Gutless Pommy Wonder
 

"Phil Allison" wrote in message
...

"Keith the Gutless ****ing Pommy Wonder "



** Not up to having a technical debate with ANYONE

- ARE you Keith ?


So you continue to post your BRAIN DEAD insults while hiding your
identity.

How bloody PATHETIC !!!

Typical, of countless, useless pommy wastes of space and all usenet
cretins.

**** OFF







...... Phool


You said it!

Still can't sleep, eh?

Clue: Just try *counting* the sheep, don't try shagging them all.....

(Gotta be 01:30 now....??)

Gutless Pommy Wonder
 

"Keith the Gutless ****ing Pommy Wonder "


** Not up to having a technical debate with ANYONE

- ARE you Keith ?


So you STILL continue to post your BRAIN DEAD insults while hiding
your identity.

How bloody PATHETIC !!!

Typical, of countless, useless pommy wastes of space and all usenet cretins.

**** THE HELL OFF






....... Phil

Measuring audio power ...
 

In article , Arfa Daily
writes

"tony sayer" wrote in message
...
In article , Arfa Daily
writes
Ok, so who knows a bit about measuring audio power ? Setting aside any
furious arguments about peak power, rms power, average power, backpeddling
average peak music power on any given friday in March etc, does an audio
power meter sum the power in both half cycles to arrive at a reading, or
just one.

I guess what I'm asking is half wave reccy ahead of the meter, or full
wave
bridge ?

Arfa



Is this the arfa daily who's a service tech?..


FWIW if its just the output of an audio amp I just use two bloody great
8 ohm resistors on a large heatsink with stout cables to reduce ohmic
losses, and connect that to the amp and use me trusty Fluke bench DMM to
measure the AC power developed when running a sine wave with the Hewlett
Packard distortion analyser keeping note of the distortion level to see
when its going into clip.

Measure that at a few different frequencies and square the AC measured
volts and divide by the 8 'ommes and thats the RMS power.

Sufficient and accurate and IMHO a good indication of what the amp will
develop.....
--
Tony Sayer

Hi Tony

That's me. Useful input. Thanks.

Arfa


Thought it was. The above power test was much the same whilst at Neve,
Audix, Audiolab, and SCPD.. AKA the BBC...;-))
--
Tony Sayer

Measuring audio power ...
 

On Sun, 25 Jun 2006 13:40:03 +0100, Jim Lesurf
wrote:

In article , Don Pearce
wrote:


The type of rectifier doesn't make a great deal of difference, although
full wave probably has the edge on accuracy. Don't put a capacitor after
it, just let the meter do the averaging, then do the sums: power = v
squared / R.

I'd be wary of this unless I knew the details of the meter. I've seen some
that can give odd results when asked to give a dc level in the presence of
much ac. e.g. One I recall seemed to only sample the input at a low rate,
so became confused as the level flutuations 'beat' with its sampling rate.

Slainte,

Jim

I reckoned that the chosen method (and prologue) indicated no great
ambition for accuracy, more a wish to get some sort of idea. Now
damping the meter movement with a big cap is fine and it will take the
ballistics out of the equation, but it will now certainly be a peak
reading meter that doesn't correspond to apparent loudness in any but
the vaguest way.

Also, I assumed that this is a real meter with a needle, not a
sampling DMM - otherwise why the question about rectifiers? It could
simply have been used on a AC range. Mine will read Watts or dBWatts
by setting an appropriate impedance in a menu.

d

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

Measuring audio power ...
 

"Jim Lesurf"
Arfa Daily

I guess what I'm asking is half wave reccy ahead of the meter, or full
wave bridge ?

If it uses a rectifier then takes a time-average I'd expect a good one
to use a full wave precision rectifier - i.e. one that suppresses the
forward voltage drops in the diodes. Cheap enough to do at audio
frequencies.


** OPs needs real info - Jim.

Not dumb guesses from someone with no idea how a DMM actually works.



These days a meter might simply sample rapidly and work out the rms
voltage and report that.


** Pigs might fly as well.


Years ago, it might have used an analog
multiplier to obtain the square-law for audio.


** Got no idea at all how a " true rms" DMM actually operates - Jim ?

Never come across any " rms to DC " converters made by Analog Devices?

Only been around for over 20 years.



I guess people like
Burr-Brown still make these. (?) As Don has pointed out, a thermal
meter might be used in some applications.


** The ASS said no such thing.

Why cover up for the demented fool ?



These (and single diodes)
still get used for RF power measurements.


** Damn shame then how OP is asking about **audio** !!



However unless you are using a sinewave, the reported value may be
misleading. Ditto if the load isn't resistive.


** Better have a look at the AD636.

http://www.farnell.com/datasheets/57885.pdf

Covers audio band measurements very comfortably.





........ Phil

Gutless Ozzie Poof
 

"Poof Allison" wrote in message
...

