Phase inverting preamps


Apologies in advance for this newbie question. I was reading some reviews of preamps and a couple said that the preamp "inverts phasing" and that this would have to be accounted for elsewhere in the system. I know what phasing means, but how and where does one allow for it elsewhere in the system?
4yanx
If the preamp is phase inverting it is merely switching the right and left chanels, so all you have to do to correct that is switch them back again. There are several places where you can do that...you can reverse all of the individual component hookups (plug left into right and right into left), switch the left and right cables between the preamp and amp, or switch the speaker wire hookups at the amp output. Do one of those...not all three. I switched the left and right cables between my preamp and amp...that was the easiest for me.
Thanks, Phild. Does this in any way compromise sound quality? And, why would the maker of a preamp produce a unit that inverts phasing? Is there something specific they are trying to achieve that is negated by reversing the phasing elsewhere? Seems like it would be easier just to make the preamp without inverting the phase. Is it a cost savings measure?
If it's inverting phase, it's inverting push/pull (+/-) signals. To correct this, you need to change your speaker connections.

KP
I don't get it either, but I know someone here will have the answer for you. I've read an explanation before, but I forgot what it was. I vaguely remember someone saying that it was a design choice. I don't think it's a cost saving issue as much as it is a way to keep the circuit simple (but I'm not positive about that). I really don't think there's any adverse effects. It's a clean switch, so you're okay as long as you switch it back. Most people wouldn't even notice the phase problem, but the correct phase should sound noticeably better when you compare the two. It should sound more natural. To confuse things even more...some recordings (or mic'd instruments within a recording) are out of phase. That's out of your control, but you can sleep soundly knowing you did your part to fix your system phase. :-) You may want to ask the manufacturer of your preamp...they should be able to tell you if your's in phase inverting. You could also pick up a test record or CD (Hi-Fi News and Record Reviews, or others) that have a phase test...usually just a voice saying, "Yo...dis be da right chanel" and "Yo...dis be da left". If you're hearing the voices from the wrong speaker, you should check all of your connections and make sure they're correct. If they are, you know that some component is inverting the phase. My CD and LP source were both backward, so I assumed it was my preamp.
Hi Killerpiglet...I won't bet my life on this, but I think that what you're talking about (inverting push/pull) is signal polarity, which isn't the same thing as phase inversion.
I have a Croft Vitale pre-amp. The manual states:

"Important: Pre-amps WITH gain invert phase, therefore you must connect the loudspeaker terminals so that (the +VE speaker cable is connected to the -VE terminal) & (the -VE speaker cable is connected to the +VE terminal on the loudspeaker only)"

This is verbatim, including confusing punctuation. I thought it meant to switch the + and - connections for each channel on the amp, but after reading Killerpiglet and Phild, I'm confused. Especially since I don't know what "VE" means.
After reading this instruction from the manual, can you help me and explain? Thanks.
--Neil
Ouch, guys, it isn't left and right that are inverted. It is as KP said above, pos and neg. Just connect each pos speaker terminal on the back of your amp to the neg terminal on the speaker. They say they do it to save a gain stage necessary to flip the signal 180 degrees back to positive polarity. "Phase inversion" is commonly used to refer to reversed polarity.
Gee, and here I thought I was the only one confused! :-) As I understand things so far, if you have a preamp that has inversed phasing (polarity), one must "flip-flop" traditional connections at the SPEAKER posts (i.e. positive to negative and negative to positive). Correct? I imagine that experienced hands here at Audiogon will find this dilemna at least mildly amusing, so excuse my (our) confusion.

My readings said that the inverse phasing must be accounted for SOMEWHERE in the system. Does it make a difference WHERE this occurs? Who has the authoritative word on this subject?!
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.
There seems to be a lot of confusion about this. There always is. Mr. Ghost is correct.

Phase and polarity are NOT the same thing. A phase shift is a shift in time. A change in polarity is a change from a positive to a negative, or vice versa.

A simple example would be a 20 Hz sine wave that starts at zero volts, goes to a positive peak then decreases until it crosses zero, going negative until it reaches a negative peak and then returns to zero. Like this little symbol ~ .This is one complete cycle of 360 degrees. This happens 20 times a second so each cycle takes .05 seconds.

If this exact same signal had it's polarity inverted, it would start off going negative instead of positive, but would start at the same time.

If this exact same signal was phase shifted 180 degrees, it would start off going the same direction, but it would do so 1/2 cycle (.025 seconds) later or earlier in time.

Thus the comment about "flip the signal 180 degrees back to positive polarity" is wrong. If you are dealing with a repetitive waveform like a pure 20 Hz sine wave, than a phase shift of 180 degrees will look just like a polarity inversion. Draw a picture and check it out. But music is not so simple.

