A very nice new Nelson Pass Paper.
http://www.passdiy.com/pdf/articles/...n_feedback.pdf
Clark
A very nice new Nelson Pass Paper.
http://www.passdiy.com/pdf/articles/...n_feedback.pdf
Clark
Information is not Knowledge; Knowledge is not Wisdom
Too many audiophiles listen with their eyes instead of their ears
Nelson is so cool...
"Accusations are occasionally made that objectivists can't hear, and conversely that subjectivists hear things that aren't there. This being the entertainment industry, I hope everyone is having a good time."
Widget
Hi ClarkQuoted by Nelson Pass:
Linear distortions affect the amplitude and phase of audio signals, but don't show up on harmonic distortion analyzers as added frequency components that weren't there in the first place.
I finally had the time to really read this posting.
Boy, this sure explains something of a mystery to me. At one time, I had a Crown Power-Tech 1 hooked up to my old 030 system. And after a while, this unit's fan noise really got to me. So, I decided to upgrade to a Crown K1, just to get rid of the fan noise. From the very first moment that I heard a sound coming from the Crown K1, I was stunned by how much better it sounded when compared to the Crown PT1.
Oh, sure both amps sounded real clean. And, it's not like I really needed the extra power.
But, the dynamic range seemed so much better with the Crown K1. Louder passages sounded kind of sloppy and slightly exaggerated with the Crown PT1, while the Crown K1 reproduced everything in a much more defined and natural sounding way.
So, I just figured that the PT1 was just a cheap "Entry level" consumer product, knocked off to fill a need of low budget DJs. While the more expensive K1 was made to be a "Main Stream" product worthy of carrying the "Crown" name. It is one thing to develop a personal opinion about something like this. But, it's really nice to come across a scientific explanation for why a K1 can sound so much better then a PT1. And the answer is lower linear distortion.
Thanks for posting this,
Baron030
Originally Posted by Mr. Widget
Beat me to it!
Yeah - thanks, Clark.
bo
"Indeed, not!!"
You are quite welcome, guys, but of course it is Nelson we have to thank - again!
As a nice way to thank him for this paper, perhaps you could post here the items and ideas you find of interest, and why, as Baron030 has kindly done. I personally find the simplicity of the paper deceptive; the whole seems much greater than the parts, and the familiarity of the different parts is swept away by the startling things revealed by Nelson's observations about what this means to amplifier users and designers.
Personally, my ears have been telling me that feedback is not a good idea. Well worth minimizing or avoiding, and that is what I have been working towards. It is also a relief to find corroboration of my long held belief/observation that amps with more as opposed to fewer gain stages do not sound very good. Another reason why I can't get excited about Japanese receivers, for instance.
Am I correct in concluding that distortions introduced by network crossovers, autotransformers and transformers are linear in nature?
Clark
Information is not Knowledge; Knowledge is not Wisdom
Too many audiophiles listen with their eyes instead of their ears
http://www.6moons.com/industryfeatur...tortion_3.html
"Customers have also been known to change their mind over a period of time."
Love it
I wonder where we would be if negative feedback was the norm with the way a dynamic driver works..as in a seperate coil for feedback?
I mean almost every driver has non linear distortion of one kind or another.
People pick over amps but forget that most drivers have a shit load more non linear distortion as in when the voice coil goes in over the Pole past the gap the inductance increases and when it goes out the inductance decease so this effects the HF response on that half of the cycle.
I expect this is more of an issue for a two way system where the poor old woofer is doing double time producing a kick drum while the Fat lady sings sweet Jesus.
Some of the more exotic drivers have a shorted turn, extended pole's or demodulation (aluminum) rings to help reduce the issue but why not do it the dumb easy way and apply a dose of feedback?
Nelson Pass
We would be about there where all these speakers were presented.I wonder where we would be if negative feedback was the norm with the way a dynamic driver works..? I mean almost every driver has non linear distortion of one kind or another.
All problems with feedback would be present in an increased way - frequency response, phase behaviour. (I hear already an Audiophile saying he can hear the gain-bandwidth-productbut why not do it the dumb easy way and apply a dose of feedback?).
There are different ways to apply feedback. Already in the old days there was at least one tube amp which had a simple resistor network at the output incorporating the speaker for increasing positive or negative feedback. In this way the damping could be adjusted.
This seems to be a simple method of aligning a speaker enclosure combination. But this would mean to sell speaker and amp as a unit, which needs service from time to time. It is easier to sell different cables.
Just my two cents.
__________
Peter
Hi Peter,
I recall the Philips Motional Feedback speakers.
They had impressive bass.
I recall some progress here. One stated goal of the latest high end drivers from Northridge is the reduction of distortion to amplifier specs.
Sounds like the Super 12?Some of the more exotic drivers have a shorted turn, extended pole's or demodulation (aluminum) rings to help reduce the issue but why not do it the dumb easy way and apply a dose of feedback?
That is where current source amps come in. Nelson again!People pick over amps but forget that most drivers have a shit load more non linear distortion as in when the voice coil goes in over the Pole past the gap the inductance increases and when it goes out the inductance decease so this effects the HF response on that half of the cycle.
