Class/type of amp ?

[N_Cook]

Before wrapping up a Mackie SRM450 powered speaker I took some
representative DC voltages on the complementary pair power devices of the
bass driver amp, for me and all else, future reference.
-42, -88, -42.8
41.2, 88, 42
What would the circuit type/ class name be, for this sort of biasing?

in comparison for horn side amp, same devices
0, -43, -.55
..55 , 43, 0

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

 

[Arfa Daily]

"N_Cook" <diverse@tcp.co.uk> wrote in message
news:gi5780$dhl$1@news.motzarella.org...

Before wrapping up a Mackie SRM450 powered speaker I took some
representative DC voltages on the complementary pair power devices of the
bass driver amp, for me and all else, future reference.
-42, -88, -42.8
41.2, 88, 42
What would the circuit type/ class name be, for this sort of biasing?

in comparison for horn side amp, same devices
0, -43, -.55
.55 , 43, 0

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/




Class "G" maybe, where the supply on the output devices doubles 'on the fly'

depending on current demand (as in amperes)? Lots of amplifiers are now. The
supplies are often designated "VH" and "VL". First units I ever came across
which used it, were an Aiwa series of hifis, which did the supply switching
with a pair of FETs. I think this covers the principles

http://www.wipo.int/pctdb/en/wo.jsp?wo=2007136919&IA=US2007064546&DISPLAY=DESC

Arfa

 

[N_Cook]

Arfa Daily <arfa.daily@ntlworld.com> wrote in message
news:vup1l.11389$cN2.9806@newsfe17.ams2...

"N_Cook" <diverse@tcp.co.uk> wrote in message
news:gi5780$dhl$1@news.motzarella.org...
Before wrapping up a Mackie SRM450 powered speaker I took some
representative DC voltages on the complementary pair power devices of
the
bass driver amp, for me and all else, future reference.
-42, -88, -42.8
41.2, 88, 42
What would the circuit type/ class name be, for this sort of biasing?

in comparison for horn side amp, same devices
0, -43, -.55
.55 , 43, 0

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/




Class "G" maybe, where the supply on the output devices doubles 'on the
fly'
depending on current demand (as in amperes)? Lots of amplifiers are now.
The
supplies are often designated "VH" and "VL". First units I ever came
across
which used it, were an Aiwa series of hifis, which did the supply
switching
with a pair of FETs. I think this covers the principles


http://www.wipo.int/pctdb/en/wo.jsp?wo=2007136919&IA=US2007064546&DISPLAY=DE

SC

Arfa

I don't have the schematic or even saw the track-side of the Mackie board
but that explains the presence of power FETs

Do you know if the pdf of that OCR'd doc (so no schema) is publicly
available, I could not find it explicitly on that page.



--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

 

[Gareth Magennis]

"Arfa Daily" <arfa.daily@ntlworld.com> wrote in message
news:vup1l.11389$cN2.9806@newsfe17.ams2...

"N_Cook" <diverse@tcp.co.uk> wrote in message
news:gi5780$dhl$1@news.motzarella.org...
Before wrapping up a Mackie SRM450 powered speaker I took some
representative DC voltages on the complementary pair power devices of the
bass driver amp, for me and all else, future reference.
-42, -88, -42.8
41.2, 88, 42
What would the circuit type/ class name be, for this sort of biasing?

in comparison for horn side amp, same devices
0, -43, -.55
.55 , 43, 0

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/




Class "G" maybe, where the supply on the output devices doubles 'on the
fly' depending on current demand (as in amperes)? Lots of amplifiers are
now. The supplies are often designated "VH" and "VL". First units I ever
came across which used it, were an Aiwa series of hifis, which did the
supply switching with a pair of FETs. I think this covers the principles

http://www.wipo.int/pctdb/en/wo.jsp?wo=2007136919&IA=US2007064546&DISPLAY=DESC

Arfa

Indeed, the SRM450 Bass amp has 2 supplies : +-45v and +-80v. The higher
voltages are switched in with IRFP150 and 160 Fets.

The HF amp is conventional, using just the +-45v supply.



Gareth.

 

[Arfa Daily]

"N_Cook" <diverse@tcp.co.uk> wrote in message
news:gi5bke$hud$1@news.motzarella.org...

Arfa Daily <arfa.daily@ntlworld.com> wrote in message
news:vup1l.11389$cN2.9806@newsfe17.ams2...

"N_Cook" <diverse@tcp.co.uk> wrote in message
news:gi5780$dhl$1@news.motzarella.org...
Before wrapping up a Mackie SRM450 powered speaker I took some
representative DC voltages on the complementary pair power devices of
the
bass driver amp, for me and all else, future reference.
-42, -88, -42.8
41.2, 88, 42
What would the circuit type/ class name be, for this sort of biasing?

in comparison for horn side amp, same devices
0, -43, -.55
.55 , 43, 0

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/




Class "G" maybe, where the supply on the output devices doubles 'on the
fly'
depending on current demand (as in amperes)? Lots of amplifiers are now.
The
supplies are often designated "VH" and "VL". First units I ever came
across
which used it, were an Aiwa series of hifis, which did the supply
switching
with a pair of FETs. I think this covers the principles


http://www.wipo.int/pctdb/en/wo.jsp?wo=2007136919&IA=US2007064546&DISPLAY=DE
SC

Arfa




I don't have the schematic or even saw the track-side of the Mackie board
but that explains the presence of power FETs

Do you know if the pdf of that OCR'd doc (so no schema) is publicly
available, I could not find it explicitly on that page.

