Adcom 5400 Power Amp Distortion - Need Help [Archive] - Audio & Video Forums


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08-18-2005, 11:57 AM
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.


08-18-2005, 05:28 PM
PE board here:
They have quite a few EE over that way that are pretty sharp. The only thing I can think of is dirty pots but really im clueless.

08-19-2005, 07:40 AM
Thanks for the suggestion. I will post there as well. I was just wondering whether this was a common problem with this amplifier.


08-20-2005, 08:14 AM
Just a quick note here. Have you checked if the speakers are actually ok? Played them through another setup to make sure there is no problem with them. I had a problem with a speaker that had a bad interenal connection. I thought it was my amp also. But turned out to be the speaker.
my .02 cents

08-20-2005, 03:32 PM
There are a lot of things it could be but since it happens with a low input signal. I would guess that the amplifier circuits are not getting the voltage they should from the power supply. My reasoning is that if something fails in the amp circuit, itself, the result is most frequently a short which causes protection circuits to shut everything down. The fact that it will play at low levels without triping the termal indicaior suggests something amiss in the power supply.

In any case this is not likely to be something you can fix yourself without a schematic and some experience in diagnosing problems inside the enclosure.

08-22-2005, 07:48 AM
yes, I have checked to make sure it's not the speakers (they play without problems on another receiver).

Yes, I suspect it's the power supply section. Someone else has suggested rail fuses so I'll check those as well.

I'm fairly comfortable checking the circuit with a schematic. I should have one soon.


08-28-2005, 07:28 PM
Problem turned out to be a couple of blown rail fuses. Thanks for all the responses.