be sure that there are few around actually remembering tube amps with knob for variable damping factor ....... and more than few , of later date, remembering articles and schematics of same
some amps even had portion of knob rotation marked with negative sign
Positive feedback takes us into the realm of nonlinear dynamics, exponential curves and pre-compensation of the inherent nonlinear property of air and loudspeaker-drivers.
It is no wonder why people prefer Triodes and SITs with their nonlinear exponential transfer curves, inherent speed and large unhindered voltage swing.
Intentional utilization of strong nonlinearity in structural dynamics - ScienceDirect
A link to a great article not directly about audio and electronics. The article contains great pieces of data about the benefits of nonlinear dynamics and why we should go one step further then just strive for low amounts of distortion. Once the distortion is below a certain threshold then there are much more important issues to consider. And it is no coincidence that Nelson Pass uses SITs, circuits that emulate the exponential transfer curves of Triodes and other means of exploring nonlinear dynamic effects in audio reproduction.
I have not built any amplifiers in a while. My focus has been on helping my 15 year old son with his car audio builds.
Cheers,
Johannes
It is no wonder why people prefer Triodes and SITs with their nonlinear exponential transfer curves, inherent speed and large unhindered voltage swing.
Intentional utilization of strong nonlinearity in structural dynamics - ScienceDirect
A link to a great article not directly about audio and electronics. The article contains great pieces of data about the benefits of nonlinear dynamics and why we should go one step further then just strive for low amounts of distortion. Once the distortion is below a certain threshold then there are much more important issues to consider. And it is no coincidence that Nelson Pass uses SITs, circuits that emulate the exponential transfer curves of Triodes and other means of exploring nonlinear dynamic effects in audio reproduction.
I have not built any amplifiers in a while. My focus has been on helping my 15 year old son with his car audio builds.
Cheers,
Johannes
Nonlinear acoustics - Wikipedia
A bandwidth limited amplifier is a low pass filter, and as such can not recreate non-sinusoidal waveforms with any real fidelity. Several cascaded amplifier stages with a generous negative feedback loop around is notoriously bad at recreating complex non-sinusoidal waveforms due to the "time-smear" phase issues of the feedback loop ironing out any real sharp edges in transients and the complex nonlinear character of real life musical instruments.
This is why a single stage - low or no negative feed back - SIT amplifier will sound organic and true in a way a more complex amp never can.
Positive current feedback increases the amps ability to reproduce these complex nonlinear non-sinusoidal wave forms. This is readily experienced by all who modify the F6 amp with some PCF. People who try PCF describe the exact sonic character of this in the thread about the F6.
F6 with PCF
A bandwidth limited amplifier is a low pass filter, and as such can not recreate non-sinusoidal waveforms with any real fidelity. Several cascaded amplifier stages with a generous negative feedback loop around is notoriously bad at recreating complex non-sinusoidal waveforms due to the "time-smear" phase issues of the feedback loop ironing out any real sharp edges in transients and the complex nonlinear character of real life musical instruments.
This is why a single stage - low or no negative feed back - SIT amplifier will sound organic and true in a way a more complex amp never can.
Positive current feedback increases the amps ability to reproduce these complex nonlinear non-sinusoidal wave forms. This is readily experienced by all who modify the F6 amp with some PCF. People who try PCF describe the exact sonic character of this in the thread about the F6.
F6 with PCF
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I agree. The phenomena cited almost all take place at enormous SPL. I have rarely seen nonlinear acoustics applied to normal freespace propagation of sound at levels below those that would cause permanent damage to the ear. It is frequently used for instance inside wind instruments where the properties of shock waves can shape the sound.
No they aren't, you're talking about two different things. The nonlinearity of the air is virtually impossible to measure at 90dB SPL. If you've seen measurements of speakers that require correction for the distortion of the air please post them.
Lies, Damn Lies, and Startup PR: Acoustic Nonlinearity
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That article is about nonlinear shockwave creation, which is one of many nonlinear mechanisms in audio.
From the same article.
Why should we arbitrarily decide that amplifiers must be linear when nothing else is? Why not use the inherent nonlinearity of SITs to compensate for the nonlinear behavior of air, driver suspensions etc? A correctly nonlinear amp sounds much better with a much higher definition then a purely linear amplifier.
No car has linear suspensions and no engineer working at Dodge, Volvo or Mazda would keep their employment for long if they arbitrarily simplified the road keeping specifications to only be able to handle calm sinusoidal bumps. The same principle is applicable to audio.
From the same article.
Why should we arbitrarily decide that amplifiers must be linear when nothing else is? Why not use the inherent nonlinearity of SITs to compensate for the nonlinear behavior of air, driver suspensions etc? A correctly nonlinear amp sounds much better with a much higher definition then a purely linear amplifier.
