Will preamp manufacturers tell you if the model is phase inverse?

You can use the Stereophile test CD to determine whether your polarity is correct

Hi @pops,

don’t you mean the signal is inverting since your example cites one as non-inverting and two as interting? What am I missing?

No, that example is non-inverting.

All we're doing is adding the number of gain stages in the signal path. A non-inverting component has an even number of gain stages and an inverting component has an odd number of gain stages.

Think of it this way:

• For a non-inverting component, assign 2 (or any even number).
• For an inverting component, assign 1 (or any odd number).

So: non-inverting + inverting + inverting:
2+1+1 = 4.

Even number of gain stages = non-inverting.

Cheers,
Thom @ Galibier Design

Phase or Polarity
http://totalproaudio.stevebunting.com/30/basics/phase-or-polarity/

A preamp that inverts simply outputs the negative of what's fed into it (the "inverse" wave). It won't harm anything.

That's why "inversion" is one thing and "phase" another. The phase of a signal is merely the delay associated with it. IIR (standard) filters cause different phasing at different frequencies. Digitized FIR filters do not.

To avoid confusion, pure delay (not frequency dependent) is called "latency" and this is what a digital delay can cure between speakers or speaker drivers that are not the same exact distance from your ears.

Ok, I don't understand phase.  If a preamp inverts phase, does that mean that when a speaker that would normally pump out when in phase will instead pump in when hooked up to a preamp that inverts phase?

If so, wouldn't that ruin the driver or the sound?

@thom_mackris  don't you mean the signal is inverting since your example cites one as non-inverting and two as interting?  What am I missing?

Do some tube integrated amps need the terminals reversed as well?

I have a Rogue Metis and the manual said nothing about about Phase Inverse. John at Audio Connection let me know when I bought the preamp. I called Rogue and they confirmed I needed to reverse the cables at my speakers. Nothing was ever said in any review I read on the Metis and I read them all. 

As a guy who's concerned with phase perhaps more than most, maybe I can offer some overblown advice.

First, never assume anything. The only way to check phase along the electrical path is with a signal generator and a scope, and the only worthwhile end points are at the source (output of the signal generator) and at the power amp outputs, so any inversion cancellation along the chain just washes out. That way you can just swap your speaker leads to correct an issue. Note that you probably need at least one differential (floating) probe to do this, since it's usually a bad idea to connect preamp ground to speaker terminal negative (which generally floats), and while a scope's probe ends are isolated, the ground clips are tied together internally. And note that this test, comparing phase on channel A and B of your scope, is useful only on equipment with negligible latency (e.g. analog). But there's a way out. More on that below.

Second though, a mike test is in order for the speakers. Once you've tested the woofer with the battery test mentioned before, you can check the polarity of the mike (and its preamp, if it's a dynamic mike) by comparing your test signal against the mike output, again on the scope. Ah, but now, with speakers, mikes and the distance between them, we've introduced latency. That's why a continuous sine wave is not optimal. You need tone bursts.

Third, it's been mentioned that some speakers invert phase between drivers to compensate for phase cancellation, probably a result of physical offset between voice coils. Note that this isn't putting them "in phase", it's just putting them out of phase enough to create (some) addition with a continuous sine input. To see the real story of how off they are in timing, repeated short tone bursts (with a good size gap of silence) are required. Burst generators aren't easy to come by for some reason, but any computer (laptop, e.g.) can be fitted with Audacity for free. You can generate a sine of given frequency and duration, then edit it to form a short burst with leading and trailing silence, then play it back in a loop to repeat so your scope won't have to trigger on a single burst. Now you can see whether your tone burst (hence your music) is inverted or not, plus you can check the phase of your drivers AND the delay between them A tone burst at the crossover frequency between two drivers should play through both and superimpose (add) perfectly. You may be in for a shock.

Which gets us here. If you are concerned enough with this (as I am), you employ linear-phase FIR filtering for your crossovers and equalizers. Now you know your filters aren't causing phase anomalies. And you separately amplify each driver. Any cheap desktop with a soundcard and free software will make a brilliant DSP for these purposes, and even a $50 pcie 7.1 'surround' sound card/DAC will make a superb multichannel (up to 7 discrete) line-level output. It goes without saying that in a multiamp setup (or any multi-driver setup for that matter) phase in all its aspects is very important. BTW, another advantage of such setups is the fact that you can perfectly phase your drivers (make them simultaneous) at the crossover points by simply programming delay to compensate for their physical distances, whether you use linear-phase filters or not. Which brings us back to latency. Computers and DSPs have lots of it, so you can't just A/B your input and output on a scope. But we no longer need to scope our input when using tone bursts. Audacity (e.g.) shows you the exact form of your tone burst. Now we're just analyzing output. As for the recorded phasing of actual source material, there's nothing you can do about that so forget it.

And even if you're not keen on computers, DSPs and linear phase filters, you still can make your tests with the battery, laptop, scope and mike to test with tone bursts for inversion on all your drivers. You'd be amazed (and perhaps somewhat depressed) at what I've found phasewise on a variety of equipment. I trust absolutely nothing now regarding its phasing.

Hint: try playing a tone burst at the crossover frequency of your drivers (say, mid/tweeter) and see how far off they are. You'll see why I went to DSPs.

