Has anyone used a distortion analyzer to measure an amp/preamps THD?

Can you use the speakers as a load, or does that distort the measurement.
Then I would guess an big 8 ohm load resistor is required?

Any input on the subject would be appreciated.

.....Dave

In article ,
Dave Edwards wrote:
Has anyone used a distortion analyzer to measure an amp/preamps THD?

Can you use the speakers as a load, or does that distort the measurement.
Then I would guess an big 8 ohm load resistor is required?

Any input on the subject would be appreciated.

....Dave

One thing I'd watch out for is that you may wind up overloading your speakers
if you use them for a load.

For example, if you are testing a 250wpc amplifer at full power at frequencies
between 20Hz and 20Khz you will be driving your speakers with 250wpc of 20Khz
signal, which may reduce your tweeter (or your ears) to molten slag.

If you build a dummy load get a "noninductive" load resistor (or set of
resistors); I'm currently building a stereo dummy load using suprlus Dale
noninductive resistors for testing at 4, 8, and 16 ohms.

If you build a dummy load make sure that it can handle the power input you
want, since catastrophic failure of a dummy load can damage your power
amplifer.

Mike Squires
--

Mike Squires (mikes at cs.indiana.edu) 317 233 9456 (w) 812 333 6564 (h)
mikes at siralan.org 546 N Park Ridge Rd., Bloomington, IN 47408

Michael Squires wrote:

Dave Edwards wrote:

Can you use the speakers as a load, or does that distort the measurement.
Then I would guess an big 8 ohm load resistor is required?

....Dave

One thing I'd watch out for is that you may wind up overloading your speakers
if you use them for a load.

If you build a dummy load get a "noninductive" load resistor (or set of
resistors); I'm currently building a stereo dummy load using suprlus Dale
noninductive resistors for testing at 4, 8, and 16 ohms.

Mike Squires

And then, add a 1uF / 250V capacitor that you can switch in parallel
with the load-resistor. and a self to be switched in series.

Real-world loads / speakers are far from "noninductive"
When your amp-under-test does employ some feedback it is fantastic to
see if your amp will show the same figures at various loads and other
1kHz frequencies.

Also, switching your generator to squarewaves at 1kHz or 10kHz and
studying them on an oscilloscope will tell a lot about the amp's
stability and bandwidth.

Andre

"Michael Squires"


If you build a dummy load get a "noninductive" load resistor (or set of
resistors); I'm currently building a stereo dummy load using suprlus Dale
noninductive resistors for testing at 4, 8, and 16 ohms.



** Why bother with so called "non-inductive" load resistors ??

Standard spiral wound types are still within 1% of DC value at 20 kHz.

All speakers exhibit a rising impedance curve above the audio band.



......... Phil

"Dave Edwards" wrote in message
...
Has anyone used a distortion analyzer to measure an amp/preamps THD?

Can you use the speakers as a load, or does that distort the measurement.
Then I would guess an big 8 ohm load resistor is required?

Any input on the subject would be appreciated.

....Dave

Hi Dave.
Be very cautious indeed about driving test tones
into a loudspeaker, especially at high frequencies.

For 50W power amps I use a 100W dummy load.
It's bolted to a mild steel plate. I also have a
"loudspeaker equivalent" circuit which represents a
typical two way, and was published in Stereophile.

Remember when you look at the THD figure that
the source generator also has distortion. There
seem to be differences of opinion as to what
constitutes a low distortion oscillator.
Mine has 0.03% THD at 1kHz, 0dBm. Some
are better, many are worse. Feeding this
signal into a third octave filter considerable
improves this fig, by about 6dB removing
significant amounts of the 2H and 3H.
(Thanks to Patrick for that tip)

If you come to plot the response of a power amplifier, you
may find it will be different into a dummy load than into a
real world loudspeaker, the impedance of which can be
frequency dependent.

It is useful to look at the distortion elements on a
scope to see the ratio of 2nd, 3rd, 4th etc
harmonics.

It is also interesting to measure the noise floor,
and take a look at how it is made up.

There are many other tests, square wave, IMD,
damping etc which will also tell you a great deal.

Presumably this is a tube amp? What kind?

This has the makings of a good thread. Please
tell us how you get on.

Regards to all,
Iain

"Iain Churches"


** This cretin is yet another, pig ignorant ,sub human autistic pile of
pommy ****.



For 50W power amps I use a 100W dummy load.
It's bolted to a mild steel plate.


** How asinine - sheet steel is a terrible thermal conductor.


I also have a
"loudspeaker equivalent" circuit which represents a
typical two way, and was published in Stereophile.


** A stupid waste of time.



It is useful to look at the distortion elements on a
scope to see the ratio of 2nd, 3rd, 4th etc
harmonics.


** More asinine crapology.

No way a scope trace can give that sort of info.



It is also interesting to measure the noise floor,
and take a look at how it is made up.