No car has linear suspensions and no engineer working at Dodge, Volvo or Mazda would keep their employment for long if they arbitrarily simplified the road keeping specifications to only be able to handle calm sinusoidal bumps. The same principle is applicable to audio.
Yes, this is true if you only try to measure nonlinear shock wave creation.
The nonlinear physics of musical instruments - IOPscience
I guess this article is pure fake news then....
https://www.researchgate.net/profile/Stefan_Bilbao/publication/264309826_The_Changing_Picture_of_Nonlinearity_in_Musical_Instruments_Modeling_and_Simulation/links/53d7e2a00cf2631430bfcd76/The-Changing-Picture-of-Nonlinearity-in-Musical-Instruments-Modeling-and-Simulation.pdf
More fake news disguising as science.
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No as I said...
Not the air in the listening space. It's not easy to measure the non-linearity of the air itself below 140dB SPL or more. No further comments necessary.
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I never argued that the nonlinear behavior that shape the sound and character of the tone of an instrument was shock wave creation in air. I guess it does play a role in wind instruments, but it is not the main factor.
But in order to faithfully amplify a nonlinear non-sinusoidal signal, the amp should not rely on several cascaded gain stages and generous amounts of global negative feedback for low measured THD when driving a resistor with a pure sine wave (very far from the real life working conditions of audio amplifiers).
In order to avoid the arbitrarily linearizing global negative feedback and its tendency to kill the reproduction of music, not sine waves, while at the same time keeping a good control of the drivers, PCF can really make wonders. Combine this with a nonlinear (triode like) MOSFET like the IRFPS3810 for some tunable pre-compensation of the nonlinear behavior of the driver suspensions, loudspeaker enclosure, air and acoustics of the listening space.
Cheers,
Johannes
More from the wiki article. "This phenomenon is characteristic of a non-linear system, since a linear acoustic system responds only to the driving frequency. This always occurs but the effects of geometric spreading and of absorption usually overcome the self distortion, so linear behavior usually prevails and nonlinear acoustic propagation occurs only for very large amplitudes and only near the source."
Is music loud enough? If this made an audible difference you could hear the distortion change with distance from the source.
As far as band limited amps sounding bad. All your sources are bandwidth limited more than the amp, so not buying that one.
A number of things are getting confused here.
1. Instruments produce music in all its tonal complexity. But HiFi systems reproduce music; they are not instruments, their role is to transmit complex sounds faithfully, not introduce new distortions.
2. It is possible that some people posting in this thread prefer the sound of music reproduction with a little bit of added distortion buzz to the sound of more cleanly reproduced music. It is conceivable that some HiFi systems are very "violin-like" due to their particular added distortions, just as my old Karlson enclosure was very cello-like. Pop bands seem to glory in the distortion of their electric instruments... sounds awful to me.
3. The familiar low output impedance amp be ideal for sending both sine waves and complex waves into 8-Ohm resistors but poor for driving a moving voice coil. Improving the ability of amps to drive speakers does not mean adding distortion but somehow and otherwise improving the faithful movement of the cone (although it is conceivable that the amp's distortion might rise albeit imperceptibly).
B.
1. Instruments produce music in all its tonal complexity. But HiFi systems reproduce music; they are not instruments, their role is to transmit complex sounds faithfully, not introduce new distortions.
2. It is possible that some people posting in this thread prefer the sound of music reproduction with a little bit of added distortion buzz to the sound of more cleanly reproduced music. It is conceivable that some HiFi systems are very "violin-like" due to their particular added distortions, just as my old Karlson enclosure was very cello-like. Pop bands seem to glory in the distortion of their electric instruments... sounds awful to me.
3. The familiar low output impedance amp be ideal for sending both sine waves and complex waves into 8-Ohm resistors but poor for driving a moving voice coil. Improving the ability of amps to drive speakers does not mean adding distortion but somehow and otherwise improving the faithful movement of the cone (although it is conceivable that the amp's distortion might rise albeit imperceptibly).
B.
I could imagine that INSIDE a wind instrument you have amplitudes and sound pressures high enough that the air inside the instrument behaves non-linearly, as alluded to by scott wurcer in post #165.
However, once you look at the environment outside of the instruments, probably you don't get enough sound pressure any more to have non-linear effects dominating over the linear behaviour.
With regard to band-limiting, I think that we probably should not view instruments that produce transients as bandwidth-limited. Speaking from a gut-feeling here, not having undertaken the analysis myself, I bet that you find frequency components well into the MHz range in the Fourier analysis of transients produced by some musical instruments.
