John Curl's Blowtorch preamplifier part II

[SY]

Pavel, I'm not understanding what you're getting at. This doesn't seem related to Charles's anecdote (he still hasn't allowed anyone to see the files in question to dig at why there might be audible differences). Your files seem to be single tones with added harmonics of differing orders (shades of the Stereophile Test CD!).

What am I missing?

[Alexandre]

WRT Charles claim, as I understand, the audible differences are caused by different data delivery methods used by the programmer. Just to give an example, maybe an extreme one, but representative: bursts of data vs. a continuous stream.

IMO that would make a difference in the electrical signals presented to the D/A converter. Even if you have an isolated interface, reclocking, etc.

This difference should be very difficult to measure, maybe it is very near or under the noise floor. I don´t think I would be able to hear it, but I don´t doubt that others can. Our hearing is an amazing instrument wrt sensitivity / signal to noise.

Best
Alex

[Johnloudb]

Originally Posted by SY

Pavel, I'm not understanding what you're getting at.

Just a guess, but maybe Pavel is saying that if you can't tell a difference between the files he's posted ... good luck in hearing a difference in the files Charles did.

[SY]

Originally Posted by Johnloudb

Just a guess, but maybe Pavel is saying that if you can't tell a difference between the files he's posted ... good luck in hearing a difference in the files Charles did.

Dunno. It's mysterious; maybe Pavel will explain.

I have no trouble hearing the effects of data compression, but I doubt that I would hear those same effects on sine waves.

[jan.didden]

Originally Posted by simon7000

Math can do a decent model if everything is right. I have done a bit of that. Now reality gets a chance to rear its' head. I will build two non-linear amplifiers and measure them alone and in series both ways with and without global feedback.

Almost no one ever argues with actual measurements. Some one did once but it turns out they misread just about everything in the article. (See LA Vol. 1 Letters!)

Ed how about using non-linear blocks in LTspice? You can make your amplifier chain anyway you want; just put your formula in the nl-block and look at the transient simulation output.


jan

[jcx]

I haven't seen the article(s) but I do think a recent analog BSc/EE should at least have the "cultural" knowledge of the more advanced Control theory results - certainly a MSc EE and many other engineering/science MSc today will have taken enough Control Theory courses to give the answers off hand

locally Lipschitz, memoryless weakly nonlinear systems will give the least distortion with "maximum loop gain" Global feedback

in Audio we have Cherry's “Estimates of Nonlinear Distortion in Feedback Amplifiers” JAES V48#4 2000 - the backwards "equivalent distoriton" propagation and the series expansion inversions for 2nd and 3rd order nonlinearities add up to a quite illuminating framework for thinking about distortion in our audio feedback amp designs

[john curl]

So much for the 'professors'. IF audio design was exactly the same as servo design, then it would be fairly easy to move forward. As I first learned to design amps, my main job was designing servos, yet I separate the design approaches of the two.
Everyone please remember: There are hundreds of different audio amps and preamps to chose from. Just pick one, IF you think that it is 'easy' to make a 'successful' (defined by a class A rating in 'Stereophile' or its equivalent) audio product, and have many happy customers.

[Steve Eddy]

Originally Posted by john curl

Just pick one, IF you think that it is 'easy' to make a 'successful' (defined by a class A rating in 'Stereophile' or its equivalent) audio product, and have many happy customers.

That metric has far more to do with marketing, shcmoozing and luck than it does with advanced engineering.

se

[SY]

Originally Posted by Steve Eddy

That metric has far more to do with marketing, shcmoozing and luck than it does with advanced engineering.

se

Well, it's been observed that the Stereophile Class A amps have included high feedback, low feedback, tubes, transistors, FETs, hybrids, OTL, transfomer-coupled, high bandwidth, low bandwidth, ultra-low distortion, mediocre distortion- there really is no common technological or performance thread. The only common factors are high price and pretty casework. And, of course, evaluations are not done by ear alone.

So, yeah, it would seem to be a very nice marketing coup, rather than a technical one, not that there's anything wrong with that. Designers in this fashion niche gotta eat.

[simon7000]

Originally Posted by janneman

Ed how about using non-linear blocks in LTspice? You can make your amplifier chain anyway you want; just put your formula in the nl-block and look at the transient simulation output.


jan

There are lots of ways to do the math and simulations, but actual hardware is very easy to do and leaves little room for argument.

It is even easier to speculate about the math with even less usefulness!