how can a line cord affect frequency response ?

The power cord doesn't affect frequency response, however it can affect dynamics and in some cases become an antenna for RF. When RF gets into your amplifier, then it can affect the sound in many ways:bright, lean, hard, glassy, etc. Normally, the power supply should eliminate these effects, but in some cases, it doesn't.

It never ceases to amaze me just how cheap some expensive amplifiers can be. Some factory power cords are really inexpensive. When you replace them with better quality ones, there can be a small difference in DC levels in the power supply, which you will hear. However, none of this will affect frequency response.

Whether or not you will get the same effect(s) with a Belden 14 gauge shielded power cord for 10 or 12 bucks is a whole different matter.

Regarding RF: I didn't mean to imply the line cord acted like an RF antenna when it was powered. What I was trying to say, however vague, is that it can act like an antenna and pick up RF energy. Although this energy should be eliminated in the transformer or perhaps some RF network in the PS input, there are cases where it can actually get into the amplifier itself and cause sonic problems. In this case, switching line cords may or may not make a difference. However, that being said, you still have lots of ROMAX in the walls which can pick up RF, too.

Dpac996: I believe you have bandwidth of the amplifier and bandwidth of the transformer, line cord, diodes, surge capacities, line droop, line drop, and dynamic compression all mixed up. Amplifiers simply don't work the way you describe. The power bandwidth of the transformer is typically no where near the amplifier bandwidth and sometimes it is not more than 47 toi 63 Hz. The line cord has wider BW to be sure, but keep in mind the only frequency on the line cord is 60 Hz, at least in the US.

Metro04: I do agree that materials do affect performance, but not like interconnects. Line cords only carry one frequency, 60 Hz here in the US. Interconnects can carry bandwidths from DC to 100 MHz with ease, if you use the right one.

Reb1208: Actually, if a line cord were to really seriously limit the power amp enough that it began to get warm and soft, it is more likely that dynamics will be compressed, rather than bandwidth. You might find that the low frequency peaks, not the high frequency peaks, is what got clipped. However, bandwidth below clipping, will be unaffected.

After writing that last night, it occured to me I should also elaborate a bit. When I said bandwidth, I was speaking in terms of the amplifier bandwidth, and I still state that line cords do not affect it. But since we are discussing line cords, let me relate the term "bandwidth" to line cords.

First of all, there is a voltage bandwidth and a current bandwidth but they are not the same. With respect to a line cord, the voltage bandwidth needs to be only a few Hertz wide, say 58 to 62 Hertz or so. Although the voltage bandwidth is much more than this, it doesn't have to be as long as the line cord can pass 60 Hz without loss.

The current bandwidth of the line cord, however, has to be much wider. In this case, a bandwidth from DC or a just a bit higher than DC to at least 600 Hz or so will do the job. The current BW can be higher than this without any problems.

I think I will start a new thread regarding line cord bandwidth as there is much to explain and it is really off topic from this one; probably next week sometime.

Dpak996: Triggering on both, but not at the same time! For the line cord waveforms, I'll trigger on the line. For waveforms on the filter, I'll have to trigger on the ripple, as the music signal will, or at least should, be very small in comparison. But, I can trigger on that just to see what might come up.

I am hoping to have time to check this out tomorrow night, as I should have some lab time available.

Tvad: I wasn't asking for proprietary secrets. I was asking for some data indicating their cables improvement. For example, you bought a power amplifier for your stereo, certainly you asked it was tube, solid state, what power it has, signal to noise ratio, current capacity, perhaps you even talked to the manufacturer about their philosophy in design. All of this provides good data and information, yet is not proprietary.

Metro04: I was basing my comments on basic power supply engineering. I'll start a new thread on the bandwidth requirements of line cords shortly.

Dpac996: Actually, what you want to use in that experiment is not a differntial probe, but a current probe. This is a device you can clamp on the wire and monitor the current flow through the wire. Tektronix makes several of these types of probes; the basic one with a DC to 50 MHz bandwidth is fine. I plan on doing this in the lab this week, just to see the what the bandwidth is of some cheap basic line cords versus the more expensive ones. I'll post the results in a new thread.

Mrtennis and Tvad: Gee, a cable designer said it makes a difference, so therefore it does. But, he gives no explanation for the reason, no facts, no information based on his own experience in the lab, no experimental data, nothing other than his own opinion, which is what he uses to sell cable at 500 to 2000% markup. If he could sell lots of cable based on opinion, think what hde could do with solid data and facts! What is wrong with this picture? As I have stated numerous times in the past, I am happy to be proven wrong on my opinions, but please, someone show me something other than profitable based opinion that I am wrong.

To all, a general note: Please keep in mind that power supply performance is always improved by adding large inductors in series with the capacitor filters, not by removing inductance. So simply stating that "adding inductance is bad" is wrong. Yes, it can be bad, depending upon where you put it, but let's assume the power supply engineer knows what s/he is doing. After all, you must have some faith in their skills, as you bought their amplifier! Other than cost, and they are expensive, an inductive input L or capacitive input Pi filter, are impossible to beat for power supply filters.