Crown XLS 1000 hisses with nothing connected.

[But it Hertz]

Is the noise still present when the amp is presented with a signal such that the music/speech overcomes the noise?

The hiss seems to stay at the same volume and you can't really hear it except for when it is quiet and during speech. As soon as you crank it up any you can't hear it.

In all other respects I'm really pleased with the amp.

As an aside, I use an amp through which one can hear hiss when it's turned up to 7 or more. SLAs willl definitely show the noise, even more so than your 6x9.

That's kind of what I was / am expecting. With your amp and the SLA's respectively.

[byacey]

I don't think you should be seeing 400KHz @ 0.6V on the speaker terminals. What you're seeing may be coupled through the power supply grounds between the amp and the scope, or a ground loop. Often switching supplies will kick some noise back onto the AC line despite the filters they use to prevent this.

I can't hear 400KHz, although some self professed audiofools will claim they can.

The hiss you are hearing is more likely to be caused by a noisy op amp stage on the input stage of the amp, maybe by the onboard signal processing, or gain stages not optimized for low Johnson noise in the design process. This is where all the voltage gain occurs in the power amp. However, this voltage gain is quite low compared to the preceding gain stages that all introduce cumulative noise that culminates at the end of the cable that eventually gets plugged into the amp input connector.

Because you mentioned the noise is still present with the level controls all the way down, this indicates the noise being created in the stages after the level controls, most likely the DSP.

A good power amp introduces very little noise other than what is introduced by the line level gear via the inputs.

[Ryan A]

Because you mentioned the noise is still present with the level controls all the way down, this indicates the noise being created in the stages after the level controls, most likely the DSP.

Interesting you mention the DSP...the ipr1600dsp I have also has a slight issue with this. When I select "bypass" on the crossover I hear nothing, but when selecting "low-pass" a very slight hum is present. Its not really bothersome except where there are very quiet situations. If the hiss is bothersome on the XLS I would return it too

Also, both of the amps mentioned are class D, which in my experience are not as clean as class a/b amplifiers in general.

[But it Hertz]

I don't think you should be seeing 400KHz @ 0.6V on the speaker terminals. What you're seeing may be coupled through the power supply grounds between the amp and the scope, or a ground loop. Often switching supplies will kick some noise back onto the AC line despite the filters they use to prevent this.

I can't hear 400KHz, although some self professed audiofools will claim they can.

I doubt there is a mammal alive that could hear 400Khz! I tried lifting the earth connection on the amp and the scope. No difference to report.

A good power amp introduces very little noise other than what is introduced by the line level gear via the inputs.

When I first pulled the amp out of the box I noticed one of the rack mounting "wings" at the rear had been dinged and then I noticed the box had a slightly flat corner. Perhaps this might have something to do with it? Got dropped. Something awry?

So I suppose I will contact tech support Monday and ask if the ripple & hiss is normal. If it is I'll return it and chalk this one up to experience. If not I'll exchange it and report back here.

The question is what amplifier(s) could I get that would satisfy the audiofile in me. I'm not going to all this trouble for OKish results!!

Requirements are as follows: NO HISS! Suitable for a pair of SLA's (Not Pro's) and one of the home based sub woofers. Haven't settled on a sub yet but I expect I'll build a Tuba HT to play with. Must sound fan-bleeding-tastic. Primary task will be for playing vinyl with some home theatre duties looming on the horizon when I'll turn the system into 5.1.

[But it Hertz]

I called Crown Tech Support today and spoke to a very helpful guy there who just happened to have 3 of these in his living room.

He said "... while I can tell that the amplifiers are turned on (as you can with all amplifiers), I have never had a complaint about hiss..."

He also said that they have never received a complaint about hiss on this model.

On the subject of the ripple he didn't know off the top of his head if it was normal but thought it sounded a little suspect and while there might be a little noise somewhere around the sampling frequency he said generally everything over 20Khz should be filtered out.

There was a weird moment when he thought I was complaining about being to hear 400kHz!! I guess they get all sorts calling them.

But anyhow... this one is going back tomorrow under the 30 day no matter what returns policy.