As part of my continuing efforts in subversive technical literature, I offer the second part of my "Studies On Residential Power Line Noise". Part 1 of this series is posted here.
An often recited mantra among power cable naysayers cult goes something like this:
"A power amplifier has all the required filtering it needs to remove power line noise. High priced, so-called "better" power cables are a scam." People who are hearing these so-called "improvements" are victims of placebo effect and are, in fact, having aural hallucinations."
There may be some amplifiers may not benefit from or even require a better quality power cord. Their power supplies may indeed filter out all the power line trash. I really don't know if such amplifiers exist. If they do, I imagine they would be quite expensive. All the amplifiers I currently own and have owned in the past have benefited sonically from better shielded, heavier gauge power cords with better connectors.
Some Quantitative Results
The 60 Hz track of the "Autosound 2000 Low Frequency Test CD" was used to feed a 60 Hz signal to my Parasound Halo JC 1 monoblock amplifiers. A Tektronix TDS 2012 oscilloscope was connected to the left amplifier outputs and sine wave and FFT (Fast Fourier Transform) plots were obtained. Each vertical dot on the FFT plots represents 2 dB of signal magnitude. Each horizontal dot represents 10 Hertz of frequency.
Oscilloscope readings were first taken at the left amplifier's output with the stock 14 gauge power cord attached. Next, oscilloscope readings were taken at the amplifier's output stock power cord replaced with a PS Audio xStream Statement SC power cord.
First, let us look at spectral plots of the power signals coming from the wall, the stock power cable, and the Statement SC power cable.
Figure 1. Sine wave plot of the power coming from the left new dedicated 20A outlet.
Figure 2. FFT plot of the power coming from the left new dedicated 20A outlet.
The dedicated power circuit is wired with Romex Simpull E18679 12 AWG wire. It is terminated with a PS Audio Power Port duplex receptacle.
Figure 3. Sine wave plot of the power coming from the stock JC 1 amplifier power cord.
Figure 4. FFT plot of the power coming from the stock JC 1 amplifier power cord.
The sine wave plots of the power coming from the wall and from the stock power cord (figures 1 and 3) look nearly identical with identical voltage levels. However, when we look at the frequency domain (FFT) plots, the gremlins are revealed. Comparing figures 2 and 4, we see a substantial increase in noise around the fundamental 60 Hz frequency and the 3rd, 5th, and 7th harmonics.
Figure 5. Sine wave plot of the power coming from the PS Audio xStream Statement SC amplifier power cord.
Figure 6. FFT plot of the power coming from the PS Audio xStream Statement SC
amplifier power cord.
The sine wave plots of the power coming from the wall socket, stock amplifier power cord, and Statement SC amplifier power cord all look virtually identical. When we look at the FFT plots, we see some differences. Compare the FFT plot of the power coming from the Statement SC power cord (figure 6) to the FFT plot of the power coming from the stock power cord (figure 4). Remember, everything except for that big 60 Hz spike on the left is NOISE.
Now, compare the FFT plot of the power coming from the Statement SC power cord (figure 6) to the FFT plot of the power coming from the wall (figure 2). The power coming from the Statement SC cord has less noise density at 60 Hz than the power coming from the wall.
Between the signals shown in figures 4 and 6, which would you prefer to send to your power amplifier? Some would say it does not matter. According to the conventional "wisdom", the higher noise content of the stock amplifier power cord does not matter because the amplifier's power supply filters with take care of it the way that Master Windu "took care" of Jango Fett.
Measurements Of Noise At The Power Amplifier Outputs
As stated previously, a test CD was used to input a 60 Hz signal to the power amplifiers. The signal path was as follows:
Cary Audio CD 306 SACD Pro SACD player --> Audioquest Sky XLR 1.5m Interconnects --> Pass Laboratories X0.2 Preamp --> Audioquest Sky XLR 1.0m Interconnects --> Parasound Halo JC 1 Power Amplifiers --> Tektronix TDS 2012 Oscilloscope (Left Channel)/Polk Audio SDA SRS (Stereo Dimensional Array Signature Reference System) 1.2TL loudspeaker (Right Channel). The left speaker cables were disconnected from the amplifier.
Figure 7. Sine wave plot of output from JC 1 amplifier with stock power cord.
Figure 8. FFT plot of output from JC 1 amplifier with stock power cord.
Figure 9. Sine wave plot of output from JC 1 amplifier with Statement SC power cord.
Figure 10. FFT plot of output from JC 1 amplifier with Statement SC power cord.
The sine wave plots of the 60 Hz signal taken at the left amplifier's outputs are virtually identical for the stock power cord and the Statement SC power cord (figures 7 and 9). I imagine that some audio enthusiasts would take these plots and go somersaulting down the yellow brick road while screaming "see, we told you cables didn't make a difference". However, before we go traipsing down those bricks, we should take a moment to look at the frequency domain plots. There may be some gremlins that did not show up in the time domain plots.
The spectral plots for the amplifier outputs with the stock and Statement power cords are shown in figures 8 and 10. Both plots look very good and provide evidence that the JC 1 does an excellent job of cleaning the power signal. The main difference between the FFT plots is that there is a bit less noise congestion around 60 Hz. If you copy both figures to your imaging software and flip between them or if you print them out and compare them, you will also notice a little less noise congestion throughout the frequency range.
Perhaps the stock power cord would suffice if the amplifier's outputs could send their signals to the loudspeakers without an intervening medium. Unfortunately, the signal has yet another gauntlet to run: the trip through the speaker cables.
Measurements Of Noise At The Loudspeaker Inputs
The left speaker cable was reconnected to the amplifier and the 60 Hz tone was feed to both speakers. The oscilloscope was connected to the inputs of the left speaker. Sine wave and FFT plots were obtained, first with the stock power cord attached and then with the Statement SC power cord attached.
Figure 11. Sine wave plot at input of left speaker with stock power cord.
Figure 12. FFT plot at input of left speaker with stock power cord.
Figure 13. Sine wave plot at input of left speaker with Statement SC power cord.
Figure 14. FFT plot at input of left speaker with Statement SC power cord.
Do we even need to discuss figures 11 and 13? Can we just go directly to figures 12 and 14? Thanks.
If you copy figures 12 and 14 and flip between them, you will see an increase in the noise density throughout the frequency range. You will also see an average 4 dB increase in noise magnitude. That means over twice as much noise power was being dumped into my extensively modified and esteemed SDA SRS 1.2TL speakers with the stock power cord than with the Statement SC power cord. Such a increase in noise power obscures a lot of musical and imaging detail. Bear in mind that the Audioquest Everest speaker cables are a very low noise design. In the future, I will look at the noise figures for some of my other speaker cables. However, I am not quite brave enough for that at this time.
Another thing to consider is that all speaker cables have noise in the conductors. The noise in the signal can interact with the noise in the cable and rob the signal of musical detail and imaging. It is evident that minimizing the noise entering an amplifier's power supply minimizes the noise that is output at the amplifier's output. Subsequently, less noise is available to interact with the speaker cable's noise and less cumulative noise is available to be dumped into the speaker terminals...and our ears.