Linear JFET Amplification/Audio Excellence

Thread Starter

PatrickMalarkey

Joined Oct 2, 2021
79
I might be steeped in misinformation, and I don't really want lead anyone astray, but I've been reading a semiconductor book, especially a section about JFETs. Apparently there's a region on a response graph called the "constant current" region that is linear to the gate voltage. From what I got out of my textbook, above the "pinch off" voltage is a "constant current" region that varies in milliamperes in a linear response to gate voltage. Indicating a linear Amplification by what I've deemed a non-linear device.
A JFET carries my hopes of passing the harmonics in audio sources (music); whereas a Bipolar amplifier does not. Two steps up with one step back!
 

crutschow

Joined Mar 14, 2008
28,551
Not sure what they are referring to.
Below is the LTspice simulation of a typical N-JFET showing the variation of drain current versus gate voltage.
The plot shows only a slight variation in drain current for drain voltages of 5V and 10V (green and yellow traces superimposed) , which shows it is in the constant-current region.
The straight line of the current plotted against the log gate voltage shows that the relation is logarithmic (as predicted by theory), not linear.

And bipolar amps can be made sufficiently linear (low distortion) using proper biasing and negative feedback so that they will accurately pass the harmonics in music.
Where did you get the idea that they can't?

1637903217903.png
 

LowQCab

Joined Nov 6, 2012
1,619
Your Speakers have over ~10% Distortion, guaranteed,
and your Listening-Room probably creates another ~20% Distortion, maybe more.
Current Digital-Amplifiers have Distortion-Levels that almost can't be measured,
and certainly can't be distinguished with the Human-Ear with a double-blind test.

If You generate your own "special" Distortion with your Amp,
that You personally find "magical", and or "pleasing",
then it is no longer "High-Fidelity".

Learn how to fix your Speakers and Room first, that's where the "Magic" is.
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Thread Starter

PatrickMalarkey

Joined Oct 2, 2021
79
This is my book photo, the harmonics are suppressed by coupling and bypass capacitors. I don't know why, but wonder if music is comprised of a deteriorating freq. and intensity waveform. Such waveforms are distorted by cap.s caused by their "capture effect". The capture effect is a capacitor's current-passing response to the highest applied voltage. There's a difference between FET sound quality and Bipolar sound quality.
 

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Thread Starter

PatrickMalarkey

Joined Oct 2, 2021
79
Your Speakers have over ~10% Distortion, guaranteed,
and your Listening-Room probably creates another ~20% Distortion, maybe more.
Current Digital-Amplifiers have Distortion-Levels that almost can't be measured,
and certainly can't be distinguished with the Human-Ear with a double-blind test.

If You generate your own "special" Distortion with your Amp,
that You personally find "magical", and or "pleasing",
then it is no longer "High-Fidelity".

Learn how to fix your Speakers and Room first, that's where the "Magic" is.
.
.
.
Ian0, bought a network receiver earlier this Nov. for $299.99 from Audio- advice.com. Onkyo Tx 8140. It hasn't been shipped yet because of shortages.
 

crutschow

Joined Mar 14, 2008
28,551
This is my book photo
Those characteristic curve are not of a normal JFET.
Below is the characteristic curve of a typical JFET.
As you can see, the output steps do not have linear spaced current steps vs. linear Vgs steps.
1637907127446.png
the harmonics are suppressed by coupling and bypass capacitors...
Such waveforms are distorted by cap.s caused by their "capture effect". The capture effect is a capacitor's current-passing response to the highest applied voltage
That is all a bunch of audiophile hooey.
There is no such thing as a "capture effect" in capacitors.
Well designed audio amps with good quality capacitors will not affect any music harmonics.
I don't know why, but wonder if music is comprised of a deteriorating freq. and intensity waveform.
That makes no sense whatsoever.
What is "a deteriorating freq. and intensity waveform."?
There's a difference between FET sound quality and Bipolar sound quality.
Not for well designed amplifiers which have inaudible distortion in (and above) the complete audio band.

Is that your real last name or are you trying to tell us something about your posts?
Either you have swallowed a lot of audiophile nut technical nonsense, or you are being a troll.
 
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Thread Starter

PatrickMalarkey

Joined Oct 2, 2021
79
No it doesn't make good sense, but 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?
 

