It's a circuit with an inductance and capacitance in one of two possible connections, and for the purpose of conserving generated power.

It seems like power factor correction to me. Easy to achieve at a fixed frequency (50Hz/60Hz) but not across 10 octaves of audio! The inductive component of a loudspeaker doesn't actually waste power, as it is driven from an amplifier which can be thought of is a DC to AC converter.
There are plenty of circuits which will "linearise" a loudspeaker load, making it look like a resistor, but most tests confirm that the amplifier produces lower distortion if it is driving an inductor.

 

Here's the same graph from the datasheet of a real FET. It's an ON-Semi 2SK3557, which is a particularly good audio FET.
View attachment 253596The top-right graph is the one that matches the one in your book.
The ratio between drain current and gate voltage is called Gfs, the forward transconductance. It would be nice to think that it is constant, but it isn't. It varies with drain current. Note that the graph in your book as nicely regularly spaced lines and on the real graph they get closer together as the current reduces. That makes the voltage gain in that region a proportional to the square of gate voltage. @crutschow isn't wrong when he said it was exponential. Further down the graph it IS exponential!

The key to all this is that a small enough portion of any curve is a straight line (that's the basis of calculus). If your amplifier uses only a very small portion of the curve that it is close enough to a straight line to make it linear. To keep it in that portion of the curve, you need a lot of gain and a lot of feedback.

By the way, I disagree with @LowQCab when he says that the room creates distortions. It can make the frequency response far from flat, and there can possibly be resonances, but I don't see how a room could actually add harmonics. And good speakers are much better than 10% THD these days.

Yes, okay IanO, that is not an accurate graph of JFET drain current. But tell me, is there a constant current region that if gate voltage remains within, a limited linear Amplification can be achieved?

 

Yes, okay IanO, that is not an accurate graph of JFET drain current. But tell me, is there a constant current region that if gate voltage remains within, a limited linear Amplification can be achieved?

No. The generall accepted relationship between Id and Vgs in the saturation region is:
\(
I_{DS}=I_{DSS}(1-\frac{V_{GS}}{V_P})^2
\)
(From Wikipedia)
It is square-law.
That means that the distortion will be proportional to the signal level, and it will be second harmonic.
The only way to keep distortion low is to keep the signal level low. That can be done by adding gain and feedback.

Do you have anything in mind that you want to amplify? Microphone? Guitar? Turntable?
If you are interested in JFETs you should read the works of one of their greatest advocates: Erno Borberly
https://audioxpress.com/article/JFETs-The-New-Frontier-Part-1
https://audioxpress.com/article/JFETs-The-New-Frontier-Part-2

 

Yes, okay IanO, that is not an accurate graph of JFET drain current. But tell me, is there a constant current region that if gate voltage remains within, a limited linear Amplification can be achieved?

Whoever wrote the reply with an actual "ON-semi FET drain current graph" , yes you make good sense, is negative feedback equal to a out 5 volts (pinch-off) voltage a heavy enough feedback to keep the drain current within the "constant current" portion of all the different Id-Vds graphs in my book, let me review your graph first, as it might answer my questions with this matter of a linear FET amplifier system. Give me a half hour if you would from the time you read this post, by the way our conversation has been moved somewhere that I'm not at all familiar with, so please don't count on follow-up from here.

 

When applied to a transformer at a power substation it has been common practice to use a variable amount of Farads in shunt with the secondaries for industrial customers who operate a large number of motors. Motors are more of less inductors, and by "catching" the "inductive kickback" on a capacitor, some of the electrical power can be used for the following half cycle of AC operation. That's essentially the how/why of the capacitor of a capacitor start motor and it reduces the otherwise enormous current draw on circuitry, but can also be used to conserve power.

Ummm ... no.

What you are describing is power factor correction at a very high power level in a system with wires that are miles long. Exactly zero percent of that applies to an audio amplifier. Also, the power station capacitors do not "catch" any inductive kicks. Mainly because large AC motors do not produce any when running (which is when the PF capacitors do their work), and partly because even if they did, the total energy would not be enough to produce even a flicker back at the substation.

