Feedback in audio esp wrt op-amps.

[Eeyore]

Mark wrote:

Eeyore wrote:

What is the case AIUI is that NFB can create 'new' (higher) harmonics that don't
exist with the open-loop situation. It's down to the maths of how feedback works.


And I am saying NFB CANNOT create new higher harmonics.

And it seems you are incorrect (at least when the amplifier having the feedback applied
has some non-linearity).

Graham

 

[Eeyore]

William Sommerwerck wrote:

The most common cause of audible distortion in audio gear
is clipping due to importune gain setting.

Actually, clipping is not "in" the gear.

I do wish you'd glom onto a Crown K1. You really need to hear this
amplifier -- and run it through some blind tests.

What's the K1 like then ?

Graham

 

[Arny Krueger]

"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in message
news:46CA1FF9.C759C7@hotmail.com...

William Sommerwerck wrote:

The most common cause of audible distortion in audio gear
is clipping due to importune gain setting.

Actually, clipping is not "in" the gear.

I do wish you'd glom onto a Crown K1. You really need to hear this
amplifier -- and run it through some blind tests.

What's the K1 like then ?

Something like The Second Coming?

 

[Mark]

On Aug 20, 6:06 pm, Eeyore <rabbitsfriendsandrelati...@hotmail.com>
wrote:

Mark wrote:
Eeyore wrote:

What is the case AIUI is that NFB can create 'new' (higher) harmonics that don't
exist with the open-loop situation. It's down to the maths of how feedback works.

And I am saying NFB CANNOT create new higher harmonics.

And it seems you are incorrect (at least when the amplifier having the feedback applied
has some non-linearity).

Graham

take something like crossover distortiuon for example...

in an open loop amp, crossover dist. creates lots of harmonics.

add neg feedback and they are all reduced. The high order ones are
not reduced AS MUCH as the low order ones, but they are certainly not
increased (assumming a proper design not on the verge of instability
and assuming the feedback componets themselves are linear, resistors
are usually linear for our purposes).

so after you add neg feedback the proportion of high order to low
order will change and realative to the low order there will be more
high order, but in absolute terms that are all reduced. Someone else
already said this so I am repeating...

I don't know how else to say it...
Mark

 

[Phil Allison]

"Scott Dorsey Notorious Charlatan"

It does, because a stage which is audibly blameless by itself may turn
into
a sonic disaster when it appears a few hundred times in the signal path.

** Huh ??

A few HUNDRED times ???????

The colossal fool must be on LSD.

"C'est un Nagra. C'est suisse, et tres, tres precis."

** C'est Dorsey - so you know it is total crapology.



......... Phil

 

[Eeyore]

Mark wrote:

Eeyore wrote:
Mark wrote:
Eeyore wrote:

What is the case AIUI is that NFB can create 'new' (higher) harmonics that don't
exist with the open-loop situation. It's down to the maths of how feedback works.

And I am saying NFB CANNOT create new higher harmonics.

And it seems you are incorrect (at least when the amplifier having the feedback applied
has some non-linearity).


take something like crossover distortiuon for example...

in an open loop amp, crossover dist. creates lots of harmonics.

add neg feedback and they are all reduced. The high order ones are
not reduced AS MUCH as the low order ones,

That's because of the falling loop gain with frequency of the amplifier. Not what I was
referring to.

but they are certainly not
increased (assumming a proper design not on the verge of instability
and assuming the feedback componets themselves are linear, resistors
are usually linear for our purposes).

so after you add neg feedback the proportion of high order to low
order will change and realative to the low order there will be more
high order, but in absolute terms that are all reduced. Someone else
already said this so I am repeating...

I don't know how else to say it...

You've missed the point I was making entirely. Other posters have explained it better than
myself however.

Graham

 

[Eeyore]

Phil Allison wrote:

"Scott Dorsey Notorious Charlatan"

It does, because a stage which is audibly blameless by itself may turn
into a sonic disaster when it appears a few hundred times in the signal
path.

** Huh ??

A few HUNDRED times ???????

The colossal fool must be on LSD.

The EQ section alone on a Neve V series (and derivatives) has 18 op-amp stages.

Graham

 

[Phil Allison]

" Graham Stevenson Mentally Deranged Pile of Autistic Shit."


Phil Allison wrote:

"Scott Dorsey Notorious Charlatan"

It does, because a stage which is audibly blameless by itself may turn
into a sonic disaster when it appears a few hundred times in the signal
path.

