[Iain Churches]

"Phil Allison" wrote in message
...

"John Byrns"
"Patrick Turner"

The curve downwards of the "horizontals" of the square wave is the
action of the time constant, C being discharged after the transient
uprights.

** The straight lines of the wave would become curved in that case, not
merely tilted - as they are at much lower frequencies.

It is just down to relative phase shift in the harmonics, despite it
being
only a few degrees.

Hi Phil,

The straight lines are curved, take a closer look the curvature is
easily seen in the photo.


** The lower line is DEAD straight while the upper ones have a *tiny*
curvature.

The point about the visible tilt being due to "phase shift " is that all
the frequency components of that square wave are within 1% of their
correct amplitude values as for a perfect square wave.

A phase correction network alone with fix the tilt.


OK. Now you're talking Phil:-)
Care to shout out some CR values?
I am keen to learn more about this.

TIA
Iain

[Iain Churches]

"Phil Allison" wrote in message
...


"Iain Churches Total IDIOT "


** It don't need fixing.

Good audio power amps * HAVE * 100Hz square wave responses like
-
because good audio power amps need to have sub sonic roll off
included.


My interpretation of the 100Hz square wave, by comparison with
pics in text books, is that it does not exhibit sub sonic roll-off
(which
would be shown by a trace with sides of equal height and a concave
top bar) but phase shift.


** The square wave is affected by phase shift ( ie is tilted) which is
* CAUSED * by a sub sonic roll-off.

Any stupid book that says otherwise needs to be burned !!!

A "concave " square wave shows a response dip or notch exists at the
frequency.

Bet you misread it, as always.

Hi Phil.


** Never " Hi Phil " me - **** head.

I couldn't really write "Hello Philip"
That's a greeting reserved for the Duke of Edinburgh:-)



This has been a civilised thread up to now.


** ********.


As I said before Phil, we do not all have your expertise
in audio repair, but I am pretty sure I can run circles around
you in music, both practical and theory, and in each and
every aspect of recording arts, and aural perception.
That's audio too.

Iain

[robert casey]

Some would agree with Phil, and some might say
well the production of RF sidebands, intermodulation products, are the
same
phenomena at RF or at AF, so the explanations given about the RF
behaviour
at the URL are also valid for AF, hence relevant, even if not explained
above for AF.

But there is nothing at the URL above which is relevant to phase shifted
harmonics of square waves.


Things get more fun in RF work if you do care about phase shift. Like
in video amplifiers, which are wideband systems. Near DC to say 50MHz
for high def. Get the phase shifts bad, and the image will look smeared
and ripply. Audio is less fussy about phase shift, as long as both
channels of a stereo amp have the same phase characteristics.

[Phil Allison]

"John Byrns"

Sure we can move on, getting back to square waves, it is not so much the
harmonics that are phase shifted, it is mainly the fundamental that is
phase shifted, the higher the harmonic the less the phase shift.



** Pure idiocy.

The cretin cannot understand the word "relative".



......... Phil

[Phil Allison]

"John Byrns"

** The lower line is DEAD straight while the upper ones have a *tiny*
curvature.

The point about the visible tilt being due to "phase shift " is that all
the
frequency components of that square wave are within 1% of their correct
amplitude values as for a perfect square wave.


I agree that the amplitude errors of a the square wave components is
less than 1%, but that does not imply that the tilt we see is not the
result of a time constant as Patrick originally asserted, There is no
contradiction in a simple time constant causing exactly the type of
waveform we see in Ian's photo.


** Yawn....

The point about the visible tilt being due to "phase shift " is that all the
frequency components of that square wave are within 1% of their correct
amplitude values as for a perfect square wave.

A phase correction network alone with fix the tilt.

No need to change the time constant of the LF roll off.



........ Phil

[Phil Allison]

"Iain Churches"

** The lower line is DEAD straight while the upper ones have a *tiny*
curvature.

The point about the visible tilt being due to "phase shift " is that all
the frequency components of that square wave are within 1% of their
correct amplitude values as for a perfect square wave.

A phase correction network alone with fix the tilt.


OK. Now you're talking Phil:-)
Care to shout out some CR values?
I am keen to learn more about this.


** Almost NOBODY bothers to correct LF phase shift in amplifiers (or
anything else).

Australian EE Edward Cherry ( he of " nested feedback" fame) used to
champion the idea of no phase shift in the audio band.

Darned if I can find details on the web - but it just involves a couple of
additional RC networks in the NFB loop.




........ Phil

[John Byrns]

In article ,
"Phil Allison" wrote:

"John Byrns"

Sure we can move on, getting back to square waves, it is not so much the
harmonics that are phase shifted, it is mainly the fundamental that is
phase shifted, the higher the harmonic the less the phase shift.



