[nick_charles]

Wow, the distortion may even be audible!

 
 
If you thought that was bad.....
 

 

THD+noise was ridiculously high at 25.4%. This was for the left channel; the right channel was somewhat better, at 21%. Even so, the xxxxxxxxxxxxx seems incapable of reproducing high-level low frequencies without introducing high levels of distortion 

 

[arnyk]

   
 
If you thought that was bad.....
 

 

 
IME a typical power line has about 3-5% THD. The above seems to be pretty substandard compared to a typical home wall plug.
 
Unless you  know what you are doing, don't try to measure the THD of your power line as it takes special equipment (high voltage measuring interface/probe) and training/epxerience to do this safely.

 

[nick_charles]

   
IME a typical power line has about 3-5% THD. The above seems to be pretty substandard compared to a typical home wall plug.
 
Unless you  know what you are doing, don't try to measure the THD of your power line as it takes special equipment (high voltage measuring interface/probe) and training/epxerience to do this safely.

 
 
The graph shows the harmonic distortion from a 50 Hz tone for a rather expensive DAC as measured by Stereophile

 

[arnyk]

   
 
The graph shows the harmonic distortion from a 50 Hz tone for a rather expensive DAC as measured by Stereophile

 
 
One might conclude that it is targeted at non-discriminating consumers.

 

[Speedskater]

IME a typical power line has about 3-5% THD. The above seems to be pretty substandard compared to a typical home wall plug. Unless you  know what you are doing, don't try to measure the THD of your power line as it takes special equipment (high voltage measuring interface/probe) and training/experience to do this safely.

If you meet the above requirements, try measuring the THD of the current waveform to a power amplifier. It may be 175 to 200 percent THD.

 

[arnyk]

  If you meet the above requirements, try measuring the THD of the current waveform to a power amplifier. It may be 175 to 200 percent THD.

 
..and that is probably on a good day.
 
The situation arises because the power amp circuits often need high current at high voltage, which implies drawing most of the energy from the power line on the peaks of the 60 Hz wave.
 
The real world impinges rather strongly on the idea that scrupulously clean power is required for good sound quality. It crushes it!

 

[cjl]

   
..and that is probably on a good day.
 
The situation arises because the power amp circuits often need high current at high voltage, which implies drawing most of the energy from the power line on the peaks of the 60 Hz wave.

This also has to do with efficiency - pulling power only at the peaks increases the efficiency of the power supply, but it also has the interesting effect of squaring off the peaks of the voltage waveform and causing some interesting distortion on the rising edge (since so many devices are powered by SMPS these days)
.

 

[KeithEmo]

There's a lot of good information here already, but it seems to be rather disorganized, so I'm going to try to sort it out a bit.
 
All audio equipment INTERNALLY runs on DC power (there are VERY few exceptions to this, and they are real oddball devices). With battery operated equipment, the voltages that power the actual audio circuitry may come directly from the battery, or they may be changed to a higher or lower voltage using a regulator or level shifter of some sort. With equipment that "plugs into the wall", the AC wall current is converted to DC by the equipment's power supply. This power supply could be entirely outside the equipment itself (like most "12V switchers" and "DC wall warts"), or it could be entirely inside the equipment, or it could even be divided between the two (lots of equipment uses an "AC wall wart", coupled with rectifiers and regulators inside the equipment). In all of these cases, the power supply converts the AC wall power into DC current to operate the audio circuitry. Therefore, since the original AC waveform is "destroyed" in the process, the original AC waveform should have very little effect on the audio.
 
