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CLASS AB or D

 

New member
Username: Ruckus

Oh

Post Number: 4
Registered: Apr-05
Im just about to buy 2 JL12w6v2 and I WAS going to use a JL 1000/1 but I just realised its an class AB amp, VS. a class D. What, other than efficiency, are the benefits of choosing a class D, cause I like the JL look, and I know its a strong amp, it was just a little upsetting to know that its AB instead of D, should I go with it, or is there something inplace of the JL that anyone would recommend
 

Silver Member
Username: Suleman36

Post Number: 772
Registered: Feb-05
I have 2 JL12w6v2's also and i was pushing it with my ppi pcx 2200 class AB 2 channel amp and it sounded awesome but is not as efficiant as a class D. Class AB amps are suppose to have cleaner quality sound but with alot of bass it wont be audible. By the way im selling my ppi pcx 2200 and it does 800wattsrms and is perfect match for the w6's you have.
 

skyliner17
Unregistered guest
jl audio 1000/1 amp is a class D amp, duh...
 

Gold Member
Username: Glasswolf

NorthWest, Michigan USA

Post Number: 7697
Registered: Dec-03
the JL 1000/1 and 500/1 are both class D amplifiers.
Class D are more efficient and thus run cooler with a smaller footprint. Class D are also cheaper per watt than class AB. Other than that, they are totally inferior in every way imaginable fto a good class AB amplifier. Other than using less current to produce the same power (which the JL 1000/1 class D amp will already need 100A+ to reach peak output) and class D producing less heat, why are you so upset about having a class AB amplifier?
I use three class AB amps in my car, which is set up for IASCA Pro circuit SQ events, solely because I refuse to use class D amps. They aren't nearly as clean, and produce a load more distortion at or near peak output.

 

Gold Member
Username: Glasswolf

NorthWest, Michigan USA

Post Number: 7698
Registered: Dec-03
What are Amplifier Classes?

The Class of an amplifier refers to the design of the circuitry within the amp. There are many classes used for audio amps. The following is brief description of some of the more common amplifier classes you may have heard of:

Class A: Class A amplifiers have very low distortion (lowest distortion occurs when the volume is low) however they are very inefficient and are rarely used for high power designs. The distortion is low because the transistors in the amp are biased such that they are half "on" when the amp is idling. As a result, a lot of power is dissipated even when the amp has no music playing! Class A amps are often used for "signal" level circuits (where power is small) because they maintain low distortion. Distortion for class A amps increases as the signal approaches clipping, as the signal is reaching the limits of voltage swing for the circuit. Also, some class A amps have speakers connected via capacitive coupling.

Class B: Class B amplifiers are used in low cost, low quality designs. Class B amplifiers are a lot more efficient than class A amps, however they suffer from bad distortion when the signal level is low (the distortion is called "crossover distortion"). Class B is used most often where economy of design is needed. Before the advent of IC amplifiers, class B amplifiers were common in clock radio circuits, pocket transistor radios, or other applications where quality of sound is not that critical.

Class AB: Class AB is probably the most common amplifier class for home and mobile audio and similar amplifiers. Class AB amps combine the good points of class A and B amps. They have the good efficiency of class B amps and distortion that is a lot closer to a class A amp. With such amplifiers, distortion is worst when the signal is low, and lowest when the signal is just reaching the point of clipping. Class AB amps (like class B) use pairs of transistors, both of them being biased slightly ON so that the crossover distortion (associated with Class B amps) is largely eliminated.

Class C: Class C amps are never used for audio circuits. They are commonly used in RF circuits. Class C amplifiers operate the output transistor in a state that results in tremendous distortion (it would be totally unsuitable for audio reproduction). However, the RF circuits where Class C amps are used employ filtering so that the final signal is completely acceptable. Class C amps are quite efficient.

Class D: The concept of a Class D amp has been around for a long time, however only fairly recently have they become commonly used. Due to improvements in the speed, power capacity and efficiency of modern semiconductor devices, applications using Class D amps have become affordable for the common person. Class D amplifiers use a very high frequency signal to modulate the incoming audio signal. Such amps are commonly used in car audio subwoofer amplifiers. Class D amplifiers have very good efficiency. Due to the high frequencies that are present in the audio signal, Class D amps used for car stereo applications are often limited to subwoofer frequencies, however designs are improving all the time. It will not be too long before a full band class D amp becomes commonplace.

