posted
I know that class X is basically a class D but I have not found a real explanation of the differences. From the descriptions I have seen it sounds like it is maybe a class GD. It has a switching output like class D but also a variable power supply like class G or H. Cadence actually makes an amp which they say is class GD. Is this what class X really is? Or is it something else.
Posts: 327 | From: Pleasanton & Sacramento Ca | Registered: Dec 2001
| IP: Logged |
posted
i'm curious as well...i've asked this question a few times in posts concerning class X but never got a real explanation
-------------------- To cheat is to admit defeat
--------------------------------- Loud...it's when you can see the ground move, it's when you have to force yourself to breath, it's when the rest of the world ceases to exist. Posts: 4136 | From: Denver, CO | Registered: Sep 1999
| IP: Logged |
posted
I haven't seen anything regarding class X that would lead me to believe it is anything but a marketing name to help sell a "new technology". It is coming from a company I really wouldn't expect to be doing any pioneering in electronics and circuit design.
Next I don't see any reason why anybody would want to pair a variable power supply with a class D output stage. The continously variable supplies are basically class D amps in the power supply, and are used to increase efficiency of a linear output stage. Since you limit the voltage drop across the output device you lower the power dissipation in it. A class D output device is always on or off so there is almost no voltage drop across the device when it is on.
Posts: 2575 | From: GA | Registered: May 1999
| IP: Logged |
posted
There are several different companies that have class X so I do not think that it is just used for marketing. Autotek makes both class D and class X amps and says that class X has less distortion. This would lead me to believe that there are differences between the two. Some of the companies that use class X say that it is more efficient than D. But since class D can theoretically be 100% efficient, and is therefore the most efficient amp possible then this cannot be true.
I believe that class GD would have some benefits for distortion over class D. I have heard that at low power, class D amps make some distortion because of the very low duty cycle. With a class G power supply the duty cycle of the class D output could be increased to help with distortion.
Posts: 327 | From: Pleasanton & Sacramento Ca | Registered: Dec 2001
| IP: Logged |
posted
are they part of the same parent company? could explain the multiple companies using it...
if there really were a difference then i would hope someone would've posted it by now. There has been no mention of a new chip being used (ala class T and Tripath's chip), no mention of a new kind of power supply, no mention of higher quality components, etc.
second, jc2 made a good point, this is coming from companies who aren't known for pioneering electronics (not a bad thing)
-------------------- To cheat is to admit defeat
--------------------------------- Loud...it's when you can see the ground move, it's when you have to force yourself to breath, it's when the rest of the world ceases to exist. Posts: 4136 | From: Denver, CO | Registered: Sep 1999
| IP: Logged |
quote:Originally posted by ddstang: Cadence actually makes an amp which they say is class GD. Is this what class X really is? Or is it something else.
cadence doesn't make amps.
Uhhh? They don't? Then how come many people have used them. I myself have owned 2 z7000, 4 a7's, and a a4. Cadence Go here and you'll see. Not trying to be an a$$, I've had a couple people tell me the same thing. They didn't know they make amps.
-------------------- Mike Roth
"Magic Mike"
"Haha guy, I feel so bad for you. It's like living your life with 1 ply toilet paper, and never knowing about 2 ply."- Bidnyk
"he who dies with the most posts, dies with the most toasters."- Bostonian Fats
"Good luck with that tight ass gap."- Navi
"Its genetics blame your dad not me."- Navi Posts: 7407 | From: Overland Park, Kansas | Registered: Aug 2002
| IP: Logged |
In that case saying it has less distortion than class D would be true - above a couple hundred hz. My vote - marketing.
Posts: 82 | From: Topeka, KS USA | Registered: Aug 2001
| IP: Logged |
posted
It was my understanding that a Class X amp is basically a class D amp with a high switching frequency.
A class D amp switches on and off at a certain rate to simulate the waveform of the input at the outputs. Most of them on the market right now have switching frequencies in the 500-1000 Hz range. Now to reproduce a good signal with fairly low distortion, your switching frequency needs to be at least twice the highest output frequency, which is why most class D amps are for bass (under 250 Hz) only. Now if you raise that switching frequency up to like 50,000 Hz, you can run a full range signal (20-20,000 Hz) and still have the increased efficiency of a class D amp.
-------------------- Team Shedluv Team Sweep Team Kicker Team JBL
posted
What Jarfunkz may have meant is that it's Cadence on the nameplate, but another company manufactures the actualy beast.
Not sure, but that's how I read his comment.
