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Topic: Load impedance

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Impedance

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	Cable impedance
		For ordinary coaxial cable used at reasonable frequency, the characteristic impedance depends on the dimensions of the inner and outer conductors, and on the characteristics of the dielectric material between the inner and outer conductors.
		In a nut shell the characteristic impedance of a coax cable is the square root of (the per unit length inductance divide by the per unit length capacitance).
		If two cables with different impedances are connected togerther or a cable is connected to a source which has different impedance then some kind of impdance matching is needed to avoid the signal reflections in the place where the cables are connected together.
	www.epanorama.net /documents/wiring/cable_impedance.html (4288 words)

	AKG Acoustics - Tips & Tricks - Headphones impedance (Site not responding. Last check: 2007-11-01)
		The two important electrical specifications for a pair of headphones are the impedance of the phone transducer itself and its on-the-ear sensitivity.
		To produce 200 mW in a 600-ohm load a signal of 11 V is needed.
		This shows that the advantage of high impedance headphones is that they can be used with almost any amplifier output without any risk of being damaged by overload, and you can connect up to 10 or more pairs to the same output.
	www.akg.com /products/product_tipps/powerslave,mynodeid,189,nodeid,1,id,35,_language,EN,pid,,_view,.html (333 words)

	Input impedance (Site not responding. Last check: 2007-11-01)
		The input impedance or sometimes loading impedance of a circuit or electronic device is the impedance actually experienced by a signal which is connected to its input.
		Generally in audio and hi-fi, the input impedance of components is several times higher than the output impedance connected to them.
		The maximum power at maximum efficiency will be transferred when the impedances are complex conjugate matched throughout the power chain, from the transmitter output, through the transmission line (which may be a balanced pair, a coaxial cable, or a waveguide), to the antenna system, which consists of an impedance matching device and the radiating element(s).
	www.punweb.com /article/Load_impedance (355 words)

	Speaker Impedance vs Power Output
		As we said earlier, the impedance of a speaker is its opposition to the flow of A.C. current.
		The lower the impedance, the higher the current flow (all else being equal).
		The impedances in the diagram are only to show how power output is related to load impedance.
	www.bcae1.com /spkrimp.htm (901 words)

	Impedance transformation - Chapter 13: TRANSMISSION LINES - Volume II - AC (Site not responding. Last check: 2007-11-01)
		First, calculating the line impedance: taking the 75 Ω we desire the source to "see" at the source-end of the transmission line, and multiplying by the 300 Ω load resistance, we obtain a figure of 22,500.
		This technique of impedance matching is often used to match the differing impedance values of transmission line and antenna in radio transmitter systems, because the transmitter's frequency is generally well-known and unchanging.
		When operated at a frequency corresponding to a standing wave of 1/4-wavelength along the transmission line, the line's characteristic impedance necessary for impedance transformation must be equal to the square root of the product of the source's impedance and the load's impedance.
	www.allaboutcircuits.com /vol_2/chpt_13/7.html (1205 words)

	[No title] (Site not responding. Last check: 2007-11-01)
		The power delivered to the load was determined by measuring the peak-to-peak value of the RF waveform across the resistive portion of the load with an oscilloscope, dividing this value by 2.82 to convert from peak-to-peak to RMS, squaring the result, then dividing this number by the load resistance (Equation 1).
		A calorimetric load is used by professional transmitter manufacturers, designers and broadcasters when they want a really accurate measurement of RF power output, and this requires accurate coolant flow and temperature measurement, not to mention knowledge of the specific gravity of the coolant, or humidity if the coolant is air, etc.
		Admittedly Figure 3 is not a terribly scientific plot of all the possible load impedances, but it does show a general trend to lead one to the conclusion that 10 watts output is only possible when the load is close to a perfect match and the power supply voltage is near 13.8 volts.
	www.qsl.net /km5kg/loads.htm (3308 words)

