Phase inverting preamps

The analog music signal input to your preamp is alternating current. The electrical voltage of this signal constantly swings between positive and negative in a manner corresponding to the musical information (I know this is an oversimplification).

If the preamp outputs a positive voltage when the input signal is positive, the preamp does not invert phase (more properly called polarity). In this case the output signal is identical (except for amplitude) to the input signal.

If the preamp outputs a negative voltage when the input signal is positive (and also a positive voltage when the input is negative) then the preamp is said to invert phase (or invert polarity). In this case the output signal is a mirror image of the input signal.

If you're in the camp that believes that absolute polarity doesn't matter, then just relax and enjoy the music.

If you want the system to maintain absolute polarity, then you have to flip (i.e., invert or mirror image) the positive and negative going parts of the signal one more time.

The easiest way to accomplish this is to reverse the speaker connections as described above: right power amp + to right speaker -, right power amp - to right speaker +, etc.)

It has nothing to do with reversing channels.

BTW, the point of this exercise is to keep the speaker diaphrams in polarity with the original microphone polarity. In other words when the michrophone diagram moves inward in response to an air pressure wave we want the speaker diaphrams to move inwards as well.

Trouble is, recording studios don't normally keep track of polarity, and some studio gear inverts it. Thus some recordings are correct, and others have inverted polarity.

On multitracked recordings, the absolute polarity may even differ from track to track, so that the two channel mixdown cannot be polarity correct.

Some preamps and most digital processors provide a polarity (or phase invert) switch to allow you to cope with polarity problems on the fly.

So can you hear the effect of improper polarity? I think I can, but not on all recordings. Inverted polarity usually shows up as "woolly" bass and soundstage problems.

The effect of improper polarity is called the Wood effect after the guy who first documented it. These has been much written both pro and con on this topic.

Thank you, Ghostrider! I have understood your explanation, and it makes sense. I only pray that I can remember it for the next time I wonder why the hell my BAT preamp has that "phase" switch on it, and what I'm supposed to do about it.

Ghostrider is correct about reversing the + and - on the speaker terminals. It is NOT reversing the left and right channels. Some preamp makers (Conrad Johnson, Blue Circle and others) do this because adding another otherwise unnecessary gain stage, just to make the preamp phase correct, would only degrade the sound.

I will add, that a recording that was recorded with the polarity reversed can be corrected by reversing the phase of the speakers, etc. The CD player's (or other source's) output voltage is still phase correct, even if the music was recorded with the polarity wrong. Data on a CD or LP (a piece of plastic) cannot change the actual voltage polarity of the audio component. There are some CD players that let you reverse the polarity of the recorded data at the DAC chip. This does not affect the output voltage polarity of the player itself. A loud bass note in a phase correct system that electrically pushes the woofer out, will do so regardless of how it was recorded at the studio.

Oops!!! Sorry about that! :-)

I was serious about the above though...I had all of my components hooked up correctly, but my left and right chanels were reversed when I played the HFNRR test record. It was all of my sources, so the problem has to be in my Counterpoint SA-5000, NP-100, or Merlin Battery Bamm. I switched my cables to fix the problem. (I assumed that was what people were talking about when they mentioned "phase inverting" preamps, so that explains my posts above)

Has anyone ever experienced a component flip-flopping chanels like that??

There is a BIG typo in my post above. It should say that an out of phase recording CANNOT be corrected by reversing the speaker terminals.