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Amplifier Noise Floor

Cody AOC

Cody AOC

Active Member
First off i'm going to get to the point I own a Crown XLi 2500 and a Crown XLi 800 they both have this hissing from my speakers does not matter what speakers i'm using they will have a hissing sound just loud enough that I can clearly hear it from 2 feet away at my desk in my bedroom. Is there a way I could lower this? It's just the amplifier and the speakers, amplifier is connected to my sound card from my computer which I installed it, costed me over $100 for it. I have used it without an audio source and it still does the hissing, anyway to lower it?
 
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It'll be interesting to see what others have to say about this...

I went thru a process somewhat like this when I was putting together the nearfield portion of my headphone/nearfield system.

Here's what I ran into:
(Mind you this first part was back when I was dealing with just the headphone side of the system)
The process got started when a preamp was put in the chain to use it as a headphone amp for my high impedance AKG headphones.
But the thing is that just made things worse as that preamp's inputs were really sensitive and it just amplified the already present noise.
And with the headphones in use the noise was really obvious & annoying.
So in my case it seemed obvious the noise was coming from the PC for sure.

So it became apparent that the analog outs on my soundcard were'nt gonna cut it in terms of SQ (the soundcard being used was a Creative SB Zx).

Answer to that problem was to isolate the PC by some means.
So I tried an experiment and put a cheap Fiio D3 DAC on the soundcard's optical out to see if I could drop the noise floor some.
And it worked pretty well.

Feeling pretty good about that experinent I went ahead and got a better DAC to take the D3's place (a Parasound D/AC-1000).

So now I came to the point where I was gonna finish the nearfield portion of the system (ie: adding the amp & speakers)...
And a inky black noise floor was an absolute written in stone requirement.

The preamp I mentioned above (a NAD 106) has XLR outs,so the plan was always to use those.
So I studied up on amps,,,plan was to use a 1ru "pro" style amp...
Wound up using a EV 7100 amp,cables were Mogami XLR.

Anyhow to get to the point,I got what I was after,the system's noise floor is a bottomless pit of nothingness.

I had considered using some active monitors for the nearfield part of the system,but many of those often have that "quiet hissing" situation.
I came to understand that is often a symptom of grounding issues with those.
Which is often dealt with by isolating the ground via a couple of those 3 prong -to- 2 prong adapters.
Now that's NBD with those active monitors,but it's probably not a good idea with those Crown power amps.

But that said,I'd suggest looking into the grounding situation to see what may be going on there.
And while your at it,consider the power supply side of things as well.

Beyond that,it could just be the amps themselves,I dunno really.

Good luck w/this.

Bret P.
 
Bret gave a pretty good talk on his experience.

To put it simply, ALL powered components in the signal chain generate SOME noise. If you can't hear it from your normal listening position at your normal listening levels, it's fine and probably normal. You can accentuate it by using efficient speakers and putting your ear right up to the speakers.

To put it less simply, or in more detail, read the following link and focus on "thermal noise".

http://sound.whsites.net/noise.htm

One thing about this hobby is that if you look hard enough for flaws, you'll probably find them.

Also, don't you think those amps are serious overkill for near field listening? Betcha if you used them in the high power applications they were designed for the hiss wouldn't be an issue. That's like complaining about throttle response when trying to drive a Ferrari at 15 mph.
 
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Better electronics give you lower noise. Once you you hear the difference in the fine detail that is masked by the noise floor of your electronics you will not be happy with any higher noise electronics. Ground loops, poor shielding, and bad wire connections, can add to the base noise of your system.
 
Installing a ground isolation transformer in my Polk sda interconnect made me realize just how noisy the ground is on an amp. It was enough that I questioned the designer if it somehow made the amp more powerful. His answer was no it did not but it's similar to talking over the voices in a room full of people vs. talking to someone in an empty room. The empty room naturally will work better just as a low noise floor amp will.sound better. The difference was really eye opening for me and one of my better sda upgrades.
 
