Impact of phase inversion by preamp


This will be my first post on this forum so I thought I’d pose a question I’ve always wondered about.  I have a Conrad Johnson Premier 18LS preamp that I’ve been extremely happy with since first acquiring it some years ago.  This is a solid state single ended, single stage design that inverts the phase of the input signal at the output.  The manual states that you should reverse the connections to the speakers to account for this.  Obviously this is easily done but I really can’t see how it would really matter as long as things are connected consistently between the left and right channels.  I’d be interested to hear what others have to say on this subject.
ligjo
I have a phase switch on my preamp. It usually has minimal effect. Apparently, you should switch back and forth and use whichever setting results in the best bass. Good first post!
The importance of maintaining "absolute phase" aka "polarity" in a system is controversial. One reason for that is that many recordings have been engineered with a large multitude of microphones, and have been subjected to extensive electronic post-processing, the result being that different instruments and different vocalists may have different polarities on the same recording.

Whatever difference it might make is most likely to occur on recordings that have been made with a minimal number of microphones (ideally just two or three), and that have been engineered with minimal post-processing. Some relatively small producers of classical recordings tend to be in that category.

Also, in the case of preamps which provide a polarity switch it should be kept in mind that when the position of the switch is changed, in addition to the polarity of the signal being inverted the internal circuit configuration of the preamp is being changed. Which depending on the specific design might in itself have minor but audible sonic consequences, especially in the case of preamps that are not "fully balanced," i.e., that have single-ended internal signal paths.

Regards,
-- Al

I concur with dweller, the impact is subtle, but noticeable.
You should really try using it.
BTW, there are some recordings with the phase inverted, so if you notice something 'off', just toggle the switch and see if it helps.
Bob 
Thanks for the replies guys!  There are no polarity reversal switches in any of my gear so I need to make the changes at the speaker terminals, making quick AB comparisons difficult.  I suppose when in doubt, follow the manufacturer recommendations which is what I do.  Just curious whether it really matters.
I have found that when the phase is inverted that bass will sound hollow or will be missing a bit.  Some speakers seem to be more impacted by this than others.  I can definitely hear a difference in mine. 
Easiest way to think about it
Is if phase correct the bass drivers initial movement on a note, is forward into the room, thus pushing your eardrum inwards.
The opposite happens if your system is inverted.

Cheers George
I agree with verdant there is a change in bass and detail in my system and very noticeable. I have a Bruce Moore Preamp that recommends reverse polarity which I do. I have a invert phase switch on phono pre with a remote so I can switch from my chair. So I can A/B fast. I find I use the switch a lot it's crazy because I have it switched at the speaker. Different songs sound better on the same album with the switch on and off, so for me there is no right answer whether to use it or not. I do find I use the switch off with polarity reversed 2/3 of the time maybe.

I wish I had a phase reversal switch on my preamp so many recordings vary in terms of correct or inverted phase.
Isn't there a difference between phase and polarity?  What do these switches on preamps do vs. swapping the leads on one end of the speaker cables?
Hey George....that’s exactly the way I was thinking about it.  The question is whether your ear can tell the difference.  From the other comments, it sounds like you may be able to which makes sense.

"They" whoever they are, I can't rembemer, it was said back in the 80's.
Say that "if" the inital bass driver movement is into the room, that you get a better leading edge attack to the sound of a bass note.?????
This is most probably why it's said you can only hear the difference in the bass.

Cheers George





   
To answer part of your question twoleftears, in the case of hifi equipment, swapping phase and polarity should be the same.  Phase can be “rotated” by varying amounts within 360 degrees but that would not be applicable in home hifi systems.  Rotating by 180 degrees flips the phase.  I can’t answer what specific vendors might be doing when they implement a polarity switch but as almarg stated earlier, the circuitry is being changed which could impact the sound beyond just changing polarity.
Hopefully, you can find something helpful/enlightening, in all that.  
One of the things I like about the Jeff Rowland preamps is the phase switch. I use it all the time & sometimes it makes a pretty big difference. CD's seem to be more prone to be recorded out of phase than analog LP's. Just my experience.  
I have fully balanced system. Tonearm/cartridge, cd, Atmas Sphere preamp and mono blocks . The preamp has an inversion switch. One effect Ive notice when experimenting with the switch is you can get an out of phase effect that gives you an ultra wide soundstage (sort of unbelievable) and a deadened hole in the middle.

