Adcom 5400 Power Amp Distortion - Need Help

partialresponse · 18th August 2005, 03:36 PM

I need some clues to help diagnose the source of some serious distortion in my Adcom 5400 power amp.

When I play CD's the speakers sound as though they are blown. The speakers sound as if the cones of the mid-woofers are torn but that is not the case. The highs are non-existent and the mid-range sounds partly there; grates on the ears. I cannot turn up the volume on the pre-amp past the 1/8th mark...any more than that level and the sound just becomes too distorted for listening. The Distortion Alert signal lights also glow more steadily then. The right Distortion Alert signal light lights up frequently and almost immediately; the left light occasionally. The Thermal Overload signals have not yet reacted.

I have eliminated all other upstream components (Adcom GFP 565 preamp and Sony CD player) as the source of the problem, so I'm sure it's the power amp. I've ordered a schematic and intend to dig into the amp as soon as it gets here. I'd appreciate hearing from someone who can quickly get me close to the source of the problem.

Thanks
Kofi

Miles Prower · 18th August 2005, 04:06 PM

Did you check for DC at the speakers? This could very well be due to having half of a push-pull final partially blown that's putting excessive DC on the speakers, as well as losing nearly half the signal.

anatech · 19th August 2005, 12:21 AM

Hi Kofi,
Do you have any test equipment, like a 'scope? I guess first you should open it up to see if a fuse is blown. If the fuse is, and it's heavily silvered or blackened do not replace it. Something has blown and you will only make things worse.

-Chris

partialresponse · 19th August 2005, 03:24 PM

Miles, no I haven't checked for DC - I will do that. Chris, I don't have a scope but I do have a multimeter. I will check the fuses as well.

Thanks both.

Kofi

partialresponse · 29th August 2005, 03:26 AM

Problem found...it turned out to be a couple of blown rail fuses. Thanks for the comments.

Kofi

18th August 2005, 03:36 PM	#1
partialresponse diyAudio Member Join Date: May 2005 Location: Santa Clara, CA USA	Adcom 5400 Power Amp Distortion - Need Help I need some clues to help diagnose the source of some serious distortion in my Adcom 5400 power amp. When I play CD's the speakers sound as though they are blown. The speakers sound as if the cones of the mid-woofers are torn but that is not the case. The highs are non-existent and the mid-range sounds partly there; grates on the ears. I cannot turn up the volume on the pre-amp past the 1/8th mark...any more than that level and the sound just becomes too distorted for listening. The Distortion Alert signal lights also glow more steadily then. The right Distortion Alert signal light lights up frequently and almost immediately; the left light occasionally. The Thermal Overload signals have not yet reacted. I have eliminated all other upstream components (Adcom GFP 565 preamp and Sony CD player) as the source of the problem, so I'm sure it's the power amp. I've ordered a schematic and intend to dig into the amp as soon as it gets here. I'd appreciate hearing from someone who can quickly get me close to the source of the problem. Thanks Kofi

18th August 2005, 04:06 PM	#2
Miles Prower diyAudio Member Join Date: May 2005 Location: USA Blog Entries: 2	Did you check for DC at the speakers? This could very well be due to having half of a push-pull final partially blown that's putting excessive DC on the speakers, as well as losing nearly half the signal. __________________ There are no foxes in atheistholes www.dolphin-hsl.com

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19th August 2005, 12:21 AM	#3
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi Kofi, Do you have any test equipment, like a 'scope? I guess first you should open it up to see if a fuse is blown. If the fuse is, and it's heavily silvered or blackened do not replace it. Something has blown and you will only make things worse. -Chris

19th August 2005, 03:24 PM	#4
partialresponse diyAudio Member Join Date: May 2005 Location: Santa Clara, CA USA	Miles, no I haven't checked for DC - I will do that. Chris, I don't have a scope but I do have a multimeter. I will check the fuses as well. Thanks both. Kofi

29th August 2005, 03:26 AM	#5
partialresponse diyAudio Member Join Date: May 2005 Location: Santa Clara, CA USA	Problem found...it turned out to be a couple of blown rail fuses. Thanks for the comments. Kofi

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