Don't know, to be honest. I just Googled "class G amplifier" to see if I
could find you anything on the principles, and that document seemed to cover
it pretty well. I'm sure that there must be something else out there with
diagrams. If not, let me know, and I'll scan one of the Aiwa schematics for
you. They were reasonably straightforward, as I recall.

Arfa

 

[Trevor Wilson]

"N_Cook" <diverse@tcp.co.uk> wrote in message
news:gi5780$dhl$1@news.motzarella.org...

Before wrapping up a Mackie SRM450 powered speaker I took some
representative DC voltages on the complementary pair power devices of the
bass driver amp, for me and all else, future reference.
-42, -88, -42.8
41.2, 88, 42
What would the circuit type/ class name be, for this sort of biasing?

in comparison for horn side amp, same devices
0, -43, -.55
.55 , 43, 0

**There are only Class A, Class A/B, Class B and Class D amplifiers used in
audio. Anything else is just marketing bullshit. What you have is a Class
A/B amp, with a switched rail power supply. Class H, Class G, et al are just
marketing terms.


--
Trevor Wilson
www.rageaudio.com.au

 

[Arfa Daily]

"Trevor Wilson" <trevor@_SPAMBLOCK_rageaudio.com.au> wrote in message
news:6qqe9bFe4hhcU1@mid.individual.net...

"N_Cook" <diverse@tcp.co.uk> wrote in message
news:gi5780$dhl$1@news.motzarella.org...
Before wrapping up a Mackie SRM450 powered speaker I took some
representative DC voltages on the complementary pair power devices of the
bass driver amp, for me and all else, future reference.
-42, -88, -42.8
41.2, 88, 42
What would the circuit type/ class name be, for this sort of biasing?

in comparison for horn side amp, same devices
0, -43, -.55
.55 , 43, 0

**There are only Class A, Class A/B, Class B and Class D amplifiers used
in audio. Anything else is just marketing bullshit. What you have is a
Class A/B amp, with a switched rail power supply. Class H, Class G, et al
are just marketing terms.


--
Trevor Wilson
www.rageaudio.com.au

Well, you could say that about almost anything. There are many manufacturers
that would disagree with you that it is just marketing bullshit. In fact I
can't remember ever seeing anywhere that a piece of regular Joe hifi has
ever been marketed as class G - or even class A/B. I see nothing wrong at
all with giving a derivative of an existing class, a new letter. Whilst
class G is indeed a switched rail class A/B amp, it never-the-less is
different from a fixed rail class A/B amp. Based on what you're saying, you
might as well say that class D is an invalid term, as class A and class B
and class A/B (and for that matter class C at RF as well) refer to the point
that the output devices are biased to in normal operation, whereas class D
refers to an entirely different concept of waveform reconstruction by power
device switching i.e. the fully digital output stage.

Arfa

 

[Trevor Wilson]

"Arfa Daily" <arfa.daily@ntlworld.com> wrote in message
news:AJY1l.159$_I1.41@newsfe13.ams2...

"Trevor Wilson" <trevor@_SPAMBLOCK_rageaudio.com.au> wrote in message
news:6qqe9bFe4hhcU1@mid.individual.net...



"N_Cook" <diverse@tcp.co.uk> wrote in message
news:gi5780$dhl$1@news.motzarella.org...
Before wrapping up a Mackie SRM450 powered speaker I took some
representative DC voltages on the complementary pair power devices of
the
bass driver amp, for me and all else, future reference.
-42, -88, -42.8
41.2, 88, 42
What would the circuit type/ class name be, for this sort of biasing?

in comparison for horn side amp, same devices
0, -43, -.55
.55 , 43, 0

**There are only Class A, Class A/B, Class B and Class D amplifiers used
in audio. Anything else is just marketing bullshit. What you have is a
Class A/B amp, with a switched rail power supply. Class H, Class G, et al
are just marketing terms.


--
Trevor Wilson
www.rageaudio.com.au


Well, you could say that about almost anything.

**Wrong. Classes of amplifiers are clearly and explicityly stated.

There are many manufacturers

that would disagree with you that it is just marketing bullshit.

**Of course.

In fact I

can't remember ever seeing anywhere that a piece of regular Joe hifi has
ever been marketed as class G - or even class A/B.

**Here's where I get to say: COMPLETE bullshit. Technics, Yamaha and others
have claimed Class A & Class A/B operation for their consumer (as opposed to
audiophile) grade components.

