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Effects of power cords  

post #1 of 56
Thread Starter 

I'm just shocked to hear the difference that a power cord can make. I normally use the WyWires Juice II (Blue series) which is just a modest cord, but I noticed significant improvements in dynamics and transient snap. Then I got to borrow a WyWires Gold power cord and the improvement was so far beyond what I expected from a power cord... like a component upgrade really. Just better dynamics and transients, bass slam, that kind of thing. More purity in the highs. 

 

I'm wonder what folks here have noticed in terms of effects of power cords. How much would you spend on one, and do you consider it a good value?

 

Mark

post #2 of 56
Quote:
Originally Posted by markheadphonium View Post

I'm wonder what folks here have noticed in terms of effects of power cords. How much would you spend on one, and do you consider it a good value?

-I use a professional-quality, heavy-duty cord rated at 240V/16A. At the equivalent of US$12, I consider it excellent value. It reliably feeds power to my amp without a hitch.

Whatever grid-borne noise there is, I leave to the EMC-filter in the amp and the PSU following it to sort out. So far (~15 years), it appears to be a fully transparent solution.

-OddE
post #3 of 56

Hi,

 

I'll try to elaborate a little, as I see now that while trying to be brief (I was typing it out on my phone), I think I probably succeeded better at coming across as somewhat arrogant than to explain my reasoning - which was not my intent at all.

 

So - if a power cord is sufficiently dimensioned to handle the maximum current drawn by the device powered by it, it is good.

 

In the case of Norwegian rules, 16A mandates 2.5 square millimeters (Approx. AWG13) in permanent installations. This cross section is deemed sufficient to conduct 16A continously without leading to excessive heating of the conductors.

 

Power cords would normally be somewhat less generously dimensioned, as they are not required to carry the rated current (16A in this case) contionusly - so the cord feeding my power amp (rated at 2*55W into 8ohms) is 3*1,5sqmm (AWG15.5). This would translate into an ohmic resistance of some .02ohms or so for 1.5m/5ft of cord - in turn causing a voltage drop of some 1/3 of a volt or so when the cord is run flat out (16A) as compared to the no-load voltage.

 

This voltage fluctuation should pose no problem at all to a power supply.

 

(Not that the amp is capable of drawing more than a fraction of this current - but anyway, the cord is sufficiently dimensioned.)

 

I don't know the capacitance of the wire, but at 50Hz it is a safe bet that the contributed reactance is negligible.

 

Those two factors aside - voltage drop because of inadequately sized wiring/heat generation because of cord impedance - I really cannot see any other challenges for a power cord.

 

If loads of (electrical) noise is piggybacking on the desired mains supply, it is easily handled by the power supply; if not, a mains filter might be advisable; if I were to buy one, I suspect going to a reputable dealer like RS Components, Farnell or similar would provide better bang/buck than a hi-fi dealer.

 

Anyway - if I were to determine whether I needed any kind of power conditioner/mains filter, it would be most useful to look at the DC output from the amp's power supply; if there are no noise transients present, any noise on the AC side probably wouldn't affect the sound. This is what power supplies do.

 

So, to wrap it up - I am quite convinced that if swapping power cords causes audible effects, further investigation will show that one of the cords (at least) were not up to code.

 

-Odd Erling

post #4 of 56
Thread Starter 

Thanks for clarifying. I hear significant improvements going from stock (well-built) cords to aftermarket (well-built) cords. Why the power cord makes such a difference to things like transient handling is a mystery to me. The only thing I can think is that if you have a power conditioner, you want a shielded cord to keep the power pure. But better PCs do their thing with various degrees of power conditioning or complete lack of power conditioning. 

 

I notice things like better microdynamic shading.

post #5 of 56

In my experience its not what you can hear, its what you cant.  I always make my own cables with Belden 19364 as its foil shielded and dramatically cut out any mains interference from the cable to nearby equipment or interconnects.  Especially true around valve amps where you have chokes that are super sensitive to emi.

post #6 of 56
Fascinating Fact: The power cord (as well as the power transformer for that matter) is not even in the power supply circuit the vast majority of the time. Which makes it all the more amazing that it should have such a profound effect.

se
Edited by Steve Eddy - 4/22/14 at 8:17am
post #7 of 56
Thread Starter 
Quote:
Originally Posted by Steve Eddy View Post

Fascinating Fact: The power cord (as well as the power transformer for that matter) is not even in the power supply circuit the vast majority of the time. Which makes it all the more amazing that it should have such a profound effect.

se

Can you clarify in what sense the power transformer is not in the "power supply circuit"? What other circuit could it be in?

post #8 of 56
Quote:
Originally Posted by markheadphonium View Post

Can you clarify in what sense the power transformer is not in the "power supply circuit"? What other circuit could it be in?

It's not in the power supply circuit in the sense that it's not providing any power to the power supply. It has to do with how linear power supplies work.

A linear power supply starts with a power transformer. Its primary is connected to tha AC mains. It's secondary is connected to the rectifier diodes, which only allow current to flow in one direction an thus converts AC into pulsed DC. This pulsed DC is used to charge up the power supply's reservoir capacitors. As the capacitors charge, the voltage across them increases up to the maximum power supply voltage.

