Out of phase, does it matter?

[überfuzz]

I'm trying to design a gutar amp by looking at known circuits. At the moment I'm simulating a circuit that seems ok. Only one thing the output is out of phase with the input. See Picture. Is this going to mess up the tone etc..?

[exclamationmark]

Won't make any difference. Depending on the frequency, the signal will be in and out of phase anyway. If you sim your circuit again and try extremely high or low frequencies, you will see that the phase between input and output changes. We can't hear phase difference anyway (though some might disagree...).

[Chuck H]

When Marshall built their bassman clone it was a virtual copy. But Marshall used Celestion speakers and Fender used Jensen. Vintage Jensen speakers invert the phase. So one of the differences between the Fender and the Marshall was that one played in phase with the input and the other played out of phase with the input.

As far as amp stability it could actually be of benefit since the highest strength radiant fields in the chassis wouldn't be prone to cause positive feedback.

Many amps are channel switching. But not really. They just have an additional triode added to the signal chain. This also inverts the phase. So some amps play both in phase AND out of phase depending on which "channel" your using.

I wouldn't worry about it.

[überfuzz]

Thanks for interesting input. I guess theory blinded me (one year left on Engineering Physics, shouldn't get tangled up like that). When I read your posts I sorta sobered up. If you look closely you see that the output is 90 deg behind the input. Not 'out of phase' as in 180 deg, interesting.

Slightly off topic
I seem to remember fixing a speaker where the elements were mounted with shifted polarity. Sounded dreadful! A friend of mine bought it and asked me if I could determine which element to replace. Turned out to be a nice speaker. :-)

[Chuck H]

If you look closely you see that the output is 90 deg behind the input. Not 'out of phase' as in 180 deg, interesting.

This isn't of huge concearn either. Though it could have an affect on volume related sustain. Just theorizing but it seems to me that if the input is in phase with the output you would get better fundamental acoustics for volume related sustain. At 180* you would get other harmonics. At 90* still different harmonics. Since there are attenuations, pass filters, tone stacks, coupling and load circuits throughout most preamps in guitar amps there is usually a somewhat unpredictable phase differential during the design process. I mean, you could probably predict it but it would be tedious.

If you want to see what it would sound like at a 180* phase difference or in phase you could add a phase correcting circuit in the preamp (though not within any feedback loop). Adding a capacitor and a 0V reference to the signal chain gives a roughly 30* shift. So if you do a string of three .1uf caps with 1M resistors to 0V in between that should get you the other 90* shift. You see this circuit in some amps. At that point you'll be either in phase or 180* out. Then you can swap your speaker polarity to hear it the other way. There's nothing like trying something if you want to know what it does. As I mentioned, the only audible difference should be in the acoustic feedback between the guitar and amp. But this can be significant depending on how you play. There are even limitations to how significant this affect is due to things like the guitars distance from the amp, which direction your facing, etc. So, you could try it and see for yourself or just ignore it. Either way you'll be fine. But if you try it you'll know instead of wonder.

[J M Fahey]

Vintage Jensen speakers invert the phase.

I beg your pardon?
You mean that if I wire the Red cable to the + leg in a Celestion speaker and apply a positive voltage the cone moves forward but if aI do the same in a Jensen it moves backward?
That´s a new one.
In every case the black wire going to the - leg of course.

[riz]

I thought it was JBLs that were wired "backwards"(?).

[Tom Phillips]

I always test the speaker phaseing with a battery when I wire them up to be sure that I know how the voice coils are wired.

I have heard the "Vintage Jensens are wired backwards" statement many times but, from personal experience I find the statement to be untrue. I just tested two 1961 P12R Jensens with original cones.They both move forward with positive DC applied to the red terminal. Conversly, JBL D120Fs that I have with original cones (circa 1967) move rearward with positive DC applied to the red terminal.

Tom

[Chuck H]

Well... This particular piece of info was garnered from the Gerald Weber books. The chapter went into some detail so I gave it credibility. After having the info come into question though I figured I should do some research of my own...

I only have one vintage Jensen on hand. A P12R circa late 50's(?) It came out of an old console phonograph. On my particular speaker, which still has three inches of lead from the original amp on the terminals, the polarity is indicated by a small, round, red sticker. No actual + or - printed or stamped. I assume that the red sticker is there to indicate the + lead. Whether this sticker was placed by Jensen or the phonograph manufacturere I can't say. Now... The lug with the red sticker has a black lead on it and the lug with no marking has a red lead on it!?! So it seems that any info I garner from this particular speaker is questionable. When I touch a battery + to the speaker terminal with the red sticker (black lead) the cone moves outward. I take this to mean that:

1) The speaker is correct in polarity and the phonograph manufacturer wired it backward.
2) The phonograph manufacturer used black lead as hot as is common with AC wiring (I've seen this in other vintage electronics).

Search engine research shows that at least some people support the idea that vintage Jensen AND JBL speakers are poled opposite of modern convention.

I also read that vintage Jensen speakers had NO polarity markings at all. This would be consistent with the speaker I have if the silly red sticker fell off. But if they were commonly shipped without that sticker it's possible that Fender simply wired some amps in reverse polarity???

At this point I'd love to hear from anyone here I trust that knows the truth about this.

[Steve Conner]

When phase matters, I'd just do the battery test. It's the first I've heard of the old American speakers being "the other way round", but they're not exactly common over here.

Re what Chuck was saying about phase vs. feedback assisted sustain, this is one of my pet theories about digital modelling amps. The DSP adds a time delay ("latency") of a few milliseconds to the signal path, and as sound travels about 1ft per ms in air, the effect is as if you were standing a few feet further away from the amp than you actually are.

[Enzo]

You need to keep polarity straight in the speakers.

Your electric guitar will sound like a ratiug cirtcele if you get it reversed.

[Tom Phillips]

... Gerald Weber books... credibility...

[J M Fahey]

Well... This particular piece of info was garnered from the Gerald Weber books.

*The*source for unfounded emphatically said blanket statements.
Oh well.

PS: I think the red dot was Jensen´s factory applied.
Can´t believe any serious manufacturer ships unmarked speakers.
Although some feeble minded guy might think so and write books and sell videos saying so after seeing a 50 years old speaker where the red label fell off or was rubbed away.
Unfortunately, in Internet bad data travels 10X faster and reaches 1000X more people than good data.

[Steve Conner]

Otherwise known as Kitman's Law: "Pure drivel tends to drive ordinary drivel off the TV screen"

[J M Fahey]

@ Steve C.
I remember an "anti-feedback" box was sold which *detuned* sound a bit.
Worked quite well, but was suggested *not* be used for singers and other musical uses because of said detuning.
Output frequencies were shifted down 5Hz.
Not much in higher frequencies, but a lot at lower ones.
The main suggested use was in Churches, open mic conference rooms and such.
Specially good to kill that ringing, "I´m about to feed back" nastyness.