Sunfire_Amplifier_Whitepaper 电路图.pdf

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1、 AMPLIFIER WHITEPAPER Sunfire amplifiers had their beginning over 25 years ago. After Bob Carver sold Phase Linear, which he founded in the early 1970s, and decided to start Carver Corporation, he wanted to come out with a new amplifier that would be light years ahead of anything available at that t

2、ime. He began work on a signal tracking power supply. Successfully implemented, an amplifier that incorporated such a power supply would be able to deliver lots of power, would run stone cold and would be incredibly efficient. All of the input power would become output power, it would be able to del

3、iver massive amounts of current and would drive almost any impedance down to 1 and below. It would have the potential of ultra-reliability because it would be running cold, would not require heat sinks, and because it would be so efficient the power supply could be much smaller for the equivalent ou

4、tput power in a conventional amplifier only 20% to 30% of the input power actually appears at the output of the amplifier as usable audio power. The story obviously doesnt end there SUNFIRE WHATS IN A NAME? It wasnt the greatest of beginnings Bob Carver toiled for more than a year trying to make thi

5、s design into a reality but couldnt get it to work. And so after a year of working until two in the morning he temporarily admitted defeat, set the design aside, and instead developed a different power supply called the Magnetic Field power supply. That power supply and its power amplifier became th

6、e original Carver Cube. This amp was used to start a small little audio company you may have heard of Carver Corporation. FAST FORWARD 13 YEARS In 1992, while still at Carver Corporation, Bob decided to have another go at the amp design that had earlier escaped him. He pulled out his notes from year

7、s prior, including the old patent, and this time he succeeded and succeeded in spades! The resulting amplifier was able to deliver massive power and enormous current; it could operate down to 1 and it didnt get hot. It did the impossible and fulfilled the dreams he had years ago. He dubbed that ampl

8、ifier the Lightstar. On December 17, 1992 he turned over the design to the engineering department for packaging and went on sabbatical with the intention of final tweaking and voicing upon his return. The rest of the story is best left to the attorneys, but the end result was that Bob left the compa

9、ny he had founded years earlier and embarked on a new venture. In 1993 a new Bob Carver “child” was born. At first it was Zeus Audio, named after his puppy (who sadly passed away in 2006), but Bob received a letter from an attorney who said, No, you cant name it Zeus because we represent an amplifie

10、r company who owns names like Hercules, Aphrodite, Apollo, and Zeus. No problem (he thought), and renamed the company Silvermane (taken from the color of his puppys coat). That promptly got him another letter from another Copyright 2006 Sunfire Corporation 1 RadioFans.CN 收音机爱 好者资料库 AMPLIFIER WHITEPA

11、PER attorney who wrote, No, I represent the Marvel Comics Group and we have a Superhero called Silvermane. Silvermane was out, and in 1994 Sunfire was born CONVENTIONAL AMPLIFIERS In order to understand how the Sunfire amplifier works, it is helpful to review a conventional amplifier and illustrate

12、some of the very difficult engineering problems associated with powerful, and very high current amplifiers. As you know, a conventional amplifier has a power supply; and for a 300 watt amplifier the power supply voltage is approximately 90 volts. Those 90 volts are parked way up at 90 volts above gr

13、ound. The audio signal varies under that voltage and as long as the amplitude of the audio signal remains below 90 volts, as illustrated in Figure 1, the amp will not clip or run out of power. 90 Audio Signal Figure 1 Of course, if the audio signal is required to be greater than the 90 volt power su

14、pply, the amplifier will clip as illustrated in Figure 2. 90 Volts Audio Signal Clipping Figure 2 Copyright 2006 Sunfire Corporation 2 RadioFans.CN 收音机爱 好者资料库 AMPLIFIER WHITEPAPER In a conventional amplifier, when the amplifier is delivering power to the loudspeaker load, the current flows out of th

15、e power supply, through the output transistor or transistors, and then into the load. Refer to Figure 3. Loudspeaker Output Transistor 90V Power Supply Current Flow Figure 3: As an example, assume the output voltage at the loudspeaker is 30 volts and 10 amperes of current are flowing. The current st

16、arts at the power supply and flows through the transistors; as it goes through the transistors it makes them get hot. How hot? The measure of hotness is power; voltage times amperage. Remember, there are 10 amperes flowing; and if there are 30 volts on the loudspeaker and there is a 90 volt power su