Thread Starter

PatrickMalarkey

Joined Oct 2, 2021
79
This is my book photo, the harmonics are suppressed by coupling and bypass capacitors. I don't know why, but wonder if music is comprised of a deteriorating freq. and intensity waveform. Such waveforms are distorted by cap.s caused by their "capture effect". The capture effect is a capacitor's current-passing response to the highest applied voltage. There's a difference between FET sound quality and Bipolar sound quality.
A deteriorating frequency is a slowing oscillation and deteriorating intensity is a lessening volumn, for lack of better descriptive words.
 

Thread Starter

PatrickMalarkey

Joined Oct 2, 2021
79
Those characteristic curve are not of a normal JFET.
Below is the characteristic curve of a typical JFET.
As you can see, the output steps do not have linear spaced current steps vs. linear Vgs steps.
View attachment 253590
That is all a bunch of audiophile hooey.
There is no such thing as a "capture effect" in capacitors.
Well designed audio amps with good quality capacitors will not affect any music harmonics.
That makes no sense whatsoever.
What is "a deteriorating freq. and intensity waveform."?
Not for well designed amplifiers which have inaudible distortion in (and above) the complete audio band.

Is that your real last name or are you trying to tell us something about your posts?
Either you have swallowed a lot of audiophile nut technical nonsense, or you are being a troll.
No Malarkey isn't my last name and Patrick isn't my first name, did you read the disclaimer I began my post with. I'm not a tech or engineer, isn't most of that type of work done in China etc.
 

LowQCab

Joined Nov 6, 2012
1,619
This reminds me of the Electric-Guitar guys who will bring their old Tube-Amp in and
ask to have the problem with "Short-Tube-Life" fixed,
OK fine, first things first, You need to replace ALL the ~50-year-old "Paper & Wax" Capacitors
so that the Tube-Bias can return to the designed range.
OH-NO, it's got to stay ALL ORIGINAL, or it will lose it's Mojo !!!!
All this, while they normally push the Amp HARD into Clipping 90% of the time,
not to mention that those Capacitors were pretty decent ~50-years ago,
and now they're leaky garbage, and will self-destruct.
Nothing like the performance that the Amp had when new.

Most of the time when someone says the Newer Amps don't sound as good,
it's because the Speaker(s) in the old Amp are completely shot,
and it's amazing that they still work at all.
The "extra-bad" "Tone" is easy to duplicate with an EQ-Pedal before the Amp, and
the installation of a ~20-Ohm Power-Resistor in series with the Speaker(s).
Silly boys.
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Thread Starter

PatrickMalarkey

Joined Oct 2, 2021
79
This reminds me of the Electric-Guitar guys who will bring their old Tube-Amp in and
ask to have the problem with "Short-Tube-Life" fixed,
OK fine, first things first, You need to replace ALL the ~50-year-old "Paper & Wax" Capacitors
so that the Tube-Bias can return to the designed range.
OH-NO, it's got to stay ALL ORIGINAL, or it will lose it's Mojo !!!!
All this, while they normally push the Amp HARD into Clipping 90% of the time,
not to mention that those Capacitors were pretty decent ~50-years ago,
and now they're leaky garbage, and will self-destruct.
Nothing like the performance that the Amp had when new.

Most of the time when someone says the Newer Amps don't sound as good,
it's because the Speaker(s) in the old Amp are completely shot,
and it's amazing that they still work at all.
The "extra-bad" "Tone" is easy to duplicate with an EQ-Pedal before the Amp, and
the installation of a ~20-Ohm Power-Resistor in series with the Speaker(s).
Silly boys.
.
.
.
Yes we'll im not going to argue with you or Crutchfield. Have you gotten any wind of L/C Resonance applied to the issue of transformer primaries and added shunt capacitors?
 

crutschow

Joined Mar 14, 2008
28,551
I've had two or more musicians tell me the older style amplified instruments had a better sound than the newer ones.
...........
Why would a responsible musician say that?
That's because they like the sound of the harmonic distortion and soft clipping characteristics that the old tube (not transistor) amps had.
Modern well-made solid-state amps don't have that distortion and clip more sharply when overloaded.
Instrument amplifiers for amplifying the instrument sound, and amplifiers for high-fidelity listening are two entirely different kettles of fish.
The former may prefer some distortion in the sound amplification, the latter (normally) do not.
A deteriorating frequency is a slowing oscillation and deteriorating intensity is a lessening volumn, for lack of better descriptive words.
There is no reason that, or any other odd characteristics of music, would increase distortion in an a well-designed amp.