Yes to all of the above. I have had amps in the past with an audible noise floor. I mean inherent circuit noise, not noise caused by hum loops or anything extraneous. It's usually very difficult to trace the cause. Sometimes it is just down to the design of the equipment. Zener diodes or noisy transistor junctions can introduce white noise. You can have noisy capacitors. Sometimes it is the topology of the circuit board itself with the wrong components next to each other or long parallel tracks causing noise pickup. Some of these things are correctable, but with others you may as well junk it and start again.
 
Yes there is a way, though others may not cotton to it.

Run your amplifier outputs to a 100 watt, stereo, 8-ohm L-pad. Turn everything located "upstream" up, but well before the point of any distortion, and use the L-pad as your volume control. Now, when you turn down the volume, you turn down the hiss with it.

Alternatively, use the L-pad to reduce the amp's volume to the point where the hiss no longer bothers you, and use the upstream controls as normal from that point recognizing that you will be turning them up further. This is probably the better way to do it because the other way, you could theoretically exceed the watt rating of the L-pad and never realize it because you had the volume down at a reasonable level.
 
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Cody AOC said:
First off i'm going to get to the point I own a Crown XLi 2500 and a Crown XLi 800 they both have this hissing from my speakers does not matter what speakers i'm using they will have a hissing sound just loud enough that I can clearly hear it from 2 feet away at my desk in my bedroom. Is there a way I could lower this? It's just the amplifier and the speakers, amplifier is connected to my sound card from my computer which I installed it, costed me over $100 for it. I have used it without an audio source and it still does the hissing, anyway to lower it?
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How do you have the gain set on the amps? Full tilt?
 
If the gain control or attenuator on the amps is already lowered and you still have audible noiseet, I would suggest to try with an external dac that is not usb powered. PC power supplies are usually very noisy, and not viable for an analog output stage imho.
 
toddalin said:
Yes there is a way, though others may not cotton to it.

Run your amplifier outputs to a 100 watt, stereo, 8-ohm L-pad. Turn everything located "upstream" up, but well before the point of any distortion, and use the L-pad as your volume control. Now, when you turn down the volume, you turn down the hiss with it.

Alternatively, use the L-pad to reduce the amp's volume to the point where the hiss no longer bothers you, and use the upstream controls as normal from that point recognizing that you will be turning them up further. This is probably the better way to do it because the other way, you could theoretically exceed the watt rating of the L-pad and never realize it because you had the volume down at a reasonable level.
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Yeah, this'll work,

What you're doing is increasing the gain of the Crown amps so the output signal is well above the noise floor, which will be quite loud. Then, using the "L" pad, you're attenuating the signal to a listenable level.

This isn't unlike how the original Dolby noise reduction worked except they applied this boost/cut scenario to specific frequency bands in order to bury the noise well below the signal. This is why Dolby encoded tapes tended to sound tinny when played back on non-Dolby machines. The highs were boosted in expectation of being attenuated upon playback.
 
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Everyone I wanted only to know how to mod the amplifier like changing out a component or two inside the amplifier I know it's the amplifier nothing to do with a signal into it I have disconnected the audio source and it's no different. It's not the speaker wire I use 100% OFC copper wire I use 12 AWG I have also pulled out some old wire to see if it was that made no difference. Here's the inside of the unit Crown XLi 250020171123_083702.jpg
 
I try to never say never, but I doubt a big change in noise floor will come from a change of one or two components.

People have asked but not sure I saw a response.

Does the level of hiss go down as you turn down the gain/level settings on the amps?
 
whoaru99 said:
I try to never say never, but I doubt a big change in noise floor will come from a change of one or two components.

People have asked but not sure I saw a response.

Does the level of hiss go down as you turn down the gain/level settings on the amps?
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Not really any more noticable hiss when it's all the way up or down regardless it's the same level of hiss no matter where the gain is.
 
