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lga775 15th April 2009 11:49 AM

Adcom GFA-555 mk2 left slight cracking in high freq
hi... i have an adcom bout a few years, recently my adcom gfa-555 mk2 have some cracking sound on left hand side. I am not sure what was the problem.. Can somebody help me?

bandolino 4th December 2010 05:38 AM

This reply is probably too late to help the OP, but maybe other people will read it. I have an Adcom GFA-555 mk2 with a similar problem. I purchased the amp used in the past 6 months.

What I am getting is some distortion in the treble on the right channel. I have hearing loss in the high frequencies, so I didn't notice this distortion. I brought the amp to audition some Vandersteen 2ci speakers, and the seller noticed the distortion. After switching out some speakers, cables, and components, he suggested that the distortion was probably coming from the power amp. He warned me that this type of distortion may be a fault in the amp which will damage speakers.

According to this person, an experienced audiophile, the most likely culprit is the power supply filter capacitors. In the Adcom GFA-555 mk2, these are 4 large, blue caps at 15,000uF and 100V, on either side of the toroidal transformer. These are electrolytic capacitors, which tend to go bad after 10-20 years.

That same day, I was listening to my JBL speakers with another amp, and I wasn't sure I heard any highs from the right channel. I pulled the tweeter out of the speaker and tested it with a multimeter, and sure enough, there was no continuity. I had been using the Adcom to run these speakers for a while, so it is quite likely that the amp blew the tweeter.

So, my suggestion is, that if you hear distortion of some kind, it is best to find out the problem before you blow a speaker driver. Please keep in mind that I am not at all an expert in this sort of thing, so get more information before acting on my advice.

hew128 4th December 2010 12:30 PM

Hi LGA775,

Was wondering if you located the fault?

I have an older Marantz amp which play ok until you touch the casing or it had run for a while. The amp then releases a sharp cracking sound. After a few times, then the sounds goes and you hear static.

Putting a test pen on the casing does not light up.

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