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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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What characterizes a powerFET for audio use?
Other than p channel in this case , same for BUZ901P nch
eg BUZ906P 200V, 8A ,datasheet says "POWER MOSFETS FOR AUDIO APPLICATIONS" but also "FEATURES ... (for use in) HIGH SPEED SWITCHING ... " Would a powerFET designed solely for high speed switching use and 125W rating be derated in power handling terms to only 50W say for linear 10 Hz use. Or secondary oscillation liability if paralleled up devices? or some other operational failing in audio use not found with smps say ? |
#2
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What characterizes a powerFET for audio use?
"Nutcase Kook" is a pig ignorant pommy **** Other than p channel in this case, same for BUZ901P nch eg BUZ906P 200V, 8A ,datasheet says "POWER MOSFETS FOR AUDIO APPLICATIONS" but also "FEATURES ... (for use in) HIGH SPEED SWITCHING ... " ** The Semelab app note makes it pretty clear there is a HUGE difference between "switching" and audio ( ie lateral) power mosfets. http://products.semelab-tt.com/pdf/A...nNoteAlfet.pdf Would a powerFET designed solely for high speed switching use and 125W rating be derated in power handling terms to only 50W say for linear 10 Hz use. Or secondary oscillation liability if paralleled up devices? or some other operational failing in audio use not found with smps say ? ** Yawnnnnnnnnnnnnnnn.... More brainless, ****ing TROLLING !!!!!!! FOAD you vile pommy ****head. ..... Phil |
#3
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What characterizes a powerFET for audio use?
On 01/01/2014 02:09 AM, Phil Allison wrote:
"Nutcase Kook" is a pig ignorant pommy **** Other than p channel in this case, same for BUZ901P nch eg BUZ906P 200V, 8A ,datasheet says "POWER MOSFETS FOR AUDIO APPLICATIONS" but also "FEATURES ... (for use in) HIGH SPEED SWITCHING ... " ** The Semelab app note makes it pretty clear there is a HUGE difference between "switching" and audio ( ie lateral) power mosfets. http://products.semelab-tt.com/pdf/A...nNoteAlfet.pdf Would a powerFET designed solely for high speed switching use and 125W rating be derated in power handling terms to only 50W say for linear 10 Hz use. Or secondary oscillation liability if paralleled up devices? or some other operational failing in audio use not found with smps say ? ** Yawnnnnnnnnnnnnnnn.... More brainless, ****ing TROLLING !!!!!!! FOAD you vile pommy ****head. .... Phil "Figure of Merit" in pulsed applications vs "efficiency" in linear applications. RMS Power is measured in heating ability v DC. |
#4
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What characterizes a powerFET for audio use?
"dave" wrote in message
m... "Figure of Merit" in pulsed applications vs "efficiency" in linear applications. Any (???) device can produce more peak power in pulsed mode than continuous, because it spends less time in the region where it dissipates the most power. RMS power is measured in heating ability versus DC. There is no such thing (other than in a mathematical sense) as RMS power. Voltage and current can have RMS (root-mean-square) values. Squaring voltage and dividing by resistance, or squaring current and multiplying by resistance produces the //average// power. |
#5
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What characterizes a powerFET for audio use?
On 01/01/2014 06:28 AM, William Sommerwerck wrote:
"dave" wrote in message m... "Figure of Merit" in pulsed applications vs "efficiency" in linear applications. Any (???) device can produce more peak power in pulsed mode than continuous, because it spends less time in the region where it dissipates the most power. RMS power is measured in heating ability versus DC. There is no such thing (other than in a mathematical sense) as RMS power. Voltage and current can have RMS (root-mean-square) values. Squaring voltage and dividing by resistance, or squaring current and multiplying by resistance produces the //average// power. http://www.learningaboutelectronics....-explained.php The audio duty cycle makes the device heat up more than pulsating full on/full off does. That's the spec and the spec is based on a temperature that will destroy the gate, source, drain, diode, etc. In audio service an FET is always drawing some current, due to the high turn-on threshold. The bias is just slightly above cutoff. Many amps use this quiescent current to set the bias, either measured directly or by measuring current draw at the mains. |
#6
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What characterizes a powerFET for audio use?