If the waveform of the AC power coming in is distorted, that could result in noise making its way to the audio circuitry; and, if the waveform is distorted badly enough, it could limit the amount of power that the power supply can derive from it; however, these are all situations that should not occur, and that a well designed power supply should compensate for or otherwise prevent from occurring. A regulated power supply, such as the ones used in virtually all small signal audio equipment (like DACs and preamps) should totally remove the line frequency itself, and should also totally ignore voltage fluctuations and distorted line waveforms. Because power amplifiers use large amounts of power, it is often impractical to use regulated power supplies for them, and so they may be somewhat sensitive to the condition of the incoming AC power (for example, if the AC power waveform is clipped, it may limit the amplifier's power because it limits the rail voltage slightly). Especially unusual power requirements may require specific alterations in power supply design to accommodate them, however, there should still be no direct relationship between this and how they sound beyond that.....
 
For example, if your AC power were 400 Hz instead of 60 Hz, the higher power frequency would allow you to achieve a specific level of performance using a smaller transformer and smaller filter capacitors, but you might need better filtering in other areas of the circuitry to prevent the line frequency from affecting them, and, because 400 Hz is more easily audible than 60 Hz, you would want to be more careful to prevent any annoying line-frequency noise from finding its way into the audio circuitry. Conversely, if you designed a power supply with enough filtering to work well with 400 Hz Ac power, it might be unable to work properly at 60 Hz because the parts that were adequate for 400 Hz operation weren't adequate at 60 Hz. However, assuming that "everything is working correctly", you shouldn't expect the audio you play through the audio circuitry connected to that power supply to sound different.
 
Because nothing is perfect, even though the power supplies in most equipment are designed to work under most conditions they're likely to encounter, there is still a huge market for devices that compensate for unusual situations. (For example, if your power lines happen to be noisier than usual, or their voltage varies more widely than is typical, or the power supply in a particular piece of equipment isn't as good at removing line noise as it should be, or is unusually sensitive to voltage fluctuations, then an external "power conditioner" that "fixes" the power coming in may well improve the performance of that piece of equipment under those conditions.)
 
The bottom line is that, assuming the power supply is "adequate to the job" and "well designed" you shouldn't expect the audio itself to sound any different because of the line frequency you're using, or even whether you're using a DC or AC primary power source. (Many devices, like some phono preamps, do in fact perform better when powered by a battery; however, that happens simply because "a decent battery" is in fact often in fact a better performing power supply in many ways than a badly designed AC-powered supply.)   

 

[Speedskater]

I just saw this from Ed Simon:

Quote: I'll say it again. Shielding the last three feet of 100s of feet of power line will reduce EMI into or out of your power cord less than 3% unless the noise source is within inches of your cord. So a filter is better. It filters the entire length of the power line.

The noise source is inside the amplifier! It is not line noise going into the power amplifier as much as it is amplifier power supply noise going back and into the other stages such as preamp and CD player.

A power line filter introduces extra loss. That is an issue with power amplifiers. Capacitance in the power cord adds no AC line loss.

Attached is a DC to 12 MHz. spectrum of power supply noise. The power source was a sinewave generator into a power supply. All of the noise comes from the linear power supply under test.

Also attached is the noise created just by a power transformer.

 

[arnyk]

 
If the waveform of the AC power coming in is distorted, that could result in noise making its way to the audio circuitry; and, if the waveform is distorted badly enough, it could limit the amount of power that the power supply can derive from it; however, these are all situations that should not occur, and that a well designed power supply should compensate for or otherwise prevent from occurring. A regulated power supply, such as the ones used in virtually all small signal audio equipment (like DACs and preamps) should totally remove the line frequency itself, and should also totally ignore voltage fluctuations and distorted line waveforms. Because power amplifiers use large amounts of power, it is often impractical to use regulated power supplies for them, and so they may be somewhat sensitive to the condition of the incoming AC power (for example, if the AC power waveform is clipped, it may limit the amplifier's power because it limits the rail voltage slightly). Especially unusual power requirements may require specific alterations in power supply design to accommodate them, however, there should still be no direct relationship between this and how they sound beyond that.....
 
