How much amplifier noise floor is normal?- and Crown XLS 1502 questions

[Tuocsteem]

This is my first time posting but I've been lurking for a while and I hope someone can offer advice, experience, insight or whatever else they might have on my issue.

I recently purchased a Crown XLS 1502, which has been sort of my dream amp for overkill headroom for any pair of speakers I end up getting down the line. This was partially informed by amir's review and many comments from users of asr reinforcing that this amp sounds good and provides a ton of clean enough power, even if it isn't quite hi-fi. However, as soon as I received the amp, hooked it up to my bookshelf speakers and powered it up (without any input plugged in, mind) I was immediately hit by how much noise this amp makes. The hiss coming from my tweeters is LOUD... and that's only slightly an exaggeration- it's clearly audible a meter away at my desk and if I align my head with a tweeter I can walk backwards to the other side of the room and still pick out the static from the background noise. The hiss is louder than the faint hum from the dying cfl bulb in my lamp, it's louder than my computer fans, louder than my tinnitus, clearly audible even when the hvac is running and so on. The hiss from this amplifier dwarfs all the annoying little electronic noises that I've painstakingly removed from my room and now I'm not sure what to do. I guess my question is, for any fellow xls-series owners or audiophiles in general, is this a defective unit? And even if it is, how much amplifier noise is actually normal?

More technical troubleshooting details- I replaced an ancient sony tapedeck/radio tuner combo unit which was on its last legs with the crown amp. The old amplifier exhibited some hiss within a foot of the tweeter but it was truly inaudible at both nearfield listening distance and around the room. It was also going in and out in both channels and garbling frequencies below 60hz into a rumbling mess so I'm certain that it shouldn't be producing superior sound quality to any modern replacement. The amp is hooked up to the speakers via 12ga wire and the input is rca. None of that is really relevant, though, as the system performed fine with noise with the previous amp and the crown amp produces noise even without any input at all. Setting the gain to zero or to max has no effect on the noise with no inputs, wheras setting the gain to max with a cable in the rca jack seems to start picking up local radio stations. I've tried shorting the rca inputs- no difference. Setting or removing crossovers on both channels via the built-in dsp- no difference. Running an extension cord and plugging the amp into another circuit- no difference. Moving the speaker wires and all the other electronics on my desk as far from the amp and its power cable as possible (some people say they could cause interference?) - no difference. Switching the input sensitivity from 1.4v to 0.775v increases the volume of the hiss, still with no input. My speakers are ~88db sensitivity so they shouldn't be overly sensitive to this type of noise. I don't have a preamp with XLR out to test if balanced connections fix the issue, but I doubt it will as the amp seems to generate noise as long as it's plugged in and turned on.

So I'm at a loss for what to do at this point. I'd call the amplifier unusable in its current state- it sounds great when I crank it up and sit ten feet away from the speakers but basically any track with dynamic range is ruined by this undertone of static in the quiet parts. Even nearfield at medium listening levels the setup sounds great- soundstage is fine, bass is effortless, clarity and resolution are actually both great, to my ear, except that they're constatly overlayed with this totally independent white noise. I have the option to either return the amp within 30 days or exchange it as defective but I'm stuck paying return shipping either way. I've contacted Harman's technical support and couldn't get any information about typical noise floor or whether or not my unit is even defective by their standards. If any other XLS owners could provide any input on the matter I'd greatly appreciate it- does your amp produce tweeter hiss when it's on and not playing anything and, if so, how far away can you hear it?

More generally, I know that some amount of noise in a system is inevitable but is there any way to get truly negligible noise floor, like no matter how hard you try you couldn't pick it out in a blind test whether the amp is powered on or off from nearfield listening distance? I know that amps which measure the best overall tend to also have lower noise like the Hypex, Purifi, and Benchmark examples that get tossed around here and I know that noise is inherently baked into the whole SINAD measure but measurements of idle noise and performance below one watt of output are quite scarce anywhere online. Surely you don't have to pay top dollar just to get a device that doesn't make noise when it's not even doing anything, right? I'm new to all this stuff so I'm willing to take whatever info anyone can provide- anecdotal experience with their systems noise floor, recommendations for affordable amps that are dead-silent at idle, advice about whether I should try to get harman to warranty my amp etc. etc.