I'll do some digging on the X, G, D, T, & H classes as well. AutoSound2000 may have something -> may need to scroll a bit, but here is at least 1 thread on Class D - X: AutoSound 2000 Linkage.
quote:Originally posted by Shedluv: It was my understanding that a Class X amp is basically a class D amp with a high switching frequency.
that's what class T is...higher switching frequency to allow full range operation
-------------------- To cheat is to admit defeat
--------------------------------- Loud...it's when you can see the ground move, it's when you have to force yourself to breath, it's when the rest of the world ceases to exist. Posts: 4136 | From: Denver, CO | Registered: Sep 1999
| IP: Logged |
posted
There are only 4 types of output stage configurations, and only 3 of them are linear (that is, able to reproduce the input signal in the same shape as the output).
Class A: A single transistor (or similar) is used. When no signal is being passed, the transistor is turned on half way. As the signal changes, the devices goes more on, or more off, to it's limit. Pluses: very clean sound, almost no distortion. Minuses: When no music is playing, it's half way on, and getting hot. Not too good for car audio.
Class B: Uses two transistors. When no signal is being passed, both are essentially off. When the signal goes positive, one transistor is used, when the signal goes negative, the other is used. Pluses: fairly efficienct compared to class A. Minuses: There can be some distortion as the signal switches from one transistor to the other, called crossover distortion.
Class C: A non-linear amplifier design. Won't work for audio signals, but it used in satellites and other weird stuff. Forgetaboutit! hahaha
Class D: Similar to class B, but the output devices are driven by a pulse-wifth-modulated signal. The devices turn all the way on, then off again at frequencies that are higher than you can hear. The average amount of on-time is the output level. ie: if the devices are on half the time (50%), then you get 1/2 of full output. Pluses: Very efficient, reaching upwards of 90%. Minues: Like any digitally 'chopped up' signal, it's not as good as the original. Sure is efficient though, and great for running woofers!
Class T: A marketting name created by Tripath technologies. This is a variation on Class D, and is not it's own topology. Class T is Class D, except that the modulating frequency is capable of going much higher, and as a result, the amp can play the entire audio bandwidth (20 Hz - 20 kHz). Pluses: Very efficient. Minuses: High frequency response is not very good. I have reviewed 4 so far, from different brands, and didn't like any of them. However, if you don't care what it sounds like, and you want it loud, that's the way to go.
Class X and the rest: More marketing mumbo-jumbo preying on the average consumers lack of knowledge. Don't beleive the hype, it's A, AB, B or D, there are no other options.
-------------------- Dave MacKinnon Audio Technical Editor - Performance Auto & Sound Magazine - www.pasmag.com Posts: 60 | From: Burlington, Ontario | Registered: Oct 2001
| IP: Logged |
posted
Uh...not accordiing to the Rane Audio site.
amplifier classes Audio power amplifiers were originally classified according to the relationship between the output voltage swing and the input voltage swing; thus it was primarily the design of the output stage that defined each class. Classification was based on the amount of time the output devices operate during one complete cycle of signal swing. Classes were also defined in terms of output bias current [the amount of current flowing in the output devices with no applied signal]. For discussion purposes (with the exception of class A), assume a simple output stage consisting of two complementary devices (one positive polarity and one negative polarity) using tubes (valves) or any type of transistor (bipolar, MOSFET, JFET, IGFET, IGBT, etc.).
[Historical Notes marked "GRS" provided by Gerald R. Stanley, Senior V.P. of Research, Crown International, Inc., designer of the famous Crown DC-300, inventor of the Crown K Series switchmode amplifier line and holder of 19 U.S. Patents, with four pending as of 2002.]
[GRS on amplifiers: "At first there were no amplifiers as the very thought of amplification had yet to enter the vocabulary of electronics (another word which had yet to be birthed!). The invention of a three-terminaled device (DeForest Audion U.S. patent 841,386 or later triode) was the invention in 1906 of a more sensitive radio detector and not an element for an amplifier.
By 1912 the triode had become both a vacuum tube and an amplifier (multiple names can be attached to this collective achievement). The oscillator also dates to 1912 giving proof to the saying "When you set out to make an amplifier you get an oscillator and when you attempt to make an oscillator you get an amplifier."]
[GRS on amplifier classes: "Originally it was adequate to distinguish amplifier classes only by the conduction angles of the control elements (tubes or valves). More recently it has been necessary to add distinctions that relate to topology, degrees of conduction and control methods to be able to determine class."]