This subject has been brought up a number of times, and every time it is once again pointed out that many (most?) loudspeakers have their two or three drivers wired in opposing polarities. As an example, the midrange driver will be opposite the woofer and tweeter (Wilson's, I believe). Reversing the polarity at the pre-amp will result in each driver then being opposite of what it was. What remains constant is that different frequency bands are being reproduced by drivers in polarities opposite each other. Which frequency bands do you want in "correct" polarity? Wire your speakers (or flip your pre-amp control) so as to achieve that.

But as almarg said above, many recordings are themselves already of mixed-polarity, so what does it matter?! If you play a single-polarity recording through a single-polarity loudspeaker, phase reversal should be more audible than in the above scenario. Phase reversal of the Sheffield direct-to-disk LP's is more audible than of "normal" recordings, and many of the Sheffield's are themselves in reverse polarity (a snare drum strike creates rarefaction, not compression). Sheffield recommended the playback system polarity be reversed when playing their LP's.

many (most?) loudspeakers have their two or three drivers wired in opposing polarities
hopefully to correct crossovers phase shift and not arbitrarily.

It is more than the bass that is affected. Percussion has very steep transients, sometimes exceeding 20KHz on tape and LP. On quality phase coherent systems, the effect is clearly audible by some. Not all are sensitive to it.

Expanding on what Al said regarding polarity flip circuits, even in fully balance circuitry, they are seldom in themselves inaudible. This can be demonstrated by reversing loudspeaker polarity and listening to the A:B, which is quite likely C:D.


In a balanced preamp the phase switch simply redirects the inverted phase to the non-inverted circuitry and vice versa. Its completely passive.
With many recordings the correct position is inaudible, owing to the recording being multi-tracked and mixed. The phase may be different depending on the instrument playing! So usually you only hear it on true stereo recordings, those done with only 2 or 3 mics (the latter being the Mercury process or Decca stereo tree, that sort of thing). The problem is that 50% of all recordings regardless of the media are not in absolute polarity while the other 50% are. Switching your speaker cables around to deal with this is a pain which is why we included the switch since we were making a balanced line preamp anyway.
You just have to try it and see. I seem to hear it easier with brass instruments.
In a balanced preamp the phase switch simply redirects the inverted phase to the non-inverted circuitry and vice versa. Its completely passive.

Nothing is completely passive. The more revealing the circuitry, the more it exposes component 'flaws'.

Experience with phase flip switches in active and passive balanced hardware often left something to be desired in terms of routing and hence inaudibility.

Making both halves of a balanced circuit identical is EXPENSIVE. Add in tube vagaries and the probability of a sonic delta is fairly certain. Not to all listeners, but to some.

Decades back it was demonstrated there were distinct sounds in a system on the same source:
  1.  Normal polarity to speakers
  2.  Invert channel A at source* and speakers - same Φ as 1
  3.  Invert channel B at source* and speakers - same Φ as 1
  4.  Invert both A&B at source* and speakers - same Φ as 1
*Balanced out - polarity swapped with identical but inverted polarity cables.

Theoretically all should sound the same, but they didn't. If one subscribed to OOPS, at least 2 & 3 should sound the same, but they didn't. It was postulated that the loudspeaker is an asymmetric load and depending on the other hardware, affects the sound.

ieales
Nothing is completely passive. The more revealing the circuitry, the more it exposes component ’flaws’.
Semantics. There is passive circuitry, and there is active circuitry. There’s no value in confusing the two.
Experience with phase flip switches in active and passive balanced hardware often left something to be desired in terms of routing and hence inaudibility.
Whose experience? With what hardware?
Decades back it was demonstrated there were distinct sounds in a system on the same source ...
When was that, and by whom? Where was the demonstration, what were the source and other components used?
@cleeds 
Nothing is completely passive. We may think of C in terms of uF, but there are L&R factors which pertain. Pull apart a switch and examine the contacts. One set may have a contaminants/wear/geometry that the other does not.

A great recording & electronic design engineer built an incredible sounding recording console that used mercury wetted relays as close to the active circuitry as possible to eliminate passive colorations from running traces [audible] to surface switches [audible] and back.

