[quote user="professorhat"]Been very quiet on this front now for a while... I'll admit, I was a little sarcastic on my earlier responses, but I am genuinely interested in hearing the scientific basis on why upgraded power cables can't make a difference.[/quote]
I have this feeling that there are a lot of people out there itching to respond to whatever answer is posted to this question. I already know that the general gist will be that science cannot explain everything. The human ear is complex etc. People will waffle on about skin effects, cross talk and lots of other stuff they know little about. There will also be the stock answers along the lines of "well I tried it and it worked - so did my mate, and I don't care what you say etc". The editorial team will no doubt say something along the lines of "why not just try it - you can always get your money back if it doesn't work" etc.
So, I am very tempted not to bother because I think it is a lost cause. However, you did say that you were genuinely interested and whilst your post specifically mentioned power cables only, the following addresses the issue of cables and conditioners.
Please also note that I would always advocate the use of some sort of protection against surges and spikes which can damage equipment.
Please also not that nobody claims that power cables and conditioners can make NO difference, it is just that any differences are almost immeasurable and are so small as to be indectable to the human ear.
I should also add that the following text is not mine. I have copied it from another source but as it is in the public domain, I'm sure the author won't mind if it is reproduced here. So here goes....
This is a fascinating issue! Both from a purely technical point of view, and as a commercial and psychological phenomenon.
If we break the technical aspect down a bit just to find out how much of improvement we could expect from changing power cord, or connecting a mains conditioner:
The regular mains voltage is (should be) a 50 Hz sinus, without overtones. The 50 Hz tone itself should be considered pure hum, since it has to be rectified and filtered to stop it from entering the signal path, within every device using it as a power supply.
Using an average amplifier in this example we would get something like this:
230 volts of alternating voltage feeds into the power supply. This voltage is rectified, and fed into the capacitor reservoir resulting in a typical 100 Hz ripple of below 0.1-0.5 volts superimposed onto the DC supply voltage that feeds the amplifier itself.
At full load, this ripple increases as the capacitors drain more quickly between 100 Hz cycles, typical value would be somewhere around 2-3 volts depending on the size of the capacitance used.
The amplifier itself uses open loop/closed loop gain. The open loop gain is the total amount of amplification without negative feedback implemented. Many manufacturers maximize this value and end up in the region of 100 000 times, where it is limited to avoid problems with oscillation etc. The closed loop gain determines the sensitivity of the amp. Normally, an amplification of about 40 dB is used (100 times).
The ratio between open loop/closed loop gain determines the dampening coefficient, or the factor which supply interference is reduced.
Most amps have dampening factors exceeding 100 times.
In our example, the (open loop gain/closed loop gain) comes to 1000, thus reducing supply noise with a factor 1000.
If there is 0.1 volts of supply hum when the amp is adling, the remaining output to the speakers will be about 0.1/1000= 0.0001 volts, or 0.1 mV which is not audible.
At full load, the hum voltage increases to letïs say 3 volts, resulting in an output hum level of 3/1000=3 mV, which could be audible when there is no sound, but not when the amplifier is putting out full power.
To put things in perspective, the full 230 volts of pure hum results in a few millivolts of hardly audible hum fed into the speakers. That gives us a total dampening factor of 230/0.003= 76666 times, worst case (full load)
This is how many times any incoming interefence will be reduce by before entering the speakers.
Now, if we measure the contents of other interference that may exist in the mains power, they are fractional compared to the full 230 volts. Letïs say we have a overtone at 200 Hz, at a level of 3 volts in the mains grid. This is probably not even possible, but we can use it to calculate the result.
3 volts, divided by our total dampening factor of 76000 comes to 0.0000391 volts of interference output into the speakers, almost garantueed not to be audible in a normal speaker, at least not compared to the 50-60 volts put out by the amp at the same time.
Now the interesting part arrives:
Letïs say a good mains conditioner can reduce the 3 volts of interference by a factor 10, the remaining amount is 0.3 volts. This amount reduced by the same dampening factor as above comes to 0.00000391 volts of remaining interference voltage.
Summing up the components gives us:
60 volts of total musical voltage put out by the amplifier at full power, plus 0.0000391 volts of interference equals 60.0000391 volts. This is without the conditioner.
With the conditioner the numbers would be 60.00000391 volts, a difference of 0.00003519 volts, or 0.00003519/60=0.0000005865 = 0.00005865 percent! And this is at full amplifier load.....
My personal conclusion, the aspect of filtering the mains is purely a commercial and psychological issue. Speaker cables and signal cables are placed in the direct signal path. Their influence of the sound is well known, but power cords and mains conditioners are not placed in a direct signal path, but rather subjects to the following equipments many ways of reducing noise. The effect of these devices are reduced by the same factor, in our example 76666 times.
Replacing a carpet, washing the ears or having a drink will probably make a much bigger difference.
..... did i leave anthing out?
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