Phase inverting preamps

This reminds me of the old Marshall Guitar Amp ads which ran "It comes out bigger and upsidedown." (Still one of my favorite posters.)

Whatever you want to call it, it's part of the process. For the most part, all standard active devices used as voltage amplifiers invert the signal which means if a positive voltage goes in it emerges as a larger but now negative signal. This leads to another simple point that a "preamp" is poorly named because it is an amp itself.

Phase inversion is inherant to the process. Everytime an audio signal passes through a gain stage, the polarity
(some refer to it as a 180degree in time phase change, whatever) of the signal is reversed. The output voltage moves in the opposite direction of the control Voltage. If you like tubes this reads as the grid voltage becomes more positive, the output plate voltage becomes less positive and visa versa. Mr. Marshall would add "and its bigger too."

I am happy to do my part to add to all the confusion.

Cheers,
I remain,

Paulwp,

It seems to me that if we are to have an intelligent discussion about all things audio, then we should use the correct terminology. Since phase and polarity are so frequently misused and confused, I thought I would try to help by offering an explanation. I'm sorry if I used too many words in my attempt to do so. If I offended you by pointing out the error in your post, then I apologize.

P.S. It was 371 words, not 1000. Again, I apologize if this correction offends you.

The concept of absolute phase is actually quite basic.
A simple example: you're making a live recording of an amplified band. After the signal goes through all the cabling, processes, & other equipment (including your own) what you should hear is the same phase as was originally captured by the recording microphone. This means that when the speaker cone of the originating source moves outward toward the listener in the studio, your own speaker cone at home should be moving in the same direction. If it's the opposite direction, that is being caused by a phase inversion somewhere along the way. An odd number of circuit stages could cause this, or even a miswired balanced-line cable somewhere along the way (the inverting & non-inverting paths were crossed).
Some preamps have an inversion button feature (like mine) & there is a definite difference in sound between inverted phase & not. Your ears will tell you the preferred phase for any particular recording, but you can't really rely on that approach to decide the best way to wire your speakers because it varies from one recording to another. There are some test records available, & probably some CD's as well, that have a phase test track which will help you decide the correct phase if in doubt.

I give up posting on these type of questions. Bob is right, it is simple, if an audio system has an odd number of phase inversions it will be out of phase. Some preamps have a switch to add a stage to change that kind of phase. However, if a CD was manufactured with the polarity reversed, that audio system will still have an odd number of phase inversions in the signal path and is still out phase. You end up with a sound out of phase with the polarity reversed; two different things.

It is sometimes caused by having the microphones out of phase. You will hear the difference, but it does not magically add another electrical circuit to your audio system to change your system's phase. If it does call Moulder and Scully.

In some regard your system will playing an out-of-phase sound, in phase (or an in-phase sound, out-of-phase.)

It is similar to when the AC power socket has that other type of polarity wrong. No matter which way you plug your components in, that same system with the odd number of inversions is still out of phase. Having your AC polarity wrong affects the sound, but not by reversing the phase of your system.

These reversed polarity recordings are similar. It has to be corrected at the CD player when the digital is converted to analog. There are some players that do this.

For some fun reading see:

http://www.mega.nu:8080/gallery/phase_and_polarity.html