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Audiophile cables, an interesting question. - Page 60

post #886 of 1186
Quote:
Originally Posted by elmoe View Post

Eh, there's plenty of "universally acknowledged to be nothing short of awesome" gear out there that turn out to be duds. Considering that it took a few guys on an online forum to pick apart his "scientific" article, I'd say Nelson Pass probably doesn't know as much as you think he does.

It wasn't a "scientific" article. It was just a little primer that the editor of Six Moons asked him to write.

se
post #887 of 1186
Quote:
Originally Posted by stv014 View Post
 

 

In fact, it is, since the much higher distortion with the multi-tone signals (as shown on figures 8 and 13, for example) is mainly simply because they have a higher amplitude (are not normalized to the same peak level) than the single tone input. As the distortion is simulated with a simple cubic polynomial, it will of course have a higher level when the input level is higher, but this would happen also with a single tone normalized to the same peak to peak range.

 

Ahh - good point. I admit that I just skimmed the article earlier, since I didn't have a ton of time, and I definitely agree with you here that those figures are misleading.

post #888 of 1186

Thought this was a thread on cables. Am I in the wrong place?

post #889 of 1186

Pass has written up his cable measurements too - showing numbers for loudspeaker cables where skin effect is certainly measureable but on the edge of causing enough frequency response droop to be audible by Clark's curves

 

for IC, headphone cable skin/proximity effect is an order of magnitude or more smaller and for all headphones completely below any demonstrated human hearing capability

 

 

his feedback article is a disappointment - not a positive contribution - "tsunami of distortion" is pure rhetoric - pandering to a audience with a known and uneducated position

 

the Pass Feedback article strings together a few isolated true statements but doesn't do the math for their levels/relations in real, well designed high feedback amplifiers

 

a big effect that he totally ignores is that of high gain on internal amp signal levels, how it linearizes the stages inside the amp by the huge reduction of signal in the early stages

 

 

Putzeys is much better on feedback http://www.linearaudio.nl/linearaudio.nl/images/pdf/Volume_1_BP.pdf

post #890 of 1186
Quote:
Originally Posted by Steve Eddy View Post

I'd just like to point out that while the Pass Labs gear is expensive, Nelson has been a HUGE benefactor to the DIY community.

se

That comment wasnt directed at the article. It was just a general gripe about how i perceive the rest of headfi outside of the science forum assessing the quality of audio equipment. It was pretty bitter and i should retract the statement before outsiders read it and get insulted.

My apologies.
post #891 of 1186
Quote:
Originally Posted by jcx View Post
 

Putzeys is much better on feedback http://www.linearaudio.nl/linearaudio.nl/images/pdf/Volume_1_BP.pdf

google gave me this pdf a few days ago when I was wandering about noise measurement compared to distortions from 2 sinewaves. and I have to say, I felt even more lost in space than when I watched the MIT videos about feedback, root locus killed me.(maybe it would be good to put that link with the videos, if you believe it is an interesting piece of intel?).

I find it interesting, but I clearly fail to grasp everything said.

that's really above my actual education level. the formula is:

real level of hard earned diplomas / (how many years since I didn't even think about any of this) * (alcool+drugs)²

 

post #892 of 1186
Quote:
Originally Posted by ab initio View Post
 
Quote:
Originally Posted by Steve Eddy View Post

I'd just like to point out that while the Pass Labs gear is expensive, Nelson has been a HUGE benefactor to the DIY community.

se

That comment wasnt directed at the article. It was just a general gripe about how i perceive the rest of headfi outside of the science forum assessing the quality of audio equipment. It was pretty bitter and i should retract the statement before outsiders read it and get insulted.

My apologies.


don't worry, we will all be long gone and banned, before you succesfully offend someone. ;)

post #893 of 1186
Quote:
Originally Posted by castleofargh View Post
 

google gave me this pdf a few days ago when I was wandering about noise measurement compared to distortions from 2 sinewaves. and I have to say, I felt even more lost in space than when I watched the MIT videos about feedback, root locus killed me.(maybe it would be good to put that link with the videos, if you believe it is an interesting piece of intel?).