And, your understanding of how a capacitor start motor works is incorrect.

https://en.wikipedia.org/wiki/AC_motor#Capacitor_start_motor

ak

 

No. The generall accepted relationship between Id and Vgs in the saturation region is:
\(
I_{DS}=I_{DSS}(1-\frac{V_{GS}}{V_P})^2
\)
(From Wikipedia)
It is square-law.
That means that the distortion will be proportional to the signal level, and it will be second harmonic.
The only way to keep distortion low is to keep the signal level low. That can be done by adding gain and feedback.

Do you have anything in mind that you want to amplify? Microphone? Guitar? Turntable?
If you are interested in JFETs you should read the works of one of their greatest advocates: Erno Borberly
https://audioxpress.com/article/JFETs-The-New-Frontier-Part-1
https://audioxpress.com/article/JFETs-The-New-Frontier-Part-2

Just audio Amplification, hopefully manufactured here in the USA.
However having just bought an Onkyo Network Receiver I doubt I'll ever own any better sound machine. But for lack of a better way to contribute to society and keep myself busy, I will review what I can find on Mr. Borberly, I tried to once but don't recall anything from the results. I hope I'd remember something if it related to what's already in my head. By the way distortion isn't my problem with Bipolar Amplification. My troubles are with the intensities of the harmonics of the fundamental frequencies of audio "notes" per each instrument. My understanding of musical notes is that all instruments produce roughly the same fundsmental-notes-frequenies, but their harmonics distinguish each instrument by varying intensities of each harmonic. Therefore the need for an FET amp or Bipolar amp that doesn't change or distort the harmonics.

 

Ummm ... no.

What you are describing is power factor correction at a very high power level in a system with wires that are miles long. Exactly zero percent of that applies to an audio amplifier. Also, the power station capacitors do not "catch" any inductive kicks. Mainly because large AC motors do not produce any when running (which is when the PF capacitors do their work), and partly because even if they did, the total energy would not be enough to produce even a flicker back at the substation.

And, your understanding of how a capacitor start motor works is incorrect.

https://en.wikipedia.org/wiki/AC_motor#Capacitor_start_motor

ak

Yeah, we're getting two subjects mixed, no L/C Resonance is not an audio issue.

 

I've had two or more musicians tell me the older style amplified instruments had a better sound than the newer ones. The only difference between the 50's USA and today are the type of transistor amps. used. Why would a responsible musician say that? I don't know?

I do.

It is a combination of what they have been told and the psychoacoustics of music. An amplifier that rolls off the high end gently, attenuating the high-order harmonics without a lot of frequency-dependent phase shifts, and clips the peaks gently, without introducing a *relatively* large amount of odd-order harmonics, tends to make bad audio sound better; more pleasant, less "fatiguing". A live violin can be very screechy, and a decent solid state amp will capture that with all of its imperfections. It's an electronic version of "don't shoot the messenger". If you are raised on audio with limited bandwidth and a lot of transconductance-induced harmonic distortion, and told that that "tube sound" is good, then a quality solid state amp is going to be a rude awakening.

Anyone with even an entry-level understanding of harmonics can design a solid state amp that perfectly replicates the "tube sound". In the 80's and 90's at the CES, companies sold these things. Tube sound without all of the heat and unreliability and constant replacement costs. Big money. Bob Carver did the same thing with solid state amps, producing models that sounded exactly like multi-thousand dollar amps, but for only a few hundred dollars.

Bottom line, some music sounds bad when produced live, and a good amp does nothing to clean it up. Also, the best gear of the 50's sounded nothing like the original source material. If you like that, fine. (You should see what goes on in the world of guitar fuzz pedals.) But that has nothing to do with being "better". Unfamiliar? Sure. Different? Absolutely! Better . . . ?

ak

 

I do.

It is a combination of what they have been told and the psychoacoustics of music. An amplifier that rolls off the high end gently, attenuating the high-order harmonics without a lot of frequency-dependent phase shifts, and clips the peaks gently, without introducing a *relatively* large amount of odd-order harmonics, tends to make bad audio sound better; more pleasant, less "fatiguing". A live violin can be very screechy, and a decent solid state amp will capture that with all of its imperfections. It's an electronic version of "don't shoot the messenger". If you are raised on audio with limited bandwidth and a lot of transconductance-induced harmonic distortion, and told that that "tube sound" is good, then a quality solid state amp is going to be a rude awakening.