 

[30 Ounce]

You need to at least short the input of the amp to see how quiet it will be. An open ended input will be very noisy. If you connect it to your preamp or CD player or something it should be much quieter. If not then I would find something else...

 

[Vini darko]

Hi Personally I'd send it back and eat the shipping cost. The amp is clearly no good for your use case. Wether it's faulty I cant say. But noise at that level isn't acceptable.
Edit: I hear good things about yamaha amps lack of noise floor.

 

[westyjeff]

I had a XLS 2502 connected to my Magnepan 3.7 speakers, very inefficient, I did not have any noise when the system was idling. Can you return your 1502 for a replacement?

 

[Tuocsteem]

Thanks for the quick replies everyone.

Westyjef- I can RMA the unit but I'm on the hook for return shipping whether the unit is defective or not, so I'm currently undecided on whether or not I want to stick with the crown at all (as I'd be paying triple the shipping in the end if the replacement was as noisy and needed to be returned.)

I'm currently leaning towards returning the crown and provisionally going back to the old tape deck until I find something else. I'm not entirely sure what kind of amplifier would be a good alternative, though.

 

[30 Ounce]

What speakers do you have? Highly efficient or horn speakers can reveal amp noise easily. Also, I just had an issue with noise on my new amps and it turned out to be a pair of bad cables. They were 20 foot runs so any issues with shielding will be a problem. If you can, try a different set of cables. Honestly though it sounds like the amp is just noisy or your speakers are really efficient.

 

[Blumlein 88]

What speakers are you connecting the amp to?

And yes do try it with something connected to the input even if idling with no signal.

Looking at Amir's review and specs I'd say this is likely a problem with all except very inefficient speakers if you are listening from very close to them. Plus the amp will boost any upstream noise in the source. So I'd suggest sending them back.

 

[Chrispy]

So this is with no pre or input of any kind? What happens with your preamp/input connected? What speakers? Why such a powerful amp for a nearfield setup? I've got several Crowns and don't have such issues with my ears up against the speakers....

 

[thanhh]

Hi, I am using the same amp with 2 pairs of speakers - Kef Q950 and Maggies MG12/QR. When I 1st got the amp, I sorta had the same "issue". When connect to the Maggies it's dead quite but when I connect to the Kef, I heard hissing from the tweeter. I was advised by the store I bought it from that I should adjust the gain based on how efficient my speakers are. So I have the gain fully open when using Maggies and about 11 o'clock on my Kef and they are both dead quiet. I percieve the same loudness when my preamp volume on the same position on both speakers this way.
In short, turn down the gain knob till you cannot hear the hiss anymore when connecting the Crown to you preamp or DAC (inputs plugged in as advised above). Hope this help, please excuse my English .

 

[Tuocsteem]

The speakers are infinity r162, nominal sensitivity of 88 db so they're not super sensitive. I know this system is crazy mismatched w.r.t price and power but I already had the speakers and I wanted an amp that is future proof for when I get some bigger speakers (I was actually looking at the Magnepan LRS, which partially informed my decision to get a high power amp that is stable at low impedance bridging). I'm actually quite happy with the sound of the Infinitys as they are- and they certainly can take quite a bit of power even if the XLS 1502 could blow them up if you maxed it out.

My cables are some cheap 12ga 99.99% oxygen free copper I got off amazon- there's no shielding but the runs are only 2 meters long. They don't cross any crazy emi-generating devices besides potentially the amp itself. I already mentioned in my post that I tried shorting the inputs and it didn't make any difference- and all of that is sort of a moot point as the exact same arrangement was producing very little noise with the barely-working 20+ year old tape deck I had in it before.