Cody AOC said:
Not really any more noticable hiss when it's all the way up or down regardless it's the same level of hiss no matter where the gain is.
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You say both amplifiers produce a hissing noise regardless of the speakers connected to the amps. It would be unusual for two amps to fail in the exact same way with the same symptoms. That indicates that the source of noise is likely external to the amps. I assume that you hear the hiss equally from both speakers/channels.

Try the following:

Unplug everything except power and the speakers from your amp. Turn the gain pots all the down. Do you still hear the noise?

Do you plug your amps into a surge suppressor or UPS? If so, remove it and test again.

Do you have any other electrical equipment next to your amp? Like a WiFi router, computer, laptop, Apple TV or Express, or something? Turn all that stuff off or move it into another room. You want to eliminate all sources of electromagnetic interference (EMI) near your amp, speakers, and speaker cables. Still have the noise?

If you still have noise, you can plug the amp into another circuit in your house, that is, another place in the house that has a different circuit breaker controlling the outlet. Plug the cord directly into the wall socket. Make no other connection to your amp. I suggest that you physically move the amp and a speaker to the new location. Do you still hear the noise?

If you have eliminated all external noise sources and the noise is still heard from both amps, then I can only conclude that your amps both suffer from the same ailment. Freddymac2 says it is likely generated in your front end. That is the portion of the amplifier before the signal is amplified. You say the noise does not change when changing the gain pots, then the noise must originate after the gain stage.

All this tells us is where we need to start checking voltages and waveforms with a scope. If the noise is that objectionable, you may want to take one amp in for service.
 
RTally said:
You say both amplifiers produce a hissing noise regardless of the speakers connected to the amps. It would be unusual for two amps to fail in the exact same way with the same symptoms. That indicates that the source of noise is likely external to the amps. I assume that you hear the hiss equally from both speakers/channels.

Try the following:

Unplug everything except power and the speakers from your amp. Turn the gain pots all the down. Do you still hear the noise?

Do you plug your amps into a surge suppressor or UPS? If so, remove it and test again.

Do you have any other electrical equipment next to your amp? Like a WiFi router, computer, laptop, Apple TV or Express, or something? Turn all that stuff off or move it into another room. You want to eliminate all sources of electromagnetic interference (EMI) near your amp, speakers, and speaker cables. Still have the noise?

If you still have noise, you can plug the amp into another circuit in your house, that is, another place in the house that has a different circuit breaker controlling the outlet. Plug the cord directly into the wall socket. Make no other connection to your amp. I suggest that you physically move the amp and a speaker to the new location. Do you still hear the noise?

If you have eliminated all external noise sources and the noise is still heard from both amps, then I can only conclude that your amps both suffer from the same ailment. Freddymac2 says it is likely generated in your front end. That is the portion of the amplifier before the signal is amplified. You say the noise does not change when changing the gain pots, then the noise must originate after the gain stage.

All this tells us is where we need to start checking voltages and waveforms with a scope. If the noise is that objectionable, you may want to take one amp in for service.
Click to expand...

The hissing is white noise of course all amplifiers make it to some extent but the Crowns have more than I wanted it's only threw the tweeters on any set of speakers. The one amp is connected directly into the wall socket and the other is connected in a different room on a power strip but no matter where they are plugged in with or without an audio source they do it I just think they are designed this way. The gain has been all the way down and makes no difference it's not defective since I have been using one amp for over a year and the other for 6 months or so. And they are pro audio amplifiers people call them budget amplifiers which i would agree with but as far as I know they do their rated RMS power. I think someone should dyno the Crown XLi series I really want to know if Crown is true about it.
 
whoaru99 said:
Personally, I don't believe there is anything broken, per se.

Neither amp has exceptional S/N ratio and the OP is 2 feet from the speakers. If the speakers are moderately or higher in sensitivity any inherent noise will be exacerbated.
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I use bookshelf speakers and they are 90db per watt sensitivity if you want to know what speakers they are Bic America dv62si they handel some good clean power yes they are good for the money but I use two pairs so that's 4 speakers and a klipsch sw-112 that I got for $250 new on amazon almost 2 years ago
 
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