Class A operation is where both devices conduct continuously for the entire cycle of signal swing, or the bias current flows in the output devices at all times. The key ingredient of class A operation is that both devices are always on. There is no condition where one or the other is turned off. Because of this, class A amplifiers in reality are not complementary designs. They are single-ended designs with only one type polarity output devices. They may have "bottom side" transistors but these are operated as fixed current sources, not amplifying devices. Consequently class A is the most inefficient of all power amplifier designs, averaging only around 20% (meaning you draw about 5 times as much power from the source as you deliver to the load.) Thus class A amplifiers are large, heavy and run very hot. All this is due to the amplifier constantly operating at full power. The positive effect of all this is that class A designs are inherently the most linear, with the least amount of distortion. [Much mystique and confusion surrounds the term class A. Many mistakenly think it means circuitry comprised of discrete components (as opposed to integrated circuits). Such is not the case. A great many integrated circuits incorporate class A designs, while just as many discrete component circuits do not use class A designs.] [GRS Historical Note: "Class A - The most basic of operating modes saw both single-ended and push-pull embodiments by 1913. The first known use of push-pull appears in a patent of E.F.W. Alexanderson of GE U.S. 1,173,079 filed in 1913. While Alexanderson would have been aware of other levels of biasing his push-pull stage, such as classes B and C, he would have only been able to produce a useful result with a tuned stage such as a transmitter where resonant filtering would have managed the distortion problem. Negative feedback is not understood in 1913 to be able to cope with distortion problems."]
Class B operation is the opposite of class A. Both output devices are never allowed to be on at the same time, or the bias is set so that current flow in a specific output device is zero when not stimulated with an input signal, i.e., the current in a specific output flows for one half cycle. Thus each output device is on for exactly one half of a complete sinusoidal signal cycle. Due to this operation, class B designs show high efficiency but poor linearity around the crossover region. This is due to the time it takes to turn one device off and the other device on, which translates into extreme crossover distortion. Thus restricting class B designs to power consumption critical applications, e.g., battery operated equipment, such as 2-way radio and other communications audio. [GRS Historical Note: "Class B - This class has no obvious inventor, but it does have its master and perfector. Loy Barton working for RCA developed tube designs and biasing methods to manage the open loop distortion of class B push-pull power stages. His IRE paper in 1931 titled "High Output Power from Relatively Small Tubes" is a landmark in the history of class B. Technically he only used class AB but the distinction was not in the language. Class AB is a later and probably unnecessary class fabrication."]
Class AB operation is the intermediate case. Here both devices are allowed to be on at the same time (like in class A), but just barely. The output bias is set so that current flows in a specific output device appreciably more than a half cycle but less than the entire cycle. That is, only a small amount of current is allowed to flow through both devices, unlike the complete load current of class A designs, but enough to keep each device operating so they respond instantly to input voltage demand s. Thus the inherent non-linearity of class B designs is eliminated, without the gross inefficiencies of the class A design. It is this combination of good efficiency (around 50%) with excellent linearity that makes class AB the most popular audio amplifier design.
Class AB plus B design involves two pairs of output devices: one pair operates class AB while the other (slave) pair operates class B. [GRS Historical Note: "Class AB+B is a term that I'd coined and is intended to be very descriptive but is not truly worthy of its own class. The Crown DC-300 was the first to use this mode of operation in 1968."]
Class BD Invented by Robert B. Herbert in 1971 U.S. patent 3,585,517 and improved on by Neil Edward Walker as desclosed in his 1971 U.S. patent 3,629,616. Both patents are concerned with improving original class D design efficiencies by using various bridge connections and cancellation techniques. And most recently more improvements are claimed by inventors James C. Strickland & Carlos A. Castrejon in their U.S. patent 6,097,249 assigned to Rockford Corporation in 2000 for their Fosgate-brand automotive amplifier. [GRS comments: "This is a class designation that would best be forgotten. It has been applied to multiple modulation schemes on a class D derived full-bridge. This is perhaps the most reinvented class design in recent history with "filter-less amplifiers" and other such things. An interleave of two class D full-bridge is what we actually have here, and it is a good improvement to an interleave of one class D full-bridge. However an interleave of four is actually possible on a full-bridge if one uses class I design."]
Class C use is restricted to the broadcast industry for radio frequency (RF) transmission. Its operation is characterized by turning on one device at a time for less than one half cycle. In essence, each output device is pulsed-on for some percentage of the half cycle, instead of operating continuously for the entire half cycle. This makes for an extremely efficient design capable of enormous output power. It is the magic of RF tuned circuits (flywheel effect) that overcomes the distortion create d by class C pulsed operation.
