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Message |
Patrick Turner
Guest
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 Posted:
Wed Dec 22, 2004 10:30 pm Post subject:
Power output meter amp schematic. |
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Most amps with "power" meters have VU meters
or other voltage meters which only tell you
about the output voltage of an amp.
A real power meter tells you the product of
voltage and current, so that when the load value is halved
and the output voltage is kept constant as is the case
with many amps, the power will double.
Who knows of a very simple circuit that is at least accurate
to about 10%?
There isn't a need for any greater accuracy.
Patrick Turner.
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Jon Yaeger
Guest
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| Posted:
Wed Dec 22, 2004 11:28 pm Post subject:
Re: Power output meter amp schematic. |
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in article 41C9AF35.5DE6C938@turneraudio.com.au, Patrick Turner at
info@turneraudio.com.au wrote on 12/22/04 12:30 PM:
| Quote: | Most amps with "power" meters have VU meters
or other voltage meters which only tell you
about the output voltage of an amp.
A real power meter tells you the product of
voltage and current, so that when the load value is halved
and the output voltage is kept constant as is the case
with many amps, the power will double.
Who knows of a very simple circuit that is at least accurate
to about 10%?
There isn't a need for any greater accuracy.
Patrick Turner.
|
If you don't want to reinvent the wheel, Velleman has several Power & VU
meter kits, reasonably priced. They have manuals on line, but have omitted
the schematics, for obvious reasons.
http://www.velleman.be/
Jon |
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Yves
Guest
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| Posted:
Thu Dec 23, 2004 1:06 am Post subject:
Re: Power output meter amp schematic. |
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"Patrick Turner" <info@turneraudio.com.au> a écrit dans le message de news:
41C9AF35.5DE6C938@turneraudio.com.au...
| Quote: | Most amps with "power" meters have VU meters
or other voltage meters which only tell you
about the output voltage of an amp.
A real power meter tells you the product of
voltage and current, so that when the load value is halved
and the output voltage is kept constant as is the case
with many amps, the power will double.
Who knows of a very simple circuit that is at least accurate
to about 10%?
There isn't a need for any greater accuracy.
Patrick Turner.
|
Hi Pat,
When I was active as ham, I widely used the MC1496 wich is a "doubly
balanced mixer", more exactly a "four quadrants multiplier" (If you can
"Google" you'll find tons of papers about).
It could be a good choice for implementing the U x I function according
than:
-- It can work at vy low level (tens of millivolts) and thus does not need a
large value of resistor to sample the current, nor some sort of
"preamplification". So, minimal resistor is to be added in serie with the
loudspeaker (althought it'is certainly possible to include it in the
feedback loop).
-- It easy to use it at AC level rather than DC, removing risk of thermal
drift and the need of rectifying low level signals.
-- It has some "gain" and thus ...
-- It (perhaps) delivers sufficient level to directly drive a sensitive
meter thru a simple rectifier.
Except for the PSU, I bet a "single IC" project is feasible.
My two pence !
Merry Xmas, Yves. |
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Jeff Goldsmith
Guest
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| Posted:
Thu Dec 23, 2004 1:52 am Post subject:
Re: Power output meter amp schematic. |
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I've been using Burr Brown MPY634KP analog multiplier ICs, seems they
would output an AC waveform in proportion to power from an amplifier
with about the only external component being the current sensing
resistor. You would still need a precision FW op amp rectifier to drive
(a DC) meter.
Jeff Goldsmith
Yves wrote:
| Quote: |
"Patrick Turner" <info@turneraudio.com.au> a écrit dans le message de news:
41C9AF35.5DE6C938@turneraudio.com.au...
Most amps with "power" meters have VU meters
or other voltage meters which only tell you
about the output voltage of an amp.
A real power meter tells you the product of
voltage and current, so that when the load value is halved
and the output voltage is kept constant as is the case
with many amps, the power will double.
Who knows of a very simple circuit that is at least accurate
to about 10%?
There isn't a need for any greater accuracy.
Patrick Turner.
Hi Pat,
When I was active as ham, I widely used the MC1496 wich is a "doubly
balanced mixer", more exactly a "four quadrants multiplier" (If you can
"Google" you'll find tons of papers about).
