditions of the design, I bin and match to much closer tolerance than the factory.

The matching of these transistors is perhaps the most important part of the upgrade. It’s the first thing the signal sees. If these transistors are not in balance, nothing is.

Matching transistors.

Depending on parts installed, some are replaced with better performing, more modern devices. For example, some of the driver transistors used in the GFA-555 are operated too close for comfort to their breakdown voltage, and are known to fail. A modern 250V transistor is the fix. I affix small heat sinks to the Class-A driver transistors for better reliability. They slowly burn the boards without heatsinks.


Resistors in the gain and feedback signal paths are replaced with 0.1% precision Mil-spec Dale RN55C low thermal coefficient resistors. These are then hand matched for even more precision. This assures precisely even gain between channels.

A custom power supply circuit board is included in the price for models GFA-535 and GFA-545. The soft-start board for the GFA-555 is an extra charge due to increased complexity and parts cost.


Sealed Bournes trim-pot installed for precise bias adjustment and better reliability.

20150214 14-18-37 CameraZOOM-20150214141837725

Circuit boards are cleaned and solder joints inspected and touched-up wherever needed.

New power switch and spark-supressor capacitor. (Most Adcoms do not have soft-start circuits, and so are hard on power switches.)

A high-quality X2-type snubber capacitor is installed across the AC  power input to reduce RF interference and reduce noise. Most wire-wrapping posts are removed and the wires soldered permanently. Throughout the amp, I try to reduce the number of metal-on-metal connections; to reduce resistance and improve reliability.


New RCA jacks are installed on Mark 1 amplifiers as shown below.

New as of January 2017! I am now installing local power supply bypass capacitors on the boards of GFA-535 and GFA-545 Mark 1 amplifiers.
These small capacitors are mounted directly on the board, close to the circuitry, and so are able to provide current faster than the main power supply capacitors, which are located at the end of several inches of wire. Adcom later added this feature to the Mark II models.

Binding posts are upgraded.

20141208 21-23-01 CameraZOOM-20141208212301975

The last step is to check performance under load, stress test and set bias. The amp is run into a dummy load and driven hard, heating up close to maximum, and it should show no signs of distress. It should cool itself down in a reasonable time, and the bias should track throughout the temperature range.


The amp is hooked to studio monitors and listened to. If performance is good, and no issues arise, I check the bias one more time, and call it done!

Sorry, I can’t offer service on Tuners, DACs or CD players. I also do not work on the MOSFET Adcoms like the GFA-5500 or 5802. I’m concentrating on just the classic bi-polar transistor models, and preamps.

Contact me here and we’ll get started! But please keep in mind, I have a pretty long waiting list—about 9 months at the time of this writing. But once I am working on your equipment, you will hear from me often. I’ll assign you a number in the queue, and there is a “now serving” number at the top of my website that slowly counts up as I work. You can ship when your number is getting close.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s