Power off thump - why?

Luxman Amplifiers India

jsmithe

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I am getting a power off thump a few seconds after I turn off my Crown XLi 1500. I first turn the gain(both channels) all the way down to zero on the Crown, power it off by hitting the button on it's front panel and wait a bit before I turn off the pre. While waiting, in hardly about 10 seconds and even before I turn off the pre or do anything else I get a thump that only appears to be from the right speaker. The chain is PC via USB into Topping E30 (in pre mode) going to the Crown and then into speakers.

Any idea's what I am doing wrong or what could be the likely cause?
 

jsmithe

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I decided to try and isolate the issue and physically disconnected the inputs from the Crown XLi 1500 and only kept the speakers connected. Turned the amp. on with the gain at zero and no thump. Waited a few minutes with the gain still at zero, turned the amp. off and within a few seconds I get a thump from the speaker.

Any FM's with a Crown XLi 1500 seeing the same behavior on their amp?

I am wondering if my amp. is defective and/or whether I should be concerned about damage to speakers from the power off thump? Inputs appreciated.
 

ssf

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As an experiment, I had connected two Crown xls 2502 in bridged mode to my bookshelfs. No thump even when I did not follow the proper order of turning on and turning off.

"But when you turn the system off, that energy has to go somewhere. The "thump" you occasionally hear is the power supply capacitors dissipating the energy. It's not dangerous at all. In fact, it's just another sign that the amp won't run out of steam when you really want serious sounds."

Copy pasted from somewhere else. Don't know how accurate the statement is.
 

jsmithe

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As an experiment, I had connected two Crown xls 2502 in bridged mode to my bookshelfs. No thump even when I did not follow the proper order of turning on and turning off.
See, that's what is worrying me. It looks like it's just my Crown that's doing the thump thing. Besides https://www.crownaudio.com/en/products/xli-1500 indicates the amp. has protection against power on/off thumps. I'm wondering if that circuit is broken on my amp. My experiment confirmed for me that it's not the rest of the chain but the amp. which is the source of the thump.

"But when you turn the system off, that energy has to go somewhere. The "thump" you occasionally hear is the power supply capacitors dissipating the energy. It's not dangerous at all. In fact, it's just another sign that the amp won't run out of steam when you really want serious sounds."

Copy pasted from somewhere else. Don't know how accurate the statement is.
That makes sense and is a bit of comfort, but that damn thump is quite disconcerting and the internet is, as usual, divided in opinion with some saying it's fine and the others swearing it will destroy speakers.
 

jsmithe

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Very surprising to see that on a brand new amp. As you have figured out it is nothing but current discharge but chances are it blows the tweeter. If possible get a replacement. It’s better to be safe than sorry.

Thanks @@Prodigy. It appears likely the protection circuit on one of the channels is defective since FM @@ssf indicates his XLS 2502's do not thump at turn off and the website also indicates that the amp. has protection against power on/off thumps. I've scheduled a return for replacement. You are right, I wouldn't want to risk damage to my speakers.
 

Prodigy

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Thanks @@Prodigy. It appears likely the protection circuit on one of the channels is defective since FM @@ssf indicates his XLS 2502's do not thump at turn off and the website also indicates that the amp. has protection against power on/off thumps. I've scheduled a return for replacement. You are right, I wouldn't want to risk damage to my speakers.
Good decision. If you are getting cash in return try the QSC. They are good too.
 

jsmithe

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I am getting a replacement Crown which hopefully will behave, else I will take a look at QSC. Fan noise on the QSC could be an issue though The fan on the Crown was inaudible.
 

Prodigy

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Interesting, is this likely on an amp that has possibly been sitting around for a while in it's packaging unused? You might be on to something here.
Could be no proper QA checks. These are mainly commercial amps used for PA usage and I am sure they are mass produced and and usually stored in Warehouses so that should not be a problem at all. I think it could be due to some faulty component with this one piece which may have gone unnoticed during final QC.

That said, I wanted to know, do crown’s have that fineness in it when it comes to music / movies for home use?? I have always wondered how do they stack against Home Audio PA’s.??

