Tonefiend Forum

I did promise not to do any SPICE analysis for November. That doesn't mean I'm not going to talk about harmonics! But I'm too lazy right now to make waveforms and drawings. You're just going to have to imagine this one.

Start with the premise that a signal/waveform which is symmetrical, like a sine, triangle, or square wave, will have only odd harmonics. An asymmetrical waveform will have even harmonics as well as (possibly) odd harmonics.

Now let's think about your guitar's output signal. Unless you carefully pluck at the center point of the string's length, you will have even harmonics in the guitar's signal - it will be asymmetrical.

If you amplify this cleanly, no distortion, then whether the "fat" part is on the top or bottom doesn't matter. If you put it through an amp that clips evenly on the top and bottom (like a balanced push pull amp that distorts at the phase invertor or output stage before the preamp distorts) then similarly, your guitar's polarity should not matter.

But, if you put it through something that also distorts asymmetrically, like most tube preamp stages, or a single-ended amp, then (I assert) that your guitar's polarity WILL make a difference in the output waveform/spectrum/sound.

A good example of an amp stage which distorts asymmetrically is an unbalanced push-pull output stage. Supposing the voltage gain of one side is 20, and the other side is 10. This doesn't even require a hot signal to distort. It's distorting all the time. The polarity of an incoming asymmetrical signal will certainly make a difference. If the "fat" part is amplified by the side with a gain of ten, then it becomes "fatter" - more even harmonics. If however, the fat part is amplified by 20, then it stretches out while the "thin" side is now compressed, pushing towards a more symmetrical waveform, resulting in more odd harmonics.

Anybody believe this?

Anybody tried it (like putting a polarity switch on the output of your guitar and then blasting through a single ended amp)?

Another easy-to-demonstrate possibility would be the passive diode clippers that have been discussed here. If you built it with different types of diodes to get an unbalanced distortion, then I would expect 2 different sounds depending on which direction you wired this diode pair into your guitar. How fun!