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Crown XLS 1502 and noise floor

Elgrosso

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Recently got myself a used Crown XLS 1502 for sub duties.
Works very well, plenty of power, a real bargain for the price (300e).
So good I wanted to test it on the mid-bass section, to see if I could maybe sell the current 2xNC500.
Surprise, big hum!

Since I also recently installed a flex8 I had to switch all amps to rca.
When I changed the gain on the nc500 to match, it increased the noise floor just a tiny tiny bit, ears close to the woofers (2x2 high sensitivity woofers).
But with the XLS, and rca too then, it's unbearable, not super loud but more than a simple nuisance, maybe +10db to my noise floor, really guessing here.

I tried :
1 - other rca cables that worked well in car for noise > same
2 - basic rca to xlr cable > same
3 - little ground loop isolator box on rca > worse
4 - remove ground on power plug > same
5 - lower gain from max > not much change

I didn't try:
6 - plugging dsp and amp on the same power outlet, because of #4 I can't see this changing anything.
7 - changing gain from 0.7 to 1.4v, as it would defeat the purpose

So I suppose it's just the amp itself, not that it's faulty, but just too low SNR in that case.
Funny because I replaced my hypex' on the high section with some A/B for a hiss issue.
I wonder if I could try a simple preamp or an rca to xlr converter, but that's already 100+ euros, would defeat the purpose of saving money.
I'd appreciate if anyone has an idea, otherwise I'll just keep the nc500 down there, it's great like that.
 

Chrise36

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Recently got myself a used Crown XLS 1502 for sub duties.
Works very well, plenty of power, a real bargain for the price (300e).
So good I wanted to test it on the mid-bass section, to see if I could maybe sell the current 2xNC500.
Surprise, big hum!

Since I also recently installed a flex8 I had to switch all amps to rca.
When I changed the gain on the nc500 to match, it increased the noise floor just a tiny tiny bit, ears close to the woofers (2x2 high sensitivity woofers).
But with the XLS, and rca too then, it's unbearable, not super loud but more than a simple nuisance, maybe +10db to my noise floor, really guessing here.

I tried :
1 - other rca cables that worked well in car for noise > same
2 - basic rca to xlr cable > same
3 - little ground loop isolator box on rca > worse
4 - remove ground on power plug > same
5 - lower gain from max > not much change

I didn't try:
6 - plugging dsp and amp on the same power outlet, because of #4 I can't see this changing anything.
7 - changing gain from 0.7 to 1.4v, as it would defeat the purpose

So I suppose it's just the amp itself, not that it's faulty, but just too low SNR in that case.
Funny because I replaced my hypex' on the high section with some A/B for a hiss issue.
I wonder if I could try a simple preamp or an rca to xlr converter, but that's already 100+ euros, would defeat the purpose of saving money.
I'd appreciate if anyone has an idea, otherwise I'll just keep the nc500 down there, it's great like that.
The crown should be used with a low pass filter to keep quiet just for sub duties try to power it from its own outlet.
 
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Elgrosso

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For the subs it's fine, it's on the mid-bass there’s noises (of course full active).
I supposed it wasn't a ground loop since removing the ground didn't change anything, but yeah I will try on its own outlet.
 

Chrise36

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For the subs it's fine, it's on the mid-bass there’s noises (of course full active).
I supposed it wasn't a ground loop since removing the ground didn't change anything, but yeah I will try on its own outlet.
I had the same problem testing it for mid. For subs it is fine keep the hypex for midbass or sell it and buy a cheaper one.
 
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Elgrosso

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I had the same problem testing it for mid. For subs it is fine keep the hypex for midbass or sell it and buy a cheaper one.
I like to idea to go cheap now, for the sake of it, so far it worked well (on highs).
While when I started I just picked headroom, safe, and expensive with hypex everywhere.
But I didn't find much lower price for 400/500w power.
Maybe the 700AS2 in a ghent case, but it would just save maybe 200 euros once the NCs sold.

Also I’m kind of an idiot as I forgot the subs are fed by spdif>small dac>rca, so no noise possible anyway.
If the xls is fine there it has nothing to do with its SNR or build quality.

