All 5 of my monoblock tube amplifiers are in-phase, input to output.
I do not use global negative feedback, so swapping the plate & UL tap pairs makes up for the total phase reversals of all the stages.
I do not use global negative feedback, so swapping the plate & UL tap pairs makes up for the total phase reversals of all the stages.
Very useful, still working on GNFB, I will take this back to the drawing board, might need to add another low gain stage if I'm going to try GNFB.
I will be using 5U4GB rectifier with a centre tapped 5V to reduce hum.
I've been looking at some really really old schematics and I've just noticed on one a transformer was used before the power tube to invert the phase, interesting.
I wouldn't worry too much about this. Absolute phase is a weird thing, as you've guessed. I built an 845 amp years ago, three stages, inverted phase. I just reversed the speaker leads, it sounded better that way. OTOH, I currently use PP amps that do not invert phase, but my preamp DOES. Regardless, swapping the speaker leads at the amp sounds worse. This very much depends on your speakers, your source, etc. Even if you use feedback, swapping the speaker leads is an easy way to correct phase issues.
Well, no. Did you copy this from an unknown source? Like All About Circuits?
There are a lot of misperceptions floating up in this thread. We could start the healing process by de-conflating "phase" and "polarity". These seem to some as equivalent - totally wrong - and by others as convenient or maybe conditionally similar. I would argue that the misuse of these unrelated terms causes enough confusion that we should just say no. The OP's topic is actually polarity, and this has nothing to do with phase, a totally different thing.
We should all fight against this conflation. Oh, the humanity.
All good fortune,
Chris
We should all fight against this conflation. Oh, the humanity.
All good fortune,
Chris
Phase shift is most important to consider if it has a feedback loop wrapped around it, and then polarity of signal to ensure you're putting negative polarity feedback to the earlier stage. If not using a feedback loop both aren't as important in most instances for audio gear. Outside of this, I don't feel absolute signal polarity matters much for sound reproduction. The recording industry doesn't care about absolute polarity, why should you?
In the 1980s, when folk were talking about absolute polarity, it was (temporarily) a common observation that one could improve the sound of their "stereo" every time they experimentally changed the absolute polarity (meaning both speakers). Things just got better and better! There's a lesson there in the reliability of our judgements.
On reflection, folk then realized that recordings were made with no standard of polarity, and loudspeakers with multiple drivers often have the drivers in opposite polarity, referenced to DC. Which is "right"?
All good fortune,
Chris
On reflection, folk then realized that recordings were made with no standard of polarity, and loudspeakers with multiple drivers often have the drivers in opposite polarity, referenced to DC. Which is "right"?
All good fortune,
Chris
Common Test and Measurement Standards books used for decades by the US Navy, and many commercial industries do talk about the relative phase of a signal as it goes through an amplifier's stages.
That not only includes phase from input to output of an amplifier, there are filters, and other processing devices, etc.
Phase was already an established mathematical concept, before amplifiers and speakers existed.
Polarity of a signal, relative to what?
Compression or Rarefaction of air due to a sound wave?
Music has both polarities.
The sound on the side of an Orchestra's Thunder Drum that is struck starts with a rarefaction of air.
The sound on the opposite side of an Orchestra's Thunder Drum (the side that is not struck) starts with a compression of air.
The Absolute Polarity of the Orchestra's Thunder Drum depends on which side of the diaphragm you sit on.
And then, which side was the microphone on? (the electrical connection of the microphone is not the only thing that "controls" or "determines" polarity).
Yes, all of this is often misunderstood, many are confused, and some do not pay attention to any of this.
That not only includes phase from input to output of an amplifier, there are filters, and other processing devices, etc.
Phase was already an established mathematical concept, before amplifiers and speakers existed.
Polarity of a signal, relative to what?
Compression or Rarefaction of air due to a sound wave?
Music has both polarities.
The sound on the side of an Orchestra's Thunder Drum that is struck starts with a rarefaction of air.
The sound on the opposite side of an Orchestra's Thunder Drum (the side that is not struck) starts with a compression of air.
The Absolute Polarity of the Orchestra's Thunder Drum depends on which side of the diaphragm you sit on.
And then, which side was the microphone on? (the electrical connection of the microphone is not the only thing that "controls" or "determines" polarity).
Yes, all of this is often misunderstood, many are confused, and some do not pay attention to any of this.
These are not unrelated terms. A phase shift of 180 degrees is the same thing as a reversal of polarity. Everything that passes electricity will have an effect on phase due to time of travel. A piece of wire will cause a phase lag, granted it's in the millionths of a degree in our tube amps, but it's there. It's not a factor in this case, but must be accounted for in cell phone design ( my day job for several years).
A common cathode (source, emitter) amplifier stage will cause a phase shift of 180 degrees which is equal to a polarity reversal. Two of these amplifier stages will cause a 360 degree phase shift returning the output phase to be equal to the input phase. In this case the polarities are also equal.