It could be a good choice for implementing the U x I function according
than:
-- It can work at vy low level (tens of millivolts) and thus does not need a
large value of resistor to sample the current, nor some sort of
"preamplification". So, minimal resistor is to be added in serie with the
loudspeaker (althought it'is certainly possible to include it in the
feedback loop).
-- It easy to use it at AC level rather than DC, removing risk of thermal
drift and the need of rectifying low level signals.
-- It has some "gain" and thus ...
-- It (perhaps) delivers sufficient level to directly drive a sensitive
meter thru a simple rectifier.
Except for the PSU, I bet a "single IC" project is feasible.
My two pence !
Merry Xmas, Yves. |
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Patrick Turner
Guest
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| Posted:
Thu Dec 23, 2004 8:23 am Post subject:
Re: Power output meter amp schematic. |
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Yves wrote:
| Quote: | "Patrick Turner" <info@turneraudio.com.au> a écrit dans le message de news:
41C9AF35.5DE6C938@turneraudio.com.au...
Most amps with "power" meters have VU meters
or other voltage meters which only tell you
about the output voltage of an amp.
A real power meter tells you the product of
voltage and current, so that when the load value is halved
and the output voltage is kept constant as is the case
with many amps, the power will double.
Who knows of a very simple circuit that is at least accurate
to about 10%?
There isn't a need for any greater accuracy.
Patrick Turner.
Hi Pat,
When I was active as ham, I widely used the MC1496 wich is a "doubly
balanced mixer", more exactly a "four quadrants multiplier" (If you can
"Google" you'll find tons of papers about).
It could be a good choice for implementing the U x I function according
than:
-- It can work at vy low level (tens of millivolts) and thus does not need a
large value of resistor to sample the current, nor some sort of
"preamplification". So, minimal resistor is to be added in serie with the
loudspeaker (althought it'is certainly possible to include it in the
feedback loop).
-- It easy to use it at AC level rather than DC, removing risk of thermal
drift and the need of rectifying low level signals.
-- It has some "gain" and thus ...
-- It (perhaps) delivers sufficient level to directly drive a sensitive
meter thru a simple rectifier.
Except for the PSU, I bet a "single IC" project is feasible.
My two pence !
|
I already have the psu required and the current sensing R can be the return wire
of the
common terminal for the speaker; at several amps there is enough voltage present
to mweasure the current
and if not a little step up tranny may do.
Maybe this is the way to go.
Thanks and have a good one,
Patrick Turner.
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Phil Allison
Guest
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| Posted:
Thu Dec 23, 2004 8:34 am Post subject:
Re: Power output meter amp schematic. |
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"Yves"
| Quote: |
When I was active as ham, I widely used the MC1496 wich is a "doubly
balanced mixer", more exactly a "four quadrants multiplier" (If you can
"Google" you'll find tons of papers about).
|
** The 1496 is NOT a four quadrant multiplier and cannot be used as one.
The 1495 is such a multiplier but has been obsolete and unavailable since
a decade ago.
The AD 633 is a ( trim free) four quad multiplier and is available.
.................. Phil |
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Patrick Turner
Guest
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| Posted:
Thu Dec 23, 2004 8:34 am Post subject:
Re: Power output meter amp schematic. |
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Yves wrote:
| Quote: | "Patrick Turner" <info@turneraudio.com.au> a écrit dans le message de news:
41C9AF35.5DE6C938@turneraudio.com.au...
Most amps with "power" meters have VU meters
or other voltage meters which only tell you
about the output voltage of an amp.
A real power meter tells you the product of
voltage and current, so that when the load value is halved
and the output voltage is kept constant as is the case
with many amps, the power will double.
Who knows of a very simple circuit that is at least accurate
to about 10%?
There isn't a need for any greater accuracy.
Patrick Turner.
Hi Pat,
When I was active as ham, I widely used the MC1496 wich is a "doubly
balanced mixer", more exactly a "four quadrants multiplier" (If you can
"Google" you'll find tons of papers about).
It could be a good choice for implementing the U x I function according
than:
-- It can work at vy low level (tens of millivolts) and thus does not need a
large value of resistor to sample the current, nor some sort of
"preamplification". So, minimal resistor is to be added in serie with the
loudspeaker (althought it'is certainly possible to include it in the
feedback loop).
