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Old 7th July 2009, 06:48 AM   #1
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Default Power down transient

I've got a McIntosh MC 2505 stereo power amp that has recently developped an issue. When it power downs it outputs a transient snap. My worry is it will damage my tweeters. I haven't given the internal components a look over yet but I don't expect to see anything because it still functions normally. If anyone has any suggestions or questions feel free to ask. I know this is hardly enough information to even think about diagnosing the situation but I have electronics skills so I can figure out most questions about the amp.
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Cody
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Old 7th July 2009, 08:53 AM   #2
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One possibility, especially for older amps, are aged caps, discharging at different speeds. That causes usually also turn-on thumbs.

Changing caps is anyway not a bad idea (if they're 10 years or older).

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Old 7th July 2009, 10:24 AM   #3
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It's possible that the ESR of the power supply caps has gone up with age. Replace the caps.
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Old 7th July 2009, 11:57 AM   #4
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Default Re: Power down transient

Quote:
Originally posted by cdixon.audio
I've got a McIntosh MC 2505 stereo power amp that has recently developped an issue. When it power downs it outputs a transient snap. My worry is it will damage my tweeters. I haven't given the internal components a look over yet but I don't expect to see anything because it still functions normally. If anyone has any suggestions or questions feel free to ask. I know this is hardly enough information to even think about diagnosing the situation but I have electronics skills so I can figure out most questions about the amp.
Thanks,
Cody

If it wasn't doing it before, it is not the caps deteriorating. The turn-off transient doesn't depend on the caps but on the particular topology.

If it worked finr before, it might be that there is a relay mute function that held off connecting the speakers until the amp stabilized. This is pretty standard in power amps.

If there is a relay system, check whether it is indeed defect, and then we need to figure out how to fix it.

Jan Didden
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Old 7th July 2009, 05:28 PM   #5
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I figure it is probably just the capacitors (god knows which one) discharging too quickly. It has always had a slow and low level thump when it turns off but this transient is new. I opened it up today and as I expected it looks fine besides having not been opened for 40 years(it was "born" in 1971).
Also I do not believe this amp has any relay circuitry.
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Cody
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Old 8th July 2009, 02:54 AM   #6
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An update you could say. I put the covers back on and did a little more investigating into what was happening. The right channel is the only channel that has developped this problem. It was hard to figure this out before because my amp is right next to my right speaker but it registers on the meters. The left meter will slowly fall while the right one is immediately nulled once I turn off the power(not to mention the snap that I hear). And the problem is intermittent...
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