Reactive components like the inductor and capacitor have the property to cause the current and voltages in a circuit to be out of phase with each other. This relationship varies with applied frequency. The math behind sorting this all out can get complicated in a multi stage amp, and many simplifications can be found, but as previously mentioned, too many stages without careful phase analysis can result in your negative feedback being positive (worse case) or a reduction in "phase margin" (typical case) of the design so that it can get unstable when a large complex electromechanical system (speaker) with multiple resonances in it is connected to its output.
No electrical component is perfect. A capacitor will also have some inductance (referred to in the data sheet as ESL) and some resistance (ESR). An inductor will have some capacitance which is not typically specified, and a resistance called DCR. These will combine to form a resonant circuit resulting in a resonant frequency, usually called the self resonant frequency, or SRF. The inductor will behave like a capacitor above the SRF! This is not usually an issue in audio amps, except for OPT design. Here several unwanted reactances combine to create a notch in the frequency response, which SHOULD be above the audio frequency band. This was not the case in the early Hammond 1628SE. The notch fell at 16 to 22 KHz depending on how it was connected.
These component properties can combine to create some unexpected results in a complex design, especially when more than one feedback path exists. Note that the power supply is a possible feedback path at frequency extremes. Decoupling is your friend.
My daughter played the drums back in the 90's. When the Media Vision Pro Audio Spectrum first appeared (early 44/16 audio card) I spent considerable time recording drums. As the drummer stomps the pedal on the kick drum a wave of compressed air is launched from the front drum head. When your system preserves absolute polarity (0 degree phase shift) all the way from the microphone to the amp and through the speaker, the woofer cone should move toward you on this event. I burned a CD with some of my early percussion recordings and took it over to a large Sam Ash music store and spent several hours in their "recording studio" listening to near field monitor speakers. After several trips to Sam Ash, Ace music, and a few others, I bought a pair of Yanaha NS-10M Studio monitors. They are still on my test bench today because they get percussion right. Flip the speaker wires so that the cone moves inward on a bass drum stomp......they DON'T get percussion right.
Lesson learned in the 90's.......don't put a Shure SM-57 microphone INSIDE the kick drum. It won't work so well after that test.
Phase is a time difference between two measurements of a signal. Polarity is the orientation of the probes used to measure with. These things are unrelated.
For example, if an amplifier stage had 180 deg phase shift it could not have feedback applied around it - it would oscillate. A string of these 180 deg phase shifts would make any amplifier into an oscillator with even local feedback applied.
Imagine polarity as two choices in the hookup of a transformer's secondary winding. One polarity gives the same phase shift as the other, not 180 deg apart. Swapping the wires changes polarity but not phase shift.
All good fortune,
Chris
For example, if an amplifier stage had 180 deg phase shift it could not have feedback applied around it - it would oscillate. A string of these 180 deg phase shifts would make any amplifier into an oscillator with even local feedback applied.
Imagine polarity as two choices in the hookup of a transformer's secondary winding. One polarity gives the same phase shift as the other, not 180 deg apart. Swapping the wires changes polarity but not phase shift.
All good fortune,
Chris
The two outputs of a phase inverter that has the cathodes connected together to a CCS (constant current sink), at low and mid audio frequencies,
will have a large phase shift (extremely close to 180 degrees).
But, there also will be an extremely low time difference between the two outputs (put a square wave in, and the transitions will be extremely close in time).
There is a very large phase shift, but there is essentially no time difference.
Just another example of the misunderstanding of the words: phase shift, polarity, and time difference.
Sometimes they are related, sometimes they are not related.
It depends on the situation, circuit, etc.
Your circuit may vary.
Your mileage may vary.
will have a large phase shift (extremely close to 180 degrees).
But, there also will be an extremely low time difference between the two outputs (put a square wave in, and the transitions will be extremely close in time).
There is a very large phase shift, but there is essentially no time difference.
Just another example of the misunderstanding of the words: phase shift, polarity, and time difference.
Sometimes they are related, sometimes they are not related.
It depends on the situation, circuit, etc.
Your circuit may vary.
Your mileage may vary.
That's incorrect. An amplifying stage with either or both polarities of outputs available will have very small phase shift to either output. Phase is the relative time delay between two points expressed as angle of rotation. For example, in a multi-stage amplifier, phase shifts add - how can feedback be applied?
The fact that opposite polarity looks like a 180 deg phase shift under some specific condition doesn't make them equal, and in fact they're unrelated. Folk have been misusing this coincidence forever, and it causes all kind of confusion, for example on this very thread. We should just say no. Think of the children!
All good fortune,
Chris
The fact that opposite polarity looks like a 180 deg phase shift under some specific condition doesn't make them equal, and in fact they're unrelated. Folk have been misusing this coincidence forever, and it causes all kind of confusion, for example on this very thread. We should just say no. Think of the children!
All good fortune,
Chris
Whatever you want to call the two plate outputs from the constant current sinked coupled cathodes, the plates are 180 degrees different from each other.
Put a sine wave into one of the grids, and keep the other grid constant.
It definitely is not a time difference between the plates, the plates are just at an angular difference.
I think that is why they call it a "Phase Inverter", they do not call it a "Delay Circuit".
I am too old to remember everything from my 1962 Geometry class, but I remember Sine Wave, and Cosine Wave.
