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Topic: Class A amplifier

	diyAudio Forums - My 1024W RMS CLASS A+ amplifier.
		If the bandwidth of the class B amplifier was limited relative to the class A stage the rails for the class A stage would not track the output at high frequencies.
		Actually, the class AA concept is technically inferior to the A+ method; The class A+ method drives the speaker at all times entirely from a 100% class A output stage.
		The reason the class AA method was more successful is because the A+ method was still too expensive and impractical to implement in any domestic power amplifier rated at less than several hundred watts rms.
	www.diyaudio.com /forums/showthread.php?threadid=104259&perpage=10&pagenumber=3 (831 words)

	Rebix Class D Amplifier
		Class D Amplifiers are known for their high efficiency and high power levels compared to conventional amplifiers.
		The operation of Class D amplifier is complete different to Class A and AB or B.: In a Class D power is generated by modulating the duty-cycle ratio of a constant frequency square-wave signal from a switching converter.
		Mostly used for power-audio is Class G or H because of the higher efficiency than class A or B at an Ohmic load.
	www.class-d-amplifier.nl /class-d-amplifier.htm (461 words)

	Amplifier classes of operation
		Amplifiers biased so that collector current is cut off during one-half of the input signal are classified class B. The dc operating point for this class of amplifier is set up so that base current is zero with no input signal.
		Class AB amplifiers are biased so that collector current is cut off for a portion of one alternation of the input, which results in less total input power than the class A amplifier.
		The efficiency of class C is the highest of the four classes of amplifier operations.
	www.tpub.com /neets/book7/25e.htm (1140 words)

	Amplifier classes
		Class B suffers from a fundamental problem in that the push-pull amplifier does not, in practice, move smoothly from one half of the waveform to the other half.
		This is not as efficient as the class B design which only draws current when it needs to, or the AB which is a hybrid somewhere between the two...
		For a push-pull class A amplifier, the output figure would double due to the use of two valves, to 22 watts.
	www.duncanamps.com /technical/ampclasses.html (1185 words)

	Stereophile: Halcro Logic MC20 power amplifier
		The result of his recent work, the Halcro Logic series of amplifiers, has at least one thing in common with the company's more expensive Reference series: Both lines are the intended embodiments of Candy's complete and utter loathing of distortion, and his desire to shrink and then kill it, Grover Norquist style.
		Coaxing the driver into moving in and out is what you want the amplifier to do, of course, but preferably with more in the way of finesse—and, ideally, in mimicry of the continuum that is sound.
		Now you've given the output devices an analog blueprint to follow, and their own output is amplified sound—or at least it will be, once you perform the final trick of filtering out that triangular wave's harmonics and a few other nasties.
	www.stereophile.com /solidpoweramps/406halcro (1143 words)

	Class D Amplifier (Site not responding. Last check: 2007-10-29)
		From the perspective of wasted power, the best amplifier operates in pure switching mode-Class D. Normally, the amplifier has efficiency higher than 90 percent, meaning over 90 percent of the power is delivered into the load.
		In fact, a Class D amplifier works as a power D/A converter and can be used to realize high output power, 300W or more.
		The Class D amplifier is based on an analog technique of pulse width modulation (PWM).
	www.freescale.com /webapp/sps/site/application.jsp?nodeId=023Z1Dj0TcDCpQ (485 words)

	Class A
		A class A amplifier is defined as one which is biased to a point where plate current in all the output devices flows for the entire 360 degrees of an input cycle, at the full, unclipped output of the amplifier.
		A class B amplifier is one in which the grid bias in all output tubes is set at cutoff, i.e., no plate current flows in the absence of an input signal.
		A class AB amplifier is one in which the grid bias is set so that plate current flows for more than half, but appreciably less that the full 360 degrees of the the input cycle, again measured at the full, unclipped output of the amplifier.
	www.aikenamps.com /ClassA.htm (3925 words)

	Euphonic Audio \|\| Technology: Class D Digital Amplifiers
		Class D amplifiers are highly efficient and have a great power to size ratio.
		Amplifiers in classes A, B, and AB operate their output transistors in a 'linear' mode while Class D amplifiers operate their outputs in 'switch' mode.
		A Class AB amplifier is a Class B amplifier which has a small amount of "bias" current flowing through the output transistors at all times.
	www.eaamps.com /2005/technology/classd.htm (1025 words)

	Audio FAQ » What is Amplifier Class A? What is Class B? What is Class AB?
		Class A amplifiers often consist of a driven transistor connected from output to positive power supply and a constant current transistor connected from output to negative power supply.
		Class D amplifiers use transistors that are either on or off, and almost never in-between, so they waste the least amount of power.
		Class H refers to using a Class D or switching power supply to drive the rails of a class AB or class A amplifier, so that the amplifier has excellent efficiency yet has the sound of a good class AB amplifier.
	www.dspse.com /audiofaq/2006/04/13/what-is-amplifier-class-a-what-is-class-b-what-is-class-ab (1257 words)