Because nothing is perfect, even though the power supplies in most equipment are designed to work under most conditions they're likely to encounter, there is still a huge market for devices that compensate for unusual situations. (For example, if your power lines happen to be noisier than usual, or their voltage varies more widely than is typical, or the power supply in a particular piece of equipment isn't as good at removing line noise as it should be, or is unusually sensitive to voltage fluctuations, then an external "power conditioner" that "fixes" the power coming in may well improve the performance of that piece of equipment under those conditions.)
 
The bottom line is that, assuming the power supply is "adequate to the job" and "well designed" you shouldn't expect the audio itself to sound any different because of the line frequency you're using, or even whether you're using a DC or AC primary power source. (Many devices, like some phono preamps, do in fact perform better when powered by a battery; however, that happens simply because "a decent battery" is in fact often in fact a better performing power supply in many ways than a badly designed AC-powered supply.)   

 
"If the waveform of the AC power coming in is distorted, that could result in noise making its way to the audio circuitry;"  
 
Surely you jest or have missed the point of several past posts!
 
I can guarantee you that the waveform of the AC power coming in is distorted by audio standards. Surprisingly, the evidence shows that if you have some kind of power regenerator device, its probably even worse!  Every time I've measured it, it was. And  if the AC  power is distorted on the power cord, jump a few inches of circuitry into the gear, and now it is horrifically distorted.
 
"Because nothing is perfect, even though the power supplies in most equipment are designed to work under most conditions they're likely to encounter, there is still a huge market for devices that compensate for unusual situations."
 
IME 99+% of the time, the market in question is based on ignorance and being bullied by salesmen and other audiophiles.  

 

[KeithEmo]

   
"If the waveform of the AC power coming in is distorted, that could result in noise making its way to the audio circuitry;"  
 
Surely you jest or have missed the point of several past posts!
 
I can guarantee you that the waveform of the AC power coming in is distorted by audio standards. Surprisingly, the evidence shows that if you have some kind of power regenerator device, its probably even worse!  Every time I've measured it, it was. And  if the AC  power is distorted on the power cord, jump a few inches of circuitry into the gear, and now it is horrifically distorted.
 
"Because nothing is perfect, even though the power supplies in most equipment are designed to work under most conditions they're likely to encounter, there is still a huge market for devices that compensate for unusual situations."
 
IME 99+% of the time, the market in question is based on ignorance and being bullied by salesmen and other audiophiles.  

 
Actually, I don't think I missed any of the "points" - although I'll admit to not finding all of them credible

. I was instead trying to provide a technically accurate assessment of the overall situation (which readers could then apply to the various "points" on their own). Obviously I wasn't entirely successful... so let me summarize what I believe to be the technically relevant points more clearly.
 
1) Virtually all audio equipment runs internally on DC, and every piece of equipment that does so has a "power supply" that converts the local available AC line current into an appropriate set of DC voltages for that device to run on. That power supply is supposed to be designed such that it can accept whatever comes out of your wall outlet and convert it into DC power that is good enough to run the device properly. (It should not only deliver the appropriate voltages, and sufficient current, but it should also be designed such that it removes any noise likely to be present on "a typical AC outlet" to a sufficient degree that it doesn't affect the device.)
 
2) This means that, assuming an audio device is well designed, MOST users should not need (or benefit from) external power "conditioning" or regeneration.
 
2a) If your AC power (wall outlet) is "no worse than average", then you shouldn't need a power conditioner and, if adding one makes your equipment sound better, then it's because the power supply in that equipment is NOT well designed.
 
2b) Not all equipment is well designed, and some people have AC power that is noisier than usual, or whose voltage fluctuates more than usual. In those cases, it's quite possible that a line filter or regulator might help. (However, this is only true for the small percentage of people who actually do have atypical AC power coming from their outlets.)
 