** Huh ??

A few HUNDRED times ???????

The colossal fool must be on LSD.

The EQ section alone on a Neve V series (and derivatives) has 18 op-amp
stages.

** FUCK OFF YOU ASININE TROLLING MORON !!




....... Phil

 

[Scott Dorsey]

Arny Krueger <arnyk@hotpop.com> wrote:

"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in message

I do wish you'd glom onto a Crown K1. You really need to hear this
amplifier -- and run it through some blind tests.

What's the K1 like then ?

Something like The Second Coming?

No, more like something out of Revelations.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

 

[MooseFET]

On Aug 20, 7:20 pm, Eeyore <rabbitsfriendsandrelati...@hotmail.com>
wrote:

Phil Allison wrote:
"Scott Dorsey Notorious Charlatan"

It does, because a stage which is audibly blameless by itself may turn
into a sonic disaster when it appears a few hundred times in the signal
path.

** Huh ??

A few HUNDRED times ???????

The colossal fool must be on LSD.

The EQ section alone on a Neve V series (and derivatives) has 18 op-amp stages.

It isn't hard to end up with that many. 1 per band per channel plus a
few will get you to 20 without working at it. To get above 100, you
are talking about a serious amount of more signal processing.

 

[Eeyore]

MooseFET wrote:

Eeyore wrote:
Phil Allison wrote:
"Scott Dorsey Notorious Charlatan"

It does, because a stage which is audibly blameless by itself may turn
into a sonic disaster when it appears a few hundred times in the signal
path.

** Huh ??

A few HUNDRED times ???????

The colossal fool must be on LSD.

The EQ section alone on a Neve V series (and derivatives) has 18 op-amp stages.

It isn't hard to end up with that many. 1 per band per channel plus a
few will get you to 20 without working at it. To get above 100, you
are talking about a serious amount of more signal processing.

100 sounds pretty extreme certainly.

Graham

 

[MooseFET]

On Aug 20, 6:13 pm, Mark <makol...@yahoo.com> wrote:

On Aug 20, 6:06 pm, Eeyore <rabbitsfriendsandrelati...@hotmail.com
wrote:

Mark wrote:
Eeyore wrote:

What is the case AIUI is that NFB can create 'new' (higher) harmonics that don't
exist with the open-loop situation. It's down to the maths of how feedback works.

And I am saying NFB CANNOT create new higher harmonics.

And it seems you are incorrect (at least when the amplifier having the feedback applied
has some non-linearity).

Graham

take something like crossover distortiuon for example...

No, I don't want crossover distortion.

How about thinking about a distortion that only adds, lets say the 2nd
harmonic to a sine wave. Think about what happens when that is
enclosed in a feedback loop. You take some of that second harmonic
from the output and feed it back into the input. The nonlinear
circuit takes the 2nd harmonic of the 2nd harmonic giving the forth
and sends that out the output. That forth comes back around and
around and around. A nonlinear cicrcuit that only made 2nd a harmonic
is now resulting in an infinite chain of frequencies.

in an open loop amp, crossover dist. creates lots of harmonics.

add neg feedback and they are all reduced. The high order ones are
not reduced AS MUCH as the low order ones, but they are certainly not
increased (assumming a proper design not on the verge of instability
and assuming the feedback componets themselves are linear, resistors
are usually linear for our purposes).

This is not correct. You have to have an extraordinarily large phase
margin to not have a boost in the harmonic near the gain crossover.

If G is the forward gain from the point where the distortion is made
to the output and H is the rest feedback the math looks like:

G /(1 + GH)

Here's the very ugly bit:

The distortion is often created in the output section making the G
part unity or nearly so. A stable servo loop can have a phase margin
of 30 degrees.

1/(1 + 1 * 1@(180-30)) = 1/(1 - 0.866 + j0.5)


= 1/(0.134 + j0.5)

Take ABS()

ABS(1/(0.134 + j0.5)) = 1/sqrt(0.134^2 + 0.5^2) = 1.93

Even though this amplifier is very stable, the feedback loop doubles
the amplitude of the harmonic near the gain crossover.

