Today were highlighting another GFA-555 driver rebuild we got in locally. The GFA-555 Adcom is one of the most well known and popular Adcom Power Amplifier available, released also with a GFA-555 MKII which has a different design approach.
You can read another GFA-555 we’ve restored below;
One of the biggest issues are the original electrolytic and metal film capacitors utilized in the original build quality. These silver films have a fairly higher failure rate.
The electrolytic capacitors are all replaced with a high temp (105C) low impedance type Nichicon PW with an increase in operating voltages. As well as the original metal film/mylar films to high grade MKP type polypropylene film capacitors. Another major benefit are new 1% matched BETA differential pair transistors, now thermally coupled together for better tracking.
The Driver board design is rotated out for easier access and to clean the mono/stereo operational switch. Along with new passive components new thermal compound and MICA insulators were installed. The larger format polypropylene films are located now on the foil side of the PCB with appropriate leg shielding.