Phase shift

[Leevi]

The phase shift is normal in amplifiers.
In the following pictures you can see how the bass control affects in a VOX-type tone stack.


Interesting question is how the negative feed back behaves if the the deviation is big.


In the first picture the bass control is not opened at all and in the second picture it is turned fully open.
The measurement points are input and output:


/Leevi

[jjasilli]

You are right.  Negative feedback is more problematical than generally thought, because of phase shifting in the signal, or in certain bandwidths. This seems to be more of an issue in hi-fi than in guitar amps.

[shooter]

Interesting question is how the negative feed back behaves

It's most often heard, play a single note from guitar or siggen, then switch off NFB, then on, till you notice, if you don't, it's not a problem 

I quit using NFB and "tweak" the drive path so I don't need NFB.
what I did hear playing around was an "effects" sound, but can't describe it better.

fwiw, the largest shift I've measured is ~ 40 degrees in to out, typical is ~ 20 or less