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Old 27th November 2012, 01:20 AM   #5661
robbbby is offline robbbby  Canada
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Quote:
Originally Posted by Esperado View Post
The problem comes from your preamp, if you have no problem when input shorted. Try change the phases of your preamp and amp power cords, (various combinations, with nothing else connected from your preamp) change sources to figure-out etc...
I don't have a preamp, I don't have anything hooked up. The noise is with nothing connected to the ncore input.
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Old 27th November 2012, 01:22 AM   #5662
robbbby is offline robbbby  Canada
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Originally Posted by barrows View Post
I have noted that the nCore amps may be sensitive to RF on their inputs. Example: the last pair of nCore I had here (a mono block pair built for a friend) were perfectly laid out and wired. With open inputs (not shorted) thye exhibited an extremely low noise floor, with a very smooth, soft, evenly textured hiss at the tweeter, only audible when the room was very, very quite on a calm night, with everything else in the home powered down.
When one DAC I have here was connected and powered up, the noise floor of the nCore became highly static-y, although the absolute level of the noise was still extremely low in level as to be only audible with the ear within an inch or so of the center of the tweeter. Another DAC connected to the nCores exhibited no such rough noise floor. My conclusion is that the nCore amps are sensitive to RF on their inputs, and some DACs are going to have more RF on their output than others. This worries me enough (as this energy may fold back into the music signal) that I am considering transformer coupling my DAC to the nCores.
It may be that your Mytek has enough RF on its output to create this rough noise floor.
Your POP at start up is due to the DC on the Mytek's output, and unrelated to what I ma describing here.
I've figured out the loud pop is because of the mytek, but the static that I have on my tweeter has nothing to do with the mytek. The ncores make the white noise with absolutely nothing hooked up. With DAC/PRE or without, my speakers still exhibit the same static/white noise.
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Old 27th November 2012, 02:47 AM   #5663
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Default robbbby...

I am confused: I thought you said that with the inputs shorted, there is no "bad" sound at the tweeters? If this is the case, then there is no problem with your amps. When then input is shorted, it stops RF pickup through the input (from airborne sources).
I also am a little bit confused by your use of the words "static" and "white noise". Static, I would describe as a scratchy sounding noise, not smooth in nature, with a definite rough texture. White noise, on the other hand, would be a very smooth, even sounding noise, with no texture: by definition I believe white noise is comprised of an even distribution of noise all across all frequencies, with no one frequency at a higher level than another, it should be smooth and even.
In my experience, the self noise of the nCores on their own is smooth and even textured very soft hiss, what I would describe as white noise at an extremely low level. A static like sound, would indicate a possible problem if you had that sound with the input shorted. With the inputs open, they are available to pick up airborne sources of RF, and I would not necessarily conclude that there is a problem, even if you hear a rough noise floor.
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Old 27th November 2012, 06:48 AM   #5664
Julf is offline Julf  Europe
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Originally Posted by barrows View Post
I am confused: I thought you said that with the inputs shorted, there is no "bad" sound at the tweeters?
The way I understand it is that with inputs shorted, the hiss/crackle/whatever goes away, but with open inputs (no preamp or DAC) it is there.

I agree totally open inputs will pick up noise, the output impedance of the preamp or DAC should change that. Might be worth testing with a resistor of a few kohm across the input connector pins.
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Old 27th November 2012, 07:14 AM   #5665
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I believe white noise is comprised of an even distribution of noise all across all frequencies, with no one frequency at a higher level than another, it should be smooth and even.
Yes, it is a hiss, full of treble. A hiss with all octaves equal in energy is pink noise: the flat white noise filtered by 3dB/oct on all the band.
[edit] Typo corrected.
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Last edited by Esperado; 27th November 2012 at 07:36 AM.
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Old 27th November 2012, 07:16 AM   #5666
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Yes, it is a hiss, full of treble. A hiss with all octaves equal in energy is pink noise: the flat white noise filtered by 6dB/oct on all the band.
No! -3db per octave, which requires a special filter.
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Old 27th November 2012, 07:19 AM   #5667
Julf is offline Julf  Europe
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No! -3db per octave, which requires a special filter.
I guess it depends on if you are talking amplitude/voltage dB's, or power/loudness dB's...
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Old 27th November 2012, 07:32 AM   #5668
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Originally Posted by Ouroboros View Post
No! -3db per octave, which requires a special filter.
You're right, my mistake. Shame on me !
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Old 27th November 2012, 07:53 AM   #5669
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They're the same dB's. 3dB is double power or 1.414x voltage which is the same thing

White noise has a constant power density per unit bandwidth (per Hz). Pink noise has a constant power density per LOG of unit bandwidth, e.g. per octave or per decade).

So, white noise has as much energy between 0-200Hz as between 10000Hz-10200Hz. Imagine we cut up the audio range:
Bass: 20-200Hz (one decade, 180Hz)
Mid: 200Hz-2000Hz (one decade, 1800Hz)
Treble: 2000Hz-20000Hz (one decade, 18000Hz)

Pink noise will put exactly equal amounts of power into the three ranges. White noise will put 9 times more power in the mids as in the bass, and yet another 9 times in the treble as in the mids.

How does that work out in "powerdeebees"? Well, 10*log(9)=9.5dB. 9.5dB more in the midrange than in the tweeter. 9.5dB more in the midrange than in the woofer.

How does that work out in "voltagedeebees"? Well, 9 times the power is 3 times the voltage right? So, 20*log(3)=9.5dB. 9.5dB more in the midrange than in the tweeter. 9.5dB more in the midrange than in the woofer. No difference, see?

Okay. So how does white noise sound? Well, considering that per the above white noise contains practically no bass it sounds thin, hissy and tweetery.

How do you make white noise? The simplest method is a resistor. Resistors are sources of white noise. Look up Johnson Noise for more info. Noise voltage goes up with the square root of R. Suppose you have an amplifier with a 100k resistor strapped across it. Measured over the audio range the amp sees 5.6uVrms noise. Suppose you then connect a low resistance source, say 10 ohms. Total resistance, pretty much 10 ohms. The amp now sees only 56nV.

Without source: tweetery noise. With source: quiet.

How do you make pink noise? Find a waterfall. Failing that, use a white noise source and something we call a "pinking filter". That's a 3dB/octave filter. Remember: every octave has twice the bandwidth as the one before that. So white noise puts twice the power in that higher octave. Or 1.414x the voltage. 3dB either way. So the filter needs to be something special. A 1st order filter is too steep. How to make a half order filter? You can't, but with alternating real poles and zeros you can get as close as you want.
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Old 27th November 2012, 08:40 AM   #5670
Julf is offline Julf  Europe
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Originally Posted by Bruno Putzeys View Post
They're the same dB's. 3dB is double power or 1.414x voltage which is the same thing
You are right, of course - my brain fart, caused by lack of enough morning coffee.
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