Class D operation is switching, hence the term switching power amplifier. Here the output devices are rapidly switched on and off at least twice for each cycle (Sampling Theorem). Theoretically since the output devices are either completely on or completely off they do not dissipate any power. If a device is on there is a large amount of current flowing through it, but all the voltage is across the load, so the power dissipated by the device is zero (found by multiplying the voltage across the device [zero] times the current flowing through the device [big], so 0 x big = 0); and when the device is off, the voltage is large, but the current is zero so you get the same answer. Consequently class D operation is theoretically 100% efficient, but this requires zero on-impedance switches with infinitely fast switching times -- a product we're still waiting for; meanwhile designs do exist with true efficiencies approaching 90%. [Historical note: the original use of the term "Class D" referred to switching amplifiers that employed a resonant circuit at the output to remove the harmonics of the switching frequency. Today's use is much closer to the original "Class S" designs. [GRS Historical Note: "Class D is a subset of all possible switch-mode amplifier topologies that is typified by use of the half-bridge (totem-pole) output stage that has two interconnected switches operating in time alternation. The paradigm is that of Loy Barton's class B, but uses the statistics of conduction angle to produce amplification (PWM). There are many subclasses within class D that describe the origins of the modulation. Class D is at least as old as 1954 when Bright patented a solid-state full-bridge servo amplifier U.S. 2,821,639."]
Class E operation involves amplifiers designed for rectangular input pulses, not sinusoidal audio waveforms. The output load is a tuned circuit, with the output voltage resembling a damped single pulse. Normally Class E employs a single transistor driven to act as a switch. The following terms, while generally agreed upon, are not considered "official" classifications
Class F Also known by such terms as "biharmonic," "polyharmonic," "Class DC," "single-ended Class D," "High-efficiency Class C," and "multiresonator." Another example of a tuned power amplifier, whereby the load is a tuned resonant circuit. One of the differences here is the circuit is tuned for one or more harmonic frequencies as well as the carrier frequency. See References: Krauss, et al. for complete details. [GRS Historical Note: "Classes E and F are distinguished by their resonant topology and not conduction angle else we would class them with C. A good reference to these is found in the many patents of Nathan Sokal. Also class S which is very old (1929-1930) has similar applications (resonant RF)."]
Class G operation involves changing the power supply voltage from a lower level to a higher level when larger output swings are required. There have been several ways to do this. The simplest involves a single class AB output stage that is connected to two power supply rails by a diode, or a transistor switch. The design is such that for most musical program material, the output stage is connected to the lower supply voltage, and automatically switches to the higher rails for large signal peaks [thus the nickname rail-switcher]. Another approach uses two class AB output stages, each connected to a different power supply voltage, with the magnitude of the input signal determining the signal path. Using two power supplies improves efficiency enough to allow significantly more power for a given size and weight. Class G is becoming common for pro audio designs. [Historical note: Hitachi is credited with popularizing class G designs with their 1977 Dynaharmony HMA 8300 power amplifier, however it is shown much older by GRS: "Class G - I have been searching for the proper inventor of this class, but have not been able to find a reference older than 1965 when I first encountered it in a college text "Handbook of Basic Transistor Circuits and Measurements" by Thornton et al., SEEC vol. 7. The method is introduced without references or fanfare. One is led to believe that it was common knowledge in 1965 and earlier. This is not the first known use of extended quasi-linear methods (beyond class B), as there is a dual found in Fisher U.S. 2,379,513 from 1942."]
Class H operation takes the class G design one step further and actually modulates the higher power supply voltage by the input signal. This allows the power supply to track the audio input and provide just enough voltage for optimum operation of the output devices [thus the nickname rail-tracker or tracking power amplifier]. The efficiency of class H is comparable to class G designs. [Historical note: Soundcraftsmen is credited with popularizing class H designs with their 1977 Vari-proportional MA5002 power amplifier, however like class H above GRS finds precendence: "Class H - The apparent inventor of class-H in full-blown multi-level form was Manuel Kramer of NASA in 1964 U.S. patent 3,319,175. Class H optimally applied to a full-bridge was invented in 1987 (Stanley) U.S. 4,788,452. Classes G and H are all members of a class of amplifiers that has articulated rail voltages to improve the efficiency of class B power stages. Examples are available of tracking using binarily weighted segments, (Stanley) U.S. 5,045,990. Continuously variable tracking with switch-mode PWM appears to have been first done by Hamada in 1976 U.S. 4,054,843. The ultimate rail tracker using interleaved technology is found in (Stanley) U.S. 5,513,094. Only with interleave is the converter fast enough to meet the needs of full-bandwidth audio and yet have low switching losses."]
