Adcom GFA-545; What's all the buzz about?

[musicallowb]

Hey guys. I am very new to DYI, and new with regards to mods, repairs, etc. In fact, I don't have any real formal electronics repair training, so this line of questioning is more for educational purposes, than for me actually trying any repairs myself. I saw this thread and thought it would be a great place to get some help with my particular problem. And please forgive my crude non technical terminology As a pro bassist by trade, I have built bass guitars, electronics and all. But the most complex thing I've done with audio gear is upgrade rca inputs and binding posts. Lol. Like I said...REAL new.

Anyway, I just acquired a GFA-545 (the first series, not the mkII) that is very pristine inside and out, like it was tucked away in an AV install. But when I hooked it up, there was slight distortion coming from the speakers, particularly the left side. The audio signal comes thru as it should, and no front panel lights are indicating any problems, yet the sound has a fuzzy quality to it. I already own two 535 II’s so I am quite familiar with the sound of this series of Adcom amps, and would like to benefit from the extra power of the 545.

I'm not looking for a super mod. I just want to replace (or have replaced) the most likely culprit(s) of the problem. I really have enjoyed reading this thread, and it has given me some great insight on how this whole mod world works. But frankly, at this point a lot of this stuff is above my pay grade. If I tackle this myself, where should I start? I’m not looking to fry a perfectly good amp, and if I get someone to do the work, I’d like to know what they are telling me needs to be done.

If it's any help, I did start out by replacing all the fuses, and measuring the bias at the speaker terminals. Left and right channels were 5.6mV and 5.5mV respectively. Close to spec, I think.

So what’s next?

[sakis]

what you measured is the ofset and no the bias
fuses is not the issue in your case and probably its common sense that a fuse is an on and off thing either works or not ...replacing them obviously done absolutelly nothing


eventhough the description of the problem is not acurate steps to go will be :

1- connect a source that is actually verified ( make sure that problem dont come from the source or connecting cables ) proper source is a cd player with or without a preamplifier but atleast with controlable output ... computer or mp3 player is not a proper source

2- go with ellimination procces after you make sure that there is no source issue swap left to right input leads ...if problem mooves to another speaker you have asource issue if remains in the same speaker you have an amp issue

3- swap speakers if the prblem mooves you have aspeaker issue if not amplifier is the problem

4 - Most of the problems in these amps have to do with
A)soldering where dry soldering might cause all that
B)small capacitor in the feedback area or else is dry due to age
C) dont remember if this particular amp features a Servo but many of that series with a servo had problems there ...

To be able to do any of the above you need instruments and basic skills if you dont have any of them a 545 will not forgive many mistakes ...there is a greate chance that you will blow a nice amp ...

Ducky regards
Sakis

[musicallowb]

Hi Sakis, thanks for the reply. I was strictly going by what the service manual was saying when it comes to what they called the bias adjustment. As far as sources, I was using the cd players and cables I use in my main system, both direct to the amp inputs (a Denon DCD-3300) and thru my Audionics pre with a Rotel cd player. I switched channels, swapped out several speaker and interconnect sets, and three pair of speakers. All with the same results...a slight distortion in the signal of both channels.

[musicallowb]

Hi Sakis, thanks for the reply. I was strictly going by what the service manual was saying when it comes to what they called the bias adjustment. As far as sources, I was using the cd players and cables I use in my main system, both direct to the amp inputs (a Denon DCD-3300) and thru my Audionics pre with a Rotel cd player. I switched channels, swapped out several speaker and interconnect sets, and three pair of speakers. All with the same results...a slight distortion in the signal of both channels.

[GeneZ]

Originally Posted by musicallowb

Anyway, I just acquired a GFA-545 (the first series, not the mkII) that is very pristine inside and out, like it was tucked away in an AV install. But when I hooked it up, there was slight distortion coming from the speakers, particularly the left side. The audio signal comes thru as it should, and no front panel lights are indicating any problems, yet the sound has a fuzzy quality to it. I already own two 535 II’s so I am quite familiar with the sound of this series of Adcom amps, and would like to benefit from the extra power of the 545.

I have the first series GFA 535. Same type of problem. It was explained that when the unit gets that old it may need new electrolytic caps.

Look here: Distorts after about twenty minutes

[musicallowb]

Thanks for the link GeneZ. It was definitely informative. Seems to be a pretty common issue at the 15-20 year mark. Not surprising, really.