3) Items 1) and 2) apply almost universally to small signal equipment like preamps, CD players, DACs, etc - which all have regulated power supplies. However, because power amps require large amounts of current, practicality often dictates that they are somewhat less "immune" to line noise and power fluctuations (mainly because, while virtually all small signal devices use regulated power supplies, most power amps do not). In the specific case of power amps, whose output power is usually determined/limited by their operating rail voltages, and whose rail voltages typically are not regulated, it is not uncommon for the maximum output power to be affected slightly by a really bad power waveform. (If the waveform is flattened or clipped, it will deliver a slightly lower peak voltage. This will, in turn, limit the maximum output power some amps can deliver by a few percent. However, in most cases, it won't do anything worse than that.)
 
I've never personally looked at the waveform delivered by any of the commercial "power regenerators" intended for audio equipment. However, when you talk about devices like "uninterruptible power supplies" that are designed for computer equipment, most of them deliver rather "rough" power waveforms - simply because it requires more effort to deliver a clean sine wave, and most computer equipment is VERY insensitive to the power waveform. (It wouldn't be at all surprising if the waveform put out but a typical computer UPS were bad enough that the power supply in a piece of audio equipment had trouble with it - because they're not intended to be used together. You will typically get much cleaner power from a wall outlet than from a computer UPS. (Many of the uber-expensive power regenerators specifically sold for audio use claim to deliver a clean waveform. If they don't, then you're simply wasting money...)
 
And, to specifically address one question/comment. Standard audio equipment is designed to run on whatever line voltage and frequency is available "locally" - which, for most equipment, is 50 Hz or 60 Hz. Therefore, the power supplies in such equipment are designed to work as designed at that power frequency. Assuming that the power supply is designed properly, there is no reason whatsoever to expect a different power frequency to work better. (And using a power frequency too far from the intended one could cause problems.)

 

[Speedskater]

Keith, your post #26 seems like a reasonable technical statement.  Sure a technical editor type person might want to change a word here or a sentence there, but this is a web post not an engineering paper.

 

[arnyk]

   
Actually, I don't think I missed any of the "points" - although I'll admit to not finding all of them credible

. I was instead trying to provide a technically accurate assessment of the overall situation (which readers could then apply to the various "points" on their own). Obviously I wasn't entirely successful... so let me summarize what I believe to be the technically relevant points more clearly.
 
1) Virtually all audio equipment runs internally on DC, and every piece of equipment that does so has a "power supply" that converts the local available AC line current into an appropriate set of DC voltages for that device to run on. That power supply is supposed to be designed such that it can accept whatever comes out of your wall outlet and convert it into DC power that is good enough to run the device properly. (It should not only deliver the appropriate voltages, and sufficient current, but it should also be designed such that it removes any noise likely to be present on "a typical AC outlet" to a sufficient degree that it doesn't affect the device.)
 
2) This means that, assuming an audio device is well designed, MOST users should not need (or benefit from) external power "conditioning" or regeneration.
 
2a) If your AC power (wall outlet) is "no worse than average", then you shouldn't need a power conditioner and, if adding one makes your equipment sound better, then it's because the power supply in that equipment is NOT well designed.
 
2b) Not all equipment is well designed, and some people have AC power that is noisier than usual, or whose voltage fluctuates more than usual. In those cases, it's quite possible that a line filter or regulator might help. (However, this is only true for the small percentage of people who actually do have atypical AC power coming from their outlets.

 
Well-designed audio gear is made to work with power that is much worse than average.
 
For example, the average  standard AC outlet in the US has 120 volts AC with a nominal load, but your typical piece of audio gear will operate normally when the line voltage is 100 volts or less.
 
That's a lot of latitude for bad power!

 

[KeithEmo]

   
Well-designed audio gear is made to work with power that is much worse than average.
 
For example, the average  standard AC outlet in the US has 120 volts AC with a nominal load, but your typical piece of audio gear will operate normally when the line voltage is 100 volts or less.
 
That's a lot of latitude for bad power!

 
Agreed.
 
Perhaps it would be more accurate to state that: "When designing any type of electronic gear, a good designer will design it to operate properly in the vast majority of conditions that it is likely to encounter in actual use." (And "bad power" is pretty much the norm in many places.)