ADCOM GFA-585 Limited Edition Power Amplifier


Audio upgrading of the limited edition ADCOM GFA-585 stereo power amplifier is available.  This robust amplifier is capable of operating into very low impedance or difficult speaker loads due in part to its high current design.  It is based on a triple Darlington configuration and uses no protection or current limiting circuitry other than the fuses used in the DC power supply voltage rails.

Contrary to popular belief, the GFA-585 is NOT two GFA-565 monoblocks on one chassis! A pair of GFA-565 monoblocks have twice the amount of output devices that the GFA-585 has and they are also rated for continuous operation into 2-ohm loads (with cooling fan option) where the GFA-585 is not. The GFA-565 has a much higher current capacity power supply with almost double the power supply main filter capacity. Nonetheless, the GFA-585 is a very powerful amplifier that will work well in all but the most demanding systems.

For highest performance sound, it is essential that the highest quality audio grade parts be used otherwise ultimate sound quality will be compromised.  We offer what we feel is the most comprehensive and sensible upgrade available today. 

The most common failure in this amplifier is a high DC offset voltage at the back panel speaker connectors.  This is generally caused by leakage from the original factory installed electrolytic capacitors on the driver pc boards.  The leakage residue, if left uncleaned, can eventually damage the circuit boards.  If the DC offset voltage continues to rise, it has the potential to damage speakers.

As part of our restoration and upgrade modification process, we will: 


  • Driver circuit boards will be cleaned of any leakage residue from the original factory capacitors and the circuit boards will be repaired.  (Depending on the severity of the leakage and any associated pc board damage, there may be additional repair costs incurred).  We clean boards per the official ADCOM Technical Department procedure.  
  • Install high quality audio grade capacitors and low noise metal film resistors in working driver, output stage, and power supply circuits for greater musical clarity.  Areas targeted for improvement include the input circuitry, feedback loop, output stage biasing, output stage & power supply bypassing. The main power supply receives soft recovery bridge rectifiers for drastically reduced switching noise for a quieter background.   
  • Check DC offset, check and adjust bias, before/after modification extended listening tests.




    Replacement of main power supply filter capacitors $280.

    IEC rear power connector installation is available for $149.


     Non-working amplifiers sent in for modification will incur additional repair charges. 


Manufacturer’s specifications: 250 watts RMS minimum per channel into 8 ohms or 400 watts RMS into 4 ohms at less than .02% THD; Frequency response: .7 Hz ~ 80 kHz +0/-3dB; S/N ratio: >110dB (A-weighted); Dynamic headroom: 2.1dB; Damping factor: >600. 


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