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Scooby_doobie
New member
Username: Scooby_doobie
Post Number: 4
Registered: 6-2011
| | Posted on Tuesday, June 28, 2011 - 12:36 pm: | 
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what does it mean operates on class AB/C?
...........SSB or AM, or both. |
Sitm
Intermediate Member
Username: Sitm
Post Number: 450
Registered: 1-2004
| | Posted on Tuesday, June 28, 2011 - 3:14 pm: |
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This characteristic in a amplifier allows the operator to switch between running AB or C class (see the differences below)
The SSB or AM both means that on SSB there is a "delay" that allows the amplifier to remain engaged between spoken words when the carrier drops below wattage output that keeps the amplifier transmitting. Otherwise you would get a "chatter" affect from the amplifier.
Class AB will be cleaner, but the percentage of amperage input to wattage output is less efficent.
Class C is more efficent in as there is a better amerage input to wattage output, but the signal is not as "clean" as AB class transmission.
Amplifier Classes
The classification of an amplifier as either a voltage or a power amplifier is made by comparing the characteristics of the input and output signals by measuring the amount of time in relation to the input signal that the current flows in the output circuit. We see that in a Common Emitter transistor that for the transistor to operate within its "Active Region" some form of "Base Biasing" was required. This small Base Bias voltage added to the input signal allowed the transistor to reproduce the full input waveform at its output with no loss of signal. However, by altering the position of this Base bias voltage, it is possible to operate an amplifier in an amplification mode other than that for full waveform reproduction. By changing the amplifiers Base bias voltage different ranges or modes of operation can be obtained and these are categorized according to their Classification better known as Amplifier Class.
Audio power amplifiers are classified in an alphabetical order according to their circuit configurations and mode of operation. Amplifiers are designated by different classes of operation such as class "A", class "B", class "C", class "AB", etc. These different classes of operation range from a near linear output but with low efficiency to a non-linear output but with a high efficiency. No one class of operation is "better" or "worse" than any other class with the type of operation being determined by the use of the amplifying circuit. There are typical maximum efficiencies for the various types or class of amplifier, with the most commonly used being:
Class A - has low efficiency of less than 40% but good signal reproduction and linearity.
Class B - is twice as efficient as class A amplifiers with a maximum theoretical efficiency of about 70% because the amplifying device only conducts (and uses power) for half of the input signal.
Class AB - has an efficiency rating between that of Class A and Class B but poorer signal reproduction than class A amplifiers.
Class C - is the most efficient amplifier class as only a very small portion of the input signal is amplified therefore the output signal bears very little resemblance to the input signal. Class C amplifiers have the worst signal reproduction.
Class A Operation
Class A Amplifier operation is were the entire input signal waveform is faithfully reproduced at the amplifiers output as the transistor is perfectly biased within its active region, thereby never reaching either of its Cut-off or Saturation regions. This then results in the AC input signal being perfectly "centred" between the amplifiers upper and lower signal limits as shown below.
Class A Output Waveform
In this configuration, the Class A amplifier uses the same transistor for both halves of the output waveform and due to its biasing arrangement the output transistor always has current flowing through it, even if there is no input signal. In other words the output transistors never turns "OFF". This results in the class A type of operation being very inefficient as its conversion of the DC supply power to the AC signal power delivered to the load is usually very low. Generally, the output transistor of a Class A amplifier gets very hot even when there is no input signal present so some form of heat sinking is required. The DC current flowing through the output transistor (Ic) when there is no output signal will be equal to the current flowing through the load. then a pure Class A amplifier is very inefficient.
Class B Operation
Unlike the Class A amplifier above that uses a single transistor for its output stage, the Class B Amplifier uses two complimentary transistors (an NPN and a PNP) for each half of the output waveform. One transistor conducts for the positive half of the waveform and another conducts for the negative half of the waveform. This means that each transistor spends half of its time in the active region and half its time in the Cut-off region thereby amplifying only 50% of the input signal. Class B operation has no DC bias voltage instead the transistor only conducts when the input signal is greater than the base-emitter voltage and for silicon devices is about 0.7v. Therefore, at zero input there is zero output. This then results in only half the input signal being presented at the amplifiers output giving a greater efficiency as shown below.
Class B Output Waveform
In a class B amplifier, no DC current is used to bias the transistors, so for the output transistors to start to conduct each half of the waveform, both positive and negative, they need the base-emitter voltage Vbe to be greater than the 0.7v required for a bipolar transistor to start conducting. Then the lower part of the output waveform which is below this 0.7v window will not be reproduced accurately resulting in a distorted area of the output waveform as one transistor turns "OFF" waiting for the other to turn back "ON". The result is that there is a small part of the output waveform at the zero voltage cross over point which will be distorted. This type of distortion is called Crossover Distortion and is looked at later on in this section.
Class AB Operation
The Class AB Amplifier is a compromise between the Class A and the Class B configurations above. While Class AB operation still uses two complementary transistors in its output stage a very small biasing voltage is applied to the Base of the transistor to bias it close to the Cut-off region when no input signal is present. An input signal will cause the transistor to operate as normal in its Active region thereby eliminating any crossover distortion which is present in class B configurations. A small Collector current will flow when there is no input signal but it is much less than that for the Class A amplifier configuration. This means then that the transistor will be "ON" for more than half a cycle of the waveform. This type of amplifier configuration improves both the efficiency and linearity of the amplifier circuit compared to a pure Class A configuration.