I find it interesting, but I clearly fail to grasp everything said.

that's really above my actual education level. the formula is:

real level of hard earned diplomas / (how many years since I didn't even think about any of this) * (alcool+drugs)²

 

 

 

Well as a quick refresher basically when you take a linear amplifier with a certain set of characteristics and place it in a negative feedback configuration (making sure it is stable in the process, of course) you get another linear amplifier with a different set of characteristics. Depending on what you want to achieve, you can extend bandwidth or increase input impedance. Or improve linearity for small signals. There are tradeoffs to be made, as nothing comes for free in physics (e.g. bandwidth vs gain).

 

How is this related to cabling again?


Edited by Digitalchkn - 6/5/14 at 3:43pm
post #894 of 1186

Below is an explanation by Bruno Putzeys on why people take a decent zero feedback design and add some feedback then decide it sounds worse.  He agrees that can be the result, but the problem isn't that feedback was used rather than not enough was used.   This quote is from a nice interview with his background and how he came to the opinions he holds.

 

BTW, I don't find Nelson Pass articles or products wrong.  Those I owned were good, and he has used feedback in more than he hasn't.  But they aren't as good as some of the better switching amps which what I currently use.

 

http://www.soundstageultra.com/index.php/features-menu/general-interest-interviews-menu/455-searching-for-the-extreme-bruno-putzeys-of-mola-mola-hypex-and-grimm-audio-part-one

 

BP:Of course, the next question is how to explain that when so many people disagree with that point of view. You can’t just go around saying, “Hey, I’ve made a negative-feedback amplifier that sounds great, so you are all wrong.” You have to accept that, for those people who say they tried feedback and it didn’t sound good, they had real experiences -- they didn’t make it up or start a religion. People have really, honestly heard what they have heard, and what they heard didn’t sound good. So I had to reverse-engineer all these experiments they had been doing and work out exactly what caused that particular subjective sonic experience. The “F-word” article is, in its first part, just a rundown of feedback structures and an attempt to get terminology straight. An interesting observation identified in that first section of the article is that local feedback with a bit of global feedback is, actually, identical to full global feedback -- mathematical fact. The second part looks back at the history to see what, in different scenarios, was responsible for feedback sounding bad in those particular cases. One of those you hinted at is that, if you take a simple amplifier which has acceptable distortion (just a second harmonic is what I use as an example) and you start applying feedback, harmonics will appear that were not there originally. Higher-order harmonics, even and odd, turn up out of the blue. So if you apply a little bit of feedback, the second harmonic that you wanted to reduce drops by a little, but out of the blue you get this whole smattering of high harmonics. It is quite understandable that this doesn’t sound good. That observation has been made and published by various people over the years, but the most important conclusion was never drawn: If you keep increasing feedback, if you turn the feedback knob up and up and up, you quickly hit a point where those distortion products all start coming down again and the signal does start getting cleaner. And if you get to very large amounts of feedback, the result is just supersmooth. So that is why I say that it is normal for an experimenter to experience that if you take a good-sounding zero-feedback amplifier and add 6dB of feedback, the result sounds worse. They heard that right. But had they been in a position to add 60dB, well then, suddenly they would have been confronted with a sound that is little short of magical.

 

As to how this relates to cables, well it doesn't directly.  Just a product of thread drift.  If it bothers others too much we could start a negative feedback thread if one doesn't already exist.   Of course the same Mr. Putzeys has done an excellent article measuring and explaining cables.  Finding nothing there down the limits of his measuring equipment to explain a difference one would hear in normal use.  But I do believe I have linked it some pages earlier in the thread.  Here it is again.

