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Krush

Amplifier Oscillation

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Background:

I recently purchased a Crown XLS1002 to mate to a set of KPT-456s fed by a Denon X3400H.

The Denon runs the KPTs reasonably well but is only designed for a 6 ohm load so the thermal management trips regularly when playing loud enough to be heard in other rooms.

I was using the Crown as a subwoofer amp and had no issues as such but attempted to feed the mains through the Crown amplifier.

 

Problem:

I'm getting a horrific whistle (ears are still ringing the next day) from the amplifier with or without inputs attached to the amplifier and one or both speakers connected to the amplifier running in stereo mode with no crossover enabled. Guitar center (parts express was sold out) has kindly replaced the amp once with no change in symptoms and both times calling Crown has produced no understanding of the problem, just continue replacing the amplifier.

 

Is there any diagnostics I can perform to help understand/alleviate the problem?

 

Thanks!

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I would have guessed something with the input cables but you said it did it even with no input attached. How are you connecting the speaker wire? If bare wire, try banana plugs or switch to the SpeakOn connections. I have seen a few posts where this helps w some of the Crown amps. I have two crown amps (XLi series) with absolutely no issues and have an XLS 2502 on the way to me from another forum member. There should be an explanation out there.

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13 hours ago, mike stehr said:

Maybe try a different model crown amp?

 

post-4542-0-42100000-1402160671_thumb.jpg

 

Different model in the same series or different series all together?

 

Mookie:

The gentleman i purchased them from used a XLi800 and they sounded amazing. These amps are 2-ohm stable so this isn't even outside expected loading. I forgot to mention, the gain knobs do not affect this either.

 

I've tried bare wire and banana plugs already, i'll try the speakon and get back to you.

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So basically, you never heard this noise when you used the amp on your sub and you've gotten a totally different amp that does the exact same thing?

 

Have you tried this amp on another full range speaker?

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Update:

I resolved the issue a day or two ago and have been testing my theory. I did attempt another set of speakers without issue, afterward I contacted Klipsch tech support for advice/crossover prints. The gentleman suggested attempting to bi-amp the speaker since he had this setup at home without issues.

 

Bi-amping was successful and found a mis-landed wire on the capacitor in the crossover when re-wiring. Swapping the + on the terminals/speaker was the only change made.

 

Lesson learned: This problem would have never shown up in a linear amplifier, only because i wanted to use a Class D amp was this problem present. Why the sound was not present on the Denon's inboard amp (also Class D) remains a mystery but that does explain why the thermal protection tripped regularly.

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10 hours ago, Krush said:

I resolved the issue

 

I have been wondering about this unusual problem since you posted last week. Glad to read that you fixed it.

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A mis-connected/mis-landed wire would cause a problem with any kind of power amp, Class A, AB, D, H, or whatever.  Glad to hear you got it sorted, but it’s not a poor reflection on Class D amps in any way.

 

In my system, I started with one Class D amp over ten years ago, and added a second matching amp in a horizontally bi-amped configuration a year later.  They sounded great then, and sound great today.

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