Conrad Johnson are Phase inverting 

Team

@kalali that would just swap left and right, not phase. Swapping phase involves swapping the signal and ground wires within each cable..

Why not switch the input leads at the amplifier instead of the speakers? Is there anything wrong with this approach?

You can't just invert a single ended cable. :)

You can't just swap the leads, because the outer conductor is almost always ground. You'll just end up with ground on the center, and ground on the ring.

This would work for truly balanced inputs, which are very rare in RCA inputs.

Best,

E

Remember that you want to take the entire amplification chain into account. So (for example) if you have:

• Phono stage (non-inverting)
• Line stage (inverting)
• Amplifier (inverting)

Then your signal path is non-inverting.  With multiple sources, you might have one source which results in an inverted signal and another that does not.

Cheers,
Thom @ Galibier Design

I just heard back from Nick at Rogue. The RP-1 and the RP-5 Both invert phase on ALL inputs (including phono).

 

So Rogue told you the RP1 inverts both line and phono, but JA's measurements in Stereophile showed that the phono does not invert?  Seems odd to have a manufacturer give you the wrong specs.

although phono stage preserved absolute polarity and line inputs stage inverted absolute polarity, the preamp output still inverted absolute polarity!

Wait.  So Rogue told you the RP1 inverts both line and phono, but JA's measurements in Stereophile showed that the phono does not invert?  Seems odd to have a manufacturer give you the wrong specs.  

What i never understood is if the circuit inverts polarity why doesn’t a manufacturer simply reverse the leads heading to the component’s output so that once leaving the component polarity isn’t reversed any longer.

some preamp may be easy to do like this, most may require an extra stage.

Thats a good question

So I’ve owned gear that inverted phase and the owner’s manual instructed that wiring to the speakers should be flipped. What i never understood is if the circuit inverts polarity why doesn’t a manufacturer simply reverse the leads heading to the component’s output so that once leaving the component polarity isn’t reversed any longer. 

I think the idea of having a phase inverter makes the most sense, given the possibility of a recording being inverted or not, however...

I should also point out that the simplest designs invert phase, since they use a single tube stage per channel. That's the simplest possible design. To get phase accurate, you have to add at least one more stage.

Best,

E

So much for plug and play. Lots to consider when purchasing a preamp

For the record, multi-way speakers often invert one or more drivers relative to the others to achieve correct phase matching through the crossover regions. You can see this in the Stereophile step response measurements.

In general (but not legally enforced) the woofer’s are positively aligned, and other drivers are chosen to invert or not based on phase matching to the driver below. Of course, some designer may think that mid-range phase is most important, so this is a general rule.

To test the polarity of your woofer, take a 1.5 - 9V battery and attach positive to positive. If your woofer moved outwards, then it is in positive polarity. You may even be able to tell the midrange as well.

1.5V cells are safe to use on tweets too.

Best,

E

According to the Polarity Pundit, who has probably looked into the whole polarity issue for not only CDs but also LPs, much more than anyone else, Clark Johnsen's book on the subject notwithstanding, the actual percentage of CDs that are in reverse polarity is 92%, less for LPs. Therefore you would obviously be much better off in the long run if your system was in reverse polarity. One of the most disturbing things that the Polarity Pundit’s list of audiophile CDs and labels is just HOW MANY are in reverse polarity. 😩

good point. I recognize phase in the recording process A/B ing back and forth (I have a studio), not certain if I would recognize if nothing to compare to.

Since there is no recording standard for phase, does it really matter if the pre-amp does or does not invert phase when you have a 50/50 chance that the recording will be correct?

FWIW, generally speaking, I've noted that most tubed preamps with only one tube per channel invert phase.

John Atkinson always mention absolute/inverted polarity with his Measurements :
Rogue Rp-1 phono stage preserved absolute polarity and line inputs inverted absolute polarity
https://www.stereophile.com/content/rogue-audio-rp-1-preamplifier-measurements

I just heard back from Nick at Rogue. The RP-1 and the RP-5 Both invert phase on ALL inputs (including phono). So I would need to switch speaker terminals when using. I wonder how many owners are not switching the terminals

Virtually certain that the RP-1 inverts phase--confirm with John Rutan (audioconnection on this board).  I think the added complication with that preamp is that the phono pre-amp adds another stage of inversion, bringing you back into phase.  If you care about that sort of thing (I do, others don't), it means you're switching speaker wires around when you play records....

Looks like a lot of maintenance to play records. One would think they would at least include a switch. I have heard that some amps do include a phase switch. Not certain for the phono section. I'll reach out to Rogue and get back

Ah, yes!  Good point.

it means you’re switching speaker wires around when you play records....

Or you could just invert the phono leads at the arm/cartridge and be done. I once owned a preamp that only inverted the phono stage, the line stage was normal.

Virtually certain that the RP-1 inverts phase--confirm with John Rutan (audioconnection on this board).  I think the added complication with that preamp is that the phono pre-amp adds another stage of inversion, bringing you back into phase.  If you care about that sort of thing (I do, others don't), it means you're switching speaker wires around when you play records....

In my vast experience, most manufacturers will say something about it in the manual if it does invert phase.  If it is not mentioned, then usually it does not invert phase.  Of course, there are exceptions.

I remember the older cj preamps stated it in the manual, but in really small fine print.

I know for Prima Luna no. For my current CJ ET3se the manual mentions phase inversion.