This amp started out as any other GFA-555II but has been transformed into a true high end amplifier.
Here are some upgrades and changes I did to achieve this:
I upgraded the input caps to some AudioCaps, upgraded all the signal path resistors to Allen Bradley carbon composite that to me sound “right” (they have all the detail of a metal film without the hard edge) Upgraded all the electrolytic caps (besides the large power supply caps) with Nichicon KW audio grade ones, added some Jantzon 2700uF caps bypassing the main caps which firmed up the bass and attack quite nicely. The connectors are Cardas RCA's and binding posts which were a huge improvement over the warn out stock ones.
This amp stock had pretty good sound but it can be harsh sounding in the high frequencies with a thin midrange. Now the amp is very open and the sound blooms and is very extended with sweet highs.
The last modification that I did was bypass the rail fuses. These fuses use to go between the + and – 80 VDC and the output boards. These fuses were absolutely killing the bass and musicality of the amp. After bypassing the fuses, things opened up and the amp's speed increased greatly.
Overall the amp is in decent shape. The front is very good with no obvious flaws. The top has a rough area in the paint but isn't noticeable unless you are very close.
The average price for this amp used is around $350. Parts alone were about $120 plus about 6 hours of labor. I do have the service manual that I will include. I tuned up the Bias to factory spec.
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