John Curl's Blowtorch preamplifier part II - Page 3461

john curl · 9th February 2013, 10:39 PM

Yes, you can have asymmetric waveforms, BUT you have to have generate the DC component IF you take a symmetric waveform and distort it to be asymmetric. That is what happens in power lines, as best that I can tell, and we are talking about a POWER LINE in the first place. Get real guys, note what we are discussing, rather than trying to find exceptions.

bcarso · 9th February 2013, 10:41 PM

I've conjectured that another one of the reasons people claim to like second harmonic distortion is that the low-frequency term ("d.c.", but always highpassed out in any real electroacoustic situation) gives a certain cue to the auditory system that something "big" is going on.

A project that awaits board layout is a voice coil temperature measurement system for Marshall Buck and his company Psychotechnology. Marshall had an experimental system some years back when he worked for Harman's Applied Technology division. His approach, to pick out the d.c. offset from a d.c. probe current while a.c.-coupling the main signal to do the primary heating of the driver under test, sounds straightforward enough. But if you consider the requirements on the filter and the need for stringent bandlimiting at low frequencies of the test signal, and the desire to have the d.c. probe current be fairly small, it turns out to be quite a measurement challenge. 5kW into 8 ohms while looking at an 80mV offset is really a needle in a haystack. In particular, if there is much even-harmonic distortion the d.c. component will produce a significant error. Now one can "chop" the probe signal, or reverse its polarity periodically. But I found, after a good deal of effort and experiment, a configuration for the lowpass filter chain that had low-enough distortion.

john curl · 9th February 2013, 10:42 PM

Where was this product 'caned' (your word) by reviewers? When did I say so? I am serious, you are way off base.

Speedskater · 9th February 2013, 11:24 PM

Quote:

Originally Posted by DF96

Quote:
Originally Posted by Speedskater
It maybe "pixie dust" but it's not “Floobydust”.

Thanks for correcting us. I lack a Classical education so distinguishing the latin for pixie and flooby is beyond me.

Some of the many Bob Pease “Floobydust” articles.

What's All This FLOOBYDUST Stuff, Anyhow?-part 5 | Archive content from Electronic Design

What's All This Floobydust Stuff, Anyhow? (1993) | Analog content from Electronic Design

What's All This Floobydust Stuff, Anyhow? (Part 6) | Archive content from Electronic Design

What's All This Floobydust Stuff, Anyhow? (Part 11) | Products content from Electronic Design

What's All This Floobydust Stuff, Anyhow? (Part 9) | Electromechanical content from Electronic Design

What's All This Floobydust Stuff, Anyhow? (Part 10) | Boards content from Electronic Design

scott wurcer · 9th February 2013, 11:25 PM

Quote:

Originally Posted by vacuphile

Scott, this example only proves what I already thought. Ofcourse there is no DC here. How could it be after galvanic uncoupling? The zero floats.

I thought all waveforms could be produced by simple additions of sinoids, including those caused by diodes clipping a sinewave. You can mathematically arrive at the same waveform that John created with his test setup. But then ofcourse DC does not show up. Isn't this what you originally meant?

I think we've started arguing over trivia, diodes clipping will make DC let's just say this is a sine at 0 frequency. My real complaint is over the statement that music is asymmetric (has DC) so sine wave testing is ineffective.

qusp · 11:48 PM

yep, more misdirection...

a statement about music tones/overtones containing DC morphed into an assertion about mains including it. of course it does, when rectifiers clip/fail or when switchmode supplies without power factor correction take from the positive going swing of all 3 phases, cause harmonic distortion. etc.

2 completely different things, yet one factor used to explain another.

john curl · 9th February 2013, 11:45 PM

Let's get real. A 50-60 Hz sine wave generated from the power company is free of 2'nd harmonic distortion as much as possible. WHY? Because the DC component would saturate the power transformers in the path, very easily.
This topic first occurred when the measurements made by AMES was critiqued. This is the nature of DC on the mains which is a REAL PROBLEM in many AC systems.

RNMarsh · 10th February 2013, 12:06 AM

Quote:

Originally Posted by scott wurcer

I think we've started arguing over trivia, diodes clipping will make DC let's just say this is a sine at 0 frequency. My real complaint is over the statement that music is asymmetric (has DC) so sine wave testing is ineffective.

No one has said that. Thats your reading of it. When I used the term Dc it was in reference to an average level at a short time period (not infinite time) such as a transient's average level. Everything you has addressed is off base and not about finding a model in electronic terms which describes the thd found in some caps... some more or less than others. All cap models ignore the non-linear portion of the part. Can you describe the model or make up a model that predicts the thd of an electrolytic or a ceramic (non npo)? That is what we would like to see.... a non-linear model from you that matches a measurement. That would help a lot more than going over how everything can be explained with sine wave combinations. yes. but so what? We want a model that predicts thd or any other form of distortion and backed up by measurment. Thats all we are looking for. Thx-RNMarsh

qusp · 12:30 AM

Richard, I guess you missed it, it was said and not for the first time. you seem to be on a completely different tack....its an old chestnut that gets pulled out whenever in depth testing with instruments does not match miraculous claims.

it was made in reference to the BQP, asking SY if he could repeat the testing with music signals or multitone testing that is more like 'real music' because 'real music' often has an asymmetric waveform with a DC component. Scott's post was illustrating that you can add sinewaves any way you like and still not get any DC. then there was a misdirect pointing at AC mains suply having DC, which is caused by DC being spilled back into the mains, or energy being given/taken asymmetrically from the AC, NOT the addition of more sinewaves.

