Modifing the GFA-555 PowerAmps

[mike petrek]

Looking for any help or advice in modifing the GFA-555 PowerAmps.

[WithTarragon]

The simplest mod is to bypass each PS cap with a smaller cap (22 to 47 uF). This will make the bas a bit tighter or more solid. It is not a large effect but it is an audible improvement. Some of the later series 2 versions may already have this done.

If you are more ambitious, then a larger transformer is in order. The stock one is about 700-750 VAC ( I forget the voltages). For about $125 or so, you can get a transformer that is over 1.2k VAC.

If you are even more ambitious, then regulation on the front end would be a good step. I have not tried this yet, so I have no specifics for you. It would require modifying the boards.

Even with the just the first step (bypass caps) the amp will be improved. The cost is less than $10 and the PS caps are not mounted on the board (unlike the GFA 545), so it is easily performed. You can use bipolar electrolytic (for crossover use), if you think you might mess up on the polarity.

These sell for $300-350. Add $10 in caps and this becomes a very competitive amp

Good Luck!

[anatech]

Hi Mike,
Welcome to DiyAudio!

There are many threads on building these amplifiers up. Use the search function and read some of these threads. Even if the model number is different, many things will still apply.

Remember too, these amps were well engineered. Therefore, the parts are all pretty good quality already. If you wish to change the power transformer (something I do not recommend) try other things first. Also, define what you want to achieve and work towards that end.

Finally, these are now old amps. They do need some TLC to perform as they did new. You may find this is all you really need to do to be honest with you.

-Chris

[Cal Weldon]

Hi and welcome to the forums.