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XTI-4000 issues


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Nothing comes out of the amp until the input level hits a certain point. I hooked a laptop and I can see an input level with no output. Jack up the input and I have output. After I get output I can lower the input and it seems to be normal. Turn the input down all the way and may or may not have output when I turn it back up. Any ideas? Back to Crown with it...

 

Input Y

Stereo operation

Sub amp x-over 90Hz

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Is this a newer or older XTI? It sounds like the start of the ribbon cable issue that many have. Acts like a cold solder joint, but it is the ribbon connector. One of mine did it but I bought the display/ribbon setup from Crown and it became reliable again instantly. One the amp is out of the rack, it took less than 5 minutes start to finish to fix it.

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I have one that has some ribbon cable problems. After a particularly bumpy ride on the way to a job, it can start acting up. I've never had the exact problem you describe, but re-seating the ribbon cable between the main board and the faceplate has always fixed the problems that I have.

 

Some day, I'll send it in to Crown - supposedly there's a fix and the new ones don't have the same problem.

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Back-EMF will always look like a short when a speaker is actually connected to a muted amp channel. This is because the one portion of the short detection algorothem (often) looks for current at zero voltage or leading current at zero voltage (ignoring lagging current which is the normal mode. To test that this is what is happening is to unplug the output from the muted amp channel, this removes the source of back-emf (due to vibrations of the speaker diaphragm moving the VC in the speaker's magnetic circuit generating a voltage and since a muted amp looks like a short circuit to the load, current flows... Norton/Thevenin equiv.).

 

If this resolves the false indication, the software needs to be corrected to disable the detector under muted conditions. Simple software oversight IMO. This is something an analog amplifier designer is very araew of, but with the transition to class D amps a lot of the old guys who would have understood this immediately are probably unaware since they stopped teaching such useful real world skills.

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Back-EMF will always look like a short when a speaker is actually connected to a muted amp channel. This is because the one portion of the short detection algorothem (often) looks for current at zero voltage or leading current at zero voltage (ignoring lagging current which is the normal mode. To test that this is what is happening is to unplug the output from the muted amp channel, this removes the source of back-emf (due to vibrations of the speaker diaphragm moving the VC in the speaker's magnetic circuit generating a voltage and since a muted amp looks like a short circuit to the load, current flows... Norton/Thevenin equiv.).


If this resolves the false indication, the software needs to be corrected to disable the detector under muted conditions. Simple software oversight IMO. This is something an analog amplifier designer is very araew of, but with the transition to class D amps a lot of the old guys who would have understood this immediately are probably unaware since they stopped teaching such useful real world skills.

 

Thank you for the actual explanation of this weird malfunction I found in my XTis. The drag for me is when the amp is done executing this "error" it finishes by suddenly unmuting the affected channel. :eek:

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Thank you for the actual explanation of this weird malfunction I found in my XTis. The drag for me is when the amp is done executing this "error" it finishes by suddenly unmuting the affected channel.
:eek:

 

That's called a software bonus feaure ;)

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