Importance Of Power Supply : Transformer Ratings

Thanks for the informative link. It appears that peak voltage of power supplies is important in reproducing large transients with a recommended 120V. I suppose we can't check this as most amp manufacturers don't publish this figure in the specs.

In the article:

"Using the B&W 805 speaker, with 87.5dB/W/m sensitivity, and the powerful Music Fidelity amplifier, Howard did a number of measurements of produced peak SPL from a few recorded classical pieces. He found that peak SPL can be as high as 120dB at 10 feet from the speakers."

I didn't expect the small 805's can achieve a peak of 120dB at 10 feet away. That would translate to about 110dB at 1m. I am surprised the speakers can take up to that max. SPL without going into distortion.

Ryder - power supply capacitors are recharged in very short current spikes of high amplitude. High frequency of these spikes heats-up the core of transformer while rms value heats up the copper (windings). This rms value, because of shape, is much higher than average value delivered. As a result transformer with rectifier/capacitor load needs much higher rating (at least 50% more) than transformer with resistive load.

That is important when you need large constant current (class A) while typical class AB amps have much lower requirements since average music power is only few percent of peak power and peak power is handled by power supply capacitors (unless you listen to sinewaves at full power).

Power supply capacitors are in series with the load (circuit closes thru them) and not only capacitance but also quality (ESR, inductance etc.) is important. For instance, if they used high inductance capacitors adding film capacitors will help with response but will create parallel resonance circuit that rings.

So, transformer is important but I would also pay a lot of attention to power supply caps since good ones (and a lot of them) are expensive (like slit foil caps).

Thanks Kijanki for the thoughtful explanation. It was much appreciated.