On 01/01/2014 06:28 AM, William Sommerwerck wrote:
"dave" wrote in message m... "Figure of Merit" in pulsed applications vs "efficiency" in linear applications. Any (???) device can produce more peak power in pulsed mode than continuous, because it spends less time in the region where it dissipates the most power. RMS power is measured in heating ability versus DC. There is no such thing (other than in a mathematical sense) as RMS power. Voltage and current can have RMS (root-mean-square) values. Squaring voltage and dividing by resistance, or squaring current and multiplying by resistance produces the //average// power. And FOM is used (by me) because the efficiency is above 100%. |
#7
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What characterizes a powerFET for audio use?
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#8
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What characterizes a powerFET for audio use?
On Wed, 1 Jan 2014 06:28:29 -0800, "William Sommerwerck"
wrote: "dave" wrote in message om... "Figure of Merit" in pulsed applications vs "efficiency" in linear applications. Any (???) device can produce more peak power in pulsed mode than continuous, because it spends less time in the region where it dissipates the most power. RMS power is measured in heating ability versus DC. There is no such thing (other than in a mathematical sense) as RMS power. Voltage and current can have RMS (root-mean-square) values. Squaring voltage and dividing by resistance, or squaring current and multiplying by resistance produces the //average// power. RMS power is quite real. A true-RMS voltmeter uses a pair of heating elements and thermocouples to produce a measurement because it's the best way to measure the equivalent voltage that would generate the same amount of heat. There are versions that use other methods but the thermocouple is generally the closest to the real heating value. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#9
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What characterizes a powerFET for audio use?
"Jeff Liebermann" wrote in message
... RMS power is quite real. A true-RMS voltmeter uses a pair of heating elements and thermocouples to produce a measurement because it's the best way to measure the equivalent voltage that would generate the same amount of heat. There are versions that use other methods but the thermocouple is generally the closest to the real heating value. The heating value of a waveform is the average value of its power, NOT the RMS value of its power. Many years ago I sat down and calculated this for a sine wave. I assure you, a sine wave's average power and its RMS power are not at all the same. RMS applies ONLY to voltage and current. |
#10
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What characterizes a powerFET for audio use?
"dave the dickhead " "Nutcase Kook" is a pig ignorant pommy **** Other than p channel in this case, same for BUZ901P nch eg BUZ906P 200V, 8A ,datasheet says "POWER MOSFETS FOR AUDIO APPLICATIONS" but also "FEATURES ... (for use in) HIGH SPEED SWITCHING ... " ** The Semelab app note makes it pretty clear there is a HUGE difference between "switching" and audio ( ie lateral) power mosfets. http://products.semelab-tt.com/pdf/A...nNoteAlfet.pdf Would a powerFET designed solely for high speed switching use and 125W rating be derated in power handling terms to only 50W say for linear 10 Hz use. Or secondary oscillation liability if paralleled up devices? or some other operational failing in audio use not found with smps say ? "Figure of Merit" in pulsed applications vs "efficiency" in linear applications. RMS Power is measured in heating ability v DC. ** Yaaawnnnnnnn - more stupid ****ing bull**** !!!!!!!!!!!!!! One colossal fool asks an idiotic question and even BIGGER fools reply. ..... Phil |
#11
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What characterizes a powerFET for audio use?
"William Sommerwerck" Many years ago I sat down and calculated this for a sine wave. I assure you, a sine wave's average power and its RMS power are not at all the same. RMS applies ONLY to voltage and current. ** But even a complete fool like Somer****** should know that the term "RMS power" is not meant literally. It is NOT the RMS value of the instantaneous power level. In the world of audio, it normally refers to a power measurement done using the RMS value of a sine wave (or other wave if specified ) voltage delivered into a known resistive load. A simple bit of calculus shows that the RMS value of a sine wave to be half the square root of two ( 0.7071) times its peak value. ..... Phil |
#12
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What characterizes a powerFET for audio use?
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#13
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What characterizes a powerFET for audio use?