I see nothing wrong at

all with giving a derivative of an existing class, a new letter.

**Me either. Trouble is, it is POWER SUPPLY switching. The fundamental Class
of the amplifier's operation remains Class A, Class A/B or Class B in all
such cases. Rail shifting schemes are not alterations of amplifier Class of
operation.

Whilst

class G is indeed a switched rail class A/B amp, it never-the-less is
different from a fixed rail class A/B amp.

**No, it is not. The amplifier is STILL a Class A/B (or whatever) amplifier,
with a rail switching scheme attached. Of course, that does not suit
marketers, who dreamt up fancy new terms.

Based on what you're saying, you

might as well say that class D is an invalid term,

**Fair comment.

as class A and class B

and class A/B (and for that matter class C at RF as well) refer to the
point that the output devices are biased to in normal operation, whereas
class D refers to an entirely different concept of waveform reconstruction
by power device switching i.e. the fully digital output stage.

**Indeed. The term: Class D has always troubled me. It does not fit with the
accepted Class of operation of an amplifier.


--
Trevor Wilson
www.rageaudio.com.au

 

[Arfa Daily]

"Trevor Wilson" <trevor@_SPAMBLOCK_rageaudio.com.au> wrote in message
news:6qra84FebbsqU1@mid.individual.net...

"Arfa Daily" <arfa.daily@ntlworld.com> wrote in message
news:AJY1l.159$_I1.41@newsfe13.ams2...

"Trevor Wilson" <trevor@_SPAMBLOCK_rageaudio.com.au> wrote in message
news:6qqe9bFe4hhcU1@mid.individual.net...



"N_Cook" <diverse@tcp.co.uk> wrote in message
news:gi5780$dhl$1@news.motzarella.org...
Before wrapping up a Mackie SRM450 powered speaker I took some
representative DC voltages on the complementary pair power devices of
the
bass driver amp, for me and all else, future reference.
-42, -88, -42.8
41.2, 88, 42
What would the circuit type/ class name be, for this sort of biasing?

in comparison for horn side amp, same devices
0, -43, -.55
.55 , 43, 0

**There are only Class A, Class A/B, Class B and Class D amplifiers used
in audio. Anything else is just marketing bullshit. What you have is a
Class A/B amp, with a switched rail power supply. Class H, Class G, et
al are just marketing terms.


--
Trevor Wilson
www.rageaudio.com.au


Well, you could say that about almost anything.

**Wrong. Classes of amplifiers are clearly and explicityly stated.

There are many manufacturers
that would disagree with you that it is just marketing bullshit.

**Of course.

In fact I
can't remember ever seeing anywhere that a piece of regular Joe hifi has
ever been marketed as class G - or even class A/B.

**Here's where I get to say: COMPLETE bullshit. Technics, Yamaha and
others have claimed Class A & Class A/B operation for their consumer (as
opposed to audiophile) grade components.

I see nothing wrong at
all with giving a derivative of an existing class, a new letter.

**Me either. Trouble is, it is POWER SUPPLY switching. The fundamental
Class of the amplifier's operation remains Class A, Class A/B or Class B
in all such cases. Rail shifting schemes are not alterations of amplifier
Class of operation.

Whilst
class G is indeed a switched rail class A/B amp, it never-the-less is
different from a fixed rail class A/B amp.

**No, it is not. The amplifier is STILL a Class A/B (or whatever)
amplifier, with a rail switching scheme attached. Of course, that does not
suit marketers, who dreamt up fancy new terms.

Based on what you're saying, you
might as well say that class D is an invalid term,

**Fair comment.

as class A and class B
and class A/B (and for that matter class C at RF as well) refer to the
point that the output devices are biased to in normal operation, whereas
class D refers to an entirely different concept of waveform
reconstruction by power device switching i.e. the fully digital output
stage.

**Indeed. The term: Class D has always troubled me. It does not fit with
the accepted Class of operation of an amplifier.


--
Trevor Wilson
www.rageaudio.com.au
I hear what you're saying, Trevor, but it seems to me that we are basically

just dancing around semantics. Granted, it is still a basic class AB or
whatever amplifier, but power supply switching or not, there is still
additional circuitry to detect when the higher rails are required, and it
could be argued that this circuitry is part of the power amp and its overall
design concept.

Given that you accept class D, but are not easy with it, what other
designation would you use to identify the switched rail concept as something
which 'broadly fitted in with the scheme' and allowed engineers to at least
know what it was that they were looking at ? As soon as you start giving
design concepts fancy names, every manufacturer will pick his own, and no
one will know quite where they are at ...

For sure, it's not ideal, and it does fly in the face a little, of what the
original concept of the class lettering system was about, but times move on,
and I think that for clarity, issuing this concept with a new letter, is
acceptable in practice, if not in theory, for the clarity it brings with it.

Arfa

 

[William Sommerwerck]

Class D has always troubled me. It does not fit
with the accepted class of operation of an amplifier.

