couplequestions

[goodstuff]

ok what do the different classes of amps mean? like a,b,c,d ?

What about power supplies, which is better regulated or unregulated, how can I tell the differenence?

How can I change the demeaning moniker of "junior member"? I don't enjoy being called junior, even if it just a message board.

[Randy Savage]

CLASS 'A'
Many class A amplifiers use the same transistor(s) for both halves of the audio waveform. In this configuration, the output transistor(s) always has current flowing through it, even if it has no audio signal (the output transistors never 'turn off'). The current flowing through it is D.C. A pure class 'A' amplifier is very inefficient and generally runs very hot even when there is no audio output. The current flowing through the output transistor(s) (with no audio signal) may be as much as the current which will be driven through the speaker load at FULL audio output power. Many people believe class 'A' amps to sound better than other configurations (and this may have been true at some point in time) but a well designed amplifier won't have any 'sound' and even the most critical 'ear' would be hard-pressed to tell one design from another.
NOTE: Some class A amplifiers use complimentary (separate transistors for positive and negative halves of the waveform) transistors for their output stage.


CLASS 'B'
A class 'B' amplifier uses complimentary transistors for each half of the waveform. A true class 'B' amplifier is NOT generally used for audio. In a class 'B' amplifier, there is a small part of the waveform which will be distorted. You should remember from an earlier page, that it takes approximately .6 volts (measured from base to emitter) to get a bipolar transistor to start conducting. In a pure class 'B' amplifier, the output transistors are not "biased" to an 'on' state of operation. This means that the the part of the waveform which falls within this .6 volt window will not be reproduced accurately. The output transistors for each half of the waveform (positive and negative) will each have a .6 volt area in which they will not be conducting. The distorted part of the waveform is called 'crossover' or 'notch' distortion. Remember that distortion is any unwanted variation in a signal (compared to the original signal). The diagram below shows what crossover distortion looks like.

CLASS 'AB'
As we said earlier, a class 'A' amplifier is very inefficient. This is not good for a car audio amplifier. We also said that a class 'B' amplifier will cause a signal to be distorted, which is not good in any audio amplifier. A class 'AB' amplifier is the best compromise. 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. This eliminates virtually all of the crossover distortion. The bias current is flowing because the output transistors are always conducting current (even without an audio signal). This differs from a pure class 'A' amplifier in the amount of current flow. A pure class 'A' amplifier has an enormous amount of current flowing through its output transistors with NO audio signal. A pure class 'B' amplifier has NO current flowing through its outputs with no input signal. A class 'AB' amplifier is much more efficient than the class 'A' but without the distortion of the class 'B'. MANY of the car audio amplifiers which claim to be a class 'A' amplifier are just a high bias class 'AB' design. These amplifiers are only class 'A' at very low power output levels. At higher power levels, one of the output transistors will switch off while the other output transistor is conducting. I don't want you to think that I am telling you that there are no class 'A' amplifiers. There are a few high quality mobile amplifiers which are a true class 'A' design.


CLASS 'D'
We said that class 'A' amplifiers were VERY inefficient. Class 'AB' amplifiers are also inefficient but are more more efficient than class 'A' amplifiers. Class 'AB' mobile amplifiers are generally 60% efficient when driving a 4 ohm load at maximum power (just before clipping). The reason that these amplifier configurations are inefficient is because there is a difference of potential (voltage) across the output transistors and current flowing through the output transistors. When you have voltage across the device and current flow through the device, there will be power dissipation in the form of heat. The power needed to produce this heat is wasted power. When there is (virtually) no voltage drop across a device (such as a large piece of wire or a transistor), there can be a significant amount of CURRENT flow through the device with (virtually) no power dissipation. This means that there is virtually no heat given off (highly efficient). The inverse is also true. If you have a significant amount of VOLTAGE across the device (transistor, wire...) but no current flow through the device, again, there will be no wasted power.
OK, now to the point. A class 'D' amplifier, which may also be known as a switching amplifier or a digital amplifier, utilizes output transistors which are either completely turned on or completely turned off (they're operating in switch mode). This means that when the transistors are conducting (switched on) there is virtually no voltage across the transistor and when there is a significant voltage across the transistor (switched off), there is no current flowing through the transistor. This is very similar to the operation of a switching power supply which is very efficient.





www.eatel.net

[Randy Savage]

UNregulated Power Supply:
An unregulated power supply is by far the simplest switch mode power supply (SMPS) used in mobile power amplifiers. The transistor(s) driving each half of the transformer primary winding are driven at full duty cycle. The duty cycle does not change during normal operation. No matter how low or high the battery voltage gets, the duty cycle will not change. Unless, of course, the voltage gets too low to operate. Then the supply control chip will simply quit driving the power supply FETs (the supply will shut down completely). Under normal operating conditions, the no-load rail voltage (amp idling, no audio out) will vary in direct proportion to the battery voltage.

Unregulated Power supplies and Changes in Battery Voltage:
As we mentioned above, the battery voltage is not constant. It may vary from 11.5-12.5 volts with the engine off to ~14.4 volts with the engine running. If the battery voltage is 12 volts and the transformer has a 1:2 ratio as in the previous example, the power supply will produce ±24 volts. If the battery voltage is 14.4 volts, the supply will produce ±28.8 volts (an extra 9.6 volts). This is why amplifiers with unregulated power supplies have significantly different power ratings with different battery voltages. A change in battery voltage directly effects the rail voltage. If the output transistors were 100% efficient (they aren't) and could deliver the full rail voltage to the speakers, the following calculations show you how the difference in battery voltage produces different power outputs into a 4 ohm speaker load.


