how good are class D amplifiers?
 

"Don Pearce" wrote in message
...
On Tue, 22 May 2007 09:33:16 +0100, "Serge Auckland"
wrote:

Are there many distortion analysers any more that simply null the
fundamental and display the sum of the rest?

d

--
Pearce Consulting
http://www.pearce.uk.com

Most if not all of the legacy distortion analysers will be of the nulling
sort, and lab test gear has a very long life so I suspect (but don't know
for sure) that a very high proportion of distortion analysers in regular
use
are still of that sort. Today's sales of test equipment are relatively
very
low. Studios and broadcasters rarely buy new audio test gear as they
already
have instruments for their remaining analogue stuff, and all this new
digital stuff either works or it doesn't, and anyway, if it goes wrong it
needs someone from the factory to come and see to it. When I worked for an
audio test equipment manufacturer some 10-12 years ago, it was by then
already clear that very little new audio test equipment was being sold. I
think we made more money from the recalibration charges on the existing
installed park than from selling new equipment.

OK. Kind of surprising, though, as just about everybody now possesses
a distortion meter at least as good as a nulling type. I'm talking
about a PC sound card, of course. Just needs suitable software.

d

--
Pearce Consulting
http://www.pearce.uk.com

I have two conventional nulling THD meters and of course a sound card and
software. However, for THD measurements I rarely use the sound card as it is
too difficult to use . Firstly you need an attenuator to reduce the incoming
level, as few soundcards take more than a couple of volts of input before
clipping themselves, idealy, you need a millivoltmeter in parallel with the
sound card input to make sure the level stays when it should. Then, with
software, I never really know what it's measuring and finally, unless you
have a suitable sound card and sample at 192kHz, you can't measure over the
100kHz bandwidth that most THD meters manage. I use the software test set
for analysing WAV files. For example, it's easier for me to take my laptop
to the hi-fi than test gear, so if I'm making any measurements to my room or
system, I will record the DUT as a WAV and analyse it later. For that the
software's great but for lab work, I prefer dedicated instruments.

S.



--
http://audiopages.googlepages.com

how good are class D amplifiers?
 

"Jim Lesurf" wrote in message
...
In article , Keith G
wrote:

"Trevor Wilson" wrote


**Because that is a fact. The ideal amplifier has no 'sound' of
it's
own. No amplifier is ideal.


Therefore no amplifier has no 'sound' of its own then?

**Nope. That's not what I said.



It's what it looks like to me - your words (as above): "The ideal
amplifier has no 'sound' of it's own. No amplifier is ideal." - what
conclusion could be possibly drawn from that statement other than all
amplifiers are not ideal and therefore have a 'sound'...??

I can suggest at least two "conclusions" which fit with what Trevor
said.

1) That "ideal" is defined in this context to mean what he wrote. i.e.
that
an ideal amp would/will have no "sound".


That's what he said.



2) That this isn't a matter of a false dichtomy. i.e. *some* amps
might
have no "sound". Not a matter of all or none.


That's not what he said.



In the above respect I have my doubt about the way people are trying
to use
both terms, "ideal" and "sound".

So far as I know there have been various controlled tests where no-one
listening was able to distinguish one of the amps under comparison
from
another. Also tests where no-one was able to distinguish the amp
followed
by a resistive attenuator from a wire bypass. Thus I doubt it is the
case
that no amp is "ideal" in the terms Trevor used.

The reason such tests have been rare in audio mags in recent years may
be
that the reviewers got fed up with tests whose results indicated that
they
could not find reliable evidence to support their belief that they
could
hear differences, plus that doing such a test requires more time,
care, and
understanding than they could be bothered to apply. :-)


A variation on the 'if it sounds good, measure it until you know it
*isn't* good'...??



Also, the "sound" produced by the amp is as a result of feeding it
with an
imput signal and playing its output via a speaker. This definition
means it
is a result of how it may (or may not) alter the signal in a way that
has
an audible effect. That means the "sound" depends on both the signal
used
and the loudspeakers, and is based upon any signal alterations made by
the
amp in that use.

Of course, the amp may be adding audible noise/hum and making
mechanical
buzzing noises which might be a "sound" of its own. Otherwise any
"sound"
will be based on it altering the signal so that the output isn't
simply a
scaled version of the input, and the changes are large enough to be
audible.


Or not, according to the individual - which is why/how some people can
claim one amp is 'better' than another...



Personally, what I've found interesting over the years is just how
large
the changes in signal waveforms can be in some situations without
people
actually noticing, yet people say they can hear things when tests
relying
on sound alone fail to support their claim.