-- It easy to use it at AC level rather than DC, removing risk of thermal
drift and the need of rectifying low level signals.
-- It has some "gain" and thus ...
-- It (perhaps) delivers sufficient level to directly drive a sensitive
meter thru a simple rectifier.
Except for the PSU, I bet a "single IC" project is feasible.
My two pence !
Merry Xmas, Yves.
|
I could not find a meter circuit via Google for measuring audio power using the
MC1496.
The app notes don't have any typical application for the device
used as such.
Its an interesting device, and it does lots of things, but I may have to search
more later.
Maybe the old ham books I have may have something.
Patrick Turner. |
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Chris Hornbeck
Guest
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| Posted:
Thu Dec 23, 2004 8:34 am Post subject:
Re: Power output meter amp schematic. |
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On Thu, 23 Dec 2004 14:59:51 +1100, Patrick Turner
<info@turneraudio.com.au> wrote:
| Quote: | I could not find a meter circuit via Google for measuring audio power using the
MC1496.
The app notes don't have any typical application for the device
used as such.
Its an interesting device, and it does lots of things, but I may have to search
more later.
|
Jung's _IC OP-Amp Cookbook_ includes various uses as a multiplier,
and also some "precision rectifier" applications. Highly recommended.
You'll still need to make some design decisions about how to sample
current and whether to choose RMS and/or peak rectification. Or
"VU" weighting? Certainly an interesting project.
As a side topic, how important is current phase angle to your design?
A loudspeaker's reflected current may be independently interesting
to an amplifier builder.
Good fortune,
Chris Hornbeck
" ** Go choke on your damn turkey." |
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robert casey
Guest
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| Posted:
Thu Dec 23, 2004 8:34 am Post subject:
Re: Power output meter amp schematic. |
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Patrick Turner wrote:
| Quote: | Most amps with "power" meters have VU meters
or other voltage meters which only tell you
about the output voltage of an amp.
A real power meter tells you the product of
voltage and current, so that when the load value is halved
and the output voltage is kept constant as is the case
with many amps, the power will double.
Who knows of a very simple circuit that is at least accurate
to about 10%?
There isn't a need for any greater accuracy.
Patrick Turner.
|
Maybe use a dual control pentode. One grid would
have the voltage waveform feeding the speakers.
The other grid would have a current sampling resistor
between the amp's ground (speaker wire return) and
the speaker's ground. Speaker "ground" feeds the
grid, amp ground would (thru a bias circuit) feed
the cathode. The plate circuit (using a resistor)
would have the product of the waveforms on both
grids. However it would not be listenable audio!
AC couple it to something similar to a VU meter.
Use a pentagrid tube like a 6CS6 if you want to
avoid a "triode" efect you might get from G3 to
the plate when using a true pentode. See
http://pw2.netcom.com/~wa2ise/radios/elvctube.jpg
and
http://pw2.netcom.com/~wa2ise/radios/6be6vol.html
for rough ideas. Instead of a steady DC bias on the
second control grid, feed the sampled current. |
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Phil Allison
Guest
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| Posted:
Thu Dec 23, 2004 8:34 am Post subject:
Re: Power output meter amp schematic. |
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"Jeff Goldsmith"
| Quote: | I've been using Burr Brown MPY634KP analog multiplier ICs, seems they
would output an AC waveform in proportion to power from an amplifier
with about the only external component being the current sensing
resistor. You would still need a precision FW op amp rectifier to drive
(a DC) meter.
|
** Wrong.
With a resistive load, a four quad multiplier sensing voltage and current
will give precision rectification and an output that is always positive.
With a reactive load, there will be negative as well as positive swings and
these must not be rectified - to do so would mean that pure reactances
would show as dissipating power ( ie an impossibility).
............... Phil |
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Phil Allison
Guest
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| Posted:
Thu Dec 23, 2004 8:34 am Post subject:
Re: Power output meter amp schematic. |
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"Chris Hornbeck"
" Pat Turner "
| Quote: |
I could not find a meter circuit via Google for measuring audio power
using the
MC1496.
The app notes don't have any typical application for the device
used as such.
