Interesting Reads: - Bob C / Carver / Sunfire

Interesting facts/opinions about the man himself.
Post Reply
User avatar
Toy Maker
Puppet Master
Posts: 6875
Joined: Wed Oct 08, 2003 1:26 am

Interesting Reads: - Bob C / Carver / Sunfire

Post by Toy Maker » Sun Oct 28, 2007 3:41 pm

The Sunfire Amplifier, A White Paper
Conversational English, transcribed from a talk given
Bob Carver

Sunfire Corporation
P.O. Box 1589
Snohomish, WA 98290
Tel. 206-335-4748

Introduction: Bob Carver may be high end audio's most famous (or infamous) enfant terrible. Praised by many as an inventive genius, damned by others -- especially the high end trade press -- as a charlatan, he is someone who cannot be ignored. Carver's biggest sin is probably that of being an original thinker. For the high end orthodoxy, such radical thinkers are best burned at the media stake. (Bob Carver as Giordano Bruno? Perhaps.) Carver has struck once again, with his groundbreaking Sunfire amplifier. Herewith, 21st/Tone begins a new series of white papers on audio innovations. This Bob Carver article describes how he went about creating the new Sunfire. -- Ed



This amplifier had its beginning over fifteen years ago. After I sold Phase Linear, which I founded in the early 70's, and decided to start Carver Corporation, I wanted to come out with a new amplifier that would be light years ahead of anything currently available. I 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, would be incredibly efficient; all of the input power would become output power, it would be able to deliver massive amounts of current and would drive almost any impedance down to I ohm 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 output 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.) I toiled over a year trying to make this into a reality but couldn't get it to work. And so, after a year of working until two in the morning, I finally gave up and instead developed a different power supply called the Magnetic Field power supply. That power supply and its power amplifier became the original Carver "Cube." I used that to start Carver Corporation.


A little over two years ago, while still at Carver Corporation, I decided to have another go at it. I pulled out my notes from years ago, including the old patent; this time I succeeded, and succeeded in spades. The resulting amplifier was able to deliver massive power and humongous current, it could operate down to I ohm and it didn't get hot. In short, it fulfilled the original dreams I had years ago. I called that amplifier the Lightstar, and on December 17, 1992, I turned over the design to my engineering department for packaging (having completed about 95% of the work), and went on a sabbatical with the intention of final tweaking and voicing when I got back. Upon my return, I had a falling out with Carver Corporation and early last year left Carver to form Sunfire Corporation. At first it was Zeus Audio, named after my puppy, but I received a letter from an attorney who said, "No, you can't name it Zeus because we represent an amplifier company and we have names like Hercules, Aphrodite, Apollo, and Zeus." I renamed the company Silvermane, and promptly got a letter from another attorney who wrote, "No, I represent the Marvel Comics Group and we have a Superhero called Silvermane." Silvermane was out. Enter Sunfire.


In order to understand how the Sunfire amplifier works, it would be helpful to review a conventional amplifier and illustrate 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. That 90 volts is parked way up in the sky at 90 volts above ground zero. The audio signal varies under that voltage and as long as the amplitude of the audio signal remains below 90 volts, the amp will not clip or run out of power.

As an example, assume the output voltage at the loudspeaker is 30 volts, and10 amperes of current are flowing. The current starts 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 becomes amperage. Remember, there are 10 amperes flowing and if there are 30 volts on the loudspeaker and there is a 90 volt power supply, 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, that's the power going into the transistors as heat and must be gotten rid of. Hence, the transistors are mounted on a large heat sink; the heat is transferred to the heat sink and ultimately to the atmosphere.

Now, 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 heat. Since it's inefficient, there must be lots of output transistors, lots of heat sink, and the power supply has to be much larger than would ordinarily be required in order to make up for all the power that's being wasted. Instead of a 30 pound power supply, it has to be 80 pounds. Well, so what? It's not difficult to add the power supply and heat sink necessary to allow the amplifier to deliver the power. However, a problem that is very insidious exists!

