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AC mains noise Borrowed noise sniffer and tested my AC lines...

I borrowed this AC line noise sniffing device (Blue Horizon Mains Noise Analyser) today. (Do not ask from where, I do not feel at ease saying.)
This device sniffs out noise and has a range of "000" to "999" and over that it just is "MAX".
So first test was kitchen light with wall plug. "784"
Kitchen outlet tied to refrigerator (frig ON) "MAX"
Bedroom wall nothing around in use "220" wow good number.

Furutech Duplex at amplifier "013*" WHAT!!!! yes "013". That is on a direct 44 ft extension cord from 20 amp wall outlet (also Furutech) * with the C7 to the noise sniffer one way, it is 13, other way it is 20. ALL the measurements change with reversing the noise sniffer AC plug, about the same amount each time)
That extension does have an additional Furutech duplex on the cord, six feet back of amp Furutech plugs end, and that duplex has two PS Audio Noise Harvesters. The wiring is a quad twist. and each side or pair is connected to one out side. so each Noise Harvester is on one half of the quad.
So I can say the PS Audio Noise Harvesters really DO a fantastic job!!!

The other similar line (from he same 20 amp outlet) does not have any Noise Harvesters on it. And with the stereo running, it has "297" noise level. However IF I do stick one PS Audio Noise harvester in an out 3 feet back ot the one the sniffer is in. The noise drops to "143". (I cannot leave the Noise Harvester or a pair in there due to it being in use, normally, plus adding them in where the noise sniffer is, seems to make the sound go too thin.)

Another major discovery is just HOW NOISY Digital equipment really is!!! I have my two CD changers plugged into a separate power conditioner. A PS Audio P-600.
Testing the PS Audio P-600 I own (tested at 60Hz) With nothing turned on plugged into the P-600 the baseline noise is "040" With one five disc CD changer turned on the noise level jumps up to "740" With the other one only on the nose is also "740" with both on the noise jumps over "MAX" This is with a PS Audio Noise Harvester plugged into the same duplex (on the back of the P-600) as the CD changer!
On the other hand.. The Marantz SA-10 is pugged into the Furman (also with a PS Audio Noise Harvester in same duplex and that area is "032". So SOME equipment is not spewing, and some is.

This is all I have learned in a half hour of fooling around.
elizabeth

Showing 2 responses by spatialking

spatialking's avatar
spatialking
248 posts
 
@erik_squires:  Actually, when monitoring noise, one cannot include 60 Hz since that voltage will swamp everything.  It has to be filtered out along with most of the harmonics from inductive loads.   Those lower frequency inductive harmonics of 60 Hz, will get rectified in the power supply and we don't want them screwing up our measurements since they are a normal part of line power, so they are best left out of the noise measurement.  The main noise concerns start around 1 to 5 KHz or so and goes up from there to about 30 MHz.  So, a 10KHz to 30MHz analyzer is probably about optimum.  

@Elizabeth:  One possible reason the noise is lower when music is playing is the line impedance is lower since more current is flowing in the line.   The lower impedance will squash some of the lower power noise.  
spatialking's avatar
spatialking
248 posts
 
@erik_squires:  I am not sure I understand your comment about "selling that"?  Do you seriously want to define line harmonics as noise? 

They are generated by loads, such as AC units and refrigerators.   In the typical harmonic frequency range at less than 1KHz, the big problem is line voltage changes affecting unregulated power supplies in most power amps, not the harmonics that are readily rectified and stored as energy by the power supplies in our stereo equipment.  

In other words, if one is concerned about that band, one should monitor the RMS voltage from 60 to 1KHz, which is far more of a problem than line noise in the same frequency band.  However, most low level audio products, such as preamps, CD players, DAC's, etc. have regulated power supplies so line RMS voltage changes in that band become meaningless;  especially since the regulation in that band of any decent regulator these days is especially good.  Power amplifiers rarely have regulated power supplies in the high current stages and are more affected by voltage changes in the line. 

Beyond that band, especially above 10 KHz, the PSRR of most regulators starts to fall off and noise passing through the power supply does have a detrimental effect on sound quality. 

The best way to measure this stuff is not using a meter but using a spectrum analyzer with an upper bandwidth around 30 to 100 MHz.  That will give you the frequency of the noise and also the magnitude of the noise.  With that, one could correlate which frequency spectrum affects which component the most and how it affects the sound quality. 
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