Given that you accept class D, but are not easy with it, what
other designation would you use to identify the switched-rail
concept as something which 'broadly fitted in with the scheme'
and allowed engineers to at least know what it was that they
were looking at?

The original concept of "class" related to the fraction of a cycle the
device was conducting.There's A (all), B (half), AB (more than half but less
than all), and C (less than half). I can't think of any other meaningful
fractions.

There are no other classes. To call switching amps "class D", or to create
new designations for stepped B+ or stepped-bias designs thoroughly confuses
the original meaning.

As soon as you start giving design concepts fancy names,
every manufacturer will pick his own, and no one will know
quite where they are at ...

They'll do it anyhow, for marketing. If Hitachi has a class-G amplifier,
then Toshiba, even though using the same circuit, will call it class H,
simply to look original.

How about just _saying_ what it is, in simple language? That would clarify
things for the technician, in a way that tacking on a
marketing-department-selected letter would not.

 

[Arfa Daily]

"William Sommerwerck" <grizzledgeezer@comcast.net> wrote in message
news:giaq7r$qio$1@news.motzarella.org...

Class D has always troubled me. It does not fit
with the accepted class of operation of an amplifier.

Given that you accept class D, but are not easy with it, what
other designation would you use to identify the switched-rail
concept as something which 'broadly fitted in with the scheme'
and allowed engineers to at least know what it was that they
were looking at?

The original concept of "class" related to the fraction of a cycle the
device was conducting.There's A (all), B (half), AB (more than half but
less
than all), and C (less than half). I can't think of any other meaningful
fractions.

There are no other classes. To call switching amps "class D", or to create
new designations for stepped B+ or stepped-bias designs thoroughly
confuses
the original meaning.


As soon as you start giving design concepts fancy names,
every manufacturer will pick his own, and no one will know
quite where they are at ...

They'll do it anyhow, for marketing. If Hitachi has a class-G amplifier,
then Toshiba, even though using the same circuit, will call it class H,
simply to look original.

How about just _saying_ what it is, in simple language? That would clarify
things for the technician, in a way that tacking on a
marketing-department-selected letter would not.

Again William, I hear what you're saying, and I am in broad agreement.
However, when the class lettering system was first used, the world of
amplification was a much simpler place. No one would ever have conceived of
fully digital amplifiers, or ones whose rails switched 'on the fly' as a
result of output stage demand. The class G concept has been around for a
while now, and I don't think that manufacturers have, in general, gone down
the route of all having their own name for it.

As we are all fully aware, language and linguistic interpretation changes
and develops all the time. It is a fact of life that we all accept,
otherwise we would all still be saying "thee" and so on, and "gay" would
still mean carefree and happy. The same is true of electronics. Meanings
change. The world moves on. "Class G" seems to have been accepted pretty
generally by manufacturers as the designation for the type of output stage
topology under discussion, just as "Class D" is now accepted as a fully
digital amplifier, where bias points don't come into it at all, unless you
consider 'hugely on' and 'hugely off' to be valid examples of the term.

I think it is just a case of the system being expanded and adapted to
encompass new ideas, and on that basis, other than for want of being an
historic purist, I really don't have a problem with it, nor do I see why it
should be such a huge problem for others.

At the end of the day, A, AB, C etc are just arbitrary letters to identify
particular amplifier topologies, based on the way they are biased. How the
letter related to the biasing scheme still had to be learnt, and I really
don't see why the system should not have been expanded in the way that it
was, to identify other topologies - even if they are just variants or
derivatives - based on something other than bias points.

Yes, you could say that this is "A class AB amplifier with switched rails",
but how much easier to just say that it's "Class G" ... ??

Arfa

 

[William Sommerwerck]

As we are all fully aware, language and linguistic interpretation changes
and develops all the time. It is a fact of life that we all accept,
otherwise we would all still be saying "thee" and so on, and "gay" would
still mean carefree and happy. The same is true of electronics. Meanings
change. The world moves on. "Class G" seems to have been accepted pretty
generally by manufacturers as the designation for the type of output stage
topology under discussion, just as "Class D" is now accepted as a fully
digital amplifier, where bias points don't come into it at all, unless you
consider 'hugely on' and 'hugely off' to be valid examples of the term.

Arfa, please see my other post. Most class D amplifiers are analog, not
digital..

Yes, you could say that this is "A class-AB amplifier with switched
rails",
but how much easier to just say that it's "Class G" ... ??

For that to work, you'd have to have some organization -- such as the IEEE
in the US -- setting standards as to exactly what class-G topology is.

I used to own Krell amplifiers. They were billed as class A, but they were
class A "only" up to about 1/4 or 1/3 full output. Given the crest factor of
acoustically recorded music, this means the amplifier will rarely stray from
class A. But strictly speaking, the amplifier is AB, with (very) high bias.

Most amplifiers are biased only a little beyond class AB. My Parasound A21
amps are unusual, in that they're still in class A up to about one ampere,
which is high for not-horribly expensive amplifier. They are correctly
billed as high-bias class AB.