Many years ago I sat down and calculated this for a sine wave. I assure
you, a sine wave's average power and its RMS power are not at all the same. RMS applies ONLY to voltage and current. ** But even a complete fool... I can't be a complete fool, because on rare occasions you agree with me. ...like Sommerwerck should know that the term "RMS power" is not meant literally. He knows nothing of the sort. Just because people say "pressure" when they mean "force", doesn't mean pressure and force are the same thing. I see ads proclaiming that an amplifier delivers "125 watts RMS power". No, it doesn't. There is a perfectly good term for that... "continuous average power", or perhaps "continuous average sinewave power". This term has a specific meaning, and it IS NOT the same as RMS power. |
#14
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What characterizes a powerFET for audio use?
On Wed, 1 Jan 2014 14:16:52 -0800, "William Sommerwerck"
wrote: "Jeff Liebermann" wrote in message .. . RMS power is quite real. A true-RMS voltmeter uses a pair of heating elements and thermocouples to produce a measurement because it's the best way to measure the equivalent voltage that would generate the same amount of heat. There are versions that use other methods but the thermocouple is generally the closest to the real heating value. The heating value of a waveform is the average value of its power, NOT the RMS value of its power. Many years ago I sat down and calculated this for a sine wave. I assure you, a sine wave's average power and its RMS power are not at all the same. RMS applies ONLY to voltage and current. Ok, I yield to a higher authority. Heating power is average power: http://www.eznec.com/Amateur/RMS_Power.pdf However that doesn't stop nearly everyone from specifying RMS power. So, why do people buy true-RMS voltmeters? If they don't measure anything useful, why bother? [Personal drivel: I haven't forgotten about the HP4 parts. I've been busy. Today was the lost battle of the clutch master cylinder. Tomorrow will be the forgotten backdated billing for last year.] -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#15
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What characterizes a powerFET for audio use?
"William Sommer****** = IDIOT" Many years ago I sat down and calculated this for a sine wave. I assure you, a sine wave's average power and its RMS power are not at all the same. RMS applies ONLY to voltage and current. ** But even a complete fool... I can't be a complete fool, ** Yes you are and about to prove it yet again. ...like Sommerwerck should know that the term "RMS power" is not meant literally. He knows nothing of the sort. ** Proof given I see ads proclaiming that an amplifier delivers "125 watts RMS power". No, it doesn't. ** " ... the term "RMS power" is not meant literally." Cos it is not what the writer meant PLUS there is simply no such quantity if you do. ****WIT !!!!!!!!!!!! ..... Phil |
#16
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What characterizes a powerFET for audio use?
"Jeff Liebermann" Ok, I yield to a higher authority. Heating power is average power: http://www.eznec.com/Amateur/RMS_Power.pdf However that doesn't stop nearly everyone from specifying RMS power. ** There is no such quantity as " RMS power " if you are so stupid as to interpret the term literally. So, why do people buy true-RMS voltmeters? ** To get " true RMS " volts of course. If they don't measure anything useful, ** The RMS value of a voltage or current could hardly be more useful. My god, you are SOOOOOO illiterate and SOOOOO retarded. .... Phil |
#17
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What characterizes a powerFET for audio use?
On Thu, 2 Jan 2014 12:22:44 +1100, "Phil Allison"
wrote: "Jeff Liebermann" Ok, I yield to a higher authority. Heating power is average power: http://www.eznec.com/Amateur/RMS_Power.pdf However that doesn't stop nearly everyone from specifying RMS power. ** There is no such quantity as " RMS power " if you are so stupid as to interpret the term literally. Which term should be interpreted non-literally? "RMS" or "power"? Assuming a stable resistance load (i.e. no light bulbs), the RMS power is simply the square of the RMS voltage divided by the resistance. Seem literal enough for me. So, why do people buy true-RMS voltmeters? ** To get " true RMS " volts of course. Very good. But since there doesn't seem to be any correlation with heating power (despite using a thermocouple to do the measuring) and RMS volts or watts, what does the meter indication on a true RMS voltmeter actually mean? Or is it just a mathematical abstraction? If they don't measure anything useful, ** The RMS value of a voltage or current could hardly be more useful. Useful for what? Obviously not heating value. Anything I missed? My god, you are SOOOOOO illiterate and SOOOOO retarded. Very perceptive and partly true. I don't take you literally but the timing on my car is not retarded. http://www.aqdi.com/rms.htm "You have read that there is no such thing as "RMS power." Technically, you are right. However, over the years the term, regarding audio gear, has come to be applied to the measurement technique outlined above, so we use that language here, rather than terminology with which the customer is unfamiliar. Yes, the computation is mathematically an integral of the instantaneous power." https://www.google.com/#q="RMS+power" 681,000 hits on "RMS power". -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#18
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What characterizes a powerFET for audio use?
