Importance Of Power Supply : Transformer Ratings

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

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 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.

Read answer here:

http://www.enjoythemusic.com/magazine/manufacture/0708/index.html

by Simon Thacher of Spectron Audio

All The Best
Rafael

Thanks for the responses. I do know that the general rule of thumb in selecting an amp with a good power supply is by the weight of it. I am just not too sure if we can judge the quality of power supply through the numbers which most amp manufacturers do not publish in the specifications. My integrated amp is not too heavy weighing in at approximately 20 lbs. but it seems to possess ample power in reserve for transients and dynamic swings in music during loud passages.

I’ve found those with substantial often times, over built perhaps, power supplies do indeed contribute to the stability and performance level of an amp…. It’s just NOT the only thing which does however.

The power supply becomes still more important if the speaker mated to it is not optimally chosen. The PS is responsible for supplying sufficient voltage/current at whatever frequency immediately to the speakers so they will reproduce an undistorted signal. Differing freqs need more power to generate the same volume than do others. Consequently, the power sup must be able to provide the required juice or problems develop, like clipping or distortion. Neither is good and either can be damaging…. Especially to the speakers.

A fair enough rule of thumb for selecting class A or A/B amps is just to see how heavy the amp is. Again, it’s not the only aspect worthy of consideration… but it’s right up there in those type amps. Capacitors too play a big part, size, type, and number of them add to the power sups ready & reserve energy supply.

Hope that helps.

A good amp using a 400VA transformer can sound fine.If it has a 500VA tranny,it should have more reserve power when needed.That is not a guarantee for better sound though.I myself go by the sound of the amp,plus the reputation of the company making it.A high end company most likely will have a tranny big enough to perform the way they claim.♫