To respond to sepcific posts:
Chrispy- With nothing plugged into the amp but power and passive speakers the amp still generates noise. The noise remains the same whether I plug in rca through my dac or whether I connect an rca splitter straight into my motherboard out. I've tried shorting the inputs and even taking the 3.5mm jack and touching it to the case of the amp and random ground metal around the room with no effect on the noise. The static is constant as long as the amp is plugged in. I got this amp because I use my setup for both nearfield and ~3 meters away depending on my mood and I plan on getting some bigger tower speakers or maybe even a passive sub in the future. I wanted to test if headroom mattered as much as some people say it does and so far I'm convinced it helps. Plus I figured having a spare amp with a silly amount of power wouldn't hurt no matter what I end up upgrading to later on.

thanhh- Your English is perfectly fine. My issue is that no matter what I set the gain to the amplifier produces a constant amount of hissing even without an input. If I plug in an input and raise the gain to max I get a lot of noise but no setting actually makes it go quiet. If I had less sensitive speakers I might not have noticed the problem but it seems like a significant amount of the signal coming out of the amps is always noise so there's not much chance to get good dynamic range.

Based on everyone's responses I'm assuming that my unit is defective which is disappointing but hopefully fixable by getting a replacement. I'll be contacting the seller (Provantage) to see what their exchange policy is and if there's any way to get around the shipping cost. The only other option is to go through Harman's warranty repair but the tech I spoke to said they're pretty backed up right now. I'll definitely post an update when/if I get a replacement unit just so other people can know if noise is truly an issue with these amps or just quality control.

 

[Chrispy]

Speaker cables sound fine, shielding is not likely needed.

Is it a ground loop hum or hiss you're hearing?

I doubt the unit is defective. Where do you have gain set on the amp when using your dac or pc as pre?


ps What sensitivity setting are you using and what's the output voltage on your two input devuces?

 

[Tuocsteem]

It's definitely a hiss- like a constant white noise static. For nearfield listening I have the gain knobs set four or five clicks out of a total of 20 on both channels. I know that that's not very informative but it's low gain. At every setting at or below that the hissing sound is constant. My dac doesn't have volume control so I don't know what the output voltage is but switching the input voltage in the amplifier never eliminates the noise- it's at 1.4Vrms by default and switching to 0.775Vrms increases the volume of the static. There's no combination of input and output level that lowers the noise floor below a constant, noticeable hiss at listening distance. I've tried shorting the inputs already and it doesn't sound like a ground loop but I'll try a few things.

I just tried a couple of goofy potential (pun intended?) solutions:
1. Plug the amp into a non-grounded extension cord. I hooked up the amp to a cheap not-actually-grounded grounded extension cable (doesn't have third prong on the end that sticks in the outlet) and ran it to a completely separate circuit of the house. I'm aware that this is a bad idea and not good long term. Amp still hisses
2. Plug the amp into the same surge protector as my PC and Monitor (Noisiest option). Hisses as usual and I can't really tell if it affects sound quality.
3. Plug the amp directly into the wall socket that is shared with the surge protector for my PC and monitor instead of the surge protector itself. Still hisses
4. Plug the amp into its own surge protector on the same circuit as everything else. Same hiss
5. Use a proper extension cable to connect the amp to another circuit. Still hisses
6. Unplug everything? I unplugged everything in the room besides the amp and my desktop pc and turned off all the lights. Nothing but darkness and hissing.

I'm running out of ideas here but I'm willing to try whatever else might help before customer support opens up tomorrow. When I plug the amp directly into my computer's 3.5mm out I can hear some good old faint onboard audio whining but it's completely independent of the static constantly coming out of the speakers. The static seems the same whether I have a dac inline or no inputs or inputs shorted etc. I don't have anything with xlr out to test if that changes anything.