Mic pre's, EQ, recording consoles in the studio.

In the early 80's. Then state of the art LA recording studio. Participants were well regarded engineers and IIRC, some industry sales reps. Source was hot-rodded ATR-102 ½" master tape feeding Bryston amp stack and time aligned studio monitors. Test was change or no change. Blind. Most got most of the changes.
ieales
Nothing is completely passive ... Pull apart a switch and examine the contacts. One set may have a contaminants/wear/geometry that the other does not.
A mechanical switch is a passive component.

I’m sorry that you don’t have any details on the listening test:
... state of the art LA recording studio. Participants were well regarded engineers and IIRC, some industry sales reps. Source was hot-rodded ATR-102 ½" master tape feeding Bryston amp stack and time aligned studio monitors. Test was change or no change. Blind.
Without details, your claim really doesn’t mean much, except perhaps to you.
@ieales I believe the passive concept you are defending so vehemently has nothing to do with the passive comment from atmasphere. Different application. 

I'm sure you want to say something relevant I just couldn't understand your last posting if you could please elaborate more? 
Nothing is completely passive. The more revealing the circuitry, the more it exposes component 'flaws'.

Experience with phase flip switches in active and passive balanced hardware often left something to be desired in terms of routing and hence inaudibility.

Making both halves of a balanced circuit identical is EXPENSIVE. Add in tube vagaries and the probability of a sonic delta is fairly certain.
These statements are by no means universal truths :)


'Passive' refers to a component that does not involve a semiconductor or vacuum tube. Switches, sockets, capacitors, resistors, volume controls, transformers, wire and the like are considered *completely* passive.


Our MP-1 preamp was the world's first balanced line preamp for home use. The phase switch has been on it since its inception 30 years ago. Quite simply, operating the phase inversion switch is subtle- on multi-channel recordings you can't hear any effect at all. IMO whatever your experience was, it would seem to have been done with equipment that wasn't thought out all that well.

We use differential circuits for our balanced operation. This is not particularly expensive to do- our preamps are pretty affordable compared to the competition in the same class! It is true that each half of the differential amp is slightly different, but you might be amazed at how well they work- the key is a good constant current source, with which we get Common Mode Rejection Ratios (CMRR) in the neighborhood of 100dB, which is pretty good. In a nutshell, no 'sonic delta' when the inversion switch is used (unless playing a true stereo recording); but even if the differential amp is poorly balanced, its a simple fact that there is no 'sonic delta' anyway; you might want to think about why; hint: it has something to do with differential amplifiers :)




These statements are by no means universal truths :)
EXACTLY!

My point is to get people to consider what's behind the faceplate. Far too much HiFi is buzzword-bingo.

Quite simply, operating the phase inversion switch is subtle- on multi-channel recordings you can't hear any effect at all.
Then I would say that the speakers may not be well aligned. The point of the mentioned test was to determine the audibility of polarity. We used polarity correct recordings of acoustic instruments, 80's pop with all live players recorded with polarity correct mics, analogue reverb [plate and chamber] and 80's pop with drum machines, synths, digital reverb and effects. The polarity correct channel inversion was a side show to demonstrate that identical seldom exists.

100db CMMR is excellent. I've endured 'differential' circuits that barely made 60 at some frequency and drifted all over the map with temperature. No offense, but I note that neither CMRR nor the bandwidth over which 100db is attained is listed on the MP3 web page. The only mention of CMRR on the Atma-Sphere site is an explanation here http://www.atma-sphere.com/Resources/balanced.php

25 or 30 years ago Clark Johnson wrote about polarity in a book titled THE WOOD EFFECT.
If I recall it had listed many LPs and what polarity they were recorded in. This came out before CDs.
OK, you made me do it. The whole story according to the Polarity Pundit. Metaphors be with you!