"Jeff Liebermann"
Ok, I yield to a higher authority. Heating power is average power: http://www.eznec.com/Amateur/RMS_Power.pdf However that doesn't stop nearly everyone from specifying RMS power. ** There is no such quantity as " RMS power " if you are so stupid as to interpret the term literally. Which term should be interpreted non-literally? ** The term " RMS power " of course - you ****ing BLIND nut case ASSHOLE !!!!!!!!!!!! ---------------------------------------------------------- So, why do people buy true-RMS voltmeters? ** To get " true RMS " volts of course. Very good. But since there doesn't seem to be any correlation with heating power (despite using a thermocouple to do the measuring) and RMS volts or watts, ** Quite wrong - there is a very close connection. what does the meter indication on a true RMS voltmeter actually mean? Or is it just a mathematical abstraction? ** RMS voltage or current value = the DC equivalent value. So the DC power formulas: " I squared R " and " V squared / R " still apply in power calculations using AC voltages & currents. --------------------------------------------------------------------------- ** The RMS value of a voltage or current could hardly be more useful. My god, you are SOOOOOO illiterate and SOOOOO retarded. Very perceptive and partly true. ** It's completely true. You are the stupidest, most retarded, constantly lying ****wit on the NG. Get cancer and ****ing DIE ! ..... Phil |
#19
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What characterizes a powerFET for audio use?
"Jeff Liebermann" wrote in message
... OK, I yield to a higher authority. Heating power is average power: http://www.eznec.com/Amateur/RMS_Power.pdf However that doesn't stop nearly everyone from specifying RMS power. Unfortunately, no. So, why do people buy true-RMS voltmeters? If they don't measure anything useful, why bother? A fair question. Apparently, there was a time when AC power had a significant percentage of harmonics (perhaps it still does), and engineers wanted to know its "true" heating effect. |
#20
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What characterizes a powerFET for audio use?
"Jeff Liebermann" wrote in message
... http://www.eznec.com/Amateur/RMS_Power.pdf On Pg 6 it says: "The RMS value of power is not the equivalent heating power and, in fact, it doesn't represent any useful physical quantity." and: "The RMS power is different than the average power, and therefore isnt the equivalent heating power. In fact, the RMS value of the power doesnt represent anything useful." It would seem that the author finds average power different from, more useful than, and closer to heating power. Perhaps we should change the name from "true-RMS voltmeter" to "true heating average voltmeter"? Jeff, you're misreading this. The author is saying //exactly// what I said. (It's unfortunate he doesn't use a sine wave for his example, but the math would then require integral calculus.) Average power /is/ the heating power. (The rationale is that a resistor's temperature is determined by the average power applied to it.) When we know the RMS value of any repetitive waveform, we can compute its heating power by squaring that voltage (current) and dividing (multiplying) by the resistor's value. Voltmeters (of all sorts) are usually calibrated to show the RMS value //of a sine wave//. If the waveform differs, the value shown is wrong. One of the advantages of a true-RMS meter is that all readings are "equivalent" in an easily-comprehended way, regardless of the waveform -- even if that "equivalency" has little practical usefulness. (If you want to know the details of a waveform, you use a 'scope.) I remember a Popular Electronics quiz with questions about how a voltmeter (at that time, a moving-coil device) would read, depending on the waveform supplied. A key point was that the deflection was proportional to the average current flowing through the coil, but the meter was usually calibrated for the RMS value of a sinewave. |
#21
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What characterizes a powerFET for audio use?