 

http://www.audioholics.com/audio-video-cables/cable-distortion-and-dielectric-biasing-debunked

 

At the bottom of the second page are two links to the actual measurements and additional comments by BP.

post #895 of 1186
Basically to summarize Bruno, if you're going to use negative feedback, use a lot of it.

se
post #896 of 1186
Quote:
Originally Posted by esldude View Post
 

As to how this relates to cables, well it doesn't directly.  Just a product of thread drift.  If it bothers others too much we could start a negative feedback thread if one doesn't already exist.   Of course the same Mr. Putzeys has done an excellent article measuring and explaining cables.  Finding nothing there down the limits of his measuring equipment to explain a difference one would hear in normal use.  But I do believe I have linked it some pages earlier in the thread.  Here it is again.

 

http://www.audioholics.com/audio-video-cables/cable-distortion-and-dielectric-biasing-debunked

 

At the bottom of the second page are two links to the actual measurements and additional comments by BP.

 

Lovely.  Not sure I follow the point about balanced cables at it applies to headphone connectivity in particular. There is only one chassis (i.e. the amp) so the CMRR is really irrelevant from perspective of the far end (the headphone). Cable inductance and "coupling" simply yield a low pass filter effect (if any).

post #897 of 1186
You guys are all being very negative! :-P

Cheers
post #898 of 1186
Quote:
Originally Posted by elmoe View Post
 

 

Eh, there's plenty of "universally acknowledged to be nothing short of awesome" gear out there that turn out to be duds. Considering that it took a few guys on an online forum to pick apart his "scientific" article, I'd say Nelson Pass probably doesn't know as much as you think he does.

 

Yes, plenty. But just because plenty exist, there is no implication that all - or most, in fact - are. And I don't think any of his amps have been proven to be duds.

 

I don't feel the article was picked apart, but I think it was presented out of context. To me it read as though it was trying to clarify the topic of feedback. Most of you seem more knowledgable than I so you perhaps don't see what all the fuss is about, but for me as a noob, all I hear about with regards to feedback is that it is either

 

(a) EVIL. Use feedback and you might as well say your amp is made by clubbing baby seals.

 

(b) well, not evil. Used all over the place. Mathematically sensible, good results.

 

So it's confusing for a lot of folks - how come a lot of high end gear makes a song and dance about NOT using feedback while others are happily using it and getting great results. Oddly it seems important for people to advertise how LITTLE feedback they use. This cements in people minds that feedback = crap. There also seems to be some odd thing about "zero global feedback" or some such which sort of means they're using some other type of feedback, (not the type called "global") but don't want to talk about it or something.

 

For me the article basically says that feedback does more than just reduce distortion and if not used carefully, it can cause problems and excessive complexity. All the plots are just typical amps - there's no indication that they're anything even near commercial/hifi/reference standard but just segments of designs or whatever used to demonstrate what he's talking about. I don't think he took or claimed to have taken the "best" of each type and took measurements. He then went on to say that he'd prefer a simpler design with no feedback - that's just his preference. He didn't say it was absolutely better or whatever. A good designer uses the advantages of a particular topology while minimizing or eliminating its weaknesses. That's true with anything be they amps with or without feedback.

post #899 of 1186
Quote:
Originally Posted by x838nwy View Post
 

 

Yes, plenty. But just because plenty exist, there is no implication that all - or most, in fact - are. And I don't think any of his amps have been proven to be duds.

 

I don't feel the article was picked apart, but I think it was presented out of context. To me it read as though it was trying to clarify the topic of feedback. Most of you seem more knowledgable than I so you perhaps don't see what all the fuss is about, but for me as a noob, all I hear about with regards to feedback is that it is either

 

(a) EVIL. Use feedback and you might as well say your amp is made by clubbing baby seals.

 

(b) well, not evil. Used all over the place. Mathematically sensible, good results.

 

So it's confusing for a lot of folks - how come a lot of high end gear makes a song and dance about NOT using feedback while others are happily using it and getting great results. Oddly it seems important for people to advertise how LITTLE feedback they use. This cements in people minds that feedback = crap. There also seems to be some odd thing about "zero global feedback" or some such which sort of means they're using some other type of feedback, (not the type called "global") but don't want to talk about it or something.