http://www.audiogeorge.com/the-polarity-list/
@rsf507 - That seminal treatise(The Wood Effect) is mentioned in each of the articles, I referenced above. In the first listed Stereophile article; contained in a somewhat blistering response. The very first article also posts a list(at the end), of some CDs and their relative phase(with the majority of players out there), as well as a few CDPs/DACs and their phase output, which may be of some interest.
The Wood Effect was published in 1988, after the advent of the CD.
The Wood Effect. Looks like only used copies available
https://www.directtextbook.com/isbn/9780929383002
Uh, I see one on your list new for $102. Hey, that rhymes! 🤗
you'll hear a difference if your system has the ability to portray the difference...
I get similar results when I switch as merosen gets. I find the sound stage seems to be most effected when switching also as Merosen noted too its a little hollow-dead sounding in the sweet spot when switched. 
I switch it when I'm listening and doing other things in my place (cooking for example) and when I'm sitting. The larger sound scape is useful if your not sitting as I find in my place it opens up the sound and disperses it better but the sweet spot suffers dramatically. so uses for both for me. 
Hrmmm.  My first encounter was in the early 80's in Transparent Audio's humble showroom basement of a house in Hollis, Maine.  I had brought a few audiophile records to sample the Electrocompaniet Ampliwire II amplifier, which, along with early Mark Levinson, Phase Linear and a few others, marked the beginning of decent solid state sound.  Golden-eared Karen Sumner quickly nailed an out of phase recording coming from the Quad ESL 63s.  Great preamps from that day forward included switchable phase controls.  My experience is that vinyl "showed" the difference more distinctly than my digital playback in later years.  I can switch phase on my NAD M2, but rarely feel the need.  (I'm not attempting to start analog/digital controversy...both are deserving.)  That's simply my experience.  This topic does motivate me to give some of my top shelf song cuts another A/B all these years later!  Thanks for the posts.  More Peace, Pinthrift
Then I would say that the speakers may not be well aligned. The point of the mentioned test was to determine the audibility of polarity. We used polarity correct recordings of acoustic instruments, 80's pop with all live players recorded with polarity correct mics, analogue reverb [plate and chamber] and 80's pop with drum machines, synths, digital reverb and effects. The polarity correct channel inversion was a side show to demonstrate that identical seldom exists.
This statement is false. In the recording studio there is no guarantee that a certain track is inverted polarity or not. Many mixboards have polarity inversion switches, but they are there for effect, not get assure correct polarity. Some channels go through effects like reverb or phase shifters and no telling what polarity the signal is when exiting that.

In short, with any multi-channel recording all bets are off when it comes to polarity. Its a mixed bag, plain and simple.
In short, with any multi-channel recording all bets are off when it comes to polarity. Its a mixed bag, plain and simple.
Nonsense.
I polarity tested and corrected all the microphones.
I verified all the lines and electronics.
I made the recordings.
Some recordings were M-S, X-Y, spaced pair and some multi-mic.
Synthesizers are easily polarity checked with a sawtooth wave.
The tracks were 100% polarity correct.

Added effects do not alter the polarity of a recording any more than an acoustic hall alters the polarity of the instruments on stage. The phase of  an effect may differ from the signal, but the polarity remains unless purposefully inverted.


I found polarity switch can have one of three outcomes:
1- little or no effect
2- quite noticeable, but a matter of taste which way you go, or even leave you lost and undecided which one is the better
3- clear superiority of one setting versus the other
The cause must be in the recordings, as has been written in previous posts
Nonsense.
I polarity tested and corrected all the microphones.
I verified all the lines and electronics.
I made the recordings.
Some recordings were M-S, X-Y, spaced pair and some multi-mic.
Synthesizers are easily polarity checked with a sawtooth wave.
The tracks were 100% polarity correct.
Keeping in mind the simple fact that we've had a polarity switch on our preamps longer than anyone else in the world:


OK- If you have that sort of control you can pull it off (although the comment about synths is right out- don't go there- synths do all sorts of things with phase, pitch bending and portemento! However:
Added effects do not alter the polarity of a recording any more than an acoustic hall alters the polarity of the instruments on stage. The phase of an effect may differ from the signal, but the polarity remains unless purposefully inverted.
Reverb, phase shifters (think about what a phase shifter does...), EQ and the like can and do invert phase simply out of the design of the circuit, the number of gain stages and so on. If these effects exist on some tracks and not others, absolute polarity is easily lost. Now if you pay attention to those effect devices and compensate for their polarity (excepting phase shifters!), then you can make it happen.