Then, I did performed more tests:
  • dsp and amp on same outlet > same noise
  • dsp plug reversed (2 prones) > same
  • dsp off > same
  • rca unplugged > no noise
  • amp on different room outlet > lower noise
In fact lowering gain to 3 o'clock gave me the same response in rew than with NC500
And this level of gain gives me less hum than with the hypex!
Conclusion:
>> It is not the xls SNR
>> but this solution is not viable (extension from different room)

Now there is a ground plug on the flex, I could try that.
But I don't understand how it could fix anything since dsp off still gave me noise.
Not sure how to do it, what I have in mind is to cut an old power cord and wire its earth to the flex ground.
Or should I wire the dsp ground to the xls amp in some way?

Funny thing, it's really hard to un-hear the hum once you heard it.
Even everything off it feels like you still get it.
A little walk outside fixes it but the brain is a very strange while smart filter.
 

Chrise36

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I like to idea to go cheap now, for the sake of it, so far it worked well (on highs).
While when I started I just picked headroom, safe, and expensive with hypex everywhere.
But I didn't find much lower price for 400/500w power.
Maybe the 700AS2 in a ghent case, but it would just save maybe 200 euros once the NCs sold.

Also I’m kind of an idiot as I forgot the subs are fed by spdif>small dac>rca, so no noise possible anyway.
If the xls is fine there it has nothing to do with its SNR or build quality.

Then, I did performed more tests:
  • dsp and amp on same outlet > same noise
  • dsp plug reversed (2 prones) > same
  • dsp off > same
  • rca unplugged > no noise
  • amp on different room outlet > lower noise
In fact lowering gain to 3 o'clock gave me the same response in rew than with NC500
And this level of gain gives me less hum than with the hypex!
Conclusion:
>> It is not the xls SNR
>> but this solution is not viable (extension from different room)

Now there is a ground plug on the flex, I could try that.
But I don't understand how it could fix anything since dsp off still gave me noise.
Not sure how to do it, what I have in mind is to cut an old power cord and wire its earth to the flex ground.
Or should I wire the dsp ground to the xls amp in some way?

Funny thing, it's really hard to un-hear the hum once you heard it.
Even everything off it feels like you still get it.
A little walk outside fixes it but the brain is a very strange while smart filter.
Can you power the dac from battery or try from your phone just to experiment.
 
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Elgrosso

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This dac is only used for the subs, and then no noise there.
It's when I tested the xls on mid-bass in replacement of the hypex that I get the noise, when it's then fed by the rca from the flex8.

Layout:
Shd studio spdif 1&2 to dac to subs amp (xls)
Shd studio spdif 3&4 to flex 8 to 4 amps (hypex+iota)
 
Last edited:

fubarnow

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How do you use it can you describe your system with detail (outlets other devices cable type etc)?
I use mine running through the preouts on a Marantz AVR.
I use the low sensitivity output and use Full Range for Speakers.
Easy.
I use RCA Jacks.
 
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Elgrosso

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Tried bunch of things, flex ground to outlet, hdmi out, usb out, every accessory out of the system in fact > same noise.
Only a low gain like 6/7 o'clock would make it ok, but then without enough level.

It seems it’s not flex or ground related, but more about the combo of high gain amp and high sensitivity of the woofers.
Well maybe I should plug the low mids just to make sure of this, it should be even worse.

I ordered an rca to xlr buffer, the one tested here by WolfX-700, if it doesn't work I’ll just keep the NC500s.
The other solution, a linear psu, while being only a potential solution, would cost so much that there’s really no point.
 

Chrise36

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Tried bunch of things, flex ground to outlet, hdmi out, usb out, every accessory out of the system in fact > same noise.
Only a low gain like 6/7 o'clock would make it ok, but then without enough level.

It seems it’s not flex or ground related, but more about the combo of high gain amp and high sensitivity of the woofers.
Well maybe I should plug the low mids just to make sure of this, it should be even worse.

I ordered an rca to xlr buffer, the one tested here by WolfX-700, if it doesn't work I’ll just keep the NC500s.
The other solution, a linear psu, while being only a potential solution, would cost so much that there’s really no point.
Ok lets see how the adapter does
 
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Elgrosso

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So I got the box today:
preamplificateur-passif-symetriseur.jpg
preamplificateur-passif-symetriseur.jpg



Tested right away, and it worked.
Flex8 > rca > box > xlr > xls amp, lower gain at 9', for exact same FR in REW.
It added something like 8db in rew to the regular rca signal.
Noise was still there at full gain, but the voltage up allowed to reduce gain, for an acceptable final noise.
Hearable the ear on the motor, but not from listening point.