But then again, I don't know how much the "sharpness" of a transient diminishes when traveling through a few meters of air, so the very-high-frequency components might get damped down a lot before they hit the microphone.
And lastly, siding with your argument, the microphones certainly are bandwidth-limted.
Best regards,
Claas
Hello Mr. Pass. Thanks for your post. I now have a possibly [identical] application for this great patent in circuits of my so-called Class aP cascoded amplifiers.
The attached schematic is a partial for a push-pull transformer-coupled amp which uses a high voltage PSU. It is expected to meet the teaching and/or objectives of the patent
1. The left of the view shows a high impedance constant current source based on an N-Mosfet, and its isolated PSU shown as a battery. The constant current from this source [ Iccs] circulates solely in the Drain-Source channel of the Gain N-JFET.
2. The Gain N-JFET operates in the common gate configuration. Its source is biased to a positive voltage [another battery], and is driven by a negative-going analog pulse.
3. The Gain N-JFET is cascoded with a second N-JFET. The cascode N-J-FET is enabled to pass a much smaller current than [I css] so as to keep its idle power dissipation to a low extent.
4. The voltage at the source of the cascoding N-JFET is made to be ~equal to that of the floating PSU of the CCS.
5. The value of the battery voltage at the source of the Gain J-FET is adjusted so as open its drain-source channel to circulate [I css] plus the small idle current from the cascode N-JFET.
A negative-going analog pulse opens further the drain-source channel of the Gain J-FET. It pulls the voltage at the source towards ground. The new lower resistance of the Gain J-FET forces the Cascode N-JFET to open up and increase its conduction; because the voltage at its source lead was also enabled to move closer to ground. The operation of the high impedance current source is unaffected by this dynamic operation. It continues to do its thing.
Best
Anton
Attachments
I have never said that an amp should behave as an instrument.
In order to transmit complex sounds faithfully you can not use an amp with to narrow bandwidth and to high order roll of outside of that bandwidth. If you cancel out lots of distortion by introducing some distortion by not striving for a arbitrarily defined linear sine-wave reproduction, but using the inherent nature of "triody" (the right kind of nonlinearity) devices, then it is a net positive effect all around.
Why don't you question Nelson Pass when he advocates the use of SITs and writes great articles like The Sweet Spot http://www.firstwatt.com/pdf/art_sweet_spot.pdf and Introduction to Statid Induction Transistors http://www.firstwatt.com/pdf/art_sit_intro.pdf
What I am writing about is based on his articles and my experience I have gained after many years of experiments based on his articles.
I have always regarded Nelson Pass a true genius, but after many years of experiments with amplifiers and the rest of the audio reproduction chain, several years of studies of and experiments with nonlinear dynamics in many different areas, then I am at awe over his extremely deep insight into the analog amplifier design!
I am ofter wondering if he understands his own true level of pure genius himself? Like most other great inventors, he seems to be at least 20 years ahead of everybody else. This usually happens with people of great IQ who also has learned to trust their intuition more then all the established dogma.
Since when is the use of the nonlinear dynamics about "adding distortion buzz"?
From Nelson Pass article Introduction to Sits.
What is a square law if not nonlinear?
How cold you "work a loadline" without the nonlinear "square law" that works along a highly nonlinear exponential curve?
I only propose that we take his article The Sweet Spot one step further and include the (compressively) nonlinear behavior of the air inside loudspeakers, near the loudspeaker membranes, ports, the compressive nonlinearity of driver suspensions, flexing baffles etc.
Where is "adding distortion buzz" in that???
Once again... This is one mechanism of nonlinear acoustic behavior. There are many more. Everything about acoustics is nonlinear in one way or another.
I don't post about acoustic shock wave transformation in the Pass Labs part of the forum, since I consider small 10 watt amplifiers to be quite unsuitable to generate supersonic bangs and other fun acoustic phenomena.
I just mentioned the wiki article to give a reference the single quoted line
. Not because I want to advocate adding some distortion buzz or argue for supersonic or extremely high spl shockwave transformation with our low powered amps and delicate fullrange drivers.
you bet ........
however , he's taking that as nature of life , having fun along , and not taking too seriously neither himself nor others
(important note - seriousness can't be mixed with responsibility ; one can be damn silly , while deadly responsible
)
Hi Circlonanen, i read your thread with great interest. I do not have any fancy fets or sits, but i do have plenty of irf240 and irf9240 from many years ago when i was building son of zen. And recently aca.
Can you please post working schematics for small amp which uses just these vintage fets? I want to build small amp, even watt is plenty.
Thanks.
Can you please post working schematics for small amp which uses just these vintage fets? I want to build small amp, even watt is plenty.
Thanks.
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