	FEEE - Fundamentals of Electrical Engineering and Electronics: Biasing techniques
		Class A amplifiers are simpler in design, but tend to be limited to low-power signal applications for the simple reason of transistor heat dissipation.
		Class D technology is typically seen where extremely high power levels and relatively low frequencies are encountered, such as in industrial inverters (devices converting DC into AC power to run motors and other large devices) and high-performance audio amplifiers.
		Class B and class C amplifiers have quiescent current values of zero, since they are supposed to be cutoff with no signal applied.
	www.vias.org /feee/bjt_09.html (1889 words)

	Amplifier Advances
		Class D audio systems have come into their own as a practical choice for getting more audio power from a small system — or more audio power from a small battery.
		There are five basic classes of amplifier: A, B, AB, C and D. The Class A amplifier is the traditional, fully linear amplifier with active circuit elements biased into their linear operating regions.
		An AB amplifier is still more efficient than a Class A amplifier (as high as 65 percent efficiency); however, amplifier efficiency ratings are usually derived from application of steady-state sine wave tones having a low crest factor (ratio of peak signal to RMS signal).
	svconline.com /mag/avinstall_amplifier_advances (1722 words)

	Belles MB-01 Monoblock Amplifier
		Class A design requires attention to tolerances, heat needs to be dissipated, power supplies need to be sufficient in order to produce an amplifier that does not compromise performance.
		Imagine that the amplified signal is in the form of a sine wave, where the positive supply rail transistors supplies the upper (or positive) portion of the wave, and the negative supply rail transistors supplies the lower (or negative) portion of the wave.
		Class B or AB design amplifier's transition from the positive to the negative portion of the sine wave is never perfect.
	www.powermodules.com /Monoblock.html (606 words)

	Hardware Analysis - ExtremA, a reference class-A DIY amplifier - Introduction
		One is ‘optimal class B’, a setting where the transconductance of the output devices at idle is the reciprocal of the degeneration resistors.
		Amplifiers that use this approach are commonly referred to as ‘class-AB’ amplifiers.
		When an amplifier is said to ‘be’ class A, this merely means that under normal operating conditions it is not supposed to go into class B. For this design a class-A bias setting was preferred, for a number of reasons.
	www.hardwareanalysis.com /content/article/1842 (562 words)

	RF amplifier basics
		Because class A amplifiers are inherently inefficient in terms of required voltage and current, they are not generally used today in commercial broadcast transmitters.
		Instead, class B and class C amplifiers are common or variations of class B and class C circuits, such as a class AB amplifier.
		In class A, because the plate current is never cut completely off, the efficiency of a class A amplifier is low, about 30 percent, and so is the power output.
	beradio.com /departments/radio_rf_amplifier_basics (1010 words)

	RF amplifier basics
		Because class A amplifiers are inherently inefficient in terms of required voltage and current, they are not generally used today in commercial broadcast transmitters.
		Instead, class B and class C amplifiers are common or variations of class B and class C circuits, such as a class AB amplifier.
		Class AB operation is achieved by allowing a small amount of grid current to flow as required.
	radiomagonline.com /departments/radio_rf_amplifier_basics (1035 words)

	Is the Vox AC-30 really class A?
		In a class AB amplifier each tube amplifies more than half the signal, in order to reduce the distortion that occurs at the zero crossings of the waveform, which is called "crossover distortion".
		If this were a true class A amplifier, the two output phase currents (the green and purple traces) would be centered around the quiescent point (the red trace) and they would just hit the zero current axis at the same time the output starts to clip.
		The only way to make the amplifier true class A is to reduce the plate voltage and readjust the bias voltage/current to properly center the output stage operation in the correct portion of the transfer characteristics of the output tubes.
	www.aikenamps.com /VoxAC30classA_2.html (1528 words)

	Class A (Site not responding. Last check: 2007-10-29)
		I propose that a Linear Class A push-pull amp.
		Page 604 "When operating as a single tube, class a, little distortion exists because the grid signal operates in the most linear portion of the dynamic characteristic." Taking a look at the graph found on page 543, it is clear that Tremaine thinks that Class A does equate to linear operation.
		Class A is when the tube (all the tubes) in an amplifier operate only in the linear part of the curve.
	www.dock.net /tre/classa.html (498 words)

	Product Review
		Basically, Class A means that the current is already flowing in the output devices, and is diverted to the speakers when the demand is there.
		With Class A/B, when the Class A power runs out, it is then in Class B, which means that current has to be switched in when the demand is there.
		Class A/B amps are designed to supply only the amount of current needed at the time, and there is a time lag between demand and supply.
	www.hometheaterhifi.com /volume_11_1/cayin-265ai-integrated-amplifier-3-2004.html (3721 words)

	Simple Class A Amplifier
		The first amplifier circuit of which the author is aware in which a transformerless transistor design was used to give a standard of performance approaching that of the "Williamson" amplifier, was that published in Wireless World in 1961 by Tobey and Dinsdale.
		An additional characteristic of the class B output stage is that the current demand of the output transistors increases with the output signal, and this may reduce the output voltage and worsen the smoothing of the power supply, unless this is well designed.
		Since the amplifier is a straight-forward class A circuit, the distortion decreases linearly with output voltage.
	sound.westhost.com /jll_hood.htm (3508 words)

