Well this is the thing that I've always thought. No one listens to sine waves, we listen to music peaks and if anyone does happen to listen, routinely, to levels that would make the power cord matter I think their ears would be well beyond caring about power cords.
Of course in some of the systems that simon7k has worked on, the power cables, I am sure, could be very important.
I am however not one to just 'bash' the idea of cables without actually testing it first. The most powerful amp I've got will kick out around 550-580 watts into the 2.35 ohm test load I've got. This should be plenty to measure any appreciable drop due to the power cable. When I get around to doing this I will try putting an extension cord or two in the power supply line and see if it makes much of a difference.
The cap starts charging when the transformer voltage is above that stored on the capacitor and quits when the capacitor is charged to the peak voltage. Resistance does not delay when the AC line reaches it's peak. What does happen is that the inductance and reduced load in the transformer allows the peak voltage to continue to rise even after the AC line has peaked. But you still don't get more voltage into the capacitor bank.
It is easy to calculate when the transformer voltage rises above the voltage on the capacitors. If you have 63 volt peak on your capacitor bank and 5 volts of ripple this occurs at arcsin (58/63)=67 degrees it should quit at 90 degrees as that is the peak AC line voltage. Slowing the charge just due to line resistance would mean it finishes charging after the peak. However the peak out of the transformer will rise a bit as the current draw drops.
Many amplifier designers design for a maximum ripple of 1 volt, that would give them even less charging time and higher surge currents.
As has been discussed circuit theory lumps all of the transformer losses in as a single R, that is an oversimplification.
Even with a ticket for the clue train, some folks can't find the station.
Then you have a small but still measurable loss. There are ways to design power supplies so they are friendlier to the power company and the output power is not affected very much by the AC line.
One of the first amplifier manufacturers to build such a beast had to change their power cord to gain acceptance into the pro market. Folks looked at the flimsy 16 gauge power cord and based on their experience from then current power amplifiers wouldn't use them. So the manufacturer put on a much thicker power cord. That allowed them to sell to pro's even though it did not change the peak power output!
Most good amps have built in overhead to allow for input line voltage variation, for example a commercial 200W amp on my bench runs on nominal 82 VDC rails at 120 VAC in.. Is somebody going to run it into a test load with sine waves into clipping all day, no the amp will probably burn up long before the AC voltage sags to stop it from delivering excess power.
BTW most sag come from the XFMR even though its safely sized for continuous use at the rated power, much more than the15A circuit wiring. Yes if you use high power amps with poor PF on a full power continuous basis, expect some extra voltage drop at the input. Who cares, I doubt this is going to affect SQ for normal home speaker duty? heck you probably cannot run any contemporary multichannel AV equip at all 5 channels for rated power either, the internals would burn up. it's not the nature of beast ie listening to music or video. What's all this got to with a measly 3 ft long power cord, who cares about the power cord!
BTW most sag come from the XFMR even though its safely sized for continuous use at the rated power, much more than the15A circuit wiring. Yes if you use high power amps with poor PF on a full power continuous basis, expect some extra voltage drop at the input. Who cares, I doubt this is going to affect SQ for normal home speaker duty? heck you probably cannot run any contemporary multichannel AV equip at all 5 channels for rated power either, the internals would burn up. it's not the nature of beast ie listening to music or video. What's all this got to with a measly 3 ft long power cord, who cares about the power cord!
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Almost correct the loss does scale down. But if you are listening to music from a CD then you have at least 20 db of headroom. (Unless you crank it up until everything is distorted.) So your potential loss is trivial.
Just for fun look at the resistance of the unit,s fuse in use, another .05 to .1 ohms!
The issue was do power cords have an effect, the answer is depends on how you use them. They can,and the math is not to difficult, but for most users the voltage drop is not an issue. There are many other causes of reduction in fidelity that can be addressed first.
There is no electronic theory explanation is there?
Was the original question. The answer is there are reasons, RFI and voltage loss. RFI is the bigger issue as there are more switching supplies in use there will be more noise. A power cord may be designed to filter out this noise without introducing extra resistance the way a choke would. (Ferrite beads don't really have enough loss by themselves.) The voltage loss in a power cord is larger than most folks expect and in high power or high end systems may be an issue.