 

[Arfa Daily]

"William Sommerwerck" <grizzledgeezer@comcast.net> wrote in message
news:giasid$h5j$1@news.motzarella.org...

As we are all fully aware, language and linguistic interpretation changes
and develops all the time. It is a fact of life that we all accept,
otherwise we would all still be saying "thee" and so on, and "gay" would
still mean carefree and happy. The same is true of electronics. Meanings
change. The world moves on. "Class G" seems to have been accepted pretty
generally by manufacturers as the designation for the type of output
stage
topology under discussion, just as "Class D" is now accepted as a fully
digital amplifier, where bias points don't come into it at all, unless
you
consider 'hugely on' and 'hugely off' to be valid examples of the term.

Arfa, please see my other post. Most class D amplifiers are analog, not
digital..

The web in general, would seem to disagree with you on that one, William ...

http://www.pcmag.com/encyclopedia_term/0,2542,t=Class+D+amplifier&i=55417,00.asp
http://www.pcmag.com/encyclopedia_term/0,2542,t=amplifier+classes&i=55350,00.asp
http://en.wikipedia.org/wiki/Electronic_amplifier
http://www.answers.com/topic/class-d-amplifier
http://www.maxim-ic.com/glossary/index.cfm/Ac/V/ID/1063/Tm/class-D

and many many more examples. The signal in a class D amplifier is only
analogue at it's input, and at the speaker terminals after the low pass
filter that removes the HF PWM component. Thus, the whole amplifier is
fundamentally digital in the way that it amplifies the signal applied to it.

Yes, you could say that this is "A class-AB amplifier with switched
rails",
but how much easier to just say that it's "Class G" ... ??

For that to work, you'd have to have some organization -- such as the IEEE
in the US -- setting standards as to exactly what class-G topology is.

Well, to make it totally 'official', I guess that's so, but again, if you
use the web to search for definitions for class G, you will find that pretty
much all manufacturers and describers, use the same definition virtually
word for word, which would suggest that an unwritten 'standard' for what it
is, already exists.

I used to own Krell amplifiers. They were billed as class A, but they were
class A "only" up to about 1/4 or 1/3 full output. Given the crest factor
of
acoustically recorded music, this means the amplifier will rarely stray
from
class A. But strictly speaking, the amplifier is AB, with (very) high
bias.

Most amplifiers are biased only a little beyond class AB. My Parasound A21
amps are unusual, in that they're still in class A up to about one ampere,
which is high for not-horribly expensive amplifier. They are correctly
billed as high-bias class AB.

But surely, that emphasises the point that there are no true 'standards'
applied to the existing letters ?

Arfa

 

[Andrew Erickson]

In article <Lo62l.6697$Iz4.3430@newsfe19.ams2>,
"Arfa Daily" <arfa.daily@ntlworld.com> wrote:

<Much snippage>

The class G concept has been around for a
while now, and I don't think that manufacturers have, in general, gone down
the route of all having their own name for it.

The concept has been around, and the "class G" terminology has gone with
it for awhile, too, at least around 30 years. I have a book entitled
"Solid-State Power Electronics," written by one Irving Gottlieb and
copyright 1979, that identifies this circuit topology as a class-G
amplifier (and also discusses classes A, AB, B, C, D, F, and H). While
it may be argued that such a design oughtn't be given a letter
designation, it's hardly worth doing so anymore as a practical matter.

--
Andrew Erickson

"He is no fool who gives what he cannot keep to gain that which he cannot
lose." -- Jim Elliot

 

[William Sommerwerck]

Arfa, please see my other post. Most class D amplifiers are analog, not
digital..

The web in general, would seem to disagree with you on that one, William
....

http://www.pcmag.com/encyclopedia_term/0,2542,t=Class+D+amplifier&i=55417,00.asp

http://www.pcmag.com/encyclopedia_term/0,2542,t=amplifier+classes&i=55350,00.asp
http://en.wikipedia.org/wiki/Electronic_amplifier
http://www.answers.com/topic/class-d-amplifier
http://www.maxim-ic.com/glossary/index.cfm/Ac/V/ID/1063/Tm/class-D

and many many more examples. The signal in a class D amplifier is only
analogue at its input, and at the speaker terminals after the low pass
filter that removes the HF PWM component. Thus, the whole amplifier is
fundamentally digital in the way that it amplifies the signal applied to
it.

The Web is wrong. Most switching amps are analog. That is, everything varies
continuously, rather than in quantized steps.

By the way, Arfa, you're doing something intellectually invalid -- you're
"appealing to authority", rather than thinking for yourself, or explaining
what's going on.

