Steam power

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I love the term “running out of steam”. It’s an obvious reference to the beginnings of the industrial age where our world transitioned from animal power to steam power. When something runs close to its limits we say it’s running out of steam, or gas.

Recently there’s been quite a flap over on Ask Paul’s Videos. A question came to me about a subject that seems a tough one to grasp. Can preamp gain make up for low wattage? You can see the video response here.

Turns out this is a tough one for many to understand. I’ll see if I can approach it from a slightly different angle to chip away at the answer.

What’s confusing is the idea that if you put the same loudness music signal into both a big amp and a small amp, they produce the same number of watts (assuming they have the same gain – which most do).

To be more specific, let’s assume we have a 50 watt amp and a 500 watt amp, each with the same gain. Put 1 volt of music into either amp, and you will get (for this example) 30 watts out of both.

With me so far?

Using the same setup, now we will double the input voltage to both amps. Same thing happens, only the little amp will run out of steam—it can’t produce double the 30 watts and it clips. The bigger amplifier has plenty more steam available so it merrily outputs the expected 60 watts.

So, going back to the original question, can preamp gain make up for amplifier power, the answer is no. More preamp gain simply increases the input signal size to the power amplifier. It will still run out of steam at the same point. A preamp just gets it there quicker.

Hope that helps.