The comment from Mr. Brie is also a little off base. The recording is not out of phase, it has had it's polarity reversed. When you engage the phase button (should be polarity button)) you do indeed invert the signal. What was going positive will now be going negative, and vice versa. This can also be done by reversing the speaker leads. The common example is that of a drum that produces a very short WHAP sound. Lets say the initiation of the original WHAP sound caused a compression of air. The initial movement of the speaker cone should be towards the listener, which will also compress the air. If the polarity is reversed anywhere along the path form micrphone to speaker, the initial movement of the cone will be away from the listener causing the opposite. Whether this is audible is another story.
Of course, Herman. It was an attempt to account for the confusion w/re phase and polarity. But it doesnt matter in this context. All the preamp owner needs to know is to reverse his speaker cables, and not left to right as he was told. He doesnt need these 1000 word essays.
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,
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.
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.
What seems to be the root of the audible differences in polarity is that air is not symetrical in it's response to a stimulus. To test the theory simply try pushing air with your hand, now try pulling. More air is displaced by pushing than is sucked into the partial vacuum by pulling. Air is, in some sense, single ended. It would seem to indicate that a speaker diaphragm excites the air differently when moving in than it does when moving out. Can any of the scientists out there comment.
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

Ah, this stuff is all bogus. Where's my Fisher-Price Close & Play when you need it : ) Sean
>
Sugarbrie, I think you still have phase and polarity mixed up. I read the web site you point out and he describes it correctly. But your explanation does not mesh with his. I do not intend to be picking on you as most of the other peolpe who have posted to this thread have also used the terms incorrectly.

I am not trying to sound like a know it all here, but there are so many incorrect usages of the terms phase and polarity in this thread that it is hard to keep up. I assume that some are interested in this since there have a number of posts on this. So I'll try one more time.

Out of phase means to be shifted in time. Something occurs earlier or later in time than it is supposed to. You cannot invert phase. The term "phase inversion" makes absolutely no sense. It should be stricken from the English language. You can no more invert phase than you can invert time.

Let's say you play a low note and a high note on an amplified electric guitar at the exact same time. But when it is played back on your stereo, you hear the low note and then the high note a little later. This is a phase shift.
They have been shifted in time. Nothing has been inverted.

Let's say when you play the low note, the initial movement of the speaker cone from the guitar amplifier is out. But when you play it back on your stereo, the initial movement is in. This is a polarity inversion.

If you hook up a battery to your speaker terminals, plus to plus and minus to minus, the woofer will move either in or out depending on how the speaker is wired up. If you reverse the battery, it will move the other way. This is a reversal of polarity. It has nothing to do with phase.

If you record a single cycle of a sine wave and play it back, the cone will move one way and then the other, say first in then out. If you reverse the speaker leads it will move first out then in. This is a polarity inversion. If you leave the speaker leads but hit the phase button on your CD player, It will also reverse to first out then in. This is also a polarity inversion, not a change in phase. The button is labeled incorrectly.

So can you correct for a recording that was recorded with inverted polarity? Yes, definitely. Just reverse the leads on your speakers or hit the incorrectly labeled phase button on your CD player or preamp.

Can you correct for phase shifts? Possibly but it would be very, very complex.
I guess I agree that a recording with the polarity wrong has no affect on the phase of your system. The + signal (and minus) of DC current going through your hardwired system cannot be reverse solely based on music encoded on a piece of media, whether, CD, LP, or Tape. That would defy the laws of physics.

If you had a recording with multiple microphones, where some microphones were in phase and some out of phase, some sounds may cancel out in part, which is why the recording sounds off. You system won't be feeding post positive and negative current to both speaker terminals at the same time. I hope you agree that is impossible.

Put another way; if a system is phase correct and a recording has sounds out of phase; your system reproduces for your ears to hear, what that out of phase music sounds like. That reproduction of the out of phase sound is in phase. If you reverse your speaker cables that sound is not in phase. You are hearing an out of phase sound, out of phase. It may end up sounding even worse.
Bowbow, I understood what you posted and I agree except for the part about DC current. You are right that it does not feed current in both directions at the same time. The current is AC, it alternates. First it flows in one direction and then the other. The rate at which it changes direction is called the frequency. Polarity has to do with which direction it starts.

However, the statement "If you reverse your speaker cables that sound is not in phase. You are hearing an out of phase sound, out of phase" is an excellent example of the point I was trying to make earlier about the misuse of these terms.

It should read: "If you reverse your speaker cables that signal will have it's polarity inverted. You are hearing an out of phase sound with incorrect polarity." I agree that this may end up sounding worse.

I know that some of you are saying enough already, what difference does it make? Well, it makes a huge difference if you are trying to understand what is going on in your system. If I think the woofer is the little speaker and the tweeter is the big one, then we are going to have a very confused conversation about speakers. If you do not understand what polarity means, then how can you hope to determine if your system polarity is correct? On the bright side, you have a 50/50 chance no matter what you do.
Thanks to all. The intent of my original post was to determine what need be done to account for the "inverse phasing" of a preamp (subsequently clarified to note that what they should REALLY say is reversed polarity). And, I now know that the connections at the speaker posts should be reversed. That being said, I have also appreciated the more in depth discussion of the difference between phasing and polarity. While I knew there was a difference I have enjoyed hearing the nuances of the differences and the reality of inconsistencies within recording mediums.