For those who would like to read about the correct explanation of "analog
versus digital", please refer to the following references. (I can't find my
college textbooks, and I don't really think any of these are very good,
because the best explanation is graphical.) Sampling is an analog process,
that involves multiplying the signal by the sampling function, which
produces a convolution in the frequency domain. NO QUANTIZATION OCCURS. If
those convinced that sampling = digitization, let them tell me what the bit
depth is.

http://en.wikipedia.org/wiki/Nyquist%E2%80%93Shannon_sampling_theorem

http://graphics.cs.ucdavis.edu/~okreylos/PhDStudies/Winter2000/SamplingTheory.html

http://www2.egr.uh.edu/~glover/applets/Sampling/Sampling.html

Here's a quote from the last reference. Note especially the third and
next-to-last sentences.

"The signals we use in the real world, such as our voices, are called
"analog" signals. To process these signals in computers, we need to convert
the signals to "digital" form. While an analog signal is continuous in both
time and amplitude, a digital signal is discrete in both time and amplitude.
To convert a signal from continuous time to discrete time, a process called
sampling is used. The value of the signal is measured at certain intervals
in time. Each measurement is referred to as a sample. (The analog signal is
also quantized in amplitude, but that process is ignored in this
demonstration. See the Analog to Digital Conversion page for more on that.)"

The following is directed at everyone in this group -- and is not a
rhetorical question -- why is it, that when someone _explains_ to you, in a
fairly clear manner, why what you and millions of other people believe to be
true, but _is not_ -- you don't believe them? Aren't you able to think for
yourselves?

The fact that most people do not understand, and refuse to understand, the
difference between analog and digital is, to me, a little frightening,
because it touches on the willingness of human beings to believe what they
want to believe -- or worse, what "experts" tell them -- rather than the
truth.

Disclaimer: When I was a young'un, I thought that if I believed something,
it was so. In retrospect, this is ludicrous, but most people are like that.
It was many years before I recognized this error of thinking.

 

[Arfa Daily]

"William Sommerwerck" <grizzledgeezer@comcast.net> wrote in message
news:gidggj$tkd$1@news.motzarella.org...

Arfa, please see my other post. Most class D amplifiers are analog, not
digital..

The web in general, would seem to disagree with you on that one, William
...


http://www.pcmag.com/encyclopedia_term/0,2542,t=Class+D+amplifier&i=55417,00.asp

http://www.pcmag.com/encyclopedia_term/0,2542,t=amplifier+classes&i=55350,00.asp
http://en.wikipedia.org/wiki/Electronic_amplifier
http://www.answers.com/topic/class-d-amplifier
http://www.maxim-ic.com/glossary/index.cfm/Ac/V/ID/1063/Tm/class-D

and many many more examples. The signal in a class D amplifier is only
analogue at its input, and at the speaker terminals after the low pass
filter that removes the HF PWM component. Thus, the whole amplifier is
fundamentally digital in the way that it amplifies the signal applied to
it.

The Web is wrong. Most switching amps are analog. That is, everything
varies
continuously, rather than in quantized steps.

That is a confusing and not particularly true statement.

By the way, Arfa, you're doing something intellectually invalid -- you're
"appealing to authority", rather than thinking for yourself, or explaining
what's going on.

I am not.

For those who would like to read about the correct explanation of "analog
versus digital", please refer to the following references. (I can't find
my
college textbooks, and I don't really think any of these are very good,
because the best explanation is graphical.) Sampling is an analog process,
that involves multiplying the signal by the sampling function, which
produces a convolution in the frequency domain. NO QUANTIZATION OCCURS. If
those convinced that sampling = digitization, let them tell me what the
bit
depth is.

http://en.wikipedia.org/wiki/Nyquist%E2%80%93Shannon_sampling_theorem

http://graphics.cs.ucdavis.edu/~okreylos/PhDStudies/Winter2000/SamplingTheory.html

http://www2.egr.uh.edu/~glover/applets/Sampling/Sampling.html

Here's a quote from the last reference. Note especially the third and
next-to-last sentences.

"The signals we use in the real world, such as our voices, are called
"analog" signals. To process these signals in computers, we need to
convert
the signals to "digital" form. While an analog signal is continuous in
both
time and amplitude, a digital signal is discrete in both time and
amplitude.
To convert a signal from continuous time to discrete time, a process
called
sampling is used. The value of the signal is measured at certain intervals
in time. Each measurement is referred to as a sample. (The analog signal
is
also quantized in amplitude, but that process is ignored in this
demonstration. See the Analog to Digital Conversion page for more on
that.)"

The following is directed at everyone in this group -- and is not a
rhetorical question -- why is it, that when someone _explains_ to you, in
a
fairly clear manner, why what you and millions of other people believe to
be
true, but _is not_ -- you don't believe them? Aren't you able to think for
yourselves?

Because on average, in the real world, if "millions of people" believe
something, and one does not, it is not the millions who actually *are*
wrong.

The fact that most people do not understand, and refuse to understand, the
difference between analog and digital is, to me, a little frightening,
because it touches on the willingness of human beings to believe what they
want to believe -- or worse, what "experts" tell them -- rather than the
truth.