Anyone with even an entry-level understanding of harmonics can design a solid state amp that perfectly replicates the "tube sound". In the 80's and 90's at the CES, companies sold these things. Tube sound without all of the heat and unreliability and constant replacement costs. Big money. Bob Carver did the same thing with solid state amps, producing models that sounded exactly like multi-thousand dollar amps, but for only a few hundred dollars.

Bottom line, some music sounds bad when produced live, and a good amp does nothing to clean it up. Also, the best gear of the 50's sounded nothing like the original source material. If you like that, fine. (You should see what goes on in the world of guitar fuzz pedals.) But that has nothing to do with being "better". Unfamiliar? Sure. Different? Absolutely! Better . . . ?

ak

Nope, it's not a psychological phenomenon

 

Ummm ... no.

What you are describing is power factor correction at a very high power level in a system with wires that are miles long. Exactly zero percent of that applies to an audio amplifier. Also, the power station capacitors do not "catch" any inductive kicks. Mainly because large AC motors do not produce any when running (which is when the PF capacitors do their work), and partly because even if they did, the total energy would not be enough to produce even a flicker back at the substation.

And, your understanding of how a capacitor start motor works is incorrect.

https://en.wikipedia.org/wiki/AC_motor#Capacitor_start_motor

ak

Yes, but stating that detracts from it's significance in electrical power conservation. Power distribution companies are required to stay within about 3 % of unity, implying little to be gained by correcting the power factor to near unity. Far from the obvious reality when viewed from the "Resonance viewpoint". For a sustained L/C Resonance you must replace the voltage loss across the coil-winding wire-resistance ONLY. And that means a very significant amount of generated power can be conserved on a worldwide scale. Hopefully enough to buy us some time to convert our oil dependence to "cold fusion", a true "clean" nuclear source of energy. By the way, have you heard anything about the matter from a reliable source?

 

Ummm ... no.

What you are describing is power factor correction at a very high power level in a system with wires that are miles long. Exactly zero percent of that applies to an audio amplifier. Also, the power station capacitors do not "catch" any inductive kicks. Mainly because large AC motors do not produce any when running (which is when the PF capacitors do their work), and partly because even if they did, the total energy would not be enough to produce even a flicker back at the substation.

And, your understanding of how a capacitor start motor works is incorrect.

https://en.wikipedia.org/wiki/AC_motor#Capacitor_start_motor

ak

 

Well then, what is your understanding of a capacitor-run motor, and why is the shunt capacitor with an induction motor thrown out of it's connection with the motor once the motor is up to an high enough RPM?

 

Yes, but stating that detracts from it's significance in electrical power conservation. Power distribution companies are required to stay within about 3 % of unity, implying little to be gained by correcting the power factor to near unity. Far from the obvious reality when viewed from the "Resonance viewpoint". For a sustained L/C Resonance you must replace the voltage loss across the coil-winding wire-resistance ONLY. And that means a very significant amount of generated power can be conserved on a worldwide scale. Hopefully enough to buy us some time to convert our oil dependence to "cold fusion", a true "clean" nuclear source of energy. By the way, have you heard anything about the matter from a reliable source?

Careful, now: you're sailing rather close to the wind with regard to the ban on discussion of free energy projects!
With support for fossil fuels going out of fashion, there would be lots of money in cold fusion; so as we've not heard anything since Pons-Fleichman then I think we have to conclude is was an either a fraud or an anomalous result.
If you're thinking of the electricity supply grid as a resonant system, then don't forget its Q.
Every resistive heater, every filament lamp, every motor with a frictional load is reducing the Q, and the Q is the ratio of the energy lost per cycle to the energy stored, and the energy lost has to be replaced by the generators.
Stick to the topic of JFETs, or start a new thread!

 

It seems like power factor correction to me. Easy to achieve at a fixed frequency (50Hz/60Hz) but not across 10 octaves of audio! The inductive component of a loudspeaker doesn't actually waste power, as it is driven from an amplifier which can be thought of is a DC to AC converter.
There are plenty of circuits which will "linearise" a loudspeaker load, making it look like a resistor, but most tests confirm that the amplifier produces lower distortion if it is driving an inductor.