 

[Jdunk54nl]

I’m using an xls1502 and I noticed I had a hiss in my sub (I’m using it on my sub only) if I turned the gain up really beyond the 2oclock position. I had to set a 200hz low pass on the amp to fix it.

You’ve got me curious now...when I get home tonight I’m gonna plug it into my towers and see if they have a hiss.

I just purchased mine about a month ago...so possibly a bad batch...

 

[Wayne A. Pflughaupt]

I have two Crest Audio amplifiers, and speakers with over 100 dB sensitivity connected with no source input, they are both dead silent with the gains all the way up.

Regards,
Wayne A. Pflughaupt

 

[Jdunk54nl]

Yea. I thought these amps were actually designed to have the gains all the way up as the usual...at least that was my take from quite a bit of reading.

 

[Wayne A. Pflughaupt]

The Crown’s noise is spec’d at a mere 103 dB A-weighted, so that’s probably the problem. That would be a good unweighted figure (dBu,) but it’s a poor figure for A-weighting. A-weighing “ignores” the low and high frequencies, which is where noise typically is. A-weighting can “improve” a bad noise spec by up to 10 db. So basically, you never want to see an A-weighted spec than less 110-115 dB if you want to ensure a quiet amp (at least as much as you can trust the specs).

Regards,
Wayne A. Pflughaupt

 

[Jmudrick]

The Crown’s noise is spec’d at a mere 103 dB A-weighted, so that’s probably the problem. That would be a good unweighted figure (dBu,) but it’s a poor figure for A-weighting. A-weighing “ignores” the low and high frequencies, which is where noise typically is. A-weighting can “improve” a bad noise spec by up to 10 db. So basically, you never want to see less an A-weighted spec than 110-115 dB if you want to ensure a quiet amp (at least as much as you can trust the specs).

Regards,
Wayne A. Pflughaupt

Respectfully that's certainly not the problem. My XLS2502 is dead silent into my comparable Infinity IL-10. Patio cord speaker cable, gain setting 2 o'clock.

 

[Chrispy]

Well it doesn't seem the app for your gear/application and got no more ideas myself.....but yes you should be able to run full gain if you needed to, altho that may bring along more noise. Good luck!

ps one last thought....do you have an extremely quiet room?

 

[restorer-john]

Respectfully that's certainly not the problem. My XLS2502 is dead silent into my comparable Infinity IL-10. Patio cord speaker cable, gain setting 2 o'clock.

It IS the problem, @Wayne A. Pflughaupt is correct. The amplifier has an absolutely dreadful residual noise according to specifications. 0.346mV A-WTD or 346uV! Consider we are seeing D/A converters with 1-2uV noise and headphone amplifiers around the same. Plenty of decent power amplifiers have residual A-WTD noise in the 20-50uV range. I have some that are 14-18uV.

A 300wpc@8R amplifier should have S/N around the 120dB mark or around 50uV of A-WTD residual noise. The Crown is 7 times that! It is not remotely high fidelity at all.

@Tuocsteem Send it back, eat the postage and buy an amplifier that is designed for home listening environments, not sound reinforcement in a bar or club.

 

[Tuocsteem]

That's an interesting point, Wayne. It seems to me like most amplifiers in this price range barely go above a rating of 100dB SNR, though, if the manufacturer even publishes such a number and it's even rarer for inexpensive products' measurements to not be A-weighted, along with the extra confusion of measuring under the best case scenario of maximum output. I'm not entirely sure how to convert these numbers to useful figures, though.

For example, the Crown XLS 1502 spec is 103 dB SNR A-weighted at maximum output, and is rated 300Wx2 in stereo mode. If the ratio between signal and noise is 103 dB then...

