Some not very happy experience with my used GFA-555 II AMP

cnh

My experience is similar to H9s and I have run an Adcom GFA-545 (little brother at 100 W x 2 at 8 ohms) off an HK 3490 and compared it to the HK by itself.

There is no doubt in my mind that with the 545 the sound was much better (dynamics, sound stage, power, etc.). It actually opened up the HK receiver. And the 545 is supposedly rated 100 w instead of 120 w like the HK. However whereas the HK says it can do 150 w into 4 ohms. The Adcom can do pretty close to 200 watts at 4 ohms. More Head room! Until I picked up my Nakamichi pre-amp the HK/Adcom combo was good enough.

After removing the HK and putting the Nakamichi pre in, I now have an even 'better' smaller system that I'll be keeping for quite some time.

I'm really very surprised that you're experiencing 'any' difficulties with the 555 (which I also own and has never given me any problems?). Maybe your Adcom does need attention.

cnh

Hardrock.ca

I am very glad to know your HK3490/GFA-545 combo works much better than HK3490 alone.
Because this is the exact setup I have now.
This definite give a lot of hope I can the same sound some day:)

cnh wrote: »

My experience is similar to H9s and I have run an Adcom GFA-545 (little brother at 100 W x 2 at 8 ohms) off an HK 3490 and compared it to the HK by itself.

There is no doubt in my mind that with the 545 the sound was much better (dynamics, sound stage, power, etc.). It actually opened up the HK receiver. And the 545 is supposedly rated 100 w instead of 120 w like the HK. However whereas the HK says it can do 150 w into 4 ohms. The Adcom can do pretty close to 200 watts at 4 ohms. More Head room! Until I picked up my Nakamichi pre-amp the HK/Adcom combo was good enough.

After removing the HK and putting the Nakamichi pre in, I now have an even 'better' smaller system that I'll be keeping for quite some time.

I'm really very surprised that you're experiencing 'any' difficulties with the 555 (which I also own and has never given me any problems?). Maybe your Adcom does need attention.

cnh

Hardrock.ca

Thanks all your advice and suggestion, I have updates:

I have used iPod to feed GFA 555II directly and HK-3490 Front Input, the sound from HK-3490 is obviously Better and more clarity

The DC offset in GFA-555II is very small and way below 50MV

The Direct button at HK3490 button is not for "Direct 2 Ch"

Because of all the negative tests results above, I have sent the AMP to a nearby repair store to check as they are in promotion period for free check.

They have used Oscilloscope to check the wave form to detect distortion, they did found distortion, they are in the process to further diagnosis which component cause the distortion, mostly possible is some dry out caps.

Have a very nice weekend and have fun!

Joe08867

Hope they can sure the woes cheaply and quickly for you.

Hardrock.ca

Although the repair shop gave me free estimate, but the estimation they gave me is not very reasonable, so I had to take my unit back and halted my project.

I plan to learn how to upgrade/repair it myself.

Again thanks a lot for all your help!!!

lanchile

"when I turn off the power in GFA, it still sounds for a few seconds, first the left channel fade out, and then is the right, is this means anything wrong".(is this normal?).


Yes, this is "normal" some amplifiers do not use relay to cut the "discharging caps" in the power supply. What you hear is the power left in the power supply caps as they are discharging. just turn off the source first. and if you hear a "small" thump in the speakers...this is normal too.some better design you will not hear this thump as it turns off even without the relay.

20hz

Hardrock.ca wrote: »

Actually I only compare the sound from GFA-555II which uses HK3490 as preamp
and the sound directly from HK3490's speaker output. and I found the sound from GFA is not as good as the sound directly from the RECEIVER in terms of clarity and even volume!

I did not try hook it up with MP3 player yet. and I will try and thanks for the suggestions!

All amps have a differant sensitiviy rating wheras it may take more or less input power to get a desired amount of sound , the 555 has a ton of power .
But that slow growling turnoff feature I couldnt live with either , even though its normal on that design type , if you dont like it just sell the beast its still worth $250+ .
I had a later adcom 5300 mosfet series amp it sounded real nice and I dont think it had that slow turn off , I think there was a 5500 mosfet series .

inspiredsports

It sounds like the repair shop clearly identified a problem with the 555, but you didn't identify what interconnects you are using between the pre and Adcom amp. That could also be a source of problems.