 

[MooseFET]

On Aug 20, 7:16 pm, Eeyore <rabbitsfriendsandrelati...@hotmail.com>
wrote:

Mark wrote:
Eeyore wrote:
Mark wrote:
Eeyore wrote:

What is the case AIUI is that NFB can create 'new' (higher) harmonics that don't
exist with the open-loop situation. It's down to the maths of how feedback works.

And I am saying NFB CANNOT create new higher harmonics.

And it seems you are incorrect (at least when the amplifier having the feedback applied
has some non-linearity).

take something like crossover distortiuon for example...

in an open loop amp, crossover dist. creates lots of harmonics.

add neg feedback and they are all reduced. The high order ones are
not reduced AS MUCH as the low order ones,

That's because of the falling loop gain with frequency of the amplifier. Not what I was
referring to.

..... plus the increasing phase lag. Must not forget that nasty
detail :>

but they are certainly not
increased (assumming a proper design not on the verge of instability
and assuming the feedback componets themselves are linear, resistors
are usually linear for our purposes).

so after you add neg feedback the proportion of high order to low
order will change and realative to the low order there will be more
high order, but in absolute terms that are all reduced. Someone else
already said this so I am repeating...

I don't know how else to say it...

You've missed the point I was making entirely. Other posters have explained it better than
myself however.

I tried my harmonic of the harmonic argument again. Sometimes it
works sometimes not.

 

On Aug 19, 10:35 pm, D from BC <myrealaddr...@comic.com> wrote:

On Mon, 20 Aug 2007 05:19:10 +0100, Eeyore

rabbitsfriendsandrelati...@hotmail.com> wrote:

D from BC wrote:

Electronics have time delays.

Switching circuits have time delays ( Ton - Toff - Tstg etc ) . Amplifier
circuits are not normally hard switching. It's more useful to look at phase
shift with them.

Graham

I guess I think phase for repeating waveforms.
Audio is like noise.
I haven't heard someone say "That noise is lagging by 40 degrees."
2 sine waves out of sync can be expressed by degrees or time delay.

Any complex signal can be broken down into a combination of sine
waves. So you can still use the notion of phase shift.

But yeah... when it comes to feedback, time delay within a 1/2 cycle
is of concern..so I guess that's why phase is the better term.

I mentioned time delay to express the time it takes for a signal to
pass through x amount of transistors in an op amp.
After that, feeding back the signal kinda doesn't look like
instantaneous correction.

In some ways feedback is seems like continuously breaking wine glasses
on the floor.. If the clean up is done fast enough...it doesn't look
like any glasses are being broken.
Well...that's probably a crappy analogy but best I can think of...
D from BC

 

On Aug 20, 3:12 pm, klu...@panix.com (Scott Dorsey) wrote:

Mark <makol...@yahoo.com> wrote:

And I am saying NFB CANNOT create new higher harmonics.

Sure it can. Just put something that creates harmonics in the feedback
path.

Negative feedback relies on the feedback path being linear and having
low group delay. If these aren't the case, bad things can happen.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

I'm not sure I'd bring group delay into the discussion. What you need
is phase margin.

 

[Les Cargill]

MooseFET wrote:

On Aug 20, 6:13 pm, Mark <makol...@yahoo.com> wrote:
On Aug 20, 6:06 pm, Eeyore <rabbitsfriendsandrelati...@hotmail.com
wrote:

Mark wrote:
Eeyore wrote:
What is the case AIUI is that NFB can create 'new' (higher) harmonics that don't
exist with the open-loop situation. It's down to the maths of how feedback works.
And I am saying NFB CANNOT create new higher harmonics.
And it seems you are incorrect (at least when the amplifier having the feedback applied
has some non-linearity).
Graham
take something like crossover distortiuon for example...

No, I don't want crossover distortion.

How about thinking about a distortion that only adds, lets say the 2nd
harmonic to a sine wave. Think about what happens when that is
enclosed in a feedback loop. You take some of that second harmonic
from the output and feed it back into the input. The nonlinear
circuit takes the 2nd harmonic of the 2nd harmonic giving the forth
and sends that out the output. That forth comes back around and
around and around. A nonlinear cicrcuit that only made 2nd a harmonic
is now resulting in an infinite chain of frequencies.


in an open loop amp, crossover dist. creates lots of harmonics.

add neg feedback and they are all reduced. The high order ones are
not reduced AS MUCH as the low order ones, but they are certainly not
increased (assumming a proper design not on the verge of instability
and assuming the feedback componets themselves are linear, resistors
are usually linear for our purposes).

