Why do designers/manufacturers...?

Scvan, sure. How a power supply works is you have the transformer, rectifiers and filter caps. When the amp is running, it discharges the filter caps slightly between each peak of the AC power waveform. The rectifiers only conduct when the filter cap voltage is lower than that of the power transformer. What this means is that current will only flow at the peak of the incoming AC waveform.

That current spike can have some pretty steep risetimes, in order to charge the filter cap properly. A steep risetime corresponds to a high frequency. If the power cord limits the risetime at that frequency, the power supply will not charge up properly.

You can see this in an amplifier by running it at power and then substituting power cords. You can often see a difference in the power supply voltage, even though at the input of the amp the line voltage is unchanged. This is why some power cords can have an audible effect- and its also measurable. Anytime you can hear it and measure it you can also regard it as real.

Now this says nothing about the cost of the cord. It does not have to be expensive; it simply has to work.

why is it " illegal to use solid core wire in an AC power cord"? Is there a fire/heat hazard? Does that mean only that a pc must have multiple strands of wire? What exactly is "solid core wire?" Isn't all wire "solid" in a sense?

I have always wondered about all that stuff - wall socket, plug, wire, another plug, amp input socket - between the romex in the wall and the amp. Is there no way around the fire code?

Romex is solid core. If you flex it enough, it will break.

A legal power cord will be multi-stranded which means it can flex without breaking.

why is it " illegal to use solid core wire in an AC power cord"? Is there a fire/heat hazard? Does that mean only that a pc must have multiple strands of wire? What exactly is "solid core wire?" Isn't all wire "solid" in a sense?

I have always wondered about all that stuff - wall socket, plug, wire, another plug, amp input socket - between the romex in the wall and the amp. Is there no way around the fire code?
11-20-14: Lloydc

NM, (Romex is a trade name of), sheathed cable is designed by the manufactured and safety tested for its intended use by UL and CSA to be installed fixed in place. It is not intended to be used where it could be exposed to physical damage. In the US NEC Code outlines where NM cable can be used, and not used, as well as the approved wiring method used. Local electrical inspections departments have the final say where it can be used in their jurisdiction. It cannot be used as a power cord.

A stranded wire conductor is made up of several individual uninsulated bare strands of wire grouped together and then covered by an insulating material to form one larger conductor. Typical extension cords are made up of fine strand wire conductors for flexibility. Fine strand wire conductors will withstand more frequent bending at the termination ends of the male plug and female receptacle end than a solid core wire like #14 or #2 gauge wire.

Ya, but if a piece of #14 or #12 Romex are used for a power cord connected to a power amp it will not be exposed to physical damage or excessive constant bending. Well that may be true, but for anyone that uses Romex for a power cord anytime the cord is disturbed at the termination ends, plug or IEC, the solid core wire will loosen itself in the termination connection. Most male plugs use a terminal plate and screw to hold the wire in place. IEC connectors can vary from a terminal plate and screw or a lug where the wire is inserted in a lug and a screw is then tightened down on the wire. Any side to side movement will loosen the termination. Even the slightest loose termination can lead to micro arcing. If the termination is loose enough and the connected load is sufficient the connection will start series arcing. With arcing comes heat. More heat, more arcing, causes a carbon build-up. The carbon then works as a semiconductor. More arcing, more heat, more carbon.... Next comes VD, Voltage Drop, across the loose carbonized connection.

For those of you that use Romex for power cords and the cords are a few years old I suggest you check the plug and IEC terminations for tightness.

What sounds best, stranded or solid core wire? There is Lots of theory on the subject out there to read.
Many of the Hi-End aftermarket power cord manufactures make their power cords using several small solid core wires individually insulated then parallel them together to make one larger wire, be it #14, #12, #10, or even #8. I think I read somewhere #16 awg solid core wire is usually the largest size used. But don’t hold me to that.
Jim

Its all about money and inventory. It cost a lot of money to stock expensive "tweaky" stuff. This also leads to higher selling cost. A high volume manufacturer has to remain consistent. There are a lot of consumers, in fact most of them, that dont want to have to pay the increased high price of marked up tweaks.

On the other hand, the manufacturer is the one who knows best what tweaks will provide an improvement with thier product and which ones will ruin the design as they intended.

Bottom line...would you pay the higher cost of a product that has tweaks employed that you dont believe in? Or wait till the warranty runs out and go with what you believe in.

And lastly, who determines what is a tweak vs what is simply smart circuit design. Sometimes the cost of parts for a smart circuit design do cost more. No [one] designer/manufacturer has all the answers.