On 01/01/2014 05:22 PM, Phil Allison wrote:
"Jeff Liebermann" Ok, I yield to a higher authority. Heating power is average power: http://www.eznec.com/Amateur/RMS_Power.pdf However that doesn't stop nearly everyone from specifying RMS power. ** There is no such quantity as " RMS power " if you are so stupid as to interpret the term literally. So, why do people buy true-RMS voltmeters? ** To get " true RMS " volts of course. If they don't measure anything useful, ** The RMS value of a voltage or current could hardly be more useful. My god, you are SOOOOOO illiterate and SOOOOO retarded. The question was why is audio power spec is half that of DC on/off capability. It is because the device stays on all the time and because the audio waveform causes more heating. Worry about the labels and fight all you want. |
#22
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What characterizes a powerFET for audio use?
On 01/02/2014 04:05 AM, William Sommerwerck wrote:
"Jeff Liebermann" wrote in message ... http://www.eznec.com/Amateur/RMS_Power.pdf On Pg 6 it says: "The RMS value of power is not the equivalent heating power and, in fact, it doesn't represent any useful physical quantity." and: "The RMS power is different than the average power, and therefore isnt the equivalent heating power. In fact, the RMS value of the power doesnt represent anything useful." I remember a Popular Electronics quiz with questions about how a voltmeter (at that time, a moving-coil device) would read, depending on the waveform supplied. A key point was that the deflection was proportional to the average current flowing through the coil, but the meter was usually calibrated for the RMS value of a sinewave. Why do you keep quoting notes from Llewelen? He wrote a modeling program for wire antennas. We are talking about FETs. I think AVG = RMS only if waveform is pure sinewave. Otherwise you must use calorimeter or thermocouple to find true RMS. |
#23
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What characterizes a powerFET for audio use?
On Wed, 01 Jan 2014 18:49:17 -0800, Jeff Liebermann wrote:
http://www.eznec.com/Amateur/RMS_Power.pdf On Pg 6 it says: "The RMS value of power is not the equivalent heating power and, in fact, it doesn't represent any useful physical quantity." and: "The RMS power is different than the average power, and therefore isnÂt the equivalent heating power. In fact, the RMS value of the power doesnÂt represent anything useful." It would seem that the author finds average power different from, more useful than, and closer to heating power. Perhaps we should change the name from "true-RMS voltmeter" to "true heating average voltmeter"? "So it is written, so it shall be." (Ramses in the CB DeMille version of the 10 Commandments). (snipped) ISTR it used to be a DC equivalent thing, ie, you need 6Vrms ac to operate a 6VDC light bulb at spec. I think Leak confused the issue when he branded those wonderful audio amplifiers "RMS", thus putting the term in the realm of marketting. |
#24
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What characterizes a powerFET for audio use?
"dave" wrote in message
m... I remember a Popular Electronics quiz with questions about how a voltmeter (at that time, a moving-coil device) would read, depending on the waveform supplied. A key point was that the deflection was proportional to the average current flowing through the coil, but the meter was usually calibrated for the RMS value of a sinewave. Why do you keep quoting notes from Llewelen? He wrote a modeling program for wire antennas. We are talking about FETs. Who is Llewelen? I think AVG = RMS only if waveform is pure sinewave. Otherwise, you must use calorimeter or thermocouple to find true RMS. RMS and average are the same only for square waves. True RMS can be computed by analog circuits, one of which made its way in dbx devices. |
#25
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What characterizes a powerFET for audio use?
"dave" wrote in message
m... The question was why is audio power spec is half that of DC on/off capability. It is because the device stays on all the time and because the audio waveform causes more heating. Worry about the labels and fight all you want. Exactly. |
#26
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What characterizes a powerFET for audio use?
"William Sommer****** is a bull****ting ass." So, why do people buy true-RMS voltmeters? If they don't measure anything useful, why bother? A fair question. ** Wrong - it's a ****wit question. Apparently, there was a time when AC power had a significant percentage of harmonics (perhaps it still does), and engineers wanted to know its "true" heating effect. ** Nonsense. Any "moving iron" amp meter inherently reads "true RMS" values and they are as old as the hills. True RMS meters are mostly used to measure irregular signals like noise and distorted current waveforms that exist with AC to DC supply conversion. There is no way to compute these values ( from the peak or average rectified value) as there is with sine or other regular waveforms. ..... Phil |
#27
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What characterizes a powerFET for audio use?
