How does power cord affect a digital frontend?

Dmitrydr, I agree with Tok2000. I think what you say is true in theory, but that there are no well designed power supplies.

My theory is that with a CDP the primary gains of a good power cord are to prevent noise from being injected back into the 120v system of your house by the CD player. I have an old old CD player. When it is playing interference shows up on my TV. If I put a couple of ferrite rings on the power cord the interference goes away.

The power wiring in the wall will usually have harmonics of the 60 hz from radio signals, motor back-feed, fluorescent ballasts (which add current to the neutral), and other electric fields from power users on the same grid (elevator motors and machinery in the building across town.) All this noise gets into your power supply. The ability of the PS to reject this noise varies in proportion to its cost. Also, digital switching generates noise from within the cdp, further adding to the problem. The active circuitry gains up any signal, including noise, which is passed along as distortion to the components downstream.

A good power cord will filter some of the ac noise entering the power supply. This can reduce the noise from from coupling to the active circuits via stray capacitance and being gained. It can also reduce the noise generated by the cdp from reinfecting the power wiring by filtering the EMI/RF fields both from the cdp and common mode noise that can couple onto the power cord.

I have noticed the greatest improvements in digital front end from power cords that do a good job in filtering noise, such as the MIT Z-II cords, for the above reasons - I think. Cords which do the same job of filtering for a lot more money should be looked at with hand guarding wallet, IMO.

I don't claim that it doesn't exist, I'm just curious how it happens. I'm not really clear how presence of noise in AC line may affect digital signal. It may affect an analog stage in CDP, but if the data is being transferred via SPDIF interface, the analog stage is not really involved... I realize that digital signal may be affected by 'bad' SPDIF cable, especially if source or/and receiver are not exactly match to SPDIF specification, resulting in jitter. But how jitter may result from AC power even containing some noise, it anyways is converted to DC for a digital stage? The digital signal is "formatted" by crystal oscillator, not by 60Hz wave.

The greatest improvement with digital gear (Sony SCD 777 ES and Esoteric DV-50) has been with the JPS labs Digital AC. (See Art Dudley's article in the April "Stereophile".) It really works. It takes about a week of continuous use to
"break-in", but the improvement is not subtle.