But you are one in a million when it comes to this sort of thing! IOW with effectively all multi-track recordings you can't here absolute phase.

I first became cognizant of polarity in the mid 60's with the Command Series of recordings on 35mm tape. I forget how or why.

For a long time, LPs were marked as to preferred polarity. They encompassed the full gamut of recorded music from Pop to Opera. Obviously some were marked '??'

IOW with effectively all multi-track recordings you can't hear absolute phase.
I'd agree on many and maybe almost all made from the computer era forward, but there are plenty of multitrack recordings from 1955 onward when the Ampex Sel-Sync 8-track was invented that while their polarity is inverted overall, it is consistent from track to track. 

Now if you pay attention to those effect devices and compensate for their polarity (excepting phase shifters!), then you can make it happen.
When not working in a studio I knew to be polarity correct, SOP when using EQ, Limiter, etc. is to patch the track to a 2nd input, insert the device in the track and bring up the 2nd input. If the level increased, good to go. If not invert. Many mixing desks of the era included a Phase Correlation meter. It's a simple matter to use a mic of known polarity to check all the other mics in use. Of course, misteaks did happen ~<;-)

But you are one in a million when it comes to this sort of thing!
Many recording engineers I knew were every bit as concerned and delivered masters with correct polarity. Master Refs where checked to ensure the cutting house was polarity correct.
For a long time, LPs were marked as to preferred polarity. They encompassed the full gamut of recorded music from Pop to Opera.
Could you name one? I have a lot of titles in my collection and don't recall ever seeing that. The manual for my lp cutter electronics mentions nothing about it as well.
I meant that I marked polarity on the jacket, not that the LP itself was marked. The only ones I recall mentioning polarity were some D2D.

I just recalled when The Tubes "The Completion Backward Principle" was mastered, the producer, David Foster, and Fee Waybill came over with a stack of refs from all over town and New York. I'd been busting David for a few years about his 'neglect' of the mastering process. I'd heard masters and sometimes the LPs didn't 'cut it.' For whatever reason, perhaps to show I was full of [?] or the band pressured him or ????, he had multiple refs made on different lacquers from multiple labs.

At the time I think I had KEF 105.2, Yamaha separates, Oracle TT [arm, cartridge forgotten]. I'd modified both the 105's and electronics.

I forget most of the details now, except some discs were inverted polarity relative to others, verified with an oscilloscope. The best sound was a French lacquer. In the end, it was mastered at Sterling Sound. As I recall, the LP rocked!
I meant that I marked polarity on the jacket, not that the LP itself was marked.
OK- that makes more sense.
I forget most of the details now, except some discs were inverted polarity relative to others, verified with an oscilloscope.
How did you do that? You had the master tape?
some discs were inverted polarity relative to others
I only checked polarity between the reference pressings. I wanted to hear each with the same relative polarity.

As far as the mechanics, just plug a sampling scope into a tape output and check first impact. This also let me check max level and to a lesser degree compression if the wave shape was altered.

As mentioned, multitrack recording may have inconsistent polarity between tracks. I didn't record or mix the album, so I had no idea as to absolute polarity.
You seem to support my assertion that 50% of all recordings are in absolute polarity. Thus the need for a polarity (phase) switch.
I have no idea what %.

That some recordings sound better in one polarity flipped at the loudspeakers, no doubt.

Whether an upstream switch rather than speaker invert is better, I can't say. More convenient, definitely. Remote controlled, even better.

Today, I don't bother.
With regards to polarity in a multi way speaker with drivers wired out of phase to each other, my understanding is that this is done because for example the bass driver may have a second order crossover whereas the tweeter or mid driver may have a third order. You would wire one out of phase to the other so the and resulting sound would be all in phase.
Or if there is a physical distance difference to the voice coil one could be wired out of phase to the other again so the resulting music is coherently in phase when it reaches the listener.
So you should still try to observe correct polarity throughout the signal chain.Another thing to consider is older Jbl pro drivers have the black tab as the positive so some times could be inadvertently wired incorrectly
That’s real nice and everything but it’s not what we’re talking about. 
George Louis the Polarity Pundit claims 92% of CDs are in Reverse Polarity. Agree? Disagree? I don’t mean your gut reaction. Got any data? Talk amongst yourselves. Smoke if ya got em.