** Pure idiocy.

The cretin cannot understand the word "relative".

Hi Phil,

Here is what Patrick said, "But there is nothing at the URL above which
is relevant to phase shifted harmonics of square waves." Nowhere in it
does Patrick use the word "relative", so it is not actually necessary to
understand the word, although as a few here can attest I understand the
word better than most.


Regards,

John Byrns

--
Surf my web pages at, http://fmamradios.com/

[Phil Allison]

"Iain Churches"


As I said before Phil, we do not all have your expertise
in audio repair,


** Pretty blatant my "expertise" goes WAAAYY beying that.


but I am pretty sure I can run circles around
you in music, both practical and theory, and in each and
every aspect of recording arts, and aural perception.


** You are never sure if you arse is on fire or not.




........ Phil

[Phil Allison]

"John Byrns Congenital Imbecile "


Sure we can move on, getting back to square waves, it is not so much
the
harmonics that are phase shifted, it is mainly the fundamental that is
phase shifted, the higher the harmonic the less the phase shift.



** Pure idiocy.

The cretin cannot understand the word "relative".


Here is what Patrick said,


** How silly.

What a cretin.



....... Phil

[Patrick Turner]

Phil Allison wrote:

"Iain Churches"

** The lower line is DEAD straight while the upper ones have a *tiny*
curvature.

The point about the visible tilt being due to "phase shift " is that all
the frequency components of that square wave are within 1% of their
correct amplitude values as for a perfect square wave.

A phase correction network alone with fix the tilt.


OK. Now you're talking Phil:-)
Care to shout out some CR values?
I am keen to learn more about this.

** Almost NOBODY bothers to correct LF phase shift in amplifiers (or
anything else).

Australian EE Edward Cherry ( he of " nested feedback" fame) used to
champion the idea of no phase shift in the audio band.

Darned if I can find details on the web - but it just involves a couple of
additional RC networks in the NFB loop.

....... Phil

Cherry invented the idea of "nested feedback" to reduce THD to
extraordinary
levels and there was an amp called the Cresendo from around 1984....
If you built a schematic of his you had to be ever so careful not to end
up
with an oscillator.

BTW, In a tube amp with an OPT, phase shift at 3Hz is unavoidable, and
its pointless trying to remove it all.

Patrick Turner.

[Patrick Turner]

robert casey wrote:


Some would agree with Phil, and some might say
well the production of RF sidebands, intermodulation products, are the
same
phenomena at RF or at AF, so the explanations given about the RF
behaviour
at the URL are also valid for AF, hence relevant, even if not explained
above for AF.

But there is nothing at the URL above which is relevant to phase shifted
harmonics of square waves.


Things get more fun in RF work if you do care about phase shift. Like
in video amplifiers, which are wideband systems. Near DC to say 50MHz
for high def. Get the phase shifts bad, and the image will look smeared
and ripply. Audio is less fussy about phase shift, as long as both
channels of a stereo amp have the same phase characteristics.

Yes, and if you have ever built a multiplex stereo decoder for FM radio
you will find phase shift to be rather important.

Patrick Turner.

[Patrick Turner]

John Byrns wrote:

In article ,
"Phil Allison" wrote:

"John Byrns"

Sure we can move on, getting back to square waves, it is not so much the
harmonics that are phase shifted, it is mainly the fundamental that is
phase shifted, the higher the harmonic the less the phase shift.



** Pure idiocy.

The cretin cannot understand the word "relative".

Hi Phil,

Here is what Patrick said, "But there is nothing at the URL above which
is relevant to phase shifted harmonics of square waves." Nowhere in it
does Patrick use the word "relative", so it is not actually necessary to
understand the word, although as a few here can attest I understand the
word better than most.

Regards,

John Byrns

But it might have been relevant had there been mention of relative phase
shift of
the harmonics in a square wave.

Patrick Turner.

--
Surf my web pages at, http://fmamradios.com/

[John Byrns]

In article ,
Patrick Turner wrote:

John Byrns wrote:

In article ,
"Phil Allison" wrote:

"John Byrns"

Sure we can move on, getting back to square waves, it is not so much the
harmonics that are phase shifted, it is mainly the fundamental that is
phase shifted, the higher the harmonic the less the phase shift.

** Pure idiocy.

The cretin cannot understand the word "relative".

Hi Phil,

Here is what Patrick said, "But there is nothing at the URL above which
is relevant to phase shifted harmonics of square waves." Nowhere in it
does Patrick use the word "relative", so it is not actually necessary to
understand the word, although as a few here can attest I understand the
word better than most.

But it might have been relevant had there been mention of relative phase
shift of
the harmonics in a square wave.