 

For me the article basically says that feedback does more than just reduce distortion and if not used carefully, it can cause problems and excessive complexity. All the plots are just typical amps - there's no indication that they're anything even near commercial/hifi/reference standard but just segments of designs or whatever used to demonstrate what he's talking about. I don't think he took or claimed to have taken the "best" of each type and took measurements. He then went on to say that he'd prefer a simpler design with no feedback - that's just his preference. He didn't say it was absolutely better or whatever. A good designer uses the advantages of a particular topology while minimizing or eliminating its weaknesses. That's true with anything be they amps with or without feedback.

 Sure it is confusing.  Hence the reason for the hoopla.  Keep the consumer confused, use it to paint your product as different than or better than the competition and profit.  If you make feedback an issue (or anything say silver conductors) which your products uses differently or more of or less of then at least some people are likely to believe it matters and purchase your product over others. 

 

Now one has real difficulty designing good gear with no feedback.  You can have an input stage, voltage gain stage and current gain stage.  Each of which uses feedback.  But no Global feedback from output all the way back to input.  Lets you have your cake and eat it too.  HEY< HEY WE USE NO GLOBAL FEEDBACK (which puts us on the no feedback bandwagon).  While in fact they might be using plenty in a loop around each individual stage.   There are many ways to skin a cat.  More important than how is the cat ends up skinned. 

 

The final signal should be audibly clean.  You can do that without feedback great.  Do it without global feedback great.  Do it with mega-monster feedback great.  The end result is what should matter more than how it was managed.  Until you start paying for it.  Then perhaps your no feedback design costs 5 times as much with no real benefit.  Then it matters.  Then you need to imply the inherent purity of your process goes beyond the end result justifying your extra cost.   The customer is like Mulder in the X files.....he wants to believe.  He wants to believe a Zen circuit master with calm tranquility in his soul has meditated upon and developed the enlightened simplicity using no feedback that allows greater pure fidelity beyond measurements and beyond reason.  An inner peace and joy that oozes forth from his pure unadulterated audio product enlightening the listener discerning enough to go the extra mile.  One not soul nourishingly satisfied with simple complex products designed by soul killing western trained EE types. 

post #900 of 1186
Quote:
Originally Posted by esldude View Post
 

 Sure it is confusing.  Hence the reason for the hoopla.  Keep the consumer confused, use it to paint your product as different than or better than the competition and profit.  If you make feedback an issue (or anything say silver conductors) which your products uses differently or more of or less of then at least some people are likely to believe it matters and purchase your product over others. 

 

Now one has real difficulty designing good gear with no feedback.  You can have an input stage, voltage gain stage and current gain stage.  Each of which uses feedback.  But no Global feedback from output all the way back to input.  Lets you have your cake and eat it too.  HEY< HEY WE USE NO GLOBAL FEEDBACK (which puts us on the no feedback bandwagon).  While in fact they might be using plenty in a loop around each individual stage.   There are many ways to skin a cat.  More important than how is the cat ends up skinned. 

 

The final signal should be audibly clean.  You can do that without feedback great.  Do it without global feedback great.  Do it with mega-monster feedback great.  The end result is what should matter more than how it was managed.  Until you start paying for it.  Then perhaps your no feedback design costs 5 times as much with no real benefit.  Then it matters.  Then you need to imply the inherent purity of your process goes beyond the end result justifying your extra cost.   The customer is like Mulder in the X files.....he wants to believe.  He wants to believe a Zen circuit master with calm tranquility in his soul has meditated upon and developed the enlightened simplicity using no feedback that allows greater pure fidelity beyond measurements and beyond reason.  An inner peace and joy that oozes forth from his pure unadulterated audio product enlightening the listener discerning enough to go the extra mile.  One not soul nourishingly satisfied with simple complex products designed by soul killing western trained EE types. 

 

Maybe I should start buying cables from Jesus?

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