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THE FACE OF HARMONICS
Ever wanted to know how increasing overdrive in your preamp would sound? How about what harmonics
are generated in an overdiven preamp versus a clean preamp, an overdriven single ended power tube?
Want to know what harmonics and the levels that are generated by a clipped power amp signal? How about side by side
audio comparisons? You can find it all here and more, read on.
I have compiled 5 test scenerios of clean stages and overdriven stages all with photos and sound samples. Check them out,
I do not draw conclusions but leave it up to you. The test frequency is 400hz and here is an audio sample of all 5 tests, you
may be surprised at how much your bias voltages and preamp gain actually effect the sound of your amp.
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The sine wave on top is a clean signal through a triode and the sine wave on the bottom is an overdriven triode signal, note the peaks are rounded off, this produces predominently even harmonics that triodes are known for.
This is an overdriven pentode (power tube), note the clipping of the peaks, this charactistic produces predominently odd order harmonics.
This is a specrum analyzer that displays the 400hz signal (the first line) as well as each harmonic frequency generated in the amp and the level of each; the higher the line the louder the signal and the further to the right the higher the frequency.. The input freq is 400hz and the harmonic frequencies generated are 800hz, 1200hz, 1600hz, 2000hz, 2400hz and so on. As the frequencies go up they level goes down and as you increase overdrive the level of the harmonics goes up. Note the harmonics that are generated in a "clean" non-overdriven tube amp in TEST 1as compared to TEST 5.
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Here are graphs depicting what is shown on the spectrum analyzer photos. The levels are 0db to -80db and the harmonics shown are 1 through 8; 400hz, 800hz, 1200hz, 1600hz, 2000hz, 2400hz, 2800hz and 3200hz respectively.
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