Sorry, Hoppe’s Brain is not accepting new clients for equipment refurbishing or repairs. My business will eventually just sell DIY kits, so more amps can be fixed than I can do myself!

I am fully booked, with more than a year’s worth of clients lined up for amp and preamp refurbishing and repairs. I’ll be finishing up this list and that’ll be pretty much it.

Information below is for reference only for those who are on my waiting list.


I offer flat-rates on full audiophile refurbishing packages for specific models of Adcom amplifiers and pre-amplifiers. Hourly service is available for repairs and upgrades at a rate of $60/hr with a 1-hour minimum.

Flat rates cover most repairs, except for those that require expensive parts like output transistors or power transformers, so additional charges may apply. Smaller parts like resistors, capacitors and such are included.

What I do is very much like restoring a classic automobile. The equipment is completely torn down to the chassis, and re-built with better components, with more attention paid to detail than the factory possibly could.

It’s everything I do for my own equipment. Your gear is transformed into something like this GFA-555 MKII…


Or this GFA-535 MKII

Here’s the upgraded amplifier section of a GFP-750

Upgrading, customization, and hot-rodding beyond the scope of the audiophile upgrade packages is also available for hourly fees plus parts. For example, this Dual-Mono GFA-555, or this Super High-Current GFA-535.

Sorry, I no longer work on the Adcom MOSFET amplifiers such as the GFA-5802, GFA-5500, etc, or the multi-channel home-theater amplifiers. I do not service Adcom Tuners, CD Players or DACs, or the GTP series tuner/preamps. I also do not service the new Adcom “Second Edition” equipment such as the GFA-555se. I have no opinion on the quality of the new Adcom amps, having never worked on one.

I am concentrating on delivering the best possible service on only these models.


  • GFA-535 MKI and MKII – $500
  • GFA-2535 – $660
  • GFA-545 MKI and MKII – $550
  • GFA-555 MKI and MKII – $700 (Now include a new input circuit board)
  • GFA-565 – $950/$1800 per pair (Expensive, but features entirely new circuit boards to permanently fix the infamous GFA-565 leaking capacitor/DC offset issue.)
  • GFA-585 – $1400 (Same leaking capacitor issue as GFA-565 and utilizes two new GFA-565 circuit boards.)


  • GFP-1 and GFP-1A – $475
  • GFP-555 MKI and MKII – $450
  • GFP-565 – $475
  • GFP-710 and GFP-715 – $450
  • GFP-750 – $550

Amp upgrade details:

All amplifiers are converted to three-prong appliances with properly safety earth-grounded chassis. A heavier gauge 3-conductor power cord with heavy-duty plug is hard-wired in. (A power inlet jack is a $45 option, either IEC or PowerCon) An earth-loop breaker is installed between star ground and chassis for low noise.

Models GFA-535, 545 and 555 are fitted with Hoppe’s Brain power supply circuit boards. In models GFA-535 MK1, and GFA-555 MK1, these boards actually improve the amp’s noise performance.

Circuit improvements include hand-matched transistor pairs for the differential input, hand-matched feedback network resistors, signal capacitor upgrades to polypropylene and other premium types, installation of local power supply bypass capacitors, installation of heatsinks on hot-running parts, replacement of certain transistors and diodes, and addressing all known reliability issues. All solder joints are inspected and/or touched up. Details vary by model, but it’s everything I would want in my own equipment.

Every surface is cleaned, inside and out, and all wiring routed and tied as neatly as possible.


Audiophile upgrade packages for the GFA-535, GFA-545 and GFA-555 feature newly designed power supply circuit boards with many improvements over stock. For the GFA-555 MKI and GFA-535 MKI, background noise and hum are reduced significantly by the new power supply board.

On GFA-535 MK1, crappy twisty-lock speaker terminals are replaced with nice fat gold binding posts as seen below on this GFA-545)

The hated “twist lock” speaker terminals are replaced with a single set of binding posts.

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Local power supply bypass capacitors are added to the GFA-535 MKI. The MKII models have this improvement as stock. I think it makes a big improvement to the sound, so I install them on all MKI amps.

