Hi all DIYs!

I have another newbie silly question. I know (i hope)what harmonics are. but the question is how and where are they generated? if we have a tube amp with a input tube ,do this tube generates harmonics? the Caps ,the resistors? Or they are already in the input of the amp (coming from the cd player) and get amplified by the amp?

Thanks

Harmonics are produced any time the gain is non-linear. Linear gain means the graph of input voltage vs. output voltage is a straight line. If the line curves you will get frequencies in the output that were not present in the input. Why? Very hard to explain in a short forum post. But do you remember Trigonometry from high school and all those trig identifies? What happens if the gain function is a polynomial. Look at the simple case where the graph is ax+bx^2. Now if the input to the amp is a simple 1KHz sine wave test signal (written is "sin(x)" what is the output? A hint: From your old text book you look up that

sin^2(x) = (1 - cos(2x) ) / 2

So the output if the graph is ax+bX^2 must be

a * sin(x) + b * (sin(x))^2

which is (using the above identity from your book)

a * sin(x) + b * (1 - cos(2x) ) / 2

Look at the 2x. This explains a second harmonic (double the frequency)

Also as you expect if the "b" is larger the graph is more curved and the 2nd harmonic is larger.

You can explain other things like inter-modulation distortion by looking at the sum and difference trig identities.

The next level of detail has to do with the shape of the gain function and phase The easy case above is for a parabola but likely the shape is more complex than that and simple analysis using high school level math does not work but the simple case does completely explain the origin of harmonic distortion. Well, not really because now you have to ask why the gain is not linear.