"Keith the Gutless ****ing Pommy Wonder "


** Not up to having a technical debate with ANYONE

- ARE you Keith ?


So you STILL continue to post your BRAIN DEAD insults while hiding
your identity.

How bloody PATHETIC !!!

Typical, of countless, useless pommy wastes of space and all usenet
cretins.

**** THE HELL OFF


:-)

I've got it now!! You're a poof, aren't you?

(What's it got to be now - 2:30 am? You won't look your best tomorrow.....)

Ciao!

Measuring audio power ...
 

"Don Pearce" wrote in message
...
On Sun, 25 Jun 2006 13:40:03 +0100, Jim Lesurf
wrote:

In article , Don Pearce
wrote:


The type of rectifier doesn't make a great deal of difference, although
full wave probably has the edge on accuracy. Don't put a capacitor after
it, just let the meter do the averaging, then do the sums: power = v
squared / R.

I'd be wary of this unless I knew the details of the meter. I've seen some
that can give odd results when asked to give a dc level in the presence of
much ac. e.g. One I recall seemed to only sample the input at a low rate,
so became confused as the level flutuations 'beat' with its sampling rate.

Slainte,

Jim

I reckoned that the chosen method (and prologue) indicated no great
ambition for accuracy, more a wish to get some sort of idea. Now
damping the meter movement with a big cap is fine and it will take the
ballistics out of the equation, but it will now certainly be a peak
reading meter that doesn't correspond to apparent loudness in any but
the vaguest way.

Also, I assumed that this is a real meter with a needle, not a
sampling DMM - otherwise why the question about rectifiers? It could
simply have been used on a AC range. Mine will read Watts or dBWatts
by setting an appropriate impedance in a menu.

d

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

Hi Don

Yeah, you're right. No great need for any accuracy in this application.
Because of the large numbers of group amps that I'm repairing at the moment,
I've put together a big resistive load, capable of handling a couple of
hundred watts. I've put some heavy duty relay switching in it for 16, 8 and
4 ohms, with automatic power-on default to 16. One or two other useful odds
and sods like a very heavily attenuated little speaker and volume control,
so that you can leave it squeaking away up the corner on a soak test, and a
+ /- LED bar arrangement to give a rough and ready idea of output symmetry,
through socket so that a genuine cab can be substituted for the load, and a
BNC socket for my 'scope. I thought it might be useful to put a very basic
power meter on there too, just to get an idea of how much smoke an amp was
generating. So I had a little play with a couple of spare sets of relay
contacts on the load resistor switching relays, and hung a three way switch
in there too. Three pots and a half dozen resistors later, I had a meter
showing sensible readings for full scales of 10, 50 and 100 watts into 4, 8
and 16 ohm loads, but for straight DC from the bench power supply.

It was just for interest then that I asked the question about whether 'real'
meters read the power in the whole wave, or just one half. So when an amp
says its output is 50w RMS, setting aside all the debate about whether RMS
is valid, just taking it to mean what we all know the manufacturers want us
understand by that, is it 100 watts of power contained in one half cycle, or
one whole cycle. I'm sure you all know what I mean - I'm just not putting it
very well ...

Arfa

Measuring audio power ...
 

tony sayer wrote:


FWIW if its just the output of an audio amp I just use two bloody great
8 ohm resistors on a large heatsink with stout cables to reduce ohmic
losses, and connect that to the amp and use me trusty Fluke bench DMM to
measure the AC power developed when running a sine wave with the Hewlett
Packard distortion analyser keeping note of the distortion level to see
when its going into clip.

Measure that at a few different frequencies and square the AC measured
volts and divide by the 8 'ommes and thats the RMS power.

Sufficient and accurate and IMHO a good indication of what the amp will
develop.....
--
Tony Sayer

That's exactly what I do, except I use a Levell millivoltmeter. With two
large 8ohm resistors, it's easy to get a 4ohm load when needed.

S.

Measuring audio power ...
 

On Sun, 25 Jun 2006 20:01:55 GMT, "Arfa Daily"
wrote:

It was just for interest then that I asked the question about whether 'real'
meters read the power in the whole wave, or just one half. So when an amp
says its output is 50w RMS, setting aside all the debate about whether RMS
is valid, just taking it to mean what we all know the manufacturers want us
understand by that, is it 100 watts of power contained in one half cycle, or
one whole cycle. I'm sure you all know what I mean - I'm just not putting it
very well ...

Yup. "Real" audio power meters have an interesting design where the
permanent magnet in the meter is replaced by a coil, which carries the
same current as the movement. The result is that whichever way the
current flows, it sends the needle upwards, so the meter naturally
rectifies without diodes. Also, the deflection varies as the square of
the current, so it is automatically linear on a power scale.

d

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

Complete Fool
 

"Keith Gutless Wonder "



** An even dumber pommy turd than I thought.







........ Phil