On Thu, 2 Jan 2014 11:21:15 -0800, "William Sommerwerck"
wrote: Why do you keep quoting notes from Llewelen? He wrote a modeling program for wire antennas. We are talking about FETs. Who is Llewelen? Author of Eznec antenna modeling softwa http://www.eznec.com -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#28
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What characterizes a powerFET for audio use?
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#29
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What characterizes a powerFET for audio use?
"Maynard A. Philbrook Jr." And of course, no matter how you slice it, square waves at 50% duty give you the same all around. AVG and RMS = peak.. cause there is no slope in time ... ** Too complicated. Q. When you ( full wave) rectify a square wave what do you get? A. DC. With DC, the average, peak and RMS value are the same. Is any proof really needed ? ...... Phil |
#30
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What characterizes a powerFET for audio use?
"Maynard A. Philbrook Jr." And of course, no matter how you slice it, square waves at 50% duty give you the same all around. AVG and RMS = peak.. cause there is no slope in time ... ** Too complicated. Q. When you ( full wave) rectify a square wave what do you get? A. DC. With DC, the average, peak and RMS value are the same. Is any proof really needed ? And where was I disputing that? ** Yawnnnnnnnnn - wot a stupid straw man fallacy. Read what I dam well wrote - ****wit. .... Phil |
#31
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What characterizes a powerFET for audio use?
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#32
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Real RMS question
"Shaun" I used to work at an Industrial and Instrumentation repair and Calibration shop that was licensed by Beckman to repair and calibrate there DMMs. In the good ones, the RMS converted used a thermal method to determine RMS Voltage and Current. That was 18 years ago and I don't remember any details except that they used thermal measurement on a heated element. I have compared the reading on the Beckman - Then Wavetek - now I don't know if anyone is still making them, to a Fluke RMS DMM at 60 Hz and DC and the readings matched. ** No fooling........... I have always heard that if you really want to know the real value, you have to buy an RMS meter. ** That sort of nonsense *would* be said by someone who either owned an RMS meter or was selling them. Thermal RMS meters are virtually obsolete these days and have been replaced by cheap analogue RMS to DC computation ICs in many hand held DMMs OR by digital sampling computation in most DSOs. The hand held kind have a limited measurement bandwidth compared to the latter. Depends what your needs are. As Clint Eastwood might have said - " Man's gotta know the limitations of his test equipment ". ..... Phil |
#33
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What characterizes a powerFET for audio use?
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#34
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Real RMS question
On 01/02/2014 05:04 PM, Phil Allison wrote:
"Shaun" I used to work at an Industrial and Instrumentation repair and Calibration shop that was licensed by Beckman to repair and calibrate there DMMs. In the good ones, the RMS converted used a thermal method to determine RMS Voltage and Current. That was 18 years ago and I don't remember any details except that they used thermal measurement on a heated element. I have compared the reading on the Beckman - Then Wavetek - now I don't know if anyone is still making them, to a Fluke RMS DMM at 60 Hz and DC and the readings matched. ** No fooling........... I have always heard that if you really want to know the real value, you have to buy an RMS meter. ** That sort of nonsense *would* be said by someone who either owned an RMS meter or was selling them. Thermal RMS meters are virtually obsolete these days and have been replaced by cheap analogue RMS to DC computation ICs in many hand held DMMs OR by digital sampling computation in most DSOs. The hand held kind have a limited measurement bandwidth compared to the latter. Depends what your needs are. As Clint Eastwood might have said - " Man's gotta know the limitations of his test equipment ". .... Phil In television you calibrate the output power metering by operating into a full power liquid cooled dummy load and measuring the temperature of the coolant. Using computational methods on amplifier input parameters is not the preferred way to determine power (an efficiency factor must be assumed) and you must ask the FCC for special permission to use the "direct method". Dave the Re-Re |
#35
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What characterizes a powerFET for audio use?