I place little value on short duration listening tests - to much hidden
voodoo at work - my method (and the one I would recommend) is to spend a
period of many weeks or some months comparing two similar pieces of kit.
A clear choice will evolve without having to make a decision, I usually
find...

how good are class D amplifiers?
 

"Dave Plowman (News)" wrote in message
...
In article ,
Keith G wrote:
Might that be that 'remote controls' for LP decks tend to be like
hen's
teeth?

Here's mine:

http://www.apah69.dsl.pipex.com/show/AiwaRemote.JPG


Fits this deck (far right, under the name badge on the fascia panel):

http://www.apah69.dsl.pipex.com/show/AiwaDeck.JPG


If there was (or had been) a market for them, they would have been
more
widely available...

And this allows you to instantly change tracks as does a CD one?



Sure, as well as navigate backwards and forwards within the tracks like
a CD player - very handy if you are listening to, say, the '1812' whilst
straddled by the au pair and you want to synchronise the *big
finish*....

(Usually 'FFwd' in my case.... :-)

how good are class D amplifiers?
 

"Serge Auckland" wrote in
message

Indeed, and in my previous post of the criteria, it was
stated that THD should be measured at all frequencies
20-20k and refers to all powers and all loads for which
the amplifier was designed.


Measuring THD above 10 KHz can be an exercise in futility, as many upper
harmonics will be lost due to the bandpass of the UUT. It's not uncommon for
power amps to be - 3dB at 50 KHz, for example. Better to use twin-tone
measurement techniques.

how good are class D amplifiers?
 

"Serge Auckland" wrote in
message

I rarely use the sound card as it is too difficult to use
. Firstly you need an attenuator to reduce the incoming
level, as few soundcards take more than a couple of volts
of input before clipping themselves, idealy

A 5K 2 watt high quality potentiometer suffices.

you need a
millivoltmeter in parallel with the sound card input to
make sure the level stays when it should.

You mean a voltmeter across the UUT output. We often used those with the old
nulling-type analyzers for one reason or the other.

Then, with software, I never really know what it's measuring

That's your fault - a good experimentalist should be able to determine that
with a few real world measurements. On a bad day, analyze some signals
generated for the purpose. Generating complex tones is very easy these days.

unless you have a suitable sound card and sample
at 192kHz, you can't measure over the 100kHz bandwidth
that most THD meters manage.

Virtually every sound card that I'd consider to be an alternative to test
equipment samples that high.

I use the software test set
for analysing WAV files. For example, it's easier for me
to take my laptop to the hi-fi than test gear, so if I'm
making any measurements to my room or system, I will
record the DUT as a WAV and analyse it later.

Agreed - it is easy to capture data in the field, and analyze it in detail
later on.

how good are class D amplifiers?
 

"Rob" wrote in message


I simply don't get this. I've been using 5 SS amps of
late (Quad 405, Rose power amp, Cambridge AV, Behringer
A500, and that within a Pure mini system), as well as
others on and off over the years, and I feel each has 'a
sound of its own'.

Good choice of words - "I feel". IOW what your emotions tell you, not
necessarily what well-reasoned testing would tell you.

how good are class D amplifiers?
 

"Arny Krueger" wrote in message
...
"Serge Auckland" wrote in
message

I rarely use the sound card as it is too difficult to use
. Firstly you need an attenuator to reduce the incoming
level, as few soundcards take more than a couple of volts
of input before clipping themselves, idealy

A 5K 2 watt high quality potentiometer suffices.

you need a
millivoltmeter in parallel with the sound card input to
make sure the level stays when it should.

You mean a voltmeter across the UUT output. We often used those with the
old nulling-type analyzers for one reason or the other.

No, I mean across the sound card input, so I know what's going into it to
avoid it clipping. In practice, that may also be across the DUT (or UUT if
you prefer) output, but what's important to me when using a soundcard is
that I don't clip its input.

Then, with software, I never really know what it's measuring

That's your fault - a good experimentalist should be able to determine
that with a few real world measurements. On a bad day, analyze some
signals generated for the purpose. Generating complex tones is very easy
these days.

Agreed, if I could be bothered, but as I have two null-type meters
available, I really can't be fagged.

unless you have a suitable sound card and sample
at 192kHz, you can't measure over the 100kHz bandwidth
that most THD meters manage.

Virtually every sound card that I'd consider to be an alternative to test
equipment samples that high.

My current laptop's internal sound card offers 192k sampling, and it
actually works! However, I prefer to use my Digigram card for anything
serious as its noise performance is much better, but it samples only up to
48k.