IanO, those are two different subjects not intended to relate to each other, sorry for the confusion, my fault for not posting a separate thread.

 

Careful, now: you're sailing rather close to the wind with regard to the ban on discussion of free energy projects!
With support for fossil fuels going out of fashion, there would be lots of money in cold fusion; so as we've not heard anything since Pons-Fleichman then I think we have to conclude is was an either a fraud or an anomalous result.
If you're thinking of the electricity supply grid as a resonant system, then don't forget its Q.
Every resistive heater, every filament lamp, every motor with a frictional load is reducing the Q, and the Q is the ratio of the energy lost per cycle to the energy stored, and the energy lost has to be replaced by the generators.
Stick to the topic of JFETs, or start a new thread!

Please check my reply to AudioKid, and yourself. Those were two separate subjects, should have been posted in separate threads, sorry. And if there's a ban on enrrgy-related topics, well the administrators are going to have a time with my replies to the Kid.

 

"" My understanding of musical notes is that all instruments produce roughly the same fundsmental-notes-frequenies, but their harmonics distinguish each instrument by varying intensities of each harmonic. ""

Sorta-kinda close to a reasonable description.

"" Therefore the need for an FET amp or Bipolar amp that doesn't change or distort the harmonics. ""

What You are missing here is that with a high-quality, very-low-Distortion, Amplifier
What goes IN, comes OUT, only bigger.

The Harmonics produced by an Instrument are not altered in any way by an Amplifier,
unless the Amplifier ADDS ITS OWN DISTORTION.
And in that case, it most emphatically is NOT, a "High-Fidelity" Amplifier,
and, what You are proposing is an Amplifier that creates its own "special" type of distortion.

Microphones and Speakers create Distortion(s) that are
hundreds or thousands of times more significant
than any Amplifier that produces less that 0.01% THD.
Amplifiers with specs better than this are very common.
.
.
.

 

"" My understanding of musical notes is that all instruments produce roughly the same fundsmental-notes-frequenies, but their harmonics distinguish each instrument by varying intensities of each harmonic. ""

Sorta-kinda close to a reasonable description.

"" Therefore the need for an FET amp or Bipolar amp that doesn't change or distort the harmonics. ""

What You are missing here is that with a high-quality, very-low-Distortion, Amplifier
What goes IN, comes OUT, only bigger.

The Harmonics produced by an Instrument are not altered in any way by an Amplifier,
unless the Amplifier ADDS ITS OWN DISTORTION.
And in that case, it most emphatically is NOT, a "High-Fidelity" Amplifier,
and, what You are proposing is an Amplifier that creates its own "special" type of distortion.

Microphones and Speakers create Distortion(s) that are
hundreds or thousands of times more significant
than any Amplifier that produces less that 0.01% THD.
Amplifiers with specs better than this are very common.
.
.
.

All I want to encourage is an amplifier that doesn't suppress or change the harmonics of acoustical instruments, especially the differentiating harmonics between instruments. As is my understanding, such frequencies are suppressed by linear Amplification, and I can be quite wrong and appreciate my feedback.

 

All I want to encourage is an amplifier that doesn't suppress or change the harmonics of acoustical instruments, especially the differentiating harmonics between instruments. As is my understanding, such frequencies are suppressed by linear Amplification, and I can be quite wrong and appreciate my feedback.

Where would you get a ridiculous notion like that?

 

Where would you get a ridiculous notion like that?

My ears and about 50 years of listening to music that hasn't necessarily the best sound. And two musicians that liked the older style amplification. There was a notable switch to the bipolar amp in 1960, replacing the FET amplifier. You got anything you'd like to say?

 

Well then, what is your understanding of a capacitor-run motor, and why is the shunt capacitor with an induction motor thrown out of it's connection with the motor once the motor is up to an high enough RPM?

Single phase AC can only ever produce an oscillating magnetic field. To start a motor, it requires a rotating magnetic field. The capacitor produces a phase advance in the starting winding, which makes a rotating magnetic field. Because the stator lags behind the magnetic field, once the motor is rotating a single oscillating field will keep it rotating in the same direction until the load torque creates too much lag.