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-   -   GNFB and distortion (http://www.diyaudio.com/forums/solid-state/127110-gnfb-distortion.html)

myhrrhleine 28th July 2008 07:10 PM

GNFB and distortion
 
Do you truly like 2nd harmonic or third harmonic distortion?
Not me.
Why do I prefer zero GNFB feedback then?
I find the sound colouration of global NFB to be worse.
Aren't you just hearing more low-harmonic distortion?
Given otherwise identical zero-GNFB amps, I prefer the lower distortion amp.
I strive to reduce distortions with other means than GNFB because I really don't want the distortion.

How about you?.

PMA 28th July 2008 07:36 PM

Weighting of ear sensibility to an order of harmonics (audibility) is an unexceptionable fact. You will never hear -90dB 2nd. You can make your own tests, if you have equipment.

myhrrhleine 28th July 2008 09:08 PM

Quote:

Originally posted by PMA
Weighting of ear sensibility to an order of harmonics (audibility) is an unexceptionable fact. You will never hear -90dB 2nd. You can make your own tests, if you have equipment.
Then -50dB might be a problem

Juergen Knoop 28th July 2008 09:42 PM

people still work on quantifying distortion perception.
See this thesis for example:
http://projekter.aau.dk/projekter/fb...061_Thesis.pdf
regards

nigelwright7557 28th July 2008 09:49 PM

Re: GNFB and distortion
 
Quote:

Originally posted by myhrrhleine
Do you truly like 2nd harmonic or third harmonic distortion?
Not me.
Why do I prefer zero GNFB feedback then?
I find the sound colouration of global NFB to be worse.
Aren't you just hearing more low-harmonic distortion?
Given otherwise identical zero-GNFB amps, I prefer the lower distortion amp.
I strive to reduce distortions with other means than GNFB because I really don't want the distortion.

How about you?.

I prefer the warm sound of valves/tubes.

I use a valve mixer/pre amp for my disco but also play guitar through it. The guitar sounds much better through the valve pre amp.

myhrrhleine 28th July 2008 10:56 PM

Re: Re: GNFB and distortion
 
Quote:

Originally posted by nigelwright7557


I prefer the warm sound of valves/tubes.

I use a valve mixer/pre amp for my disco but also play guitar through it. The guitar sounds much better through the valve pre amp.


Given otherwise identical zero-GNFB amps, I prefer the lower distortion amp.
I strive to reduce distortions with other means than GNFB because I really don't want the distortion.

How about you?.

nigelwright7557 28th July 2008 11:00 PM

Global NFB is fine so long as you take steps to isolate the speaker from the feedback loop. A 2uH inductor goes a long way to doing this.

I think people sometimes hear things in their imagination.
I thought my first home design sounded good until I looked on the scope and there was severe cross over distortion. I hadnt set the bias properly.

Wavebourn 28th July 2008 11:24 PM

Quote:

Originally posted by myhrrhleine

Then -50dB might be a problem

Usually such level of 2'nd harmonic signifies high enough intermodulation distortions.

lineup 29th July 2008 12:10 AM

2 Attachment(s)
Quote:

Originally posted by myhrrhleine

Then -50dB might be a problem

No, actually, no :)
For Pavel Macura maybe :D
But not for one listener.

I explain:
- Tube amplifiers are know to distotion producers.
- Loudspeakers are REALLY distortion producers. Does not matter what power amplifier you use.
Valve power or Solid State power or MOSFET power.
No big difference for our loudspeaker part.
It will produce considerably more distortion than any modern amplifier.


von Schweikert are expensive High End audiophile speakers
no doubt about this :)
Still von Schweikert has a level of 0.5% THD at 1-2 Watt RMS.
1 meter away from speaker on axis.


PMA talks about the -90 dB level. He is in his dreams ;)
Because when listen with loudspeaker
and consider the Listening Room effects
( floor and ceiling and walls indirect sounds )
we are close to 1 % THD at 1 Watt.

===============================
1% = -40dB
0.0032 % = -90dB
What will dominate what we hear?
the Op-Amp THD or the Speaker THD.
===============================

I do not know what you think is correct answer.
But fortunately still I have some intact logics in my brains.

===============================

I attach the THD test curve of von Schweikert very expensive speakers.
They are NOT low or ordinary quality as of yours and mine speaker systems.
And they try to avoid Room influencis when measure
by putting Test Microphone 1 meter on Axis in front of speakers baffle.

phase_accurate 29th July 2008 06:19 AM

The distortion mechanisms of speakers and amps are quite different.
And they are perceived different. So the higher speaker THD is still less objectionable than the amp's nonlinear distortion.

Earl Gedds has a nice paper on that.

Regards

Charles


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