	Variable Amplifier Impedance
		With the 8 ohm load, both amps have a gain of 11, but the series feedback in (B) actually means that the gain to the load is 10.
		To emulate a valve amp for example, an output impedance of about 4 to 6 ohms is needed, assuming an 8 ohm load (this is the assumed nominal load impedance for all examples cited).
		The no-load voltage is 18.8V with an input of 1V, and this drops to 12.8 at 8 ohms, and 9.7V with a 4 ohm load.
	sound.westhost.com /project56.htm (2608 words)

	Load Impedance (Site not responding. Last check: 2007-11-01)
		Load Impedance is one of those "grey" areas in amp design which can be very confusing.
		The slope of the load line is simply the reciprocal of the load impedance: if the load is 4,000 ohms, then the slope is 1/4,000.
		As the load impedance gets lower, peak current draw increases (see the upper left end of the load line by Eg=0), which can be a problem if it exceeds the tube's dissipation rating for too much of the operating cycle.
	www.obsoleteelectronics.com /Transformers/Load_Impedance/load_impedance.htm (814 words)

	Loudspeaker Impedance
		Impedance is AC resistance and differs from DC resistance in that impedance changes with frequency.
		What is important to note is that the actual load at a particular frequency represented to the amplifier is dependent on the impedance at that frequency.
		In Figure-D you see an impedance curve of the Mid/High section of a touring loudspeaker whose low frequency crossover point is at 250 Hz, active, and the high frequency is passive.
	www.churchsoundcheck.com /imp1.html (971 words)

	Measuring Impedance
		The meter has a high output impedance and acts like a constant current source (the current through the load is independent of the load impedance).
		The small voltage drop across the load is proportional to the load impedance.
		If you need to know the minimum impedance of a loudspeaker (this is usually the parameter of interest when loading amplifiers and selecting cable) then use your ohm meter across the loudspeakers terminals.
	www.proacousticsusa.com /Documents/82240.htm (1328 words)

	RF Amplifier Impedance Matching - January 28th Fact-of-the-Day
		It often has been written and most people seem to believe that the output impedance of an RF amplifier should match the load impedance; so that for example, if an amplifier is driving a 50 ohm load, the amplifier output impedance should be 50 ohms.
		The source and load impedances are in series, so 500 watts would be dissipated in waste heat within the amplifier and 500 watts would be delivered to the load.
		To have high efficiency the source impedance must be small compared to the load impedance.
	www.smeter.net /daily-facts/1/fact28.php (168 words)

	How to Measure the Effective Average Impedance of Magnetic Headphones, a Piezo-Electric Ceramic Earpiece or a ...
		This is because the RF load resistance presented to the tank is raised when the diode saturation current value is reduced.
		For magnetic headphones, this resistance is higher than the average impedance of the earphones, for piezo-electric ceramic earpieces, the resistance is lower.
		The effective impedance of the two earpiece elements can be checked by determining the switch position for maximum volume with one of these connections: (1) The sleeve, to the ring and tip in parallel or (2) the ring to the tip.
	www.bentongue.com /2meaphi/2meaphi.html (1441 words)

	LOAD MODULATION IN STAGE BYPASS SCHEME
		The technique is to control the load impedance to obtain wider dynamic range over power level with simple impedance tuning (load modulation) in stage bypassing scheme.
		Load adjustment method to achieve constant efficiency across power level is shown in Figure 2.
		The bias voltage is varied to adjust the PA optimum load impedance.
	www.priorartdatabase.com /IPCOM/000131956 (517 words)

	Output Impedance
		We would then measure the current flowing through the load and the output voltage of the supply while it is loaded.
		Connect the 4 ohm load to the amplifier's output terminals and measure the output voltage again.
		The output impedance of the amplifier is 0.0104 ohms.
	www.bcae1.com /outptimp.htm (1209 words)