This is not correct. You have to have an extraordinarily large phase
margin to not have a boost in the harmonic near the gain crossover.

If G is the forward gain from the point where the distortion is made
to the output and H is the rest feedback the math looks like:

G /(1 + GH)

Here's the very ugly bit:

The distortion is often created in the output section making the G
part unity or nearly so. A stable servo loop can have a phase margin
of 30 degrees.

1/(1 + 1 * 1@(180-30)) = 1/(1 - 0.866 + j0.5)


= 1/(0.134 + j0.5)

Take ABS()

ABS(1/(0.134 + j0.5)) = 1/sqrt(0.134^2 + 0.5^2) = 1.93

Even though this amplifier is very stable, the feedback loop doubles
the amplitude of the harmonic near the gain crossover.

So for audio, put the gain crossover way out of band. Right?

--
Les Cargill

 

[D from BC]

On Mon, 20 Aug 2007 21:31:17 -0700, MooseFET <kensmith@rahul.net>
wrote:

On Aug 20, 6:13 pm, Mark <makol...@yahoo.com> wrote:
On Aug 20, 6:06 pm, Eeyore <rabbitsfriendsandrelati...@hotmail.com
wrote:

Mark wrote:
Eeyore wrote:

What is the case AIUI is that NFB can create 'new' (higher) harmonics that don't
exist with the open-loop situation. It's down to the maths of how feedback works.

And I am saying NFB CANNOT create new higher harmonics.

And it seems you are incorrect (at least when the amplifier having the feedback applied
has some non-linearity).

Graham

take something like crossover distortiuon for example...

No, I don't want crossover distortion.

How about thinking about a distortion that only adds, lets say the 2nd
harmonic to a sine wave. Think about what happens when that is
enclosed in a feedback loop. You take some of that second harmonic
from the output and feed it back into the input. The nonlinear
circuit takes the 2nd harmonic of the 2nd harmonic giving the forth
and sends that out the output. That forth comes back around and
around and around. A nonlinear cicrcuit that only made 2nd a harmonic
is now resulting in an infinite chain of frequencies.

[snip]

Cool...
Maybe call it a distortion loop.

+-<<<--------------------------------------<+
| |
sine>--summation-------nonlinear transfer (inverting)->+
|
Not completely containing a signal to cancel out the
nonlinear transfer. So some 2nd harmonic gets to pass through the
nonlinear transfer again to make...the 4th....and so and so on..
(IIRC that would be the harmonic generation sequence for a 2nd order
nonlinear transfer.)

Take 2 tone and then there's the intermodulation products.
What a painful thing to think about...

Significant magnitudes???

Cheerleader in electronics...
"2,4,6,8 what distortion do I hate."

D from BC

 

[Mr.T]

"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in message
news:46CA1FF9.C759C7@hotmail.com...

I do wish you'd glom onto a Crown K1. You really need to hear this
amplifier -- and run it through some blind tests.

What's the K1 like then ?

Like most other good amps, so good you can forget about it being the
problem, unless it's broken of course

MrT.

 

[Mr.T]

"MooseFET" <kensmith@rahul.net> wrote in message
news:1187669490.438547.314920@j4g2000prf.googlegroups.com...

It isn't hard to end up with that many. 1 per band per channel plus a
few will get you to 20 without working at it. To get above 100, you
are talking about a serious amount of more signal processing.

100 op amps on parallel channels is a far different situation than 100 *ALL
in series* with the signal.
Of course in the real world the situation is somewhere in between those
extremes.

MrT.

 

[Robert Latest]

["Followup-To:" header set to sci.electronics.design.]
Eeyore wrote:

The idea that you can 'get away' with sloppy circuitry for replay because the
source was in some way 'impaired' is totally false.

I don't think anybody proposed "sloppy" circuitry for replay. The point is
that studio audio gear is just solid, reliable, conventional good audio
stuff (none of that high-end low-oxygen power cord crap). Plenty of opamps,
plenty of NFB, plenty of digital processing, plenty of all the things that
high-enders loathe.

Since the recording studio already did 90% of the work of completely
destroying the audio signal beyond repair, it doesn't matter how much your
home audio gear adds to that.

Sometimes when I hear the golden earers talk I'm surprised that I can make
out any music at all when listening with my Cantons fed from an old Sony amp
through particularly oxygen-rich cables.

robert