You have to draw the line somewhere, and make a judgement as to who or what
an "expert" is. The dictionary defines an expert as someone who has special
skills and knowledge in a subject, and is an authority on that subject.
Would you consider that the man who comes to repair your boiler is an expert
? Or the man who troubleshoots problems at your local garage? I suspect,
like most people you probably would. So if you believed what these people
told you about the dangerous gas leak on your boiler, or that you needed
$300 worth of work doing on your car to make it run right again was the
truth, would that make you frighteningly stupid ?

Disclaimer: When I was a young'un, I thought that if I believed something,
it was so. In retrospect, this is ludicrous, but most people are like
that.
It was many years before I recognized this error of thinking.

I'm not really quite sure exactly what you're saying here about the class D
amplifier. The analogue input signal is not converted directly to any kind
of 'value' represented by a binary number, such as might be the case if you
ran it through a traditional A-D converter. Instead, it is run through a
comparator, with a triangle wave as the reference input. This results in
direct conversion to a PWM signal. I accept that this does not represent
'quantization' as such, so is not producing a 'truly digital' signal, but I
also do not believe that once the signal is in PWM form, it can either be
considered to be analogue any more.

The term "digital" may not be a strictly true one for this class of
amplifier, and in truth, there is no such thing as a fully digital amplifier
in the sense that you are advocating, but in the way that most people would
understand the term "analogue", it's not that, either. The reason that it
gets called digital, is because all of the power amplification is done with
devices that have only two states - on and off. And before you say that
those devices are linear ones in that they are transistors of one persuasion
or another, they are not used in that way in this type of output stage.

So, if you are amplifying a signal that has only two levels, using devices
driven to have only the two conditions of on or off, then I think that you
are stretching the imagination more by calling it an analogue process, than
you are by calling it a digital one.

I don't believe that there is a true term for what the process is, but I
also think that "digital" provides for a better understanding of what is
fundamentally going on, than calling it an analogue process as you would.

And for the record, I am perfectly capable of thinking for myself, thank
you, and I am quite happy that I understand the principles of the class D
amplifier, enough to be able to make valid contributions to any discussions
about it. For you to suggest that the entire web, including respected
manufacturers, has got it wrong, seems a little opinionated to me, and based
once again on dancing around terminology and semantics, as popularly
understood by the electronic engineering world at large.

Anyway, I'm not going to get into another of those long-winded pissing
contests with you over it. If you want to believe that it is an analogue
process, fine, go ahead at that. Right, wrong or indifferent, I will
continue to refer to it as a 'digital' amplifier, as most engineers and
manufacturers would, and indeed do ...

Arfa

 

[William Sommerwerck]

The Web is wrong. Most switching amps are analog. That is,
everything varies continuously, rather than in quantized steps.

That is a confusing and not particularly true statement.

It might be confusing if you've been brainwashed into thinking "pulses" =
"digital", but it is nevertheless true.

By the way, Arfa, you're doing something intellectually invalid -- you're
"appealing to authority", rather than thinking for yourself, or
explaining
what's going on.

I am not.

Then why did you post Web references as examples of what other people think?
Majority opinion is proof of nothing.

Because on average, in the real world, if "millions of people" believe
something, and one does not, it is not the millions who actually *are*
wrong.

On average. But there are exceptions. The world is not 6000 years old. Yet
millions of people believe that. The majority is not the "authority".

I'm not really quite sure exactly what you're saying here about the class
D
amplifier. The analogue input signal is not converted directly to any kind
of 'value' represented by a binary number, such as might be the case if
you ran it through a traditional A-D converter. Instead, it is run through
a
comparator, with a triangle wave as the reference input. This results in
direct conversion to a PWM signal. I accept that this does not represent
'quantization' as such, so is not producing a "truly digital" signal, but
I
also do not believe that once the signal is in PWM form, it can either be
considered to be analogue any more.

Ah! Here's the problem. It's the confusion between /waveform/ and /data/.

A pulse is just a pulse. In and of itself it means nothing. It is neither
"digital" nor "analog" -- it's just a waveform.

The issue here is how we modify a waveform to transmit data.

Suppose we sampled a signal at or above the Nyquist rate and transmitted
each sampled value as a pulse of that value. (This is easily done with a
sample-and-hold circuit.)

How is the /data/ in that series of pulses represented? Well, it varies
/continuously/, just as the original signal did. It has not been quantized,
so it cannot be represented as one of a /finite/ group of numbers. That's
analog -- continuous variation.

On the other hand, if we quantized the level of the sample data, it would
now be in digital form.

"Pulses" have nothing to do with digital. "Numbers" have nothing to do with
digital -- PCM is only one form of digital; there are others. Any time you
represent data samples with a quantized value (which can be represented by
one of a finite group of numbers, but doesn't have to be), it's digital. And
it doesn't matter a whit what the waveform looks like. Ever heard of ECL?
It used sine waves, but it was digital?

You really need to think this though, rather than reacting with a mental
knee-jerk.