Regards,
Som
 

ssf

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That said, I wanted to know, do crown’s have that fineness in it when it comes to music / movies for home use?? I have always wondered how do they stack against Home Audio PA’s.??

Disclaimer: Not an experienced ear. I own the XLS 2502. Two of them in fact.

I think Crown is a input - output amp. It does not add much other then loads of power, which is what power amps should do. Put a tube pre before it and you are good to go.

It does have a higher noise floor. Not something that anybody can pick up when sitting in their MLP and listening to their favorite music. Put your ears next to your tweeters and you will hear some noise. It's not audible from a few inches away. Fan is another problem with PA amps. On this one, it does not turn on. Don't think anyone can push it enough at home for it to turn on. And I have read that even when on, it's quite. Pairing it with sensitive speakers could increase the noise floor. Pairing it with a tube pre and laid back speakers could make it dull sounding.

Sounds great in my simple system for all kinds of music from Classical to rock to jazz to blues to Hindi music. In every genres, I find something I like in the way that the music is presented to me. In rock, the guitar is to die for, In jazz, oh the sax and not to forget the vocals . Last but not the least, lets not forget the power too !!! I stopped using my sub for 2 channel listening.

So you can only guess how it will be in a HT setup.

A review and detailed measurements of the Crown XLS2502 DriveCore (switching) 2-channel amplifier.

https://www.audiosciencereview.com/.../crown-xls2502-stereo-amplifier-review.10627/

A honest review from Thomas:

 
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jsmithe

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That said, I wanted to know, do crown’s have that fineness in it when it comes to music / movies for home use?? I have always wondered how do they stack against Home Audio PA’s.??
I have had limited listening time with the amp. before boxing it up for a return, neither have I used other home audio PA's so can't really compare. My ears may not be the best either, however from the few days I had it, I found it to have plenty of grunt, but it was not shouty (which is what comes to mind when one thinks pro amps). It did not appear to be coloring the sound. I am used to near-field listening via studio monitors so this is OK for me. Distortion, I did not notice (blame my ears or perhaps I did not drive it enough to distort). Fans are on all the time on the XLi but not audible (from about 10ft away).
 

Prodigy

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Disclaimer: Not an experienced ear. I own the XLS 2502. Two of them in fact.

I think Crown is a input - output amp. It does not add much other then loads of power, which is what power amps should do. Put a tube pre before it and you are good to go.

It does have a higher noise floor. Not something that anybody can pick up when sitting in their MLP and listening to their favorite music. Put your ears next to your tweeters and you will hear some noise. It's not audible from a few inches away. Fan is another problem with PA amps. On this one, it does not turn on. Don't think anyone can push it enough at home for it to turn on. And I have read that even when on, it's quite. Pairing it with sensitive speakers could increase the noise floor. Pairing it with a tube pre and laid back speakers could make it dull sounding.

Sounds great in my simple system for all kinds of music from Classical to rock to jazz to blues to Hindi music. In every genres, I find something I like in the way that the music is presented to me. In rock, the guitar is to die for, In jazz, oh the sax and not to forget the vocals . Last but not the least, lets not forget the power too !!! I stopped using my sub for 2 channel listening.

So you can only guess how it will be in a HT setup.

A review and detailed measurements of the Crown XLS2502 DriveCore (switching) 2-channel amplifier.

https://www.audiosciencereview.com/.../crown-xls2502-stereo-amplifier-review.10627/

A honest review from Thomas:

Looked at the Video. Great explanation as always from Thomas. He is very practical always.
So yes, I believe it all boils down to cost = performance ratio and crown does tick all right boxes at that point but I am somewhat thinking it may cause some fatigue during long listening sessions if someone has a very efficient speakers. Like he mentions, a good pre + crown + a speaker that match the combination is the way forward.
Never tried a crown till date.

May be I should keep an eye on For Sale section. :p
Could be a great option to add 2 sealed passive subs ;)
 
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Kumar442244

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I used the Topping E30 in pre mode.
What speakers are you using with it?
Does the pre have speaker protection? this could also be a reason for the Thud noise.
@Prodigy Remember? we had this concern while testing the tube pre.
I am also contemplating to get a XLi800 to power my totems. Couldnt find much review on crown's XLi series usage with pure stereo.
 
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