	[No title] (Site not responding. Last check: 2007-11-01)
		The output impedance shall be less than 15% of nominal load impedance.
		The load impedance shall be 4 (18 v), 8 (25 v), 16 (36 v), 62 (70 v) ohms ungrounded.
		The input impedance shall be 70,000 ohm volume control, and the source impedance 125/150 and 500/600 ohms with 15095 or 4665 plug-in transformer.
	www.triodeel.com /1569spec.txt (343 words)

	PXI 5412 Load Impedance - Signal Generators - NI Discussion Forums
		The default setting for load impedance for the NI 5412, and all NI signal generators is 50 ohms.
		When the actual load is 50 ohms and niFgen is configured for 50 ohms load impedance, you will get 5 V out in your case.
		You're confusing the Load Impedance and Output Impedance.
	forums.ni.com /ni/board/message?board.id=310&message.id=585 (546 words)

	HTGuide Forum - High impedance monitors
		Panasonic specifies that the load be in the 6-8 ohm range.
		Load impedance sensitivity can be a problem, because many of the better tweeters are in the 4-6 ohm range, partly to get the sensitivity up.
		MTMs wtih higher impedance require special midwoofers made with higher VC impedance- even then, they're usually not over 10 or 12 ohms each, so finished speaker impedance is around 5-6 ohms nominal- as are most so called 8 ohm speakers.
	www.htguide.com /forum/showthread.php4?s=54ce3a99a9918f51352a8c7806cb5186&t=18104 (267 words)

	Impedance, and how it affects audio equipment
		To be meaningful, the impedance should be quoted at at specific frequency, or preferably at a range of frequencies.
		The reactive load imposed on the amplifier by a speaker load causes far higher dissipation in the output transistors than the simple resistive load generally assumed during testing.
		Generally, it is desirable that the output impedance is low, and the destination impedance high, and this is the case with the majority of modern equipment.
	sound.westhost.com /impedanc.htm (5822 words)

	Measuring Input and Output Impedance (Site not responding. Last check: 2007-11-01)
		From the AC impedance triangle, the input or output impedance of a two terminal network can be determined by measuring the small signal AC currents and voltages.
		For the input, the voltage is measured across the input terminals and the current measured by inserting the meter in series with the signal generator.
		A fixed load resistor is used and the output voltage is measured first with full load, then without the load.
	www.mitedu.freeserve.co.uk /Theory/inzoz.htm (508 words)

	LOAD IMPEDANCE
		The total impedance of the external circuit between the output electrodes or beyond the output reference plane.
		impedância de carga (charging impedance), imitância de carga (load immittance).
		inmitancia de carga (load immittance), impedancia de carga (charging impedance).
	www.websters-online-dictionary.org /definition/english/lo/load+impedance.html (218 words)

	Internet Sound Institute - Ohm - a Definition
		Although impedance and resistance are not interchangeable terms, they are similar in concept.
		If, for example, the amplifier in Figure 4 had a minimum load impedance of 2-ohms (check the back of the amplifier or the manual for this information), we could have connected two more 8-ohm loudspeakers in parallel for a total of four loudspeakers.
		Keep in mind that every time you double the number of loudspeakers (with the same impedance) connected in parallel, the total load impedance is cut in half.
	www.soundinstitute.com /article_detail.cfm/ID/99 (804 words)

	Matching the Impedance of Space - October 24th Fact-of-the-Day (Site not responding. Last check: 2007-11-01)
		Maximum power transfer from a line to a load occurs when the impedance of the load matches the characteristic impedance of the line.
		Where the load is an antenna, the impedance of the antenna should therefore ideally match the impedance of the line.
		Therefore, an efficient antenna is a device that converts RF power into electromagnetic radiation while transforming the impedance of a line to the 377-ohm impedance of space.
	www.smeter.net /daily-facts/10/fact24.php (165 words)