It never hurts to go into more detail, as long as you know what you're talking about! Those who find it boring or something they already know can easily click to the next topic. :-)
Herman, I think we all including Sugarbrie agree; it is just a matter of terminology. I have a Conrad Johnson preamp and in the owners manual CJ uses the term phase inversion, not polarity to describe reversing the speaker wires. So even the manufacturers interchange the two terms.
Yes, I agree with both of you (Herman and Bowbow). It is just terminology.
Ok, you guys are right. If major manufacturers like CJ don't use the term correctly, it silly of me to think that I could have any impact. Don Quixote, windmills, that sort of thing.

On second thought, it has always bothered me that the weatherman on TV always says when the sun will rise and set when we all know that it doesn't really rise, it is the rotation of the earth that causes this apparent motion. I better give him a call.
Herman: Rent a copy of the movie "The Green Berets" staring John Wayne. There is this one very nice sunset scene on the beach in Vietnam. It is interesting because the Vietnam coast faces east!! Talk about phase inversion!!
To KP. Thank you. I’ve a integrated amp that inverts signal and know one has been able to explain correctly what to do as a solution. Attaching right speaker cable to left and left cable speaker to right works.  Just as you stated  I now have correct phase and polarity. 
Just a for your information: every gain stage of any preamp or amp inverts the polarity. So if you have a preamp, or an amp with one or three gain stages the result will be, compared to the input, a reversed polarity at the output.
If the amplifier of preamp has an even number of gain stages, two or four, it will have the same polarity at output as the input.

The number of gain stages are a design philosophy matter. And a lot of great preamps use three gain stages.

IMO since about a third of all recording have totally screwed up polarity due to mixing etc, and a third have reversed polarity, and a third correct polarity..

What does it matter???
I have a reverse polarity switch on my preamp anyway.
Sometimes I can notice flipping it can clarify the sound. Sometimes not. I own dipoles, and those speakers make it easier to hear polarity.
I see a LOT of completely wrong information here. 

@elizabeth 
No. Gain stages have nothing to do with inverting the signal. Gain stages invert the signal only when the gain device is operated in common source or equivalent mode for the particular gain device. That's the mode that gets you only voltage gain 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. Common drain and common gate modes get you only current gain or both current and voltage gain, respectively, and both of those modes are non-inverting. It has nothing to do with swapping left and right channels. You can't just rewire your RCA cables backwards either. Swapping the polarity of the speaker cables is the easy fix. If we're talking about an inverting phono pre-amp, you should reverse the wires to the cartridge. 
Just had a bit more time to read over this....

@herman 
For the intent of this discussion, you're really splitting hairs with the terms "phase" and "polarity". I signal that's experiencing 180 degrees of phase shift is the EXACT same thing as inverting it's polarity. Maybe there is some phase shifting going on inside a component somewhere, a few degrees + or - here or there, but that's the nature of the beast. But that's not what we're talking about here. 
Whether or not hairs are being split is a matter of opinion. That you are incorrect is a fact.  As I stated earlier, a phase shift is a difference  in time whereas inverted polarity means a change from positive to negative or vice versa. 

I don't have any illusion that any of this discussion will change the terminology, but I do think we should understand that phase and polarity are not the EXACT same thing just because audiophiles use the terms interchangeably. 

If you take a pure sine wave and shift it 180 degrees then it will look EXACTLY the same on an oscilloscope and will sound EXACTLY  the same. However, if you take a "signal" containing many different frequencies like music you get a much different result. Since each frequency has a different period,  if you shift each frequency by the same number of degrees  it will sound different because each frequency is shifted by a different amount of time which results in a waveform that is not the EXACT same thing.  That is a reason why speaker crossovers distort the signal. Here is a discussion of it.

https://www.passlabs.com/press/phase-coherent-crossover-networks


Phase or Polarity?
http://totalproaudio.stevebunting.com/30/basics/phase-or-polarity/
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. 
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.
It isn’t a "problem" to break it down as a different time shift for different frequencies, it is the reality and why it causes distortion. While I agree that it is more common to talk about degrees of shift, the degrees don’t adequately describe what is actually happening. If I remember my theory, the cutoff frequency is shifted 45 degrees in a one pole high pass filter. Frequencies below the cutoff are shifted more and those above are shifted less. This shift in time, more for some and less for others, results in a form of distortion

BTW we usually describe signals in terms of the time domain (what is the voltage ) or the frequency domain (what frequencies are present) . For instance.. a perfect square wave in the time domain is described by the voltage at any point in time, what you will see on an oscilloscope. In the frequency domain it is described as consisting of a fundamental frequency and an infinite series of odd harmonics of ever decreasing amplitudes, what you see on a spectrum analyzer. If you apply a square wave to a crossover what comes out is no longer square because the different frequencies are shifted in time by different amounts. They are also attenuated by different amounts which along with the change in phase creates something other than a square wave.


Never heard of a polarity domain.
@herman 
I understand what you're saying. I meant a spacial domain. Waves can be modeled quite nicely with no time considerations. 
I couldn’t read this post- But- the answer is simple. Reverse the speaker cables to your speakers.  Simple and easy. By the way when you become a serious listener you will buy a preamp with a “ phase inversion” switch. 
@ptss 
Why????