The problem is this. The output transistors that amplifier designers use are big 20 ampere output transistors. I use them, they are used in small amplifiers and large amplifiers. They are used in high end amplifiers and are even used in most of the big receivers these days. It's a standard part in our industry. It's the big Motorola, Toshiba the Sanyo or Sony equivalent. This transistor is rated at 20 amperes. However, it's only able to deliver 20 amperes if there are 10 volts or less across it. That's because it's a 200 watt 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. Not very much current. If a designer wants to have an amplifier that's 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 them. Remember, they are not good for 20 amperes, they are really only good for a small portion of that, especially when driving low impedance loads.

Consequently, a designer has to parallel many, many output transistors. He or she must mount these transistors on huge heat sinks, and, because the amplifier is not very efficient it must have a huge power supply. Since each transistor draws its own idling current, the amplifier tends to run hot when it is just sitting there at idle. Biasing issues become very severe problems. To this day, solutions are still being sought. For example, Nelson Pass uses the sliding biasing circuit, and Krell uses a four-tiered switchable dynamic biasing circuit. Engineers and designers forever fret over whether they're going to bias their amplifiers Class A, or Class AB, or use a sliding bias scheme. Big problem. Still, amplifiers that can deliver these awesome and majestic currents do exist, but to get there you have to reach up to the big Mark Levinson's, Thresholds, the big Jeff Roland's, even the massive Krell's. Those amplifiers can deliver the performance, but they are very expensive -- starting at about $8,000. There is a better way.


In the Sunfire amplifier, that 90 volt power supply voltage that I mentioned earlier is removed from being parked 90 volts above ground, and is brought down and parked at only 6 volts above ground. The 90 volts no longer exists. Then, at any moment in time, regardless of what the output of the amplifier is, that 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 volts. 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 lies the beauty of the Tracking Downconverter.

Now, consider the previous example. The amplifier was delivering 30 volts to the load and10 amperes of current were flowing. That example resulted in 600 watts of power in the output transistors. In the Sunfire amplifier, that same 10 amperes is not dropping across 60 volts. Instead, it's dropping across 6 volts so the power is only 6 volts times 10 amps -- 60 watts wasted rather than 600 watts. Ten times less -- an order of magnitude less. It's so little power that the amplifier does not have a heat sink; it doesn't 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 ohm. And because of its increased efficiency, the power supply doesn't have to weigh 80 pounds. The power supply can be a reasonable 30 pounds.

But here's 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 200 watt limit). In the Sunfire, since there are only 6 volts across the transistors 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 the Sunfire I used 12 output transistors per channel, each capable of 20 amperes; that represents a peak to peak output current of over 240 amperes. And it can do so into varnishing low load impedances. That's a staggering amount of current. That's what is required to have an amplifier with the performance of a $10,000 machine.


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 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 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 is10. (The input current 10 amperes multiplied at the output by 10 for 100 amperes. A conventional amp could never do that, i.e. 10 amps in equals 10 amps out.) . It's this remarkable property of a Tracking Downconverter that allows the amplifier 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 power just continuously doubles. A scientist would say "load invariant". Have you ever lusted for a $7,000 - $20,000 Mark Levinson, Roland, Krell, or Boulder amplifier?

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, the design is not yet complete. The amplifier needs to be listened to. Listening to an amplifier in its design process is potentially the most time consuming, and is where the art of amplifier design enters the picture. When I listen, I first use a female vocalist and make certain that she can be accurately located in an acoustic space between the speakers and in such a way that a believable halo of space surrounds her, and she becomes palpably three dimensional. Also, I want her voice to be soft, musical, lyrical and have a great deal of believability. After the female voice, I listen to the male voice using baritones for the chestiness in the human male voice. When that part of the work is completed, I go to the symphony. I have in my head a template of what a symphony orchestra should sound like. I close my eyes and fit the sound of that symphony orchestra in my head, to the sound that my amplifier is making through the loudspeakers. In the case of the Sunfire, since human voice reproduction was so stunning, I found that the symphony orchestra locked in and I didn't have to do anything --- sort of like getting flesh tones correct on a color television receiver, all the other colors often lock in with very little effort. Getting the flesh tones correct is the most difficult process of designing a color set. But I digress. This effort was because I wanted a totally accurate amplifier.