The late Siegfried Linkwitz (co-inventer of the Linkwitz-Riley filter used for high-end speaker crossovers) whom I consider as being one of the best audio speaker designers ever, used low-distortion solid-state amps for all his bi and tri amp speaker designs (go to his website if you want some interesting information on accurately reproducing the sound stage of the original recorded music, making the speakers seem to disappear).
That's good enough reason for me to conclude that nothing today is better for accurately reproducing music than a good solid-state amp, no magic-sauce needed.
 
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Ian0

Joined Aug 7, 2020
4,146
This is my book photo, the harmonics are suppressed by coupling and bypass capacitors. I don't know why, but wonder if music is comprised of a deteriorating freq. and intensity waveform. Such waveforms are distorted by cap.s caused by their "capture effect". The capture effect is a capacitor's current-passing response to the highest applied voltage. There's a difference between FET sound quality and Bipolar sound quality.
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.
2SK3557.pngThe 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.
 

crutschow

Joined Mar 14, 2008
28,551
Further down the graph it IS exponential!
It shows in the varying distance between the (mostly) horizontal lines of drain current at the center of the graph for the linear steps in Vgs, and that occurs between all the steps.
That's from the exponential relation between the drain current and Vgs, which is true for all currents.
 
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Audioguru again

Joined Oct 21, 2019
4,129
Harmonics are not suppressed by coupling capacitors. Harmonics are high frequencies, coupling capacitor values too low suppress only very low frequencies.
Old vacuum tube amplifiers used an output transformer that suppressed high frequency harmonics and musicians liked that sound because the transformer also suppressed high frequency distortion produced by the vacuum tubes.

We can hear to 20kHz. Modern hifi amplifiers have a flat frequency response to 50kHz or more and have distortion that is lower than anybody can hear.

Many cheap speakers, especially horns produce lots of distortion but I have never heard distortion on hifi speakers.
 

Thread Starter

PatrickMalarkey

Joined Oct 2, 2021
79
No.
What L/C resonance?
How is added shunt capacitors to transformer (audio or power?) primaries an issue?
It's a circuit with an inductance and capacitance in one of two possible connections, and for the purpose of conserving generated power. One series and the other shunt. 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.
Again, such is common with the transformers secondaries, but should be found useful on the primary side too, of the substation stepdown transformers.
L/C: L stands for an inductive reactance and C indicates a capacitive reactance. My book that I had on that is more than 41 years old and written by some fellow that taught workers at RCA, back when RCA was a major business here in the States.
 

LowQCab

Joined Nov 6, 2012
1,619
"" Many cheap speakers, especially horns produce lots of distortion,
but I have never heard distortion on hifi speakers. ""


I would clarify that to say that, YES,
there are many really bad, and/or cheap, Speaker designs ( of any type ).
But well designed Horns can't be touched by any "Direct-Radiator" type Speaker.

"High-Fidelity" is, of course, a loose term, and there are many different types of Distortion,
some are "more-obvious" than others, and
some are "more-acceptable" than other types.

Any "Ported" Speaker Cabinet has a ton of "Transient-Response" Distortion,
but most people find it to be "acceptable", or have no clue that it even exists,
personally, I don't find it acceptable at all, and I've built numerous versions of all types of Cabinets.
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"" Old vacuum tube amplifiers used an output transformer that suppressed high frequency harmonics
and musicians liked that sound because the transformer also suppressed high frequency distortion
produced by the vacuum tubes. ""

Add to that,
a ~12" Speaker that can't reproduce anything over around ~6 to ~8khz ,
and if it does, it's in a very tight "beam" straight out of the center of the Cone.
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crutschow

Joined Mar 14, 2008
28,551
It's a circuit with an inductance and capacitance in one of two possible connections, and for the purpose of conserving generated power.
What does that have to do with the subject of this post?
L/C: L stands for an inductive reactance and C indicates a capacitive reactance.
Not exactly.
L stands for the value of inductance and C stands for the value of capacitance.
Reactance only occurs when an AC signal is applied to the elements.
 
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