Local power supply bypass capacitors added to GFA-535 MKI


Same as GFA-535 above, except the 545 does not suffer from the buzz in the right channel. Nevertheless, I include a custom-designed power supply circuit board for this model. The new power supply board is nicer than the original in several ways.

Options: Dual-mono high-current power supply upgrade, Details here. $450



All GFA-555 upgrades now include the installation of local power supply bypass caps on the amplifier input board. This used to be a a extra-cost option, and it is a good bit of additional work, but I feel it makes such a great improvement to the sound that I now include it as standard.

I also install local bypass caps on the output modules of the GFA-555 MKI. The GFA-555 MKII already has them on the output modules.

The four large capacitors are local power supply bypasses, added for additional smoothing and reduced noise. You can also see that I've removed all wire-wrap posts and soldered the wires directly.
Local power-supply bypass capacitors installed on GFA-555 MKII, now included as standard.
Local power supply bypass capacitors added to output modules of GFA-555 MKI, paralleled with polypropylene caps mounted underneath. Capacitors are Panasonic ED, ultra high-endurance 105C 12,000 hour.


    • Power supply filter capacitor replacement – $375. NEW! Capacitor replacement now includes a custom soft-start power supply board, with several benefits over the original configuration. Total power supply capacitance is increased from 60,000uF to 108,000uF. Background noise at the speaker terminals is reduced dramatically. Wire lengths are reduced as well as the number of physical connections.
    • Dual-mono high-current power supply upgrade. Includes two new 500VA power transformers and soft-start power supply board. Details here, except that particular amp uses the old-style chassis mount capacitors instead of the new soft-start power supply board. – $750
    • IEC or Neutrik Powercon modular power input jack – $45 (No cable included)


The GFA-2535 is basically a 4-channel version of the GFA-535.

GFA-565 Mono-bloc

The GFA-565 is an amazing amplifier, perhaps the best one Adcom made, but nearly every one of them has a circuit board ruined by leaky capacitors. The amp sends DC to the speakers, frying the woofer’s voice coil.

A little background… Adcom got hit with a bad batch of Elna branded electrolytic capacitors that tend to explode and spray conductive electrolyte all over the input board, causing a dangerous DC offset to appear at the speaker terminals. Nearly all GFA-565’s suffer from this, and it’s a notoriously difficult problem to fix properly. The electrolyte gets everywhere, corroding traces, and causing current leakage between components. Cleaning it all off is very difficult, and amps that seem to be fixed can fail later on and blow out speakers.

So, instead of trying to clean the board, and repair the corroded traces, I just replace it with a new board that I’ve developed. Layout is identical to the original, but the quality is actually quite a bit nicer! 2-layers, plated-through-holes, and just really gorgeous machining and precision. Just ten years ago, this kind of circuit board quality was totally out-of-reach for a small business or DIY’er!

See my detailed blog post on the topic here…

It’s very labor-intensive to populate the new board, transferring components from the old board to the new, and the rest from new parts. Thus, the high price to refurbish a 565. However, I believe this the only way to guarantee an excellent result that lasts!

And as long as I’m re-populating a whole new board, I take the opportunity to upgrade pretty much everything! I use precision, low thermal-coefficient metal-film resistors from Dale and Yageo. 0.1% tolerance resistors are used wherever matching is important. Polyester capacitors are upgraded to Polypropylene. Precision hand-matched transistors are installed in the input section. Even the board headers are changed to gold-plated Molex nano-fit connectors. Absurdly high-endurance capacitors replace the ones that originally failed.

Hoppe’s Brain GFA-565 input board versus crusty old board
  • Options: Power supply filter capacitor replacement, upgraded from 2x 35,000uF to 2×47,000uF – $275


The GFA-585 suffers from the same exploded capacitor issue as the GFA-565. (See above)

Yes, it’s true… The GFA-585 is basically a stereo GFA-565. The amplifier circuit is identical. The only real difference is that the power supply is shared between two channels, and is a little smaller overall versus a pair of 565 power supplies. There are 10 output transistors per channel instead of 20. Still, it’s a MONSTER! I measured 485WPC into 4 ohms. The 565 is just that much crazier.