17、pply, that means there are 60 volts across the transistors. Again, the power is equal to volts times amps 60 volts times 10 amps equals 600 watts! That is not the power going to the load, thats the power going into the transistors as heat that must be dissipated. Hence, the transistors are mounted o

18、n a large heat sink; the heat is transferred to the heat sink and ultimately to the air around the unit ever notice how hot youre A/V cabinet gets? Since the amplifier is only about 20% to 30% efficient, a lot more power has to go into the amplifier than comes out because 600 watts is going up in he

19、at. Since its inefficient, there must be lots of output transistors, lots of heat sink(s), and the power supply has to be much larger than would ordinarily be required in order to make up for all the power thats being wasted. Instead of a 30 pound power supply, it has to be 80 pounds. Well, so what?

20、 Its not difficult to add power supply and heat sink(s) necessary to allow the amplifier to deliver the power. However, an insidious problem exists the output transistors that amplifier designers use are big 20 ampere output transistors. They are used in large, high end amplifiers and most of the bi

21、g receivers these days. It is a standard part in the electronics industry that is rated at 20 amperes. However, its only able to deliver 20 amperes if there are 10 volts or less across it. Thats because its a 200 Copyright 2006 Sunfire Corporation 3 RadioFans.CN 收音机爱 好者资料库 AMPLIFIER WHITEPAPER watt

22、part and can never dissipate more than 200 watts or its rating is exceeded. At 50 volts, for example, it can deliver only 4 amperes because 4 times 50 is 200. At 90 volts it can deliver only 2.2 amperes. Going back to the earlier example with 60 volts across it, it can deliver only 3.3 amperes. If a

23、 designer wants to have an amplifier thats able to deliver lots of current into very low impedance loads, to deliver current in an unvarying way, no matter how difficult the loudspeaker impedance, no matter what the phase angle, he or she must use many paralleled output transistors lots and lots of

24、them. In this case, they will not output the full 20 amperes, only a small portion of that, especially when driving low impedance loads. Consequently, a designer has to parallel many, many output transistors. These transistors arrays must be mounted on huge heat sinks to dissipate all the power wast

25、ed as heat. And to make matter worse, because the amplifier is not very efficient it must have a huge power supply if youve ever “popped the hood” on an amplifier or receiver youve likely seen this in action. Since each transistor draws its own idling current, the amplifier tends to run hot when it

26、is just sitting there at idle. Biasing issues become very severe problems and to this day other manufacturers are still searching for solutions. Engineers and designers forever fret over whether theyre going to bias their amplifiers Class A, Class AB, or use a sliding bias scheme. Amplifiers that ca

27、n deliver these awesome and majestic currents do exist, but to get there you would have to reach up to the ones that are very expensive starting at about $8,000. There is a better way. SUNFIRES TRACKING DOWNCONVERTER In the Sunfire amplifier, that 90 volt power supply voltage that was mentioned earl

28、ier is no longer “parked” at 90 volts above ground. Instead it is brought down and parked at only 6 volts above ground; the 90 volt constant no longer exists! Then, at any moment in time, regardless of what the output of the amplifier is, the power supply voltage will always be 6 volts above the out

29、put signal. Lets read that again, because that was the breakthrough “At any moment in time, regardless of what the output of the amplifier is, the power supply voltage will always be 6 volts above the output signal.” If the output signal is zero, the output of the Tracking Downconverter will be 6 vo

30、lts. If the output of the power amplifier is 30 volts, as in the previous example, the output of the Tracking Downconverter will be 36 volts. The voltage across the transistors remains a constant, unvarying 6 volts. Therein lays the beauty of the Tracking Downconverter. Now, consider the earlier “po

31、or conventional amp” example. The amplifier was delivering 30 volts to the load and 10 amperes of current were flowing. That example resulted in 600 watts of power in the output transistors. Consider Figure 4 on the next page. Copyright 2006 Sunfire Corporation 4 AMPLIFIER WHITEPAPER Voltage output

32、of Tracking Downconverter Audio Signal 6 Volts 6 Volts Figure 4 In the Sunfire amplifier, that same 10 amperes is not dropping across 60 volts. Instead, its dropping across 6 volts so the power is only 6 volts times 10 amps 60 watts wasted rather than 600 watts. Ten times less thats an order of magn