Class AB Output Waveform
The class of operation for an amplifier is very important and is based on the amount of transistor bias required for operation as well as the amplitude required for the input signal. Amplifier classification takes into account the portion of the input signal in which the transistor conducts as well as determining both the efficiency and the amount of power that the switching transistor both consumes and dissipates in the form of wasted heat.
Badly designed amplifiers especially the Class "A" types may also require larger power transistors, more expensive heat sinks, cooling fans, or even an increase in the size of the power supply required to deliver the extra power required by the amplifier. Power converted into heat from transistors, resistors or any other component for that matter, makes any electronic circuit inefficient and will result in the premature failure of the device. So why use a Class A amplifier if its efficiency is less than 40% compared to a Class B amplifier that has a higher efficiency rating of over 70%. Basically, a Class A amplifier gives a much more linear output meaning that it has, Linearity over a larger frequency response even if it does consume large amounts of DC power.
If you are searching for others to give you the "wow are you crystal clear" you would want the AB class. If you are more concerned about being "loud" or not having to have a enormous power supply then Class C will be your demon.
You can run more wattage with less amperage with Class C, but your signal will not be a clean and repoduced as well as it would be with a good class AB amplifier. |
Scooby_doobie
New member
Username: Scooby_doobie
Post Number: 5
Registered: 6-2011
| | Posted on Thursday, June 30, 2011 - 8:13 pm: |
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So i can only transmit on AM on this amp? |
Scooby_doobie
New member
Username: Scooby_doobie
Post Number: 6
Registered: 6-2011
| | Posted on Thursday, June 30, 2011 - 9:03 pm: |
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so this amp will work on SSB, CW, AM and FM?
im a little lost......sorry for my nubie-ness. |
Sitm
Intermediate Member
Username: Sitm
Post Number: 455
Registered: 1-2004
| | Posted on Friday, July 01, 2011 - 10:04 am: |
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No, this amp will transmit on SSB, CW, AM, FM.
When transmitting on SSB just select delay. I would suggest transmitting on SSB in the AB mode.
You just change the effectiveness and signal reproduction quality when you change from class C or Class AB specifically designed for those of us that treasure a clean signal over loud. Generally a SSB users preference as to where an AM user prefers Class C LOUD AUDIO.
Class C has greater amperage to wattage effectiveness, but you lose signal reprodution quality.
Class AB has greater signal reprodution but less amperage to wattage conversion.
I am not posting this in the technical terms that this information is generaly relayed in but in as much laymens terms that I can convey.
Your signal will be "much" cleaner and clearer in the AB mode, but the amplifier will not produce as high of wattage output to Amperage usage.
Your signal will have more wattage in Class C mode but will not be as clean and clear (not as much signal reproduction as AB)
Maybe this will help.
If you run say a Texas Star 500 (which is AB) you should have a minimum of 60 amp power supply (this is my opinion). If you use say a 500 watt class C amplifier you would be able to run it effetively with say a 40 amp power supply.
Case in point.
KL-503 Mobile Amp class C amp from copper electronics recommends 30 amps max needed. (always purchase 10 amps more than recommended.)
Texas Star DX 500V class AB from copper electronics recommends 45 amps max. (always purchase 10 amps more than recommended)
With the Texas Star 1600 you have both options to run AB (clean sideband signal) or Class C (hammer down am audio monster)
This is why you will occasionally have someone saying (what is up with Texas Star, my bla bla bla amp will produce more wattage output and cost half as much) They fail to understand that they are most likely running a class C amp as where the Texas Star is a class AB. Generally a cleaner running amplifier will cost more to produce as quality has a price.
Does this make it easier to understand? |
Sitm
Intermediate Member
Username: Sitm
Post Number: 456
Registered: 1-2004
| | Posted on Friday, July 01, 2011 - 10:05 am: |
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There is no such thing as a stupid question Scooby. If I can help answer I will. |
Scooby_doobie
New member
Username: Scooby_doobie
Post Number: 8
Registered: 6-2011
| | Posted on Friday, July 01, 2011 - 8:53 pm: |
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Yes! now i got the idea, thanks alot Sitm.
so how many amps should i run the 1600 X with?.....and one more question, what should i use to drive this little sucker? |
Sitm
Intermediate Member
Username: Sitm
Post Number: 459
Registered: 1-2004
| | Posted on Tuesday, July 05, 2011 - 9:53 am: |
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In my opinion I would say that you need a power supply that has a surge rating of at least 150 amps to see maximum numbers on the unit in A/B mode. |
Drlholland
New member
Username: Drlholland
Post Number: 1
Registered: 11-2012
| | Posted on Saturday, November 24, 2012 - 5:56 pm: |
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I have a ts dx 1600x in the mail and was wondering if there is anything that should be done to it to operate on 11 meters as well as 10 meters. I dont like the idea of having anyone inside my equipment, that is why i bought a new one. From what i have read it should work out of the box on am 11 meters if needed. I have a General Grant with 2 2SC-2290`s that should be plenty to drive it with. I talk mostly ssb that what i liked about the dx-1600x as far as ab c class. The C class amplifiers arent as clean on ssb and you often have to add it to the price on a fatboy and xforce BIG amps. Im very excited to get this amp in the mail and hope that i can hook it up and use it when it gets here. Thanks DH |
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