Clark
Information is not Knowledge; Knowledge is not Wisdom
Too many audiophiles listen with their eyes instead of their ears
Clark,
Better keep an eye on the Xmax of those Super 12's
Did you know the F2 has particularly long time constant in the Current Source to avoid turn on thumps?
Back to normal trivia there is another nice article around how Nelson uses various techniques to reduce distorion at low levels and I think Pass Labs ran an advertisement about this called leaving class A or words to that effect
In the amp I use most of the time (the X250.5) it is SE biased a tiny bit, the push pull class A to a modest power level then A/B.
You cannot hear those transitions but it retains a certain resolve and sweetness at flea power levels. This amp has very little of any kind of distortion because of susy tm bit there is a hint of warmth.
On the other hand using the Aleph J there is a certain character of 2nd harmonic while at the same time it has incredible resolving power with the 2SJ109 Jfet front end.
The XA amps are different again. They retain the resolution of the Aleph but without the 2nd harmonic content and have the dynamic contrast of the X Series.
So for those who say all amps sound the same ....well I dont have to say any more.
As a designer and builder of "musical instrument" amplifiers, I found out very early on that the facts and figures that one can extract from charts and graphs are quite meaningless. Most of them deal with constant state at one particular frequency. Musical instrument amplifiers show up problems way faster than would a HiFi amplifier. Guitar amplifiers when pushed into overdrive will either sound "musical" or "like a "chainsaw"! The main tool that I use is my ears. I know I am onto something when the result has a "pleasing" sound. Even order harmonics are pleasing to the ear and most of my designs are enhanced in this area. Odd order harmonics are not good. IM distortion is hugely important, every different note changes the way the others sound. I can never understand why audiophiles like their little full range speaker systems. I am sure that we could design a "perfect" speaker to cover all the audio spectrum equally well but how can such a speaker be expected to deliver perfect highs when it is also trying to deliver 30Hz at the same time. The same goes with amplifiers. Active multiway systems were made to try to combat this problem and the Greatful Dead did it to the extreme by having a separate multyway system for each instrument. In a perfect world the "system" is suposed to accurately reproduce the source material. When we listen to recorded music most of the time we don't know what it sounded like in the first place and we make our listening decision on what sounds pleasing to us. Another person may say it sounds bad. In my opinion the stats of a peice of equipment don't mean jack if it sounds like crap. Let your ears be the judge.
A great point. It is being largely heeded these days. You can still find listeners trying to get a five, six or eight inch Lowther (or Fostex) and a complicated horn to do it all, but most are augmenting the top, bottom or both. And in some cases using new drivers designed for the new range. In other words, Full Range Augmented has largely replaced Single Driver. I have been messing around with the Hammer Dynamics Super 12 lately and am having outstanding results. Here is what I have learned so far.
*Giant speakers like my 4345's with smooth 18 inch woofers are flat to 30hz. Everything else, and I mean everything, use a sub. Almost every large, expensive speaker is still weak down there.
*Modern tweeters with modern materials and engineering were not available when full range was king. If they had been, they would have used them with Lowthers back then. At least after hifi found the last octave.
*Since great tweeters are to be had for the price of a meal, make the full range cone larger. Tens are good, twelves are better. Bass in simple enclosures is now good to 40 or 50hz. The dynamics become realistic again.
*If you care about the quality of the sound, not having any crossover between 40hz and 9k or 10khz really does kick the crap out of almost everything that does. The meaty heart of the musical range does not take kindly to being split up, networked, phase shifted and time misaligned. The resulting linear distortions are audible as all get out once you have something to compare to. They are major and, as you say, elude commonly encountered measurement but are easy to hear. Further proof, my Mesa Boogie with a twelve inch 200 watt EVM does not have these problems either.
I was at a live unamplified jazz gig last night, a cabaret setting, sitting ten feet away. I was shocked how the trumpet, alto sax and drums sounded so close to what I hear at home. I was straining to hear a difference. I can honestly say that only the drums suffered at home. Those dynamics and transients still challenge even the best systems. Only compression drivers and horns have a chance there, and I won't hold my breath waiting for a 40hz to 9700hz driver & horn combo.
Here is a thread on the topic: http://audioheritage.org/vbulletin/s...ad.php?t=21286
Clark
Information is not Knowledge; Knowledge is not Wisdom
Too many audiophiles listen with their eyes instead of their ears
Which in my opinoin, sound far less musical. They got "thump", but nothing else...
You are making me lonely for my 4345's and I'm sitting right in front of them!
I can opine, much of what little you "miss" can possibly be found with improvements upstream, to the front-end of your system. A few months back I moved to a Bryston BP26 DA pre-amp, and the improvement was pretty staggering - particularly to all manner of percussion. It reminded me of when I went away from the standard (i.e., lesser) condenser mics for overhead micing, and started using the Neumann KM184's. It was that big a change...
Bo,
So you have upgraded from the Onkyo to the Adcom and now the Bryston preamp. Wow.
The front end of Clark's system is minimalist and the digital source is right up there.
There are currently 1 users browsing this thread. (0 members and 1 guests)
Posting Permissions
Reply With Quote