In a home theater both issues probably don't matter. Yes if you really tried to play your home theater system full volume it would fail. The FTC has relaxed the rules for how power amplifiers must perform.
if I detected an issue with SQ the fix probably would not revolve around a redesigned power cord.
isn´t better to buy a UPS instead of spending money on expensive cables ? UPS stabilizes the 110v or 220v , removes humm noises etc ?
http://www.apc.com/products/family/index.cfm?id=165
http://www.apc.com/products/family/index.cfm?id=165
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no that's a common misconception. A UPS is a backup power system, using inverters of variable quality. Normally it's a pass through switch, until it detects a brownout or blackout, then the battery operated inverter is switched over for an hour or less depending on loads and battery VAs. Ferro-resonant XFMRs are used for poorly regulated or varying line voltages, but they tend to distort the sinewave too. Line conditioners (power filters) are useful for cleaning up noise over specific parts of the spectrum.
cheap UPS can have extremely bad conducted EMI
the real deal is a motor-generator - Motor-generator - Wikipedia, the free encyclopedia
then power the motor-generator from batteries
the real deal is a motor-generator - Motor-generator - Wikipedia, the free encyclopedia
then power the motor-generator from batteries
I remember a long time ago a friend brought in a $300 power cord in my system for a test. We did not hear any improvement at all but an obvious degrade to sound. That was the only time I ever tested a power cord. So we did hear a difference. Whether it was a result of psychological effect or not, I don't know. The fact is that I have been using power cords I bought for $2.
Anyway, I guess power cord RCL would be so small to the power supply that we can safely ignore them.
If I would think of a reason why power cords could make a difference in sound, I would be more interested in investigating GROUND resistance and/or GROUND loop return, more than anything else. I don't think the small RCL on the power wires would have much effect on sound, but any two active components are connected to each other by interconnect shield and by earth (ground) return. Here, a lower ground return resistance could translate to lower distortion, if the interconnection between the two systems is inadequate. So I think power cords could make a difference in sound under some circumstantces.
Regards,
Bill
Anyway, I guess power cord RCL would be so small to the power supply that we can safely ignore them.
If I would think of a reason why power cords could make a difference in sound, I would be more interested in investigating GROUND resistance and/or GROUND loop return, more than anything else. I don't think the small RCL on the power wires would have much effect on sound, but any two active components are connected to each other by interconnect shield and by earth (ground) return. Here, a lower ground return resistance could translate to lower distortion, if the interconnection between the two systems is inadequate. So I think power cords could make a difference in sound under some circumstantces.
Regards,
Bill
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Signal goes from source (e.g. preamp) to target (e.g. power amp). A signal must have a current return. Where does the current return? It returns via the ground.
The ground return can go via two paths. First is the interconnect shield. Second is the earth wire via the power cord.
Any resistance in the ground return path introduces a voltage. This voltage is distortion to the orginal signal.
This is basically ohms law, nothing mysterious.
So if the system interconnection is inadequate, a power cord with thick earth wire will provide a lower resistance ground path. This can reduce distortion.
In addition, if the two system components do not have the same ground potential, which is the cause of GROUP LOOP hum, a thicker earth wire would reduce that potential.
On the other hand, I have designed my own system that does not depend on the earth ground return, and I am happily living with my $2 power cords.
Regards,
Bill
The ground return can go via two paths. First is the interconnect shield. Second is the earth wire via the power cord.
Any resistance in the ground return path introduces a voltage. This voltage is distortion to the orginal signal.
This is basically ohms law, nothing mysterious.
So if the system interconnection is inadequate, a power cord with thick earth wire will provide a lower resistance ground path. This can reduce distortion.
In addition, if the two system components do not have the same ground potential, which is the cause of GROUP LOOP hum, a thicker earth wire would reduce that potential.
On the other hand, I have designed my own system that does not depend on the earth ground return, and I am happily living with my $2 power cords.
Regards,
Bill
The frequency range in Audio can cause the returns to use two different paths, frequency dependant, low frequency return will be biased towards the low resistive path, that cna be via the gorund connections of the power cords, the higher frequencys will be biased towards the least inductive path so will use the return path of the interconnect.
Yes, but these two paths are both low resistance relatively low inductance paths and both linear (contact problems aside). No mechanism for inducing distortion. Hum loops maybe.
'High quality' (i.e. ridiculously expensive) mains leads might sound worse if they force signal return current to go through a poor contact on the earth socket, or if they shorten and make more spiky the PSU charging pulses. There is therefore a case for using the cheapest safe mains lead you can find.
'High quality' (i.e. ridiculously expensive) mains leads might sound worse if they force signal return current to go through a poor contact on the earth socket, or if they shorten and make more spiky the PSU charging pulses. There is therefore a case for using the cheapest safe mains lead you can find.
Reviewers have a vested interest in claiming that everything makes a difference, and that the difference is a large and important one. This is how they make their living. As long as a big enough fraction of the public trust reviewers' opinions, their business and financial well-being is safe.
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