Class T: Class T (Tripath) is similar to class D with these exceptions: This class does not use analog feed back like its class D cousin. The f e e d b a c k is digital and is taken ahead of the output filter, avoiding the phase shift of this filter. Because class D or T amplifier distortion arises from timing errors, the class T amplifier feeds back timing information. The other distinction is that this amplifier uses a digital signal processor to convert the analog input to a PWM signal and process the f e e d b a c k information. The processor looks at the f e e d b a c k information and makes timing adjustments. Because the f e e d b a c k loop does not include the output filter, the class T amplifier is inherently more stable and can operate over the full audio band. Most listeners can not hear the difference between class T and good class AB designs. Both class D and T designs share one problem: they consume extra power at idle. Because the high frequency waveform is present at all times, even when there is no audio present, the amplifiers generate some residual heat. Some of these amplifiers actually turn off in the absence of music, and can be annoying if there is too much delay turning back on.

Class G: Class G improves efficiency in another way: an ordinary class AB amplifier is driven by a multi-rail power supply. A 500 watt amplifier might have three positive rails and three negative rails. The rail voltages might be 70 volts, 50 volts, and 25 volts. As the output of the amplifier moves close to 25 volts, the supply is switched the 50 volt rail. As the output moves close to the 50 volt rail, the supply is switched to the 70 volt rail. These designs are sometimes called "Rail Switchers". This design improves efficiency by reducing the "wasted" voltage on the output transistors. This voltage is the difference between the positive (red) supply and the audio output (blue). Class G can be as efficient as class D or T. While a class G design is more complex, it is based on a class AB amplifier and can have the same clean characteristics as well.

Class H: Class H is similar to class G, except the rail voltage is modulated by the input signal. The power supply rail is always just a bit higher than the output signal, keeping the voltage across the transistors small and the output transistors cool. The modulating power supply rail voltage is created by similar circuitry that you would find in a class D amplifier. In terms of complexity, this type of amplifier could be thought of as a class D amplifier driving a class AB amplifier and is therefore fairly complex.

Other classes: There are many other classes of amplifiers. Most of these are variations of the class AB design, however they result in higher efficiency for designs that require very high output levels (500W and up for example).
At this time I will not go into the details of all of these other classes.

from:
http://www.wickedcases.com/caraudio/amplifiers.html
more on amp specs here:
http://www.wickedcases.com/caraudio/ampspecs.html
 

New member
Username: Ruckus

Oh

Post Number: 7
Registered: Apr-05
so is 2% THD high for an amp.....like the PPI?
 

Gold Member
Username: Carguy

Post Number: 2457
Registered: Nov-04
In your car, 1% - 2% THD won't be detectable. Your engine noise will drown any THD coming from your car speakers.
Glass, hope you didn't have to type all of that!
 

Gold Member
Username: James1115

Wilton, Ct

Post Number: 2460
Registered: Dec-04
for some reason I think he had that info readily available:-)
 

Silver Member
Username: Suleman36

Post Number: 821
Registered: Feb-05
isaac let him know about my ppi pcx 2200 im selling ebay. He will save alot more money going with that cause its 800watts rms and underated. The 12w6v2's are 400rms a piece so its a nice combo. like you said the 2% THD wont be audible.
 

Gold Member
Username: James1115

Wilton, Ct

Post Number: 2463
Registered: Dec-04
whats a link for your amp mo?
 

Silver Member
Username: Suleman36

Post Number: 824
Registered: Feb-05
http://search.ebay.com/ppi-pcx_W0QQfromZR41

its the 3rd amp down. PPI PCX 2200
 

Gold Member
Username: Carguy

Post Number: 2471
Registered: Nov-04
Mark, check out MO's amp on sale. It is a very nice amp and I think it's going for under $300 too.
 

Gold Member
Username: Jonathan_f

GA USA

Post Number: 3765
Registered: May-04
He wrote that tutorial for other sites, but he had it on tap :-)
 

Gold Member
Username: James1115

Wilton, Ct

Post Number: 2466
Registered: Dec-04
thats what I figured. I wish I knew a fraction of what he knows, you also Jon, and Isaac lol!
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