They were said to be 90 Degrees "Out of Phase".
Hmm, that word Phase keeps coming up.
I do not remember anybody in that class talking about the time difference of those two waves.
Generally:
The time delay through an amplifier is a constant.
But the phase shift through that same amplifier is not constant; the degrees of phase shift increases as the frequency is increased.
Just my opinions
Put a sine wave into one of the grids, and keep the other grid constant.
It definitely is not a time difference between the plates, the plates are just at an angular difference.
I think that is why they call it a "Phase Inverter", they do not call it a "Delay Circuit".
I am too old to remember everything from my 1962 Geometry class, but I remember Sine Wave, and Cosine Wave.
They were said to be 90 Degrees "Out of Phase".
Hmm, that word Phase keeps coming up.
I do not remember anybody in that class talking about the time difference of those two waves.
Generally:
The time delay through an amplifier is a constant.
But the phase shift through that same amplifier is not constant; the degrees of phase shift increases as the frequency is increased.
Just my opinions
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1962? We must be almost exactly the same age, fellow Geezer. Maybe the best part of Geezerhood is the freedom to argue arcane topics at all hours. A luxury we couldn't have imagined for most of a (seriously) working life.
Let me put my argument two ways: First, time is unidirectional, so it's not possible to have a negative phase difference between a point in an amplifier causally downstream from another point. Whether we were taught it correctly or not (and I certainly wasn't) phase angle can only increase as signal passes through an amplifier. Each stage, each series'd reactive element adds phase angle, each unto its nature. It's not physically possible to subtract angle because time is unidirectional (unless you're a photon, then everything happens at the same time. must be confusing).
Second, we're taught rotating vectors and their basic trig in a context of simple repetitive single frequency waveforms that started at the Big Bang and will last forever (both actually required for them to be repetitive). In this model, time doesn't matter so can be abstracted out. And from this model, we all grew up conflating 180 deg phase difference with an inversion of polarity, because it's true in that model. But actual amplifiers don't have internal 180 deg phase differences (meaning the sum of all phase angles though the amplifier and back through the feedback network if used), except at frequency extremes where loop gain must be less than 1 for stability) and do have causality and an arrow of time.
Polarity is an abstract that depends completely on how you choose to connect your metering contacts to the measured point. Put the red on one side, the black on the other, or reverse them, you haven't changed anything. It's true independent of time or "phase" or anything else.
All good fortune fellow Geezer,
Chris
Let me put my argument two ways: First, time is unidirectional, so it's not possible to have a negative phase difference between a point in an amplifier causally downstream from another point. Whether we were taught it correctly or not (and I certainly wasn't) phase angle can only increase as signal passes through an amplifier. Each stage, each series'd reactive element adds phase angle, each unto its nature. It's not physically possible to subtract angle because time is unidirectional (unless you're a photon, then everything happens at the same time. must be confusing).
Second, we're taught rotating vectors and their basic trig in a context of simple repetitive single frequency waveforms that started at the Big Bang and will last forever (both actually required for them to be repetitive). In this model, time doesn't matter so can be abstracted out. And from this model, we all grew up conflating 180 deg phase difference with an inversion of polarity, because it's true in that model. But actual amplifiers don't have internal 180 deg phase differences (meaning the sum of all phase angles though the amplifier and back through the feedback network if used), except at frequency extremes where loop gain must be less than 1 for stability) and do have causality and an arrow of time.
Polarity is an abstract that depends completely on how you choose to connect your metering contacts to the measured point. Put the red on one side, the black on the other, or reverse them, you haven't changed anything. It's true independent of time or "phase" or anything else.
All good fortune fellow Geezer,
Chris
Thank you for providing a better example, and still framed within a time vs. magnitude model. Although these two waveforms are based on a continuous (time invariant) model, they still show, better than I could explain, the difference. The conflation is deeply engraved into all of us, so a hard sell. Maybe thinking in terms of an impulse might be a useful approach, but your example is better.
All good fortune, and thank you for your insight,
Chris
All good fortune, and thank you for your insight,
Chris
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And this is the true origin of phase, a generator which produces a single frequency, continuously, with multiple (for AC power distribution, 3) outputs, referenced to Earth at the same frequency (of course) and at simultaneously different phases. Notably, power taken from the difference between any two "phases" is also a sine/cosign wave and at the same frequency as any of the phases observed separately. Folk who do big-ish SR jobs use this routinely for PA power from 440 3-phase to 208 (???) single phase.
From this early AC power generation technology, which looking back with an imaginative eye looks pretty amazingly inventive (all first principles stuff in those days and internet latency of decades), we (the 1920s we) extrapolated into the hot new field of electronics, and the world exploded.
All good fortune,
Chris
From this early AC power generation technology, which looking back with an imaginative eye looks pretty amazingly inventive (all first principles stuff in those days and internet latency of decades), we (the 1920s we) extrapolated into the hot new field of electronics, and the world exploded.
All good fortune,
Chris
This is a great visual representation. I had a really hard time wrapping my head around the concept back in Eltec 208 until it was shown to me this way on the chalkboard 🙂