Jung's _IC OP-Amp Cookbook_ includes various uses as a multiplier,
and also some "precision rectifier" applications. Highly recommended.
|
** My copy of the second edition has no mention of it.
There are several pages on the ( now obsolete) MC 1495 though.
| Quote: | You'll still need to make some design decisions about how to sample
current and whether to choose RMS and/or peak rectification.
|
** Since the aim is to measure true power in a speaker load, the use of
rectification or RMS conversion after the multiplier would be **quite
wrong**. The average value of the multiplier's output will be proportional
to the true power in the load.
| Quote: | As a side topic, how important is current phase angle to your design?
|
** Using a four quad multiplier takes care of that.
| Quote: | A loudspeaker's reflected current may be independently interesting
to an amplifier builder.
|
** When the voltage and current in a (reactive) speaker load have opposite
polarities - then the multiplier will give a negative output signal. At
all other times it will be positive. This is why it is essential not to
rectify it - that would make reactive power into real power. A capacitor
or pure inductor used for a load should show zero reading on a true power
meter.
.............. Phil |
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Jeff Goldsmith
Guest
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| Posted:
Thu Dec 23, 2004 3:55 pm Post subject:
Re: Power output meter amp schematic. |
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You're right, Phil. It's even simpler than it seemed to me at the
time.
Jeff Goldsmith
Phil Allison wrote:
| Quote: |
"Jeff Goldsmith"
I've been using Burr Brown MPY634KP analog multiplier ICs, seems they
would output an AC waveform in proportion to power from an amplifier
with about the only external component being the current sensing
resistor. You would still need a precision FW op amp rectifier to drive
(a DC) meter.
** Wrong.
With a resistive load, a four quad multiplier sensing voltage and current
will give precision rectification and an output that is always positive.
With a reactive load, there will be negative as well as positive swings and
these must not be rectified - to do so would mean that pure reactances
would show as dissipating power ( ie an impossibility).
.............. Phil |
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John Stewart
Guest
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| Posted:
Thu Dec 23, 2004 5:43 pm Post subject:
Re: Power output meter amp schematic. |
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Patrick Turner wrote:
| Quote: | Most amps with "power" meters have VU meters
or other voltage meters which only tell you
about the output voltage of an amp.
A real power meter tells you the product of
voltage and current, so that when the load value is halved
and the output voltage is kept constant as is the case
with many amps, the power will double.
Who knows of a very simple circuit that is at least accurate
to about 10%?
There isn't a need for any greater accuracy.
Patrick Turner.
|
For something you could try see ABSE.
One page, about 300K.
Cheers, John Stewart |
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Adam Stouffer
Guest
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| Posted:
Thu Dec 23, 2004 9:14 pm Post subject:
Re: Power output meter amp schematic. |
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Chris Hornbeck wrote:
| Quote: | Jung's _IC OP-Amp Cookbook_ includes various uses as a multiplier,
and also some "precision rectifier" applications. Highly recommended.
You'll still need to make some design decisions about how to sample
current and whether to choose RMS and/or peak rectification. Or
"VU" weighting? Certainly an interesting project.
As a side topic, how important is current phase angle to your design?
A loudspeaker's reflected current may be independently interesting
to an amplifier builder.
|
Anyone thought of going the software route and using a PIC chip for the
calculations. They have built in ADCs and everything.
Adam |
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Ruud Broens
Guest
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| Posted:
Thu Dec 23, 2004 11:08 pm Post subject:
Re: Power output meter amp schematic. |
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"Adam Stouffer" <adam_stouffer@hotmail.com> wrote in message
news:O9Cyd.8245$rL3.6162@trnddc03...
: Chris Hornbeck wrote:
:
: > Jung's _IC OP-Amp Cookbook_ includes various uses as a multiplier,
: > and also some "precision rectifier" applications. Highly
recommended.
: >
: > You'll still need to make some design decisions about how to sample
: > current and whether to choose RMS and/or peak rectification. Or
: > "VU" weighting? Certainly an interesting project.
: >
: > As a side topic, how important is current phase angle to your
design?
: > A loudspeaker's reflected current may be independently interesting
: > to an amplifier builder.
:
: Anyone thought of going the software route and using a PIC chip for
the
: calculations. They have built in ADCs and everything.
:
:
:
: Adam
At the pricing these days, you'd start to think of 'm
as basic building blocks, yes. Interesting option, for sure.
Rudy |
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