At that point I had an amplifier that was tremendous -- lots of current, lots of voltage, incredible performance and then I added a unique feature: A choice of outputs -- voltage source output and current source output. Let me explain. 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 have 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 output impedance. It's this high output impedance that is primarily responsible for at least 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 an open sound stage that is wider than it would be with a solid state amplifier. This musical presentation is very sumptuous and lovely to listen to, is quite captivating and the main reason many people love vacuum tube amplifiers.

Now, back to the Sunfire. Sunfire has two sets of output terminals on the back. One is a voltage source output with very low impedance. The other is a current source output with a higher impedance (current source) output characteristic. The choice of which to use is up to you. If you wish a solid state kind of sound, use the voltage source output terminals. If you want the vacuum tube sound, use the current source output terminals. Or, and this is the best part, you can bi-wire your speakers. Use the voltage source to the woofer, and wire the current source to the upper range of the system. That way you have the tight slam impact bass that a solid state amplifier can deliver, and you have the glow to the midrange, the sumptuous sound stage, and soft, delicately detailed highs that current source amplifiers typically deliver, i.e., vacuum tube amplifiers. The best of both worlds -- Again, when wired that way, you have tight bass, a beautiful sound stage, a sumptuous high end and a very believable sense of layered depth to the sound stage that is simply not available from a solid state amplifier. (At least from normal output impedance solid state amplifiers.)


The input stage is a low noise FET operational amplifier operated in a forced Class A single ended mode. The output of this stage drives balanced Class A level shifters and a balanced Class A voltage stage that swings the full rail of 250 volts peak to peak. The remainder of the current gain stages run full balanced with a constant VCE of 6 volts to the loudspeaker. It is heavily biased into the Class A region for small signals and Class AB region for large signals. Since the power dissipation in the output stages under simple quiescent bias conditions is 15 times less than a regular amplifier for the same output power, much more idle current can be used. The issue of how to bias this amplifier becomes moot -- all but irrelevant. All of the biasing issues simply evaporate because of the 6 volts. Even though it has a vacuum tube output characteristic on the current source output terminals, there is not a vacuum tube inside at all -- except for the meter pilot lamp, it's fully solid state.


Coming in from the outside world, we find a conventional main power supply; a large power transformer and filter capacitors. The output of this power supply feeds the Tracking Downconverter. The output of the Tracking Downconverter is fully regulated and tracks the audio, receiving its input signal from the same signal that drives the main amplifier. Essentially, the Tracking Downconverter is another power amplifier because its output voltage is in synchronism with, and tracks the audio signal, always above it a constant 6 volts. The input to the downconverter is a small signal Class A Motorola transistor. The output of this transistor drives a Texas Instrument PWM digital comparator. The output of the comparator drives a Hewlett Packard precision optocoupler which level shifts the digital control pulses to the gates of 12 International Rectifier Hexfets. The final output is smoothed into a continuously varying tracking voltage by the main energy storage downconverter inductor wound with humongous #12 wire on a low loss non-saturating ferrite inductor. The final energy storage capacitor is a 6.8 microfarad low ESR unit, and 12 dB of feedback is taken from this capacitor to the input stage. Finally, a Shotky free wheeling diode provides the energy return path for the Hexfet side of the downconverter inductor.


Many amplifier testers will operate an amplifier into an essentially dead short circuit and give it a pulse of 500 microseconds or 20 microseconds or even one-thousandth of a second and measure the output current. This test is only a parlor trick since the output current can be very large, but since the load impedance is zero, and power is I squared R, no matter how large the current, the output power is zero. It is a parlor trick. The amplifier could never sustain those huge currents for more than a few hundred microseconds because if it did, the transistors would blow up.