There are many other tests, square wave, IMD,
damping etc which will also tell you a great deal.



** But not if you are a PIG ignorant **** like "Churches " with no clue
at all.



This has the makings of a good thread.


** It has the makings of a really dumb TROLL !!!



Please
tell us how you get on.


** Go drop dead.




.......... Phil

"Dave Edwards" wrote in message


Has anyone used a distortion analyzer to measure an
amp/preamps THD?

About a million people, more or less.

Can you use the speakers as a load, or does that distort
the measurement.

The most likely outcome of using speakers for dummy loads is frying them.

Then I would guess an big 8 ohm load
resistor is required?

That's the simpistic way. Here are good examples:

http://www.arcol.co.uk/uploads/products/hsseries-10.pdf

http://www.mouser.com/catalog/625/490.pdf

Any input on the subject would be appreciated.

The most practical way to get more realistic results is to use a loudspeaker
simulator such as this one:

http://www.pcabx.com/product/amplifiers/index.htm

(please see bottom of page)

"Phil Allison" wrote in message

"Michael Squires"


If you build a dummy load get a "noninductive" load
resistor (or set of resistors); I'm currently building a
stereo dummy load using suprlus Dale noninductive
resistors for testing at 4, 8, and 16 ohms.


** Why bother with so called "non-inductive" load
resistors ??
Standard spiral wound types are still within 1% of DC
value at 20 kHz.


Agreed that 4-8 ohm wirewound resistors aren't all that inductive.

More likely is that cheap wirewound resistors tend to have a fairly large
temperature coefficient.

All speakers exhibit a rising impedance curve above the
audio band.

As does speaker cable.

"Arny Krueger"
"Phil Allison"

** Why bother with so called "non-inductive" load
resistors ??
Standard spiral wound types are still within 1% of DC
value at 20 kHz.


Agreed that 4-8 ohm wirewound resistors aren't all that inductive.

More likely is that cheap wirewound resistors tend to have a fairly large
temperature coefficient.



** Not true at all.

Resistors have to be within their rated tolerance when operated at full
rated power.

Typical, cheap wire would types are quoted as having +/-150 ppm per degree
C tempco - so only change by around 2% or so at full power in fee air.

If you submerge a ceramic cased or tubular load resistor in water, the temp
will stay low and the power rating increase by up to 10 times.




........ Phil

On Tue, 7 Mar 2006 19:04:48 +1100, "Phil Allison"
wrote:

"Iain Churches"

It is useful to look at the distortion elements on a
scope to see the ratio of 2nd, 3rd, 4th etc
harmonics.


** More asinine crapology.

No way a scope trace can give that sort of info.

On the contrary, any good distortion analyzer will
have scaled input replicas and distortion products
available as outputs to a dual-trace scope.

Besides visual analysis of amplifier biasing, etc.
this is also the only way do things like FM tuner
alignments, if you want to charge money for results.

A scope trace is the *only* good way to get that
sort of info.

Good fortune,

Chris Hornbeck

"Chris Hornbeck" = a ****WIT !!

"Iain Churches"

It is useful to look at the distortion elements on a
scope to see the ratio of 2nd, 3rd, 4th etc
harmonics.


** More asinine crapology.

No way a scope trace can give that sort of info.


On the contrary, any good distortion analyzer will
have scaled input replicas and distortion products
available as outputs to a dual-trace scope.


** You are a congenital, ****ing ass - Hornbeck.

The residual THD waveform does not supply actual harmonic ratios !!!!


SO **** OFF - YOU BRAIN DEAD ASS !




........... Phil

On Thu, 9 Mar 2006 13:44:36 +1100, "Phil Allison"
wrote:

No way a scope trace can give that sort of info.


On the contrary, any good distortion analyzer will
have scaled input replicas and distortion products
available as outputs to a dual-trace scope.


** You are a congenital, ****ing ass - Hornbeck.

Likely true, but what's the relevance?


The residual THD waveform does not supply actual harmonic ratios !!!!

Of course it does; you only need to look. It's
completely intuitive and obvious. Have you
ever actually seen a distortion analyzer trace?
Seems unlikely.

Good fortune,

Chris Hornbeck

"Chris Hornbeck"

another CRIMINAL LIAR !!

and another ****ING context SNIPPER !!!


"Iain Churches"

It is useful to look at the distortion elements on a
scope to see the ratio of 2nd, 3rd, 4th etc
harmonics.



No way a scope trace can give that sort of info.


On the contrary, any good distortion analyzer will
have scaled input replicas and distortion products
available as outputs to a dual-trace scope.


** You are a congenital, ****ing ass - Hornbeck.

Likely true, but what's the relevance?


** ****wit.


The residual THD waveform does not supply actual harmonic ratios !!!!

Of course it does; you only need to look.


** LIAR !!


It's completely intuitive and obvious.


** LIAR !!

Have you
ever actually seen a distortion analyzer trace?


