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Old 16th March 2013, 06:37 PM   #2841
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Quote:
Originally Posted by RNMarsh View Post
Well then, let me throw this out there --->

One of the reasons for going low gnfb -in my mind- wa to get a constant amount of fb at all frequencies. back in the day, I didnt have such good test equipment for measuring distortion.

I thought that the way sound was described sort of followed the thd curve. --- best at low freqs and progressively worse as the freqs when higher.... that high freq rise at the top end. Still a characteristic of many amps -- pre or power. As we know there are many mechanisms at work.

But limiting this to just the thd and amount of feedback here -- What if -- the harmonic structure did not change with freq ?? What ever the relationship between harmonics at low or mid was the same at the high freqs? Same ratios etc.

Wouldnt that have a sameness to the sound across the audible band? No more, the mids sound this way and the highs sound that way. The character would be the same/similar.

In fact, that is what you get in test performance and in listening results. If the harmonics are high enough to hear or the chain/system has harmonics high enough levels to hear differences. there is no other way to get this kind of favorable result (is there?)... assuming a falling open loop within audio feq band and varying feedback margins/amount of etal.

Thx-RNMarsh
You are right about the sound, however there is a different cause than harmonic amplitude.
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Old 16th March 2013, 09:29 PM   #2842
dadod is offline dadod  Croatia
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Quote:
Originally Posted by RNMarsh View Post
Well then, let me throw this out there --->

One of the reasons for going low gnfb -in my mind- wa to get a constant amount of fb at all frequencies. back in the day, I didnt have such good test equipment for measuring distortion.

I thought that the way sound was described sort of followed the thd curve. --- best at low freqs and progressively worse as the freqs when higher.... that high freq rise at the top end. Still a characteristic of many amps -- pre or power. As we know there are many mechanisms at work.

But limiting this to just the thd and amount of feedback here -- What if -- the harmonic structure did not change with freq ?? What ever the relationship between harmonics at low or mid was the same at the high freqs? Same ratios etc.

Wouldnt that have a sameness to the sound across the audible band? No more, the mids sound this way and the highs sound that way. The character would be the same/similar.

In fact, that is what you get in test performance and in listening results. If the harmonics are high enough to hear or the chain/system has harmonics high enough levels to hear differences. there is no other way to get this kind of favorable result (is there?)... assuming a falling open loop within audio feq band and varying feedback margins/amount of etal.

Thx-RNMarsh
Do you think that an amp with the loop gain like this would sound better?
Damir
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Old 16th March 2013, 09:51 PM   #2843
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But music or speech isn't white. I would think you'd have to take into account the power spectrum and further weight the more audible frequencies.
Just dont see the down side of having more loop gain where there is more energy hence higher signal amplitudes and increased distortion.

Thanks
-Antonio
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Old 16th March 2013, 10:05 PM   #2844
dadod is offline dadod  Croatia
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I just ask a questions. Here are FFTs for 20Hz, 1kHz, 10kHz and 20kHz for the same output voltage(60 Vpp).
Damir
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Old 17th March 2013, 05:38 AM   #2845
RNMarsh is offline RNMarsh  United States
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When the same amount of gnfb is used at all freqs, the distortion harmonics are alike at all freqs.; Same level and number and relationship/ratio. I believe this type of distortion pattern is well accepted as best sounding.

As I have said in earlier comments -- levels below -100dB are not audible to me and would be a desireable goal for all parts of the recording/playback system - keeping the total accumilated system thd below audibility.

Sorry but SIMs dont count. Only actual, live operating circuits and systems.

Here is a moderate gnfb line level amp that has the same THD and same harmonic structure at all freqs in the BW of interest. Only 2H and 3H. The important issue is that it looks the same at any freq tested...same level and number of harmonics and relative levels to one another.

Anyway, this characteristic is why, IMO, amps with low or no gnfb are liked by so many people.

Thx-RNMarsh
1-10KHz THD.jpg

Last edited by RNMarsh; 17th March 2013 at 05:43 AM.
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Old 17th March 2013, 06:32 AM   #2846
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Quote:
Originally Posted by RNMarsh View Post
Sorry but SIMs dont count. Only actual, live operating circuits and systems.
But somewhere we have to start when design, and then do the measurement on the built amp. I hope you do not advocate to design without simulation?
Damir
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Old 17th March 2013, 07:37 AM   #2847
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When the same amount of gnfb is used at all freqs, the distortion harmonics are alike at all freqs.; Same level and number and relationship/ratio. I believe this type of distortion pattern is well accepted as best sounding.
As noted by a previous poster, you (and the many others who support this theory) miss that the frequency spectrum of music is not white. A circuit with measured frequency-independent distortion characteristics will in fact distort the bass range of real music more than the high-frequency portion.

Samuel
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Old 17th March 2013, 07:52 AM   #2848
RNMarsh is offline RNMarsh  United States
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Seems reasonable. However, there is also a continuity that doesnt exist in any other type of distortion pattern. A sameness of character from top to bottom. What I am describing does not sound/heard as you describe.... worse in the bass. So maybe I am not characterizing it well enough. or weighting is something that lends a more constant or even quality. Well, its been easy to hear a pattern of distortion change that is uncharacteristci sounding from the falling open-loop gain etc and its distortion pattern. Worse or better.... it is different from typical pattern often found..... A flat thd plot vs one that rises at the higher freqs.

Thx-RNmarsh
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Old 17th March 2013, 11:22 AM   #2849
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Quote:
Originally Posted by RNMarsh View Post
As I have said in earlier comments -- levels below -100dB are not audible to me and would be a desireable goal for all parts of the recording/playback system - keeping the total accumilated system thd below audibility.
What if the rising thd plot still is below -100dB at the highest frequency you are able to perceive ?
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Old 17th March 2013, 04:57 PM   #2850
RNMarsh is offline RNMarsh  United States
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Originally Posted by jacco vermeulen View Post
What if the rising thd plot still is below -100dB at the highest frequency you are able to perceive ?
Then you are on double-safe ground. And, would focus on construction, parts selection, shielding, grounding, interfacing, impedances, loading, controls, power supply, etc to not spoil the pristine amp. The goal then being to have the entire system -from source to speaker - not accumulate any issues that would intrude.

-Thx-RNMarsh

Last edited by RNMarsh; 17th March 2013 at 05:02 PM.
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