And here's the salient point. The rectifier diodes don't turn on until the voltage at the transformer's secondary is about 0.7 volts higher than the voltage across the capacitors. So if you have a power supply such as this and there's no load after the capacitors to draw current from them and hence reduce the voltage across them, the rectifier diodes would never turn back on. With the rectifier diodes turned off (fundamentally no different than if you'd flipped a switch), then the power transformer and everything upstream of it is effectively out of the circuit.

Of course in a real world power supply, there will be a load drawing current from the capacitors which will result in the voltage across them dropping, until such time as the voltage across them is at least 0.7 volts lower than the voltage across the transformer's secondary at which point the rectifier diodes will turn on and current will flow from the transformer into the capacitors to recharge them.

But because the AC mains operates at 50 or 60 Hz, and because you don't want the voltage across the capacitors to drop too much before they're recharged, there will only be a small window of time when the voltage across the transformer's secondary is 0.7 volts or greater than the voltage across the capacitors. This can be as little as a few milliseconds, once every 1/60th or 1/120th of a second depending on whether you're using half wave rectification or full wave rectification (assuming 60 Hz AC mains). So the vast majority of the time, the diodes are switched off and the power transformer and everything upstream are effectively out of the circuit.

Which is why I find it so amazing that power cords are supposedly able to have all these effects on the sound, as if it's assumed that it is always in the circuit working continuously like an interconnect or loudspeaker cable.

se
post #9 of 56
Thread Starter 

By that same reasoning power conditioning couldn't help anything either. I find you don't have to spend a lot on power conditioning to get obvious effects, while power cords are a little more finicky.

post #10 of 56

I do use mains filters as they can cleanup the noise floor a bit, especially if your hearing clicks/pops or interference from other devices.  Having said that i have no idea how they make a damn bit of difference to anything that is converting AC to DC.  /shrugs shoulders

post #11 of 56
Quote:
Originally Posted by markheadphonium View Post

By that same reasoning power conditioning couldn't help anything either.

Power conditioning can help remove noise that can get into a component's grounding system. Different issue from what I was talking about.

se
post #12 of 56
Quote:
Originally Posted by Steve Eddy View Post


It's not in the power supply circuit in the sense that it's not providing any power to the power supply. It has to do with how linear power supplies work.

A linear power supply starts with a power transformer. Its primary is connected to tha AC mains. It's secondary is connected to the rectifier diodes, which only allow current to flow in one direction an thus converts AC into pulsed DC. This pulsed DC is used to charge up the power supply's reservoir capacitors. As the capacitors charge, the voltage across them increases up to the maximum power supply voltage.

And here's the salient point. The rectifier diodes don't turn on until the voltage at the transformer's secondary is about 0.7 volts higher than the voltage across the capacitors. So if you have a power supply such as this and there's no load after the capacitors to draw current from them and hence reduce the voltage across them, the rectifier diodes would never turn back on. With the rectifier diodes turned off (fundamentally no different than if you'd flipped a switch), then the power transformer and everything upstream of it is effectively out of the circuit.

Of course in a real world power supply, there will be a load drawing current from the capacitors which will result in the voltage across them dropping, until such time as the voltage across them is at least 0.7 volts lower than the voltage across the transformer's secondary at which point the rectifier diodes will turn on and current will flow from the transformer into the capacitors to recharge them.

But because the AC mains operates at 50 or 60 Hz, and because you don't want the voltage across the capacitors to drop too much before they're recharged, there will only be a small window of time when the voltage across the transformer's secondary is 0.7 volts or greater than the voltage across the capacitors. This can be as little as a few milliseconds, once every 1/60th or 1/120th of a second depending on whether you're using half wave rectification or full wave rectification (assuming 60 Hz AC mains). So the vast majority of the time, the diodes are switched off and the power transformer and everything upstream are effectively out of the circuit.

Which is why I find it so amazing that power cords are supposedly able to have all these effects on the sound, as if it's assumed that it is always in the circuit working continuously like an interconnect or loudspeaker cable.

se

 

Time to open up my amps and upgrade that cabling from the capacitors to gold wire then. :D

post #13 of 56
Quote:
Originally Posted by elmoe View Post

Time to open up my amps and upgrade that cabling from the capacitors to gold wire then. biggrin.gif

tongue.gif

se
post #14 of 56
Quote:
Originally Posted by Steve Eddy View Post

Which is why I find it so amazing that power cords are supposedly able to have all these effects on the sound, as if it's assumed that it is always in the circuit working continuously like an interconnect or loudspeaker cable.

 

Actually, in the case of two interconnected hifi devices with 3 wires power cables (and not using ground loop breakers), the earth wire is most probably the audio return for an important part of the signal and is thus continuously in the signal path.

 

If you believe in interconnects, which btw I don't, it's quite logical to believe in power cables.

post #15 of 56
Quote:
Originally Posted by 00940 View Post

Actually, in the case of two interconnected hifi devices with 3 wires power cables (and not using ground loop breakers), the earth wire is most probably the audio return for an important part of the signal and is thus continuously in the signal path.

Yes, but it's not the mains return path. The mains return path is the hot and neutral wires in the power cord.

se
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