I use the software test set
for analysing WAV files. For example, it's easier for me
to take my laptop to the hi-fi than test gear, so if I'm
making any measurements to my room or system, I will
record the DUT as a WAV and analyse it later.

Agreed - it is easy to capture data in the field, and analyze it in detail
later on.

If I were still a practicing engineer I would probably get with modernity
and have PC based test tools, but as now my engineering is for personal
pleasure only, I have a set of old-fashioned instruments that are good
enough for the purpose of hobbying. If noise/distortion etc is below what I
can measure, I go and worry about other things.

S.

--
http://audiopages.googlepages.com

how good are class D amplifiers?
 

In article , Serge Auckland
wrote:


"Jim Lesurf" wrote in message
...


I'd also tend to use a THD+Noise value as otherwise effects like PSU
intermod might be missed as their components don't crop up at
harmonics of the test frequency in most cases. I've seen amps where
the THD value was low, but where there was much more LF garbage due to


Indeed, and in my previous post of the criteria, it was stated that THD
should be measured at all frequencies 20-20k and refers to all powers
and all loads for which the amplifier was designed. In practice, the
measurements are actually THD+N as this is what distortion meters
actually measure. Of course the use of a harmonic analyser for
distortion measurement won't pick up the +N component, but as a
practicing engineer, I found the use of such an instrument to be
tedious in the extreme, and unnecessary when an overall THD+N figure
was so easily achieved.

Well, I've used both 'traditional' THD+N kit that works by nulling or
filtering the test sinusoid, and a specan/generator that autofinds the
harmonics and works out THD. The second didn't seem at all 'tedious' to use
as it automated the process. It was also faster than the old distortion
kits I used to use that took some seconds to null down for low distortion.

I suspect that people use either form of kit, whichever is to hand. The
difficulty with this being what we discuss above.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

how good are class D amplifiers?
 

In article , Don Pearce
wrote:
On Tue, 22 May 2007 09:19:09 +0100, "Serge Auckland"
wrote:

Indeed, and in my previous post of the criteria, it was stated that THD
should be measured at all frequencies 20-20k and refers to all powers
and all loads for which the amplifier was designed. In practice, the
measurements are actually THD+N as this is what distortion meters
actually measure. Of course the use of a harmonic analyser for
distortion measurement won't pick up the +N component, but as a
practicing engineer, I found the use of such an instrument to be
tedious in the extreme, and unnecessary when an overall THD+N figure
was so easily achieved.

S.


The problem becomes more complex when you use an FFT analyser, as I
suspect most are these days. You then need to consider the number of
points in the FFT, and the way they display noise. Discrete signals are
easy - whatever you do with the FFT, they look the same size, but the
"+noise" bit will change with the number of points.

Erm. It should be the total noise in the audio range. This means that
however many bins it was divided into becomes irrelevant as they are then
summed. Although I'd agree that a small fraction of the noise will be in
the input signal bin and would be 'lost'.

In recent years I've tended to use a Stanford Instruments unit that
combines a test waveform generator and an FFT specan, and 'automates' the
process as you wish. The trick, of course, is to know what process to
specifiy and to understand how to interpret the results - especially when
the spectrum on the screen isn't simple. :-)

The noise floor problem is more significant when reviews simply display the
floor value in terms of the per-bin level without having any clue what
resolution bandwidth they are using. In those cases your comment does
indeed apply, and makes the floors shown in some magazines worthless.
Having tried discuss this with one or two people I fear that this issue
whooshes over the head of some of them. Although there are others who
clearly understand it, but don't use such meaningless plots.

Are there many distortion analysers any more that simply null the
fundamental and display the sum of the rest?

Dunno. The last one I used a lot was the Sound Technology 1000A about two
decades ago. This was very nice, but took a few seconds to settle into a
null, etc, whenever you altered anything. Worked down to about 0.002%
though, IIRC. I think that part of the delay was for the light bulb in the
oscillator to settle when you changed frequency. ;-

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

how good are class D amplifiers?
 

"Arny Krueger" wrote in message
. ..
"Rob" wrote in message


I simply don't get this. I've been using 5 SS amps of
late (Quad 405, Rose power amp, Cambridge AV, Behringer
A500, and that within a Pure mini system), as well as
others on and off over the years, and I feel each has 'a
sound of its own'.

Good choice of words - "I feel". IOW what your emotions tell you, not
necessarily what well-reasoned testing would tell you.



Yep, why waste time *listening* to a bit of kit when you could just
stick a meter on it....??