class C: Each transistor conducts less than half a cycle. Since this
gives rather extreme distorsion it is not useful for audio, but is
very efficient and obviously useful for radio.
class D: Pulse width modulation, ie. very different from the other
classes. There were some class D amplifiers back in the 70s, but
I don't think they made much success then. There are some class
D kits around for audio, eg. from LC audio and Zetex, and I
understand that it is quite common in car stereo (for efficiency
reasons) and subwoofers (efficiency, plus distorsion figures are
much better for low frequencies). Class D is very efficient since
the transistors work in switching mode.
class E: Don't really know what it is, but is said to be a method
to reduce power dissipation and is only used for radio.
class G: Two class B amps in parallel connected two rails of
different voltages. The one with higher rail voltages is only used
for high power and is otherwise on standby.
class H: Varies the supply voltage according to power need.
Not sure how or why. Presumably the purpose is to increase
efficiency, so I suppose a switching supply with variable output
is used, but I'm only guessing here.
class S: Said to be a low-power class A amp driving a load which
is backed up with a class B stage, the latter making the load
appear to have a higher impedance. Don't think I understand
quite what this means.
(Source for those classes I didn't already know about is
Randy Sloanes power amp book)
gives rather extreme distorsion it is not useful for audio, but is
very efficient and obviously useful for radio.
class D: Pulse width modulation, ie. very different from the other
classes. There were some class D amplifiers back in the 70s, but
I don't think they made much success then. There are some class
D kits around for audio, eg. from LC audio and Zetex, and I
understand that it is quite common in car stereo (for efficiency
reasons) and subwoofers (efficiency, plus distorsion figures are
much better for low frequencies). Class D is very efficient since
the transistors work in switching mode.
class E: Don't really know what it is, but is said to be a method
to reduce power dissipation and is only used for radio.
class G: Two class B amps in parallel connected two rails of
different voltages. The one with higher rail voltages is only used
for high power and is otherwise on standby.
class H: Varies the supply voltage according to power need.
Not sure how or why. Presumably the purpose is to increase
efficiency, so I suppose a switching supply with variable output
is used, but I'm only guessing here.
class S: Said to be a low-power class A amp driving a load which
is backed up with a class B stage, the latter making the load
appear to have a higher impedance. Don't think I understand
quite what this means.
(Source for those classes I didn't already know about is
Randy Sloanes power amp book)
amp classes
FYI - a cool chip to try class-h out with is the Philips TDA1562Q. The app note shows the entire circuit. You can make a 70 watt amp with only a 12v input, with no switching power supply.
I started this from memory, then decided to look it up. These definitions are from Audiolab's glossary
Class H amplifier - 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. The efficiency of class H is comparable to class G designs.
Class G amplifier - 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. 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.
Class D amplifier - 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. Since the output devices are either completely on or completely off they do not theoretically dissipate any power. 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%.
Class AB plus B amplifier - Class AB plus B design involves two pairs of output devices: one pair operates class AB while the other (slave) pair operates class B.
Class AB amplifier - Class AB operation allows both devices 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 demands. 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 B amplifier - 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.
Class A amplifier - 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 are single-ended designs with only one type polarityoutput devices. Class A is the most inefficient of all power amplifier designs, averaging only around 20%. Because of this, 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.
Matt
FYI - a cool chip to try class-h out with is the Philips TDA1562Q. The app note shows the entire circuit. You can make a 70 watt amp with only a 12v input, with no switching power supply.
I started this from memory, then decided to look it up. These definitions are from Audiolab's glossary
Class H amplifier - 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. The efficiency of class H is comparable to class G designs.
Class G amplifier - 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. 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.
Class D amplifier - 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. Since the output devices are either completely on or completely off they do not theoretically dissipate any power. 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%.
Class AB plus B amplifier - Class AB plus B design involves two pairs of output devices: one pair operates class AB while the other (slave) pair operates class B.
Class AB amplifier - Class AB operation allows both devices 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 demands. 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 B amplifier - 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.
Class A amplifier - 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 are single-ended designs with only one type polarityoutput devices. Class A is the most inefficient of all power amplifier designs, averaging only around 20%. Because of this, 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.
Matt
Douglas Self's book has a full chapter on Class G:
http://www.dself.demon.co.uk/book.htm
It if a pretty informative book.
He also has a small section of his site on Class G:
http://www.dself.demon.co.uk/ampins/g.htm
--
Brian
http://www.dself.demon.co.uk/book.htm
It if a pretty informative book.
He also has a small section of his site on Class G:
http://www.dself.demon.co.uk/ampins/g.htm
--
Brian
I found that and some similar ones, but also a non-IEEE
reference to a Class A and Class B.
