Phase inverting preamps

Phild suggested switching either the leads between the preamp and amp, or speaker cables.

Well, when I recently hooked up the Herron preamp (absolute polarity inverting) to the Herron monoblock amps for an evaluation I reversed the preamp to amp leads. Result - absolutely no soundstage and poorly controlled bass. I was so disappointed that I was about to send everything back. Someone suggested putting the preamp to amp leads back to "normal" and reversing the speaker cables. I did and bingo, everything was as I expected them to be.

Don't know if this is unique with Keith's gear. Can't explain it but that was my experience.

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.