Stiffly regulated power supplies
In an unregulated power supply, the engineers simply use the transformer ratio along with the primary voltage to determine the rail voltage but battery voltage fluctuations (and copper and core losses) cause the secondary rail voltage to fluctuate. In a stiffly regulated power supply, there is a circuit which continually monitors the rail voltage and varies the duty cycle to keep the rail voltage very close or exactly at the target voltage. At no point in time, under normal operating conditions, will the rail voltage fall below the target voltage.

If, in a regulated power supply, we want a total secondary target voltage of 48 volts (±24 volts) with a 12 volt battery voltage (as in the first example) we could use a 1:2 ratio but as soon as a load is placed on the power supply rails (because you turned up the volume), the rail voltage sags, even if the power supply pushes the FET duty cycle drive to 50% (as high as it can go). Why? The transformer doesn't have enough ratio to overcome losses (due to inefficiencies). If we increase the ratio to 1:3, the control chip in a regulated power supply will reduce the duty cycle to prevent overshooting the target voltage (when there is little or no audio output). Now, when current is drawn from the power supply rails, the duty cycle is increased just enough to maintain the target voltage. In a stiffly regulated power supply, the transformer ratio may be 50 or 60 percent higher than in a non regulated power supply. An amplifier with a stiffly regulated power supply can typically double the power output when the impedance is halved (4 ohms to 2 ohms per channel for example). The tradeoff (and there are always tradeoffs in any type of design) with stiffly regulated supplies is a somewhat lower efficiency and a reduction of power output with lighter loads (Stay tuned, I'll explain in the next section). If you remember the Ohm's law formula for power P=E^2/R, you can see that the power output will double if the resistance is cut in half when the voltage applied across the speaker load remains constant (regulated, in this case). This type of power supply can generally maintain its rated power output over a large range of battery voltages.

One Drawback of Tight Regulation:
From the previous example, remember that the ratio was 1:3 but the target voltage was only 48 volts (±24 volts). If the power supply with the 1:3 transformer was allowed to drive the FETs at a full 50% duty cycle, as in the unregulated power supply, the no load rail voltage would be 72 volts (±36 volts). This means that the amplifier has the capability to produce higher rail voltage and therefore more power output into light (4 ohm stereo) loads but is limited by regulation. Some manufacturers use the stiffly regulated power supply so that they can say that the amplifiers can double their rated output by reducing the impedance by half (this is considered to be a big deal by some consumers). Others may use a regulated supply because some components are sensitive to high voltage and they are being run close to their maximum safe operating levels. This, for example, happens when an engineer is trying to maximize capacitance with limited space (higher voltage capacitors with the same capacitance would be physically larger). The stiff regulation also makes it easier to maintain proper biasing of the output transistors which may (but not necessarily) mean better sound quality at low volume.

Moderately-regulated power supply:
MANY amplifiers fall into this category. This, in my opinion, is the best of both worlds. This type of power supply uses a transformer ratio slightly higher than that needed to produce its target voltage. It's duty cycle (typically) is less than 50% when the battery voltage is greater than 12 volts (actual voltage determined by the circuit designer) and/or there is very little current flowing from the rails (when the amp is at idle). As soon as the rail voltage falls below the target voltage, the duty cycle quickly goes to ~50% (full duty cycle). This type of power supply will prevent an overvoltage condition on the secondary of the power supply and is also very efficient.

[maylar]

What he said...

Your title will change with the number of posts you make. I think Junior goes away after 25 or 30. After 300 you can change it to whatever you want. Please don't use that as a reason to post nonsense.

[tommyk90]

Originally posted by maylar
What he said...
After 300 you can change it to whatever you want. Please don't use that as a reason to post nonsense.

Yes, that seems to be the trend these days. Kinda degrading this forum. I've gotten where i am by posting useful advice (well most of the time anyways) and have learned a great deal in the process. Just come around here more often, read most of the current trends, then you can start posting info of your own. Just don't go around posting nonsense like some of the people have lately.

[goodstuff]

umm...umm...hmm...ok... so in english which do y'all prefer, regulated or unregulated? what about classes? d?...I was able to follow some of that but I don't have a degree in electrical engineering or anything and it looks like a lot of the info is textbook stuff and no I have not posted useless bullshiznit..i've been trying to help peeps on here it seems like a lot of them have a tough time with the easy stuff and thats about all I know ...so that explains why people are answering questions that have been answered by someone else....anyways thanks for the info

[maylar]

Originally posted by drfunnepantz
umm...umm...hmm...ok... so in english which do y'all prefer, regulated or unregulated? what about classes? d?...

Hehe... yea, it tends to get techie around here sometimes. So, in simpler terms:

The vast majority of amps are Class AB. They have wide frequency response, very low distortion and low noise. Used for all applications, especially main amps. Their downside is that they draw almost twice as much power from your electrical system as they put out in audio.

Class D amps are far more efficient, so they take less demand from your electrical system for a given output power. But they have very limited frequency response, higher distortion and higher noise. They're used exclusively for sub amps. Most are mono (one channel). I would recommend a Class D sub amp for anything over 500 watts.

Amps with regulated supplies have better performance, in that their output power does not change with system voltage. They cost more than unregulated systems, and tend to be bigger and heavier because of the extra circuitry and heatsinks. I would prefer a unit that was regulated, but I would not make that one of the primary selection criteria.

My comment about posting nonsense was not aimed at you. Just at the lamers who post "me too" 300 times to get their post count up.

Hope I helped.