	Load Impedance for Transistor Circuit
		The drawing shows a portion of a monolithic circuit in which a transistor, operated in the reverse mode, is used as a load impedance of another transistor.
		Emitter terminal 9 of T2 is connected to a source of positive potential and the reverse avalanche breakdown characteristic of T2 is used as the load impedance of T1.
		With this arrangement the monolithic circuit is much smaller than the case where a resistor or a series of diodes is used as the load impedance of T1.
	www.priorartdatabase.com /IPCOM/000071581 (322 words)

	The equivalent circuit of open cable (Site not responding. Last check: 2007-11-01)
		When a cable is teminated with a load impedance Zt, it is well known that the refrection coefficient at the load end is expressed as follows.
		On the other hand, if the load impedance becomes to zero, all the transmitted energy is reflected at a reverse phase (r == -1).
		Now, is it right to think that a load of infinite impedance is connected to the end of cable, in case of a so-called "open cable" where nothing is connected to the end of the cable ?
	www.mogami-wire.co.jp /e/puzzle/pzl-12.html (194 words)

	ampage > Music Electronics > Guitar Amps : 1 : Should speaker impedance be halved when using 6L6s in 5E
		There is no absolute output impedance for vacuum tubes at least for what we are after as guitar players.
		The recommended plate impedance that a manufacturer suggests is a "best case" trade-off between output power and distortion.
		Varying the load impedance that the tube sees within a reasonable amount will affect distortion content but may not hurt output power too much.
	www.firebottle.com /fireforum/ff.cgi?cmd=vt&fid=ga&tid=1096599453hVLOE2t (491 words)

	About impedance Matching and power (Site not responding. Last check: 2007-11-01)
		We are taught that the maximum transfer of power occurs when the impedance of the source equals the load.
		Folks are always trying to match their microphones impedance to their pre amps input or audio drive to modulator etc. what they should be trying to achieve is a match of the desirable impedance.
		Matching the impedance of a car battery to a load would probably cause a fire and explode the battery, but maximum power would be transferred to the load, at least till something burnt or exploded.
	www.qsl.net /wa5bxo/power.html (274 words)

	Grounded-Cathode Transformer-Coupled Amplifier
		The output transformer works as an electrical lever that magnifies the load impedance presented to the output tubes to better match the output tubes high output impedance and magnifies the output tubes current swings, while it reduces the output tubes' voltage swings and output impedance to better match the loudspeaker's low impedance.
		This is actually their reflected impedance, as in itself a transformer has no intrinsic impedance, only a winding ratio between primary and secondary windings (just as a magnifying glass has a magnification rating, but no intrinsic magnified image).
		(Actually, the load that a single output tube sees is not constant in all but the strictest class-A push-pull amplifier, as the mutual coupling between primary halves works to present a curved load-line as tubes slowly switch on and off.
	www.glass-ware.com /programs/TCJ_Programs_files/page0017.htm (259 words)

	The Tube CAD Journal: Mixed Topologies Amplifiers
		However, the constant current source aspect is still false, as even in the case where no load impedance is attached, the bottom tube is still not working into a constant current source, as the impedance represented by top tube falls quite short of infinity.
		Certainly, a pentode just might offer a higher impedance, although the screen bias circuit (the resistor and capacitor), because they are in parallel with the pentode, shunt the pentode, reducing its effectiveness as a constant current source.
		It is the load itself that creates a second possible current path, as with a load, the current can flow from the bottom tube into the load or from the load into the top tube.
	www.tubecad.com /articles_2002/SRPP_Deconstructed/page4.html (269 words)

	Simple Op-Amp-based Headphone Amplifiers
		An amplifier’ input impedance can be an important piece of information, as many amplifiers are often cascaded and one amplifier’s input impedance becomes another amplifier’s load impedance.
		An amplifier’s output impedance and the load impedance define the amplifier’s damping factor, as the damping factor is but the ratio of load impedance divided by the output impedance, thus the ridiculously high values of 400 or even 1000.
		Measuring the output impedance evolves the strategy as the measuring of the input impedance.
	www.beigebag.com /case_amp3.htm (472 words)

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