Class D and Power Cables

Yes, power cables make a difference, maybe even more so for class D.

If you want to know the theory:

In a conventional power supply (transformer, rectifier, filter capacitors), once the filter caps are charged the amplifier circuit only draws their voltage (stored electrons) down slightly between peaks of the AC mains waveform.

So the rectifiers will only be conducting for a short time on the peaks of the AC power to charge the filter caps. This means that the power cord has to be able to allow very high frequency bursts of current (since the period of time that the rectifiers are conducting might be quite short) through without limiting. This can be quite measurable BTW.

Its hard to imagine that a switching power supply and/or amplifier that relies on high frequency switching won't be affected by this phenomena.

Bottom line is the power cord needs to handle high currents at very high frequencies.

If you encounter anyone who says power cords don't make a difference, direct them to this post.

Ralph, I don't necessarily disagree, and I would suspect that in general Class D amps may indeed tend to be more sensitive to power cord differences than other classes. But wouldn't the limiting of high frequency high current bursts typically be mainly a function of the house wiring, not the power cord, due to their difference in length, and hence inductance?

Although it would certainly seem conceivable that in some cases other power cord effects, such as voltage losses and coupling of amplifier-generated noise from the power wiring to other parts of the system, could be disproportionately affected by the power cord in comparison to the house wiring.

Best regards,
-- Al

Hi Al, I'm sure external wiring has effects. But we don't get to change that stuff very often, so we also don't get to see how it affects things. The power cable OTOH is something that is easily experienced, and I have been able to correlate audible effects based on some fairly simple measurements.

The other thing I did not mention is voltage drop across the power cord. This can affect any larger amplifier that has a large current draw. I've seen a 2 volt drop across the cord rob an amplifier of nearly 30% of its output power!

How can that be Ralph?? 2 volts drop = 30% output power reduction??

Thankyou Ralph and Al for a learning exsperience with the post the both of you done, I highly enjoy what the both of you always have to say., cheers