Take a conventional amplifier and do such a test with it and you can have incredibly high currents for a few hundred microseconds, but not for long. The amplifier would blow up because for the high voltages that exist across the transistors during that moment in time, the transistors are rated for only a few amperes (not tens or hundreds of amperes). However, this test does tell the amplifier tester a lot about the protection circuits. A skilled tester can determine whether the amplifier has current limiters or power-fold back protection circuits, or whether it doesn't have any protection circuits at all and relies on fuses alone. It does not tell anything about how much useful current the amplifier can deliver. A conventional amplifier may deliver 60 amperes or more for 100 microseconds but could not, under those conditions, ever deliver more than 8 amperes of current for longer than that. Not exactly a high current amplifier. Again, it tells us something about the action of the protection circuits, but not about the current capability of the amplifier. By comparison, the Sunfire could deliver those huge currents all day long -- far longer than a few hundred microseconds.


1) Full output current from each transistor is always available up to 20 amperes per transistor.

2) Massive output current is available even at low output impedances.

3) Heat sinks are not required.

4) Power continuously doubles down to below 1 ohm.

5) Most of the input power goes to the load, therefore, the power supply can weigh 30 pounds instead of 80 pounds. The amplifier can supply humongous current, massive output power, tremendous voltage, runs cool, and is very efficient.

6) Only 12 output transistors are needed per channel for peak-to-peak current of 240 amps.

7) Bias current and idling current issues become irrelevant and nonproblematic.

8) The Tracking Downconverter multiplies current in the same ratio that the output voltage is reduced and it does so automatically by its intrinsic nature.

9) At high impedances, it delivers high voltage and high current. At low impedances or difficult impedances, it delivers even more current, delivering awesome and difficult to believe amounts.

10) When biwired, Sunfire delivers incredible bass whack and a huge three dimensional sound stage with detail retrieval so stunning that you will often hear musicians breathing.

11 ) Costs far less than any other amplifier in the world that has Sunfire's performance. All because of science and the uncanny Tracking Downconverter.


My philosophy regarding amplifier design is embodied in this new Sunfire amplifier. The amplifier speaks for itself, but I would like to address some of the details:

INTEGRATED CIRCUIT OPERATIONAL AMPLIFIERS -- In the past, monolithic integrated circuit operational amplifiers (op amps) have received a bad rap for use in audio circuits, and for good reason. My experience has been that if a sampling of op amps, all from the same manufacturer, and all the same number, are tested, one finds that about one in fifteen will exhibit some crossover notch distortion. The reason for this is that most op amps operate with a Class AB output stage, but they do not have a control for adjusting the idling current.

Since an op amp is subject to the same limitations that a big amplifier is, some of the units will exhibit large crossover notch distortion, most will exhibit none, and a few of them will actually run slightly warmer than intended. In high speed mass production the op amp idling current is set by the design of the circuit, but it does not come with an adjustment to allow for variations in idling current. This problem may be completely eliminated by operating op amps in what's known as forced Class A operation. This is very easy to do. All that is required is a current source or a simple pull up resistor installed at the output of the amplifier. This forces one transistor to be always off and the other transistor to be continuously operating as a single ended Class A output device. As long as the op amp is operated within the new current source limit, the output will be totally free of crossover notch distortion. The practical result is that any family of op amps can be used with absolute assurance that all of them, time after time again, will not have crossover non-linearities.

