Hoppe’s Brain Refurbished ADCOM GFA-555 MK1


Fully refurbished ADCOM GFA-555 MK1 with new input board and power supply.

Out of stock


Hoppe’s Brain Refurbished Adcom GFA-555 MK1

Completely rebuilt Adcom GFA-555 with “The works”. All new electronic components except for the output transistors and power transformer.

This amp represents everything I have learned about the GFA-555 over the years. It is meticulously assembled and thoroughly tested. For more restoration details, see my blog post “A tour of a Hoppe’s Brain GFA-555 Restoration” This amp is the same as the one in the article, but with the addition of the new input board.


  • New Hoppe’s Brain BFA-555 input board with all new, top-shelf components. The board features integrated bypass capacitors, and an improved layout over the original, due to the 2-layer design. PCB traces are made wider and shorter, with a ground-plane poured over the top layer. Heat sinks are added to the driver transistors to address a known reliability issue.
  • New soft-start power supply with 27,000uF capacitors! (Stock is 15,000uF)
  • Relocation of the power transformer, and improved star-ground topology results in incredibly low background noise.
  • Amp has been converted to a 3-wire, grounded chassis appliance. Power cord is upgraded to 14ga. An earth-loop-breaker in the power supply prevents ground loops.
  • Large gold-plated binding posts
  • Chassis-mount RCA jacks.
  • Bypass capacitors added to the output modules for improved high-frequency transient response.

Performance meets all expectations. 243WPC into 8 ohms at <0.1% THD+N, and 344WPC into 4 ohms. Distortion is around 0.02% across most of the power band. View a PDF of the performance report here.

Cosmetic condition 8.5/10. A gorgeous amp! This amp has been well taken care of, but shows some signs of use. The are some light scuffs along the top edge, and these have been touched up with enamel, and are only noticeable on close inspection.


Additional information

Weight 608 oz
Dimensions 22 × 16 × 16 in

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