RNMarsh · 10th February 2013, 12:39 AM

Quote:

Originally Posted by qusp

Richard, I guess you missed it, it was said and not for the first time. you seem to be on a completely different tack....its an old chestnut that gets pulled out whenever in depth testing with instruments does not match miraculous claims.

it was made in reference to the BQP, asking SY if he could repeat the testing with music signals or multitone testing that is more like 'real music' because 'real music' often has an asymmetric waveform with a DC component. Scott's post was illustrating that you can add sinewaves any way you like and still not get any DC. then there was a misdirect pointing at AC mains suply having DC, which is caused by DC being spilled back into the mains, or energy being given/taken asymmetrically from the AC, NOT the addition of more sinewaves.

OK. Geeeez. neeeeever mind.

9th February 2013, 11:40 PM	#34606
qusp is choosing a less facetious title... diyAudio Member Join Date: Oct 2009 Location: Brisbane, Australia	yep, more misdirection... a statement about music tones/overtones containing DC morphed into an assertion about mains including it. of course it does, when rectifiers clip/fail or when switchmode supplies without power factor correction take from the positive going swing of all 3 phases, cause harmonic distortion. etc. 2 completely different things, yet one factor used to explain another. Last edited by qusp; 9th February 2013 at 11:48 PM.

10th February 2013, 12:19 AM	#34609
qusp is choosing a less facetious title... diyAudio Member Join Date: Oct 2009 Location: Brisbane, Australia	Richard, I guess you missed it, it was said and not for the first time. you seem to be on a completely different tack....its an old chestnut that gets pulled out whenever in depth testing with instruments does not match miraculous claims. it was made in reference to the BQP, asking SY if he could repeat the testing with music signals or multitone testing that is more like 'real music' because 'real music' often has an asymmetric waveform with a DC component. Scott's post was illustrating that you can add sinewaves any way you like and still not get any DC. then there was a misdirect pointing at AC mains suply having DC, which is caused by DC being spilled back into the mains, or energy being given/taken asymmetrically from the AC, NOT the addition of more sinewaves. Last edited by qusp; 10th February 2013 at 12:30 AM. Reason: Brain Explosion

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9th February 2013, 10:39 PM	#34601
john curl diyAudio Member Join Date: Jul 2003 Location: berkeley ca	Yes, you can have asymmetric waveforms, BUT you have to have generate the DC component IF you take a symmetric waveform and distort it to be asymmetric. That is what happens in power lines, as best that I can tell, and we are talking about a POWER LINE in the first place. Get real guys, note what we are discussing, rather than trying to find exceptions.

9th February 2013, 10:41 PM	#34602
bcarso diyAudio Member Join Date: May 2005 Location: Canoga Park, California	I've conjectured that another one of the reasons people claim to like second harmonic distortion is that the low-frequency term ("d.c.", but always highpassed out in any real electroacoustic situation) gives a certain cue to the auditory system that something "big" is going on. A project that awaits board layout is a voice coil temperature measurement system for Marshall Buck and his company Psychotechnology. Marshall had an experimental system some years back when he worked for Harman's Applied Technology division. His approach, to pick out the d.c. offset from a d.c. probe current while a.c.-coupling the main signal to do the primary heating of the driver under test, sounds straightforward enough. But if you consider the requirements on the filter and the need for stringent bandlimiting at low frequencies of the test signal, and the desire to have the d.c. probe current be fairly small, it turns out to be quite a measurement challenge. 5kW into 8 ohms while looking at an 80mV offset is really a needle in a haystack. In particular, if there is much even-harmonic distortion the d.c. component will produce a significant error. Now one can "chop" the probe signal, or reverse its polarity periodically. But I found, after a good deal of effort and experiment, a configuration for the lowpass filter chain that had low-enough distortion.

9th February 2013, 10:42 PM	#34603
john curl diyAudio Member Join Date: Jul 2003 Location: berkeley ca	Where was this product 'caned' (your word) by reviewers? When did I say so? I am serious, you are way off base.

9th February 2013, 11:45 PM	#34607
john curl diyAudio Member Join Date: Jul 2003 Location: berkeley ca	Let's get real. A 50-60 Hz sine wave generated from the power company is free of 2'nd harmonic distortion as much as possible. WHY? Because the DC component would saturate the power transformers in the path, very easily. This topic first occurred when the measurements made by AMES was critiqued. This is the nature of DC on the mains which is a REAL PROBLEM in many AC systems.