33、itude! Its so little power that the amplifier does not have a heat sink, it simply doesnt need one. There is not a heat sink to be seen in this amplifier, yet it can deliver well over 2,000 watts into 1. And because of its increased efficiency, the power supply doesnt have to weigh 80 pounds. The po

34、wer supply can be a reasonable 30 pounds. But heres the best part remember that a 20 ampere transistor can only deliver the full 20 amperes if there are 10 volts or less across it (because of its intrinsic 200 watt limit). In the Sunfire amplifier, since there are only 6 volts across the transistors

35、 at all times, the full output current of 20 amperes can be delivered from each output transistor instead of 2, 3 or 4 amperes as in a conventional amplifier. Because each output transistor can deliver its full 20 amperes, the amp can deliver lots and lots of current into low impedance loads. In mod

36、ern Sunfire amplifers, 18 output transistors are used per channel, each capable of 20 amperes. That represents a potential peak to peak output current of over 240 amperes! And it can do so into vanishing low load impedances. Thats a staggering amount of current, and what is required to have an ampli

37、fier with the performance of a $10,000 machine. Copyright 2006 Sunfire Corporation 5 AMPLIFIER WHITEPAPER A remarkable feature of the Tracking Downconverter is its intrinsic and unique ability to transform high voltage and low current to low voltage and high current. For example, if the input power

38、to the Downconverter is being delivered at a very high voltage, the output power can be delivered at a very high current. The transformation ratio; i.e., how much the current is increased is in the same proportion that the voltage is decreased. In the case of the Sunfire, the power supply voltage is

39、 2 times 125 volts, approximately 250 volts. Therefore, if the input current is 10 amperes and the output voltage is 25 volts, corresponding to a difficult or low load impedance, the output current will be 100 amperes because 250 divided by 25 is 10. (The input current 10 amperes multiplied at the o

40、utput by 10 for 100 amperes. A conventional amp could never do that, i.e. 10 amps in equals 10 amps out.) See Figure 5. Down Converter Inductor INPUT 10 Amps 125 Volts RMS Hexfet Diode Energy Storage Capacitor Load Figure 5 It is this remarkable property of a Tracking Downconverter that allows the a

41、mplifier to deliver tons of current into vanishing low load impedances. It is also the property that allows the amp to run cold, to have a smaller power supply than would conventionally be required, and to possess a very flat output voltage characteristic. Whenever the load impedance is halved, the

42、power just continuously doubles. A scientist would call this load invariant. At that point in the design, the Sunfire was an amplifier that could deliver almost limitless current, almost limitless voltage and deliver both simultaneously for tremendous output power and runs cold. However, at this poi

43、nt in the design, its full benefits were not yet realized. The amplifier needed to be listened to. Copyright 2006 Sunfire Corporation 6 AMPLIFIER WHITEPAPER TO HEAR IS TO FEEL Listening to an amplifier in its design process is potentially the most time consuming, and is where the art of amplifier de

44、sign enters the picture. Bob first used a female vocalist to make certain that she could be accurately located in an acoustic space between the speakers and in such a way that a believable halo of space surrounded her and she became palpably three dimensional. Also, her voice was soft, musical, lyri

45、cal and had a great deal of believability. After the female voice, he listened to the male voice using baritones to listen for the “chestiness” in the male voice. When that part of the work was completed, he went to the symphony in spirit at least. Since human voice reproduction was so stunning in h

46、is first listening tests, he found that the symphony orchestra locked in and there wasnt much tweaking needed sort of like getting flesh tones correct on a color television, all the other colors often lock in with very little effort. At that point Sunfire had an amplifier that was tremendous. It had

47、 lots of current, lots of voltage, incredible performance, but there was still more to come. CURRENT SOURCE VOLTAGE SOURCE A transistor is inherently a voltage source device; whenever an amplifier designer designs an amplifier with transistors, the result is a solid state amp that will typically hav

48、e a very low output impedance approaching zero. A vacuum tube, on the other hand, is intrinsically a current source device. If an amplifier designer builds an amplifier out of vacuum tubes, he or she typically ends up with an amplifier that has a current source output characteristic, i.e., a higher

49、output impedance. Its this high output impedance that is primarily responsible for 80% to 90% of what makes a vacuum tube amplifier sound like a vacuum tube amplifier a glow to the midrange, a soft high end, typically a layered stage depth and often a sound stage that is wider than it would be with a solid state amplifier. This musical presentation is very pleasing and