I am slightly embarrassed at giving Web references on this topic, which is
what I object to -- appealing to authority. But "you" -- meaning the people
in this group -- should have a sufficient /understanding/ of math and
electronics so that the light bulb goes on when you hear a correct
explanation. "Ah! That's right! I hadn't understood it before! Now I do."

I have to apologize a bit, because I certainly don't understand everything
new the first time I'm exposed to it. But I make an effort to understand
it -- not blindly accept or reject it. I generally don't believe things I
don't understand.

The term "digital" may not be a strictly true one for this class of
amplifier, and in truth, there is no such thing as a fully digital
amplifier
in the sense that you are advocating, but in the way that most people
would
understand the term "analogue", it's not that, either. The reason that it
gets called digital, is because all of the power amplification is done
with
devices that have only two states - on and off. And before you say that
those devices are linear ones in that they are transistors of one
persuasion
or another, they are not used in that way in this type of output stage.

So, if you are amplifying a signal that has only two levels, using devices
driven to have only the two conditions of on or off, then I think that you
are stretching the imagination more by calling it an analogue process,
than
you are by calling it a digital one.

Again, you misunderstand. A PWM signal /does not/ have two levels. If it's
analog, it has an infinite number of levels (widths). If it's digital, it
has a finite number of levels (widths). The data (signal) IS NOT conveyed by
the signal level (which remains constant), but by the pulse width, which can
vary continuously (analog) or in steps (digital).

I don't believe that there is a true term for what the process is, but I
also think that "digital" provides for a better understanding of what is
fundamentally going on, than calling it an analogue process as you would.

And for the record, I am perfectly capable of thinking for myself, thank
you, and I am quite happy that I understand the principles of the class D
amplifier, enough to be able to make valid contributions to any
discussions
about it. For you to suggest that the entire web, including respected
manufacturers, has got it wrong, seems a little opinionated to me, and
based
once again on dancing around terminology and semantics, as popularly
understood by the electronic engineering world at large.

Are you interested in actually understanding things, or in simply parrotting
the majority belief? Does truth = what the majority believe? Really?

About 30 years ago, Pioneer introduced an FM tuner with a pulse-counting
detector. (Pioneer wasn't the first; Fisher had one about 15 years earlier.)
This was billed as digital, when it was wholly analog.

"Truth is truth. You can't have opinions about truth." -- Friendly Professor
Peter Schickele

This is not a pissing contest. This is my attempt to get other people to
THINK.

 

[Eeyore]

N_Cook wrote:

Before wrapping up a Mackie SRM450 powered speaker I took some
representative DC voltages on the complementary pair power devices of the
bass driver amp, for me and all else, future reference.
-42, -88, -42.8
41.2, 88, 42
What would the circuit type/ class name be, for this sort of biasing?

Class G or H. It's supply switching to reduce dissipation. Done it myself.
Big amps may have 3 rails.

Graham

 

[Eeyore]

William Sommerwerck wrote:

There are no other classes. To call switching amps "class D", or to create
new designations for stepped B+ or stepped-bias designs thoroughly confuses
the original meaning.

So what would you call them ?

As soon as you start giving design concepts fancy names,
every manufacturer will pick his own, and no one will know
quite where they are at ...

They'll do it anyhow, for marketing. If Hitachi has a class-G amplifier,
then Toshiba, even though using the same circuit, will call it class H,
simply to look original.

WRONG. Class G and H use quite different circuits.

Graham

 

[bz]

I"William Sommerwerck" <grizzledgeezer@comcast.net> wrote in
news:gig2ai$l71$1@news.motzarella.org:

Ah! Here's the problem. It's the confusion between /waveform/ and
/data/.

A pulse is just a pulse. In and of itself it means nothing. It is
neither "digital" nor "analog" -- it's just a waveform.

The issue here is how we modify a waveform to transmit data.

Suppose we sampled a signal at or above the Nyquist rate and transmitted
each sampled value as a pulse of that value. (This is easily done with a
sample-and-hold circuit.)

How is the /data/ in that series of pulses represented? Well, it varies
/continuously/, just as the original signal did. It has not been
quantized, so it cannot be represented as one of a /finite/ group of
numbers. That's analog -- continuous variation.

On the other hand, if we quantized the level of the sample data, it
would now be in digital form.

In general, your argument is correct and Arfa is mistook.

However one quibble: simply chopping the time stream up into integral
slices and restricting the level (or width [or frequency {or phase}]) of
an output signal to specific levels does not "really" 'digitize' the data.
Doing an analogue to digital conversion and transmitting the data in the
form of a stream of digitized information (as opposed to one out of 1024
possible levels, for example) is essential in order for the information to
be 'digital' [in my mind].

Although restricting the data to particular levels might be a quantum leap
forward in efficiency, it doesn't really make the processing of the data
'digital' {although one could argue that it HAS been digitized into 'BASE
1024', I think that is really cheating}.

In any case, it has been an interesting discussion to follow. Thank you
BOTH.







--
bz 73 de N5BZ k

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

bz+ser@ch100-5.chem.lsu.edu remove ch100-5 to avoid spam trap