I'm not entirely sure where to go from these numbers. Assuming that noise is constant at all levels of output and independent of thd, then the simplest thing would be to calculate directly from the dB ratings. If you speakers are 88dB sensitivity (as mine are) then at 300W per channel, assuming there are no reflections then you have an spl of 115.8 dB at 1 meter from the speakers. I have no idea what I'm doing but I'm plugging things into online calculators, specifically this for that last number. Then 115.8 dB - 103 dB = 12.8 dB noise across the board at one meter, problem solved. I have a feeling it's not that simple, though, as this number is both way above the noise floor of any room and simultaneously seems to imply that the only way to get true inaudibility at one meter is to have SNR=Max SPL which not a single power amplifier in the world, even the Benchmark, achieves with higher sensitivity speakers. Despite all of this, it seems like plenty of people have no issue at all with tweeter hiss, idle noise etc. and describe their amps as dead silent even with very efficient horn setups.

I've tried to do some calculations to take amir's measured SINAD and THD before clipping to reverse engineer the true uV residual noise but as far as I can tell such calculations are fundamentally imprecise due to rounding etc. when you're dealing with huge absolute differences in signal strength (such as +103 dB SNR or -80dB THD). Some preliminary calculations would suggest 336 watts @ 4 ohms with 0.008% distortion and 100dB SNR as measured by amir here then you have effectively 36.6606V coming out from the amp (assuming power factor of 1 so I don't drive myself crazy...) and a "thd" of -81.938 dB (even though it's probably THD+N but assume noise is negligible in a calculation that results in the noise haha...) then you get a resultant SINAD of 81.87 (at full output so ear-bleedingly loud and maximal clean signal strength for this amplifier) and RMS noise of 129.6 uV (microvolts) equivalent to 13.31 effective bits according to this calculator which specifically warns against using it for calculations of this sort. Notably, increasing SNR to anything greater than -THD has a vanishingly small effect on SINAD as the two are summed to get THD+N. So with this 129.6 uV number with which we can do... absolutely nothing, as far as I can tell. You could try to treat it as an output voltage so with the same 8 ohm, 88dB speakers that would be a terrifying 0.001 Watt = 61dB of noise at one meter and I'm pretty sure no system is that bad.

To respond to your question, Chrispy- I wouldn't say that I have a quiet room but I guess I'm very well-accustomed to the noises that are to be expected here. I once had a cheap decibel meter to measure the noise floor and it never quite got down to its 30dB minimum reading while I was in the room but at the same time I can pretty clearly hear all the obvious noise sources. I can hear my computer fans (but I did tear them all out and replace with noctuas a while back because of noise issues), I can hear the fluorescent lights when they're on, I can hear the cicadas outside, the occasional car or train that goes by, the hvac system when it kicks in, pretty much everything my neighbors do when they're in the yard... I don't claim to have supersensitive hearing or anything but I very much do not like unexpected noises that I can't easily tune out like hissing and humming and whining from poorly designed electronics. As far as I can tell most true background noise evenly spread and biased towards lower frequencies anyway as those tend to travel through and around obstacles more effectively so a tweeter hissing away at 2-10 kHz with a waveguide pointed straight at your ear is going to be annoying even if it's well below the noise floor of your room.

I do have to say that this whole troubleshooting and research process has made me much more interested in details that most measurements fail to capture like super low-level <1 Watt performance, residual noise and noise floor of components in a system, true unweighted SNR values and noise measurements done below peak SPL. I'd hope to see more of such things in reviews on this site and others and, if anyone has recommendations for dead-silent electronics then I'm all ears (and no I'm not really into headphones anymore. Unless someone has a way of rigging up one of those THX AAA amp to deliver a cool 2x20 watts or so into 8 ohms while maintaining those crazy measurements- you never know, there might be a market for near-field enthusiasts.)

I do find it somewhat ironic how my major concern with the 1502 was the actual mechanical fan inside creating noise. Somehow this thing manages to take mains electricity and nothing else to generate electronic noise louder than its mechanical noise as I've never heard the fan unless I crank up the sound and put my head against the back of the amp.