Phase inverting preamps

herman

If you take a pure sine wave and shift it 180 degrees then it will look EXACTLY the same on an oscilloscope ...

Pretty much!

... and will sound EXACTLY the same

That is very debatable. My preamp has a phase invert switch and on some recordings, the difference is very audible.

When you invert the polarity on your preamp it is not inverting a sine wave, it is inverting a complex musical waveform. The initial WHACK on a drum has much more energy in one polarity than the other. It the initial sound is a compression and you change it to a rarefaction by inverting polarity it may well sound different

Play a pure tone (one frequency) then  invert it to see if you can tell a difference. Hint... you can't.

Some folks can hear polarity, some cannot. Part of it may be learning curve.. where folks just need to learn what to listen for. Some of it may be equipment, and a LOT of it is in each recording.

Glad that kosst_amojan agrees with me that preamps each gain stage inverts. "" which is all you need in a pre-amp since the load a pre-amp drives is of high impedance and requires very little current ""
 (even though he is definitely trying to show his uber knowledge of possible configurations,... All major brand preamps commercially sold invert each stage. LOL)

@herman 
Yeah, you're technically right. I get it. The terms shouldn't be used interchangably. That said, phase isn't described in terms of units of delay. It's described in terms of degrees of rotation for a given moment irrespective of time. The problem with breaking it down as a function of time shift is that time shift would be different for every frequency. Phase isn't a time domain phenomenon. It's a polarity domain phenomenon. 

@elizabeth 

No... I'm not agreeing with you. It's entirely possible to build a succession of gain stages that don't invert at all. For instance, an input stage running in common gate modes will give you some voltage gain and buffer better going into an attenuator, and the successive stage can run in common drain to give some current gain to drive a low impedance amp. That's basically how a 2 stage differential amplifier works.