"Might have been" is a bit like Monday morning quarterbacking.


Regards,

John Byrns

--
Surf my web pages at, http://fmamradios.com/

[Iain Churches]

"Phil Allison" wrote in message
...

"Iain Churches"


As I said before Phil, we do not all have your expertise
in audio repair,


** Pretty blatant my "expertise" goes WAAAYY beying that.

And probably way beyond also:-)

But my point still stands.

Iain

[RdM]

Patrick Turner mentions in
. au:

If the waves were 10Hz square waves, you'd see the defineite curve
better;
1hz square waves would show what looked like pulses....

BTW, here are some pics of 10Hz square waves from a "conventional" SS amp, and
a Sansui AU-517 DC-200kHz amp, and a "pulse" input. (Large pic; scroll down.)
http://www.classicsansui.net/images/...7/AUTU517d.jpg
This amp is near the middle of that range - 1980's? - I don't know; the 919
claimed DC-500kHz for the power amp section, with a 200V/uS slew rate.
http://www.classicsansui.net/Integra...Amplifiers.htm

[Iain Churches]

I have copied Patrick's post from the "direct coupling" thread to
a new thread, as much of it is concerned with critical
damping, another major stumbling block for many of us who build
PP amps with NFB. We are at the juncture when Patrick asks
how my amp performs into a 0.22µF cap. I include firstly
his post in full. It asks a lot of key questions to which
it will take me some time to find the answers.

Regards to all
Iain


"Patrick Turner" wrote in message
...

What's the trace look like when you have nothing but 0.22uF at across
the output terminals,
and a low level 5kHz square wave with the full amount of GNFB applied?

:-(((( I was hoping you would not ask at this juncture.
The amp is stable into open circuit, but goes totally bananas (HF
oscillation) with a 0.22µF connected.

Under exactly what schematic conditions were the pics of the waveforms
recorded?
Pure open loop with no shelving networks and maximum LF extensions?

With/without NFB?

High level/low level?


Each time a wave form is shown, a full specification of the test should
be given for the waveform to have any scientific or useful relevance to
ppl capable of making good amplifiers without outside assistances, ie,
they
know enough.

So why does the amp oscillate with a 0.22uF?

What happens with 0.047, 0.1, 0.47, 1.0 , 2.0 and 4.7 uF ?


What happens with 1mH?


What is the open loop sine wave response at low levels especially at
between 32khz and 320kHz?



And what about the power bandwidth open loop where the sine wave
response is measured at where thd just under 1%?



What effect is there with HF stability during tests with FB with when
running a 10Hz signal at just above the onset of
OPT saturation?
Are there any bursts of RF during LF staturation?


What does the CRO trace do when you change from using a 1khz signal at
clipping suddenly
to -20dB? Does the trace wobble up and down before settling?


Can you provoke the amp into slow oscillations by using bursts of 1khz
signals that go
from no signal to about 10dB input voltage over load and off again?



What happens when you change the burst F to 100Hz, 10kHz?



With the rated R load at the output, what is the error signal sine wave
response
like at the output of V1 between 1Hz and 1MHz?


At what F does the OPT exhibit series or parallel resonances?


Does the total plate current to the output stage at -20db signal, R
load, remain constant
between 1Hz and 1MHz?



What is the output resistance with NFB and without?



What is the Rout at 40Hz and 20kHz, with/without GNFB?

At the 1kHz clipping level, what is the increase in plate current?
What about at 40Hz and 20kHz?

What does the 5 kHz square wave signal look like at each anode of the
output stage
with NFB? without NFB?

With GNFB, is there only very slight ringing with a 5kHz square wave at
the output, ie, less than 3dB overshoot,
maybe 2 cycles of ringing F,
but lots more ringing at each output stage anode?

What is the output R load required to be for pure class A operation up
to clipping?

What is the graph profile of the power output vs RL at 2% thd, (
clipping )
for 1kHz, for all R loads of 1,2,3,4,5,6,8,12,16,24,32,64 ohms?

What does this tell you about load matching of the amp?

You have a 2uF, and connect 1.5ohms in series with it, and have 15 ohms
across this R+C
in parallel. Is this an approximate minimum model load for a well known
ESL?

You try such a load on your amp. What is the sine wave response at low
level to 100kHz?
What about at -6dB? What is the maximum power response curve with such a
load
between 1Hz and 1MHz?

Assuming you are able to tame the gross oscillations with a pure 0.22uF
load,
and you think you have optimum critical damping, so no cap causes
oscillations, what is the maximum
power bandwidth with thd not exceeding 2%, and with the rated load R?
with 3 times R? with R/2?

With NFB connected, With various values of pure C connected as loads,
what is the low level sine wave response for
all C chosen? does any value of C load cause the sine wave response to
rise more than
10dB above the 1 kHz rated R load output level?