** Nearly every day for two decades.




........... Phil

"Chris Hornbeck" wrote in message
...
On Tue, 7 Mar 2006 19:04:48 +1100, "Phil Allison"
wrote:

"Iain Churches"

It is useful to look at the distortion elements on a
scope to see the ratio of 2nd, 3rd, 4th etc
harmonics.


** More asinine crapology.

No way a scope trace can give that sort of info.

On the contrary, any good distortion analyzer will
have scaled input replicas and distortion products
available as outputs to a dual-trace scope.

Besides visual analysis of amplifier biasing, etc.
this is also the only way do things like FM tuner
alignments, if you want to charge money for results.

A scope trace is the *only* good way to get that
sort of info.

Good fortune,

Chris Hornbeck


Good morning Chris. I don't usually reply to Phil.
I have found that looking at the output of the analyser
to be most informative. I have both the trusty
HP 334A and a Ferrograph RTS/ATU. Just as
you describe, one can see the pure input signal
on one trace of the scope, and the output
distortion in multiples of the original 2H, 3H 4H
etc on the other.

Looking at the noise floor is also
interesting, especially when comparing the same
tube type by different makers.

Once I began to understand what
was going on here, I wanted to buy a
spectrum analyser to learn more.
It's a fascinating subject.

Regards to all
Iain

Phil Allison wrote:

"Chris Hornbeck" = a ****WIT !!

"Iain Churches"

It is useful to look at the distortion elements on a
scope to see the ratio of 2nd, 3rd, 4th etc
harmonics.


** More asinine crapology.

No way a scope trace can give that sort of info.


On the contrary, any good distortion analyzer will
have scaled input replicas and distortion products
available as outputs to a dual-trace scope.

** You are a congenital, ****ing ass - Hornbeck.

The residual THD waveform does not supply actual harmonic ratios !!!!

SO **** OFF - YOU BRAIN DEAD ASS !

.......... Phil

Phil, if anything seems true, it is that your mind lacks life, not
Chris's.

Where you have a distortion analyser which filters out each harmonic
above a fundemental
then each could well be viewd on a second CRO trace showing the
fundemtal.
I have been meaning to build such an item with high Q filters for
2,3,4,5,6,7,8,9,10th harmonics above 1kHz,
but its all too easy to do it with a program on an old PC, if I wanted to
that is.
Distortion analysers also can display the amounts of harmonics for a
given test signal
as a series of peaks on a cathode ray display screen.

But the analysis of the content within the total harmonic or residual
harmonic wave form cannot
be accurtately be made just viewing the THD alone; one must filter out
the harmonics fromm the THD
to establish content.

Stick to engineering methods Phil, your comments about brain health,
death, anuses, et all, are most unwelcome,
dis-informative, and indicate a complete lack of debating skills and
proove you are primarily only capable of
attrocious netiquette..

Patrick Turner.

On Thu, 09 Mar 2006 02:22:04 GMT, Chris Hornbeck
wrote:

On Tue, 7 Mar 2006 19:04:48 +1100, "Phil Allison"
wrote:

"Iain Churches"

It is useful to look at the distortion elements on a
scope to see the ratio of 2nd, 3rd, 4th etc
harmonics.


** More asinine crapology.

No way a scope trace can give that sort of info.

On the contrary, any good distortion analyzer will
have scaled input replicas and distortion products
available as outputs to a dual-trace scope.

Besides visual analysis of amplifier biasing, etc.
this is also the only way do things like FM tuner
alignments, if you want to charge money for results.

A scope trace is the *only* good way to get that
sort of info.

Of course, there is an obvious alternative, that Churches doesn't know
the difference between a 'scope and a rectum paralyser.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

"Patrick Turner"


But the analysis of the content within the total harmonic or residual
harmonic wave form cannot
be accurtately be made just viewing the THD alone;


** Which is EXACTLY what I stated:

" No way a scope trace ( of THD residual ) can give that sort of info."

Now kindly insert your head back up your bony arse where it is most
familiar.





......... Phil

"Stewart Pinkerton" wrote in message
...

Of course, there is an obvious alternative, that Churches doesn't know
the difference between a 'scope and a rectum paralyser.
--

It's flattering that you get up so early in the mornings
to write your daily dose of coarse vitriol, Lord Pinkerton.

Now off with you to the dark Satanic post rom:-)

Iain

"Iain Churches" wrote in message
...

"Stewart Pinkerton" wrote in message
...

Of course, there is an obvious alternative, that Churches doesn't know
the difference between a 'scope and a rectum paralyser.
--

It's flattering that you get up so early in the mornings
to write your daily dose of coarse vitriol, Lord Pinkerton.

Now off with you to the dark Satanic post rom:-)

Iain

And I thought you where just a smart **** with me, seems you make a hobby
out of insulting people.
So whats the Gay scene like in Finland, or where ever the hell you infest.


bassett