In the past, this problem has given op amps a very bad name for use in audio circuits and, from my perspective, unnecessarily so. Yet, as you can see, not without good reason. In my designs, whenever I use an op amp, I always use a current source at its output. The choice of whether to use an op amp or to use discrete components is a matter of application. For example, for low distortion small signal requirements, an op amp is definitely the way to go. Normally, an op amp will have better power supply rejection and will be far more linear. In the case of FET input amplifiers, vanishing low offset voltages and great immunity to input rectification accrue. Slew rates can be as high as we please and distortion as low as we please, depending on the choice of op amps. However, in other applications, for example, one with large signal swings, a discrete circuit is best when higher current is required than is normally available from integrated circuit op amps.

In conclusion, for a small signal amplifier operating on plus and minus 15 volts, I would always chose a good op amp. I would never build a discrete one unless I had a very special application, i.e. high current or high voltage output.


I design with discrete circuits whenever I have complex feedback issues, or when I have complex signal processing issues in which control voltages must be developed for muting circuits, protection circuits, or dynamic control circuits as in a prologic decoder and, of course, in the output stages and driver stages of high power, high current audio amplifiers.


I prefer to use film capacitors for coupling capacitors and to use electrolytic and/or film capacitors in bypass applications. I prefer to use ceramic capacitors in high frequency feedback systems and for certain high frequency bypass applications. I use electrolytics for energy storage and will use an electrolytic capacitor as a coupling capacitor provided that under no condition is the voltage across the capacitor allowed to vary at all. This means that a very large coupling capacitor has to be used at the lowest frequency of interest and it must be approximately 100 times larger than normally required. Hence, an electrolytic can't be used in a filter circuit or critical timing circuit. In that case I would use either a film capacitor or a precision ceramic capacitor.

Further, I believe that ceramic capacitors are best for high frequency stabilization in feedback loops, and the use of film capacitors in that application is something that relatively inexperienced designers do, and for the most part I consider to be a fad having essentially zero scientific substance. When you examine a circuit that I design, you will find a mixture of electrolytic capacitors, ceramic capacitors tantalum capacitors, film capacitors, low ESR film capacitors, and high current capacitors, depending on the particular application. Each type of capacitor has its advantages and disadvantages when used in any particular circuit. The choices you will see in my circuit designs are the ones that I believe yield the best results and the best sound.


I believe that the output stage of a power amplifier is best served by designing and building it with bipolar transistors simply because bipolar transistors are more linear, can deliver more current, and will typically have better SOA (Safe Operating Area) specifications for simultaneous voltage and current when compared to an equivalent mosfet. If a very high performing amplifier is desired, bipolar transistors are the exclusive way to go and you can see this by simply surveying the amplifiers on the market. All the very expensive, very high current, high performing amplifiers in the $8,000, $10,000, $15,000 price range use bipolar transistors. Not one is designed using mosfets. Bipolars are best in audio output stages. The use of mosfets in audio output stages, again, is basically in my opinion, a fad. Excellent results, of course, can be obtained in lower priced, lower powered amplifiers using mosfets.

(Brand name of International Rectifier mosfets)

I design high power clocking circuits using mosfets because that's where their advantage lies. If a device is going to be on or off, then a mosfet is definitely the way to go because Safe Operating Area considerations are not an issue, and their high speed and lack of storage time can yield incredible efficiencies. In those applications they are extremely rugged -- far more rugged than bipolar transistors -- just the opposite of when used as a linear output device, in which case bipolars are more rugged than mosfets.

To summarize, I use bipolars for linear operation, and mosfets in digital applications. Given the choice, I would never do otherwise. (Given the best of both devices currently available.)


My choice of using precision parts is based on my scientific view of the world. It's not based on myth or fads. For example, in my Sunfire, I use the fastest, lowest transition time, highest precision digital comparator on the face of the earth. That is a Hewlett Packard HCPL-2611 because the circuit performs best when using the best precision available. In the case of circuit performance, I ordinarily use 1% precision resistors because by using 1% resistors, assembly and manufacturing efficiencies are vastly increased because provisions for adjusting the circuit to come into specifications are not required. Each circuit works the same as the previous circuit time after time after time in a manufacturing environment.