	ZED AUDIO CORPORATION
		Class A/B is just a class B amplifier with the output stage idling current set to some tens or maybe hundreds of milliamps.
		The class A amplifiers noise can be improved by using an electronic regulator which filters out most of the power supply noise BUT to use these the power supply voltage pre-regulator must be higher.
		Class B amplifiers by definition have zero dissipation in the output stages at idle BUT all amplifiers for audio are designated A-B. The reason we introduce a small amount of idling current in the output transistors in order to get rid of crossover distortion.
	www.zedaudio.com /Technical/Amplifier-Efficiency.htm (1310 words)

	UniValve 15-Watt Class-A Amplifier Head
		The THD UniValve is a Single-Ended Class A amplifier head with a single output tube that can be switched at will among many octal-based power tubes, including 6L6, EL34, 6550, 7027, KT90, KT88, KT77 and KT66, for different tones without re-biasing the amp.
		What is Class A? Class A is a term given to an amp that runs its tubes at full current all the time, unlike most tube amps that alternate between running one set of tubes and the other set, each for one half of the wave.
		The upshot is that Class A operation has its own unique tone characteristics that set it apart from other tube amp classes.
	www.mercenary.com /un15clamhe.html (701 words)

	HeadWize - Project: A 50mW Class-A Headphone Amplifier by Rohit Balkishan
		The signal to be amplified is applied to the non-inverting input (this is determined by where the CE stage gets it's input from) and the -ve feedback network applies a part of the output of the CE stage to the inverting input.
		Another thing to be noted is that due to the VFB topology, any change in temperature or supply voltage appears as a common-mode signal at the amp's inputs and is suppressed (of course the temperature range must reasonably within the operating range of the individual devices).
		The amplifier may be used with headphones having an impedance of 32 Ohms or higher.
	headwize.com /projects/showfile.php?file=balkishan1_prj.htm (2937 words)

	Audio DesignLine \| Design and analysis of a basic class D amplifier
		Class AB amplifiers are very similar to class B amplifiers, but their performance is improved by the addition of two diodes that eliminate the crossover region and allows both transistors to be turned on at the same time.
		Class D amplifiers are not new, but recent advances in the technology of semi-conductor devices have regenerated interest in developing them.
		Class D amplifiers consist mainly of 3 stages: the input switching stage, the power amplification stage, and the output filter stage.
	www.audiodesignline.com /175006800 (4298 words)

	Class D/Class A Composite Audio Amplifier
		The Class D output is a slave to the master Class A output, which implies, firstly, that the Class D stage can not function by itself, and secondly, the possibility of instability if it assists too much.
		A Class D amplifier is characterised by the output transistors being switched at a frequency above that of the required bandwidth, and the resultant output then low pass filtered.
		The Class A amplifier (considered ideal) follows it, and the resulting extra current causes an immediate switch in the Class D driver circuit to deliver current from the positive rail.
	www.livstones.freeserve.co.uk /Dreport.html (2239 words)

	Page Title
		The simplest tube amplifier exploits the average tube linestage’s ability to swing easily ±30 volts; the Zen amplifier, the average solid-state linestage’s ability to work into a low load impedance (4300 ohms).
		In the amplifier shown to the right, the output is fed into the cathode in the phase as the input; which means that the gain, distortion, and the output impedance are reduced, but the drive requirement goes up.
		Unfortunately, I deleted the email long ago, but his contention was that such an amplifier could NOT amplify, as the tube was working as a cathode follower.
	www.tubecad.com /index_files/page0027.htm (602 words)

	The Class-A Amplifier Site - Hiraga 20W Class-A
		At the present time it is difficult to find diagrams of high quality class A amplifiers, moreover, the circuit described offers many benefits, in particular a great simplicity of construction.
		The design of the chassis for a class A amplifier inevitably passes to the installation of the heatsinks.
		On the sides, the power is limited to 30 W class A for a stereo apparatus.
	www.btinternet.com /~tcaas/hiraga2.htm (2206 words)

	.:www.dussun.com_卓越技术真实演绎
		The “Hyper Class A” is a “Green” Class A solution, whose technically successful adaptive-bias circuit achieves the extra large class A power output objective under conditions of low-power consumption and low heat producing.
		This situation is different from the traditional pure class A amplifiers’ inevitable situation of returning to class B when the speaker load impedance goes down, and is much close to the ideal class A amplifier essence.
		The preamplifier stage and power amplifier stage are open to the user, allowing the user to use V6i’s either preamplifier stage or power amplifier stage.
	www.dussun.com /english/v6.html (383 words)

	Hardware Analysis - Investigating the force that drives IT.
		Most commercial amplifiers offer mediocre performance and distortion figures, the here presented design offers nearly immeasurable distortion levels you'll be hard pressed to find with any commercial or DIY amplifier.
		NuForce' Reference amplifiers have been advertised as being the power amplifier of the year and have received awards from various magazines.
		Amplifiers in kit form have been available for years, now Hypex enters the market with kits based on class-D technology that offer outstanding features and sound quality.
	www.hardwareanalysis.com (645 words)

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