The input boards are slightly different physically. But a pair of GFA-565 boards can be adapted to power a GFA-585 with just a little modification.

Yes, the service is expensive, but it’s nearly as much work as a pair of GFA-565’s; populating two input boards from scratch, and modifying them to work in the 585. But it’s such a fantastic amplifier, that I think it’s still a bargain compared to buying a new amp at this level.

Pre-amplifier upgrade details:

Please note: I do not service the Adcom GTP preamps like the GTP-400, GTP-450 and GTP-500. While they are nice units for the price, they were Adcom’s budget product line, and are not up to the same quality standards as the GFP models, and are unpleasant to work on. Sorry.

All electrolytic capacitors replaced with premium types. In signal paths, this is usually Nichicon Fine-Gold or Muse, and in power supply applications, Panasonic FC. (If you have a favorite brand or type of capacitor I am happy to oblige.)

Polyester bypass caps are upgraded to Polypropylene. There are some in the main power supply, and some close to each preamp section. (Phono preamp, tone controls, etc)

The OEM power supply capacitors are usually Jamicons, which are only so-so quality. I install better quality units from Panasonic, Nichicon, Cornell Dubilier, etc, sometimes with a higher capacitance and/or voltage rating.

Op-Amps in the GFP-555 are upgraded to TI/Burr Brown OPA134 and OPA2134. However, op-amps of your choice can be substituted as long as they’re appropriate. I can also install gold-plated sockets so you can roll your own. X7R type ceramic supply bypass caps are installed between V+ and V-.

The GFP-565 needs no op-amp upgrades, in my opinion, and it’s design does not lend itself to op-amp tinkering.

New and slightly better output relay installed.

All controls checked for scratchiness, chemically cleaned, lubricated and exercised repeatedly.

“Listen” and “Record” slider switches are physically disassembled for cleaning.

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

RCA jacks polished.

Control knobs are tightened if needed.

New power switch.


GFP-555, GFP-565


  • IEC or Neutrik Powercon modular power input jack – $45 (No cable included)
  • Gain of the GFP-555 and 565 is pretty high, 19.6db, which is much more than most people ever need, and so the volume control is rarely ever turned past 12:00. This is bad for noise and channel tracking. It’s better to use more of the travel of the potentiometer. Gain can be lowered from 19.6db to anything you want; 12db is a good choice for most systems. — No charge

GFP-1, GFP-1a

Note: Price is higher for GFP-1 and GFP-1a versus GFP-555 due to the fact that it’s a discrete design—no op-amp chips—and so is more complex and contains a lot more capacitors to change. But it’s a very cool unit!


  • IEC or Neutrik Powercon modular power input jack – $45 (No cable included)


See here for details on GFP-750 upgrade.


  • PLUG-IN GAIN MODULES. The GFP-750 is unusual in that the gain of the amplifier is set by the resistance of the balance control. Most people don’t use their balance controls anyways, so this affords and opportunity to customize the gain of the preamp. The GFP-750’s sound is affected by this gain setting, so this affords another way to customize your system. 7 pairs of precision-matched gain modules are provided for settings between 6-12db, or whatever value you want. — $120

Demand for my services has been truly amazing! So I have a long waiting list—at least 10 months! Please don’t consider me if you need a fast turn-around. I take my time with each piece of equipment, just as if it were my own. Because of this attention to detail, my field failure rate is extremely low. I want my customers to be completely delighted with their equipment, and I want it to last a very, very long time.

I use a “Take a number” system to manage my waiting list. Once you engage my services, you’ll be given a number in the queue.  The “Now serving” number counts up, and is displayed at the top of my website. When your number is getting close, you can send your stuff in.

Contact me here to get started! Please keep in mind, I may not answer your email for as long as a month. But once I am working on your equipment, you will hear from me often, at every step of the process. Thank you!