Is there a way to tell the cause of distortion from the harmonics?
I looked at a bad (just crap straight out of the factory) Chinese preamp and found that it had little 2. and 3. harmonics but real bad 4.
Without having had opened the case, I was baffled. I had seen 3. and other odd harmonics but never 4.
That raised the question whether there are some wise rules from experience or theory as to what to look for as the cause.
Usually you can not see anything wrong on the scope so you have to go by the spectrum alone.
I am looking for something like:
strongest harmonic: | likely cause: |
First | relax this is what you wanted |
Second | saturation towards one polarity |
Third | symmetric limiting |
Forth | asymmetric supply |
Fifth | same as 3. |
Even | asymmetry |
Odd | symmetric limiting |
There should be a list of things to check/look for.