What is the amount of boost to the HF below 20kHz due to having C loads
connected when GNFB is connected at low levels?

What value of C is required to cause the 20kHz sine wave at low levels
to increase by 3 dB?

What is the sine wave low level response with and without GNFB when very
carefully measuring between 0.5Hz and 100Hz
so that your sig gene sag at LF is fully compensated for, and you have
no input capacitor to tailor
a LF pole external to the amp signal path?

What is the phase shift plot for the amp at low levels, rated R load?
With open loop, without shelving networks?
With open loop, with shelving networks?
With NFB for both situations?
Note, oscillation may prevent the phase response measuring with GNFB and
no shelving networks.

How much do you rely on the cap shunting the reistor feeding back the
GNFB?
What is the effect of too high a C value here?
To small a value?
How do you determine the value of this important C?

Do you need Zobel networks acoss each 1/2 primary of the OPT?
Across any other windings or part therof?
Why?



I could maybe think of another 10 questions, but that will do for now.

Only YOU can answer them, and I suggest you prepare some exercize book
graph paper drawn up using the
8mm between horizontal lines to show 3dB steps in response levels, and
then
divide the page vertically into columns for F beginning at 5Hz to 10Hz,
then 100Hz, 1kHz, 10kHz, 100kHz, and 1MHz.

Try drawing 12 even spaces between say 10Hz and 100Hz.
This way you can nominate each vertical line at
10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82 and 100 for the decade of
F, and you have a nice logarithmic
page notated, even though line spacing are equal. Interpolation
will allow postioning of even number frequencies.

Notice that the scal is the same as standard resistor values.

It is derived by simply starting with 1.0, then multiplying
by 1.2115 as you move up in value. 1.2115 to the power of 12 = 10.0
approx.

With a log page, the distance between 1.0 and 2.0 = that between 2.0 and
4.0
and between 4.0 and 8.0. Distances between octaves are equal.

Thus slopes of attenuation for RC networks have the same slope for the
same order
attenuation anywhere along the graph.

You could spend all day plotting with a PC unless you have a program
which does it automatically.
Then when you have a response saved, you click "print".
Or perhaps you post the responses someplace for the group to inspect and
comment.

Do you know where I can download a FREE program which will plot a
response of anything?
I have a couple of old spare PCs, two with W98se, so I could set one up
where its dusty and dirty, in my work shed, and proceed more
modernisticly.
Do I need a sheet of plastic over the PC?
I'll answer for you, YES.

Plotting by hand with a PC may be way too slow. My way is quick for a
"hand job",
so you give yourself more time for more questions, more answers,
and building a better amp..

If you had a pink noise source of even noise spread, and a suitable
selective filter,
this may also be used for response measurements, and more.
Pink noise is like music, very like heavy metal music at least,
except that musical tones have some harmonicly related waves, pink noise
has randomly varying
F, phase and amplitude.

HOWEVER, if you could find a signal sweep that puts out a slowly
changing F sine wave between
1Hz and 1MHz, ( or split into a number of CALIBRATED bands ), you might
be able to plot
amplitude in dB against F very much faster than my method using pencil
and paper in a book
if you had an old response plot grapher machine. They used to use a roll
of paper with a pencil/pen driven
with a dc motor. Maybe there are a few around left over from 1960.
I don't fancy making one up myself, and the PC option looks much easier,
and it would be more accurate..

Patrick Turner.

[Patrick Turner]

Iain Churches wrote:

I have copied Patrick's post from the "direct coupling" thread to
a new thread, as much of it is concerned with critical
damping, another major stumbling block for many of us who build
PP amps with NFB.

Not only PP amps, but the same critical damping issues
et all with NFB are just as important with SE amps with NFB.


We are at the juncture when Patrick asks
how my amp performs into a 0.22µF cap. I include firstly
his post in full. It asks a lot of key questions to which
it will take me some time to find the answers.

Take your time.

snip the rest, awaiting answers.

Patrick Turner

[Iain Churches]

"Patrick Turner" wrote in message
...


Iain Churches wrote:

I have copied Patrick's post from the "direct coupling" thread to
a new thread, as much of it is concerned with critical
damping, another major stumbling block for many of us who build
PP amps with NFB.

Not only PP amps, but the same critical damping issues
et all with NFB are just as important with SE amps with NFB.


We are at the juncture when Patrick asks
how my amp performs into a 0.22µF cap. I include firstly
his post in full. It asks a lot of key questions to which
it will take me some time to find the answers.

Take your time.

snip the rest, awaiting answers.

Patrick Turner


OK. Thanks for your patience:-)
I have the first (short) instalment
ready for the new thread.

Iain