The original GFA555 was a tank with two handles and a good amp. The redesigned GFA555 took on a different, more modern appearance. The GFA555II looked the same as the redesigned GFA555 with the addition of a thermal protection indicator on the front face. According to the Adcom GFA-555II manual the GFA555II added these improvements:
1- A larger transformer (driving lower loads @ high levels)
2- Non-polarized capacitors.
3- A servo circuit to prevent woofer "biasing" and low frequency distortion.
4- Larger heatsinks for more stable thermal temperature.
5- More cooling vents on top and sides.
6- Gold plated brass RCA input jacks.
7- Thermal overload LED on front face. (The big giveaway)
Again, the GFA555 and GFA555II look the same @ a glance but the thermal LED on the right side face let's you know it's the GFA555II. (Not to mention the model plate on the rear.)
1- A larger transformer (driving lower loads @ high levels)
2- Non-polarized capacitors.
3- A servo circuit to prevent woofer "biasing" and low frequency distortion.
4- Larger heatsinks for more stable thermal temperature.
5- More cooling vents on top and sides.
6- Gold plated brass RCA input jacks.
7- Thermal overload LED on front face. (The big giveaway)
Again, the GFA555 and GFA555II look the same @ a glance but the thermal LED on the right side face let's you know it's the GFA555II. (Not to mention the model plate on the rear.)