Class I operation invented and named by Gerald R. Stanley for amplifiers based on his patent U.S. 5,657,219 covering opposed current converters. [GRS explains: The "I" of the class is short for "interleave" as this is the only four-quadrant converter known that uses two switches yet has an interleave number of 2 in the terminology of interleave. When used with fixed-frequency natural two-sided PWM it forms a theoretically optimum converter having the least unnecessary/undesirable PWM spectra. A good reference is found in the IEEE Transactions on Power Electronics Vol. 14, No. 2, March 1999, pages 372-380."]
Class J operation is the category/name suggested by Gerald R. Stanley for amplifiers that combine class B and class D where converters act in parallel to drive the load. [GRS elaborates: "There are serious problems with the power efficiency of these products when processing fast signals into arbitrary loads. The class B stage is used to actively remove the ripple of the class D stage and other distortion problems that plague class D. No solution is offered for the MOSFET CSOA (current safe operating area) problem of class D. To solve that problem it would be necessary to parallel a class I and class B amplifier but this would be without merit as the class I amplifier generally does not need the class B amplifier to meet fidelity requirements."]
Class S First invented in 1932, this technique is used for both amplification and amplitude modulation. Similar to Class D except the rectangular PWM voltage waveform is applied to a low-pass filter that allows only the slowly varying dc or average voltage component to appear across the load. Essentially this is what is termed "Class D" today. See References: Krauss for details.
[Final GRS Amplifier Historical Note: "All of our amplifier classes have thrived under a very important invention, without which most would have floundered. That invention is, of course, negative feedback. Harold Black in 1927 changed our world forever while riding to work on the Lackawanna Ferry. (See U.S. patent 2,102,671.) Harold Black did not stop there however, he also in 1953 wrote the text "Modulation Theory" which we today use to understand the fundamentals of PWM. In 1935, Terman, in his now famous "Fundamentals of Radio" handbook, wrote that it was good that class B was only used in places like radio stations as there needed to be an engineer on duty full time to keep the bias tweaked to where the distortion was acceptable. Thanks go to Harold Black for changing all that and leading us into the next century of amplification."]
-------------------- Team Image Dynamics/Zapco/Werewolf/JK Lab Team Kinetik Sick Bastard Audio SQ Who feels it knows it Posts: 7996 | From: Charlotte,NC USA | Registered: May 1999
| IP: Logged |
posted
That's some pretty interesting reading Winslow.
So, My interpretations of Class A, B, C and D are essentially correct, although your quotes explain them in much more detail.
I did neglect Class E. My oversight. Sadly, it's not used for audio either.
As your quote says, the rest are "not considered official classifications".
Class F is non-linear, as above. Class G is tracking power supply AB (Carver) Class H is class G is class AB Class I us poorly described, and looks like it's not used for audio. Class J, as per definition is B and D together Class S, as per definition is D
Not trying to pick a fight lad, I just feel really bad that so many companies try to confuse consumers with useless information.
I only set out to explain the output device topology and try and clarify things.
-------------------- Dave MacKinnon Audio Technical Editor - Performance Auto & Sound Magazine - www.pasmag.com Posts: 60 | From: Burlington, Ontario | Registered: Oct 2001
| IP: Logged |
I wonder if the Rockford BD line of amps would be a hybrid B/D design or a class J?
But for me, there are only 2 types of amps you should buy for the car- class a and a/b...lol.
-------------------- Team Image Dynamics/Zapco/Werewolf/JK Lab Team Kinetik Sick Bastard Audio SQ Who feels it knows it Posts: 7996 | From: Charlotte,NC USA | Registered: May 1999
| IP: Logged |
posted
I have a white paper from the Rockford amps here somewhere. I have done a couple reviews on them.
Two things to note: They behave very well, much like a Class B (or AB) amp in terms of the output waveform shaped when clipping. So many class D amps go saddleback or weird. The Rockford just produced a nice square wave with no ringing or anything odd.
These amps are VERY efficient. Amongst the top all the amps I have tested. I like them!
I will try and dig up the white paper...
-------------------- Dave MacKinnon Audio Technical Editor - Performance Auto & Sound Magazine - www.pasmag.com Posts: 60 | From: Burlington, Ontario | Registered: Oct 2001
| IP: Logged |
posted
Class I is used for audio. It is the mode used in the Crown K1, K2, and CS4000 pro-sound amps as well as the new JBL-Crown 6000W car amp. As the previous post explained, with the great quotes from the god (to me anyway) of audio engineers, Class I is a form of interlieved class D that is full bandwidth and very efficient.
Printer-friendly view of this topic