The description bears a strong resemblance to a Stasis
amp, which was patent # 4,107,619 which describes
a Class A stage connected directly to the load, but
current bootrapped by an external amplifier, typically but
not limited to a Class B or AB amplifier.
woops! looks like the comment I was responding to
disappeared.....
reference to a Class A and Class B.
The description bears a strong resemblance to a Stasis
amp, which was patent # 4,107,619 which describes
a Class A stage connected directly to the load, but
current bootrapped by an external amplifier, typically but
not limited to a Class B or AB amplifier.
woops! looks like the comment I was responding to
disappeared.....
I was having posting problems with uploading the file in ascii mode instead of binary. It should work now:
http://brian.prohosting.com/class_s.pdf
--
Brian
http://brian.prohosting.com/class_s.pdf
--
Brian
Why.
The how is over my head. The why is straight forward and applies to class H, D, B.A.S.H. and other schemes. The objective is to reduce the physical size and mass of the amplifier for a given power level. While a fanatic audiphile may put low priority on size and weight, a ordinary consumer or even a not-so-fanatic audiophile may think keeping the size of the amplifier (specially in a multichannnel system) inconspicuous is a major condsieration. Since the biggest driver of amplifier size and weight is the heatsink, it is really thermal efficiency that is being chased.
This is nothing new. It's why most amps are class B rather than A. The problem is that in every case sonic performance is sacrificed to some degree. In the case of B vs. A, the higher distortion of B has been (in general) reduced to where most people feel it is not normally audible. Self claims his class G design which seems to be an extension of this "blameless" amp in many ways is very close to Class B performance.
Then there is Carver who got into this some years ago and the latest Sunfire reciever is a good example of what motivates designers in this regard.
The audiphile issue is: what compromise are you willing to make.
The how is over my head. The why is straight forward and applies to class H, D, B.A.S.H. and other schemes. The objective is to reduce the physical size and mass of the amplifier for a given power level. While a fanatic audiphile may put low priority on size and weight, a ordinary consumer or even a not-so-fanatic audiophile may think keeping the size of the amplifier (specially in a multichannnel system) inconspicuous is a major condsieration. Since the biggest driver of amplifier size and weight is the heatsink, it is really thermal efficiency that is being chased.
This is nothing new. It's why most amps are class B rather than A. The problem is that in every case sonic performance is sacrificed to some degree. In the case of B vs. A, the higher distortion of B has been (in general) reduced to where most people feel it is not normally audible. Self claims his class G design which seems to be an extension of this "blameless" amp in many ways is very close to Class B performance.
Then there is Carver who got into this some years ago and the latest Sunfire reciever is a good example of what motivates designers in this regard.
The audiphile issue is: what compromise are you willing to make.
What I see is a lot of people going to a lot of trouble to
save a couple watts. I've done it, but as the years go
by it just seems busy and uninteresting.
If you really want to save a watt, buy efficient speakers.
Mine are about 100 dB/watt, and I can get the same level
with 1 watt as 100 watts driving an 80 dB speaker. And
I think it sounds better.
save a couple watts. I've done it, but as the years go
by it just seems busy and uninteresting.
If you really want to save a watt, buy efficient speakers.
Mine are about 100 dB/watt, and I can get the same level
with 1 watt as 100 watts driving an 80 dB speaker. And
I think it sounds better.
Can't argue with that. The problem is that some people get very obsesive about speakers. For instance, I can't imagine giving up my Magnepans
, which are a classic case of inefficient speakers. So I have to accept that I've got to live with a fairly inconvenient amp. A gainclone won't cut it. Fortunately I only have a pair, and not the largest model. If I just had to have a full 5.1 set up using the larger models I would be up to my ears in watts whether I wanted to be or not.And it's not the watts per se in sense of conserving natural resources, it's saving the space and weight needed to dissapate the heat from those watts.
For instance, I can't imagine giving up my Magnepans
Just went to check out what Magnepans are all about. They look like nice speakers, but one has to wonder when stuff like this is on their website:
http://www.magnepan.com/1-800-474-1646/index.html
It is so light that when a piece of it is dropped from a height of 6 feet it takes and average of 5 seconds for it to reach the floor.
Last time I checked, physics said that mass had nothing to do with the speed at which an object fell.
Just went to check out what Magnepans are all about. They look like nice speakers, but one has to wonder when stuff like this is on their website:
http://www.magnepan.com/1-800-474-1646/index.html
It is so light that when a piece of it is dropped from a height of 6 feet it takes and average of 5 seconds for it to reach the floor.
Last time I checked, physics said that mass had nothing to do with the speed at which an object fell.
Nelson Pass said:
That's what I've tried to make obvious to many people, but they keep on buying heavy amps and cheap speakers. Where are those very sensitive speakers of the 70's with amps about a 100 or 200 Watts (you could fill any room/hall with those combination)??
BTW, Nelson what is the sensitivity of your speakers?
HB.
Then again... the Cuda will likely catch more eyes - Status
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