A question to mr Pass about the document; Audio, distortion and feedback.

gaetan8888 · 19th December 2010, 07:51 PM

Hello mr Pass

About your document; Audio, distortion and feedback.

How do you proceed to do the IM thd test with 7 non-harmonically related tones ?

Thank

Bye

Gaetan

Nelson Pass · 19th December 2010, 09:03 PM

This was done by simulation. In this case, I have arbitrarily
picked 7 frequencies of equal amplitude from a fundamental
of 1 up to 29 and calculated the distortion through a device
having 1% 2nd and 1% 3rd harmonic distortion and displayed
the input waveform vs the distortion.

You could do the same thing with 7 generators and a low
distortion subtractive circuit (given the high numbers, any
decent op amp would do)

There is nothing special about the test - I simply wanted to
illustrate how badly this stuff piles up.

gaetan8888 · 09:14 PM

Hello mr Pass

Did you used LTspice ?

If so, do you still have the sim file ?

I would like to use your SPICE directive and try that simulation with my diy amps circuit using my LTspice software.

Thank

Bye

Gaetan

Nelson Pass · 20th December 2010, 10:47 PM

I used Excel

Blues · 20th December 2010, 11:06 PM

Quote:

Originally Posted by Nelson Pass

I used Excel

Zen Mod · 20th December 2010, 11:26 PM

Quote:

Originally Posted by Nelson Pass

........

The Pass Pub: The High-End Off Topic Thread

CanAm Man · 22nd December 2010, 01:47 AM

I'm a tad disappointed, Papa. I would have thought you had used a log-log-decitrig slide rule!

Nelson Pass · 23rd December 2010, 02:25 AM

I needed some automated graphics-
I don't have all the time in the world.

CanAm Man · 24th December 2010, 12:44 AM

Papa..... Point well made......

Although I don't think I could have gotten through college physics without my K&E 'rule...... But then again, I think we only had three elementry particles to contend with, "back in the good old days"....!

May you have a great holiday season, Mr Pass. And may your 2011 be filled with only the most enjoyable products of the Napa and Sonoma Vallley.....!!

gaetan8888 · 11:26 AM

Hello mr. Pass

Again about your document: Audio, distortion and feedback.

There is this graphic, I include an image of it.

In this graphic and theoretically the best sound are at both end of it, so; an amp with no feedback or with 40 db feedback will have a very low distortions in the higher thd harmonics, and so a better sound.

After tests and listening tests on various amps circuits, I found out that if I use a high level of global negative feedback the amp sound much less good than if I use a low level of global negative feedback.

From your experiences and knowledges, do you have any explanations of why, even if according to the graph, a 40 db feedback will give very low distortions in the higher thd harmonics, in reality it sound much less good than if I use a low level of global negative feedback ?

Thank

Bye

Gaetan

19th December 2010, 07:51 PM	#1
gaetan8888 diyAudio Member Join Date: Apr 2007	A question to mr Pass about the document; Audio, distortion and feedback. Hello mr Pass About your document; Audio, distortion and feedback. How do you proceed to do the IM thd test with 7 non-harmonically related tones ? Thank Bye Gaetan

19th December 2010, 09:12 PM	#3
gaetan8888 diyAudio Member Join Date: Apr 2007	Hello mr Pass Did you used LTspice ? If so, do you still have the sim file ? I would like to use your SPICE directive and try that simulation with my diy amps circuit using my LTspice software. Thank Bye Gaetan Last edited by gaetan8888; 19th December 2010 at 09:14 PM.

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19th December 2010, 09:03 PM	#2
Nelson Pass The one and only Join Date: Mar 2001	This was done by simulation. In this case, I have arbitrarily picked 7 frequencies of equal amplitude from a fundamental of 1 up to 29 and calculated the distortion through a device having 1% 2nd and 1% 3rd harmonic distortion and displayed the input waveform vs the distortion. You could do the same thing with 7 generators and a low distortion subtractive circuit (given the high numbers, any decent op amp would do) There is nothing special about the test - I simply wanted to illustrate how badly this stuff piles up.

20th December 2010, 10:47 PM	#4
Nelson Pass The one and only Join Date: Mar 2001	I used Excel

22nd December 2010, 01:47 AM	#7
CanAm Man diyAudio Member Join Date: Sep 2006 Location: Colorado Springs, CO	I'm a tad disappointed, Papa. I would have thought you had used a log-log-decitrig slide rule!

23rd December 2010, 02:25 AM	#8
Nelson Pass The one and only Join Date: Mar 2001	I needed some automated graphics- I don't have all the time in the world.

24th December 2010, 12:44 AM	#9
CanAm Man diyAudio Member Join Date: Sep 2006 Location: Colorado Springs, CO	Papa..... Point well made...... Although I don't think I could have gotten through college physics without my K&E 'rule...... But then again, I think we only had three elementry particles to contend with, "back in the good old days"....! May you have a great holiday season, Mr Pass. And may your 2011 be filled with only the most enjoyable products of the Napa and Sonoma Vallley.....!!

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