William Sommerwerck wrote: "Jeff Liebermann" wrote in message ... OK, I yield to a higher authority. Heating power is average power: http://www.eznec.com/Amateur/RMS_Power.pdf However that doesn't stop nearly everyone from specifying RMS power. Unfortunately, no. So, why do people buy true-RMS voltmeters? If they don't measure anything useful, why bother? A fair question. Apparently, there was a time when AC power had a significant percentage of harmonics (perhaps it still does), and engineers wanted to know its "true" heating effect. This is my favorite True RMS meter. Section three is a description of how it works. The AC power line is anything but a clean sine wave. Switching power supplies and older electronics with a single diode in the power supply distort it, even more. The single diode causes a DC component on your power, which confuses a simple analog meter. Three phase is even worse, with all the harmonics on the neutral. There were a lot of fires in office buildings and factories after the PC became widespread. It used to be to code to use a smaller neutral on three phase, than the tree phase lines. The harmonics caused the neutral to overheat and in some cases, started fires. I like this Fluke for many reasons, including the ability to read to ..01 dB variations in a signal. I used one to test the -3dB points on video filters, up to 20 MHz. For anything higher I used a Boonton 9200 RF voltmeter. Before someone smarts off, Video isn't just television. We produced equipment with selectable bandwidth from DC10 KHz to DC40 MHz in 16 customer specified bandwidths. SDI digital video was 270 MHz, and HD is even higher. http://www.ko4bb.com/Manuals/Fluke/Fluke_8920A_8921A_True_RMS_Voltmeter_Operation_and %20_Service_Manual_Oct78.pdf -- Anyone wanting to run for any political office in the US should have to have a DD214, and a honorable discharge. |
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Real RMS question
"dave the autistic fool " As Clint Eastwood might have said - " Man's gotta know the limitations of his test equipment ". In television you calibrate the output power metering by operating into a full power liquid cooled dummy load and measuring the temperature of the coolant. ** That would be for the actual transmitter on VHF or UHF - right ? Same idea as using a glass of water and a thermometer test the power RF power of a microwave oven. Got SFA to do with the topic. ..... Phil |
#37
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What characterizes a powerFET for audio use?
"dave the pig ignorant autistic IDIOT " The question was why is audio power spec is half that of DC on/off capability. ** No it was not. It is because the device stays on all the time and because the audio waveform causes more heating. ** A maker's max dissipation spec for a semiconductor is not related to the application. It is only related to the device itself. Normally, the figure given is for *ideal* operating conditions - like when mounted on an infinite heatsink held at 20C. ..... Phil |
#38
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What characterizes a powerFET for audio use?
On 01/03/2014 07:33 PM, Phil Allison wrote:
"dave the pig ignorant autistic IDIOT" The question was why is audio power spec is half that of DC on/off capability. ** No it was not. It is because the device stays on all the time and because the audio waveform causes more heating. ** A maker's max dissipation spec for a semiconductor is not related to the application. It is only related to the device itself. Normally, the figure given is for *ideal* operating conditions - like when mounted on an infinite heatsink held at 20C. .... Phil Odd. I thought Maximum values were on the data sheet. Anyway, a MOSFET used as a switch makes less heat so it can have a higher current rating than one used class AB. |
#39
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What characterizes a powerFET for audio use?
dave wrote: On 01/03/2014 07:33 PM, Phil Allison wrote: "dave the pig ignorant autistic IDIOT" The question was why is audio power spec is half that of DC on/off capability. ** No it was not. It is because the device stays on all the time and because the audio waveform causes more heating. ** A maker's max dissipation spec for a semiconductor is not related to the application. It is only related to the device itself. Normally, the figure given is for *ideal* operating conditions - like when mounted on an infinite heatsink held at 20C. .... Phil Odd. I thought Maximum values were on the data sheet. Anyway, a MOSFET used as a switch makes less heat so it can have a higher current rating than one used class AB. 'Safe Operating Area' is more important than individual maximums. -- Anyone wanting to run for any political office in the US should have to have a DD214, and a honorable discharge. |
#40
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Real RMS question
Phil Allison skrev:
Same idea as using a glass of water and a thermometer test the power RF power of a microwave oven. Just don't leave the thermometer in the microwave oven with the power on. Measure the temperature of the cold water, then measure the time for it to boil. Preferably in a microwave-safe plastic container. I measured the power of my previous oven to 230W... Leif -- Husk kørelys bagpå, hvis din bilfabrikant har taget den idiotiske beslutning at undlade det. |
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