But now the box itself made some noise :p
Not much and I think it should be ok once hidden in the rack.
(btw it’s a nice little box, sturdy and good finish, it could even make a good amp case for small class D)

In the mean time I tried an NC122mp here as well, with xlr input only.
When I tried with a simple rca to xlr cable the levels were too low.
With the box levels are ok, but final noise is the same than with the xls, so no point.
Its gain is not adjustable (or I just don't know how).

So it’s clearly not the amps alone that cause this noise, but the interaction with my woofer setup.
Maybe I forgot to say, but the motors are outside, well everything is outside since there’s no box :D


IMG_2459.jpg


Not sure I’ll keep the box, because I’ve made some new voltage measurements on all amps with sine.
And it appears again that with my last flex tune I need even less watts than last time.
The more I tune the less power I need, and since I don't use Dirac anymore I don't need to keep a 10dB power reserve down low.
Now I just need to find an amp that has the lowest noise possible, and something like 150w@4ohms or 2x75@8ohms.
So I will try the IOTA pa3 that are actually running the rest, just to check.
2x45w at 8ohms is a little short but I would gladly sacrifice 2/3 dBs for a lower noise.
 

Chrise36

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So I got the box today:
preamplificateur-passif-symetriseur.jpg
preamplificateur-passif-symetriseur.jpg



Tested right away, and it worked.
Flex8 > rca > box > xlr > xls amp, lower gain at 9', for exact same FR in REW.
It added something like 8db in rew to the regular rca signal.
Noise was still there at full gain, but the voltage up allowed to reduce gain, for an acceptable final noise.
Hearable the ear on the motor, but not from listening point.

But now the box itself made some noise :p
Not much and I think it should be ok once hidden in the rack.
(btw it’s a nice little box, sturdy and good finish, it could even make a good amp case for small class D)

In the mean time I tried an NC122mp here as well, with xlr input only.
When I tried with a simple rca to xlr cable the levels were too low.
With the box levels are ok, but final noise is the same than with the xls, so no point.
Its gain is not adjustable (or I just don't know how).

So it’s clearly not the amps alone that cause this noise, but the interaction with my woofer setup.
Maybe I forgot to say, but the motors are outside, well everything is outside since there’s no box :D


View attachment 263360


Not sure I’ll keep the box, because I’ve made some new voltage measurements on all amps with sine.
And it appears again that with my last flex tune I need even less watts than last time.
The more I tune the less power I need, and since I don't use Dirac anymore I don't need to keep a 10dB power reserve down low.
Now I just need to find an amp that has the lowest noise possible, and something like 150w@4ohms or 2x75@8ohms.
So I will try the IOTA pa3 that are actually running the rest, just to check.
2x45w at 8ohms is a little short but I would gladly sacrifice 2/3 dBs for a lower noise.
You could have bought a Topping d10b to run the xls with balanced for the same money which is a better solution i think. If you eq your subs you would eq on pc and from topping spdif out to shd.
 
Last edited:

Chrise36

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Nope, the flex8 is analog out only, and the spdif from shd studio is used is for the subs.
Pc (source + eapo) to Usb out with eq to d10b to xls and from d10b to shd studio to flex 8 (reverse eq ) to 4 amps.
 
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Elgrosso

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And a nightmare to tune :p
The goal with the flex8 was to smooth the process, it was enough of a burden to tune one side at a time and then integrate subs.
Now it’s much smoother, easier to test things, but at the cost of noise compared to multiple shds.
No I’ll just leave the xls on subs.
And more important, now I know I don’t need 300+ watts on mid-bass anyway.
 

Chrise36

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And a nightmare to tune :p
The goal with the flex8 was to smooth the process, it was enough of a burden to tune one side at a time and then integrate subs.
Now it’s much smoother, easier to test things, but at the cost of noise compared to multiple shds.
No I’ll just leave the xls on subs.
And more important, now I know I don’t need 300+ watts on mid-bass anyway.
The other solution would be a good balanced dac to drive the xls but xls on subs is simpler and better i think.
 

DWPress

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I had trouble with a XLS-1502 as well when I was using it just for sub use but nothing to do with SNR - the damn fan kept ramping up every time I went extra loud (which I like to do on occasion). Active XO systems are wonderful for the last few bits of improvements one can do to a whole system but tracking down bugs is sometimes frustrating.
 

Chrise36

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I had trouble with a XLS-1502 as well when I was using it just for sub use but nothing to do with SNR - the damn fan kept ramping up every time I went extra loud (which I like to do on occasion). Active XO systems are wonderful for the last few bits of improvements one can do to a whole system but tracking down bugs is sometimes frustrating.
How did you address the issue?
 
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