I think that false beliefs, especially in audio, have given rise to some really wild designs, for example, $25,000 nine watt audio amplifiers. You will never find me designing such equipment -- I simply do not believe in it. However, I love to read about such designs, and I love to think and talk about them. I'm overjoyed there are people in this world who do design amplifiers like that. It's part of what makes audio so much fun.

The VXM Network,

User avatar
Toy Maker
Puppet Master
Posts: 6875
Joined: Wed Oct 08, 2003 1:26 am

Interesting read

Post by Toy Maker » Wed Nov 07, 2007 1:36 am

User avatar
Posts: 5426
Joined: Sat Jun 30, 2007 1:43 pm
Location: Tampa, FL

Post by engtaz » Wed Nov 07, 2007 6:02 am

Thanks for the info.


Posts: 7809
Joined: Mon Oct 16, 2006 5:39 pm
Location: The tube lair in Charlotte, NC

Post by treitz3 » Wed Nov 07, 2007 6:13 pm

I see you found it. Good deal! This kind of info. is the shiznit! :D :D :D =D>
In search of accurate reproduction of music. Real sound is my reference and while perfection may not be attainable? If I chase it, I might just catch excellence.

The best way to enjoy digital music reproduction is to never listen to a good analogue reproduction.

User avatar
(Pair of Silver 9t's)
Posts: 2951
Joined: Wed Oct 27, 2004 6:18 pm
Location: the World We Skate Our 'Choppers' Thru

Post by maddmaxxx » Wed Nov 07, 2007 9:16 pm

-what does 'shiznit' meen ?

-i just want to be 'hip' these days, not 'unkuul' 8)
-* © Küül ®™ /mx...
-Too hip gotta book
-"Don't BAN me Bro!"...el/doro

User avatar
Toy Maker
Puppet Master
Posts: 6875
Joined: Wed Oct 08, 2003 1:26 am

Post by Toy Maker » Wed Nov 07, 2007 10:22 pm

maddmaxxx wrote:-what does 'shiznit' meen ?

-i just want to be 'hip' these days, not 'unkuul' 8)
Translation from Ghetto to White folk...
"This kind of info. is the shiznit!" would translate to:
"This kind of info. is the shit!" or for the REALLY White folk...
"This kind of information, it just what I have been looking for."

Posts: 7809
Joined: Mon Oct 16, 2006 5:39 pm
Location: The tube lair in Charlotte, NC

Post by treitz3 » Wed Nov 07, 2007 10:30 pm

Exactamundo! :p

Don't finizzzle my minizzzle!
In search of accurate reproduction of music. Real sound is my reference and while perfection may not be attainable? If I chase it, I might just catch excellence.

The best way to enjoy digital music reproduction is to never listen to a good analogue reproduction.

User avatar
R.I.P. Friend
R.I.P. Friend
Posts: 13360
Joined: Sun Jan 14, 2007 11:53 am
Location: TN Native Languishing in VA

Post by TNRabbit » Wed Nov 07, 2007 10:39 pm

'Fo Shizzle!

From FrankieD's lips to your ears: Sunfire - a quiet box of endless power.

Sunfire TG-IV/400~7 Amp
Carver SD/A-360 CDP
Benchmark DAC-1
Active bi-amp: Ashly XR-1001 & 2 Rane PEQ-15s
Main: HotRodded AL-IIIs
Sub: Klipsch RT-12d
Center: Sunfire CRS-3c
Surround: Sunfire CRS-3 (x 2)

OconeeOrange wrote:"Gary likes to play it 'loud' as do I. His system begs you turn it up until you die"

RIP WIlliam B. Dibble, 1948-2012. I'll miss you my friend.

User avatar
Toy Maker
Puppet Master
Posts: 6875
Joined: Wed Oct 08, 2003 1:26 am

Post by Toy Maker » Wed Nov 07, 2007 11:29 pm

My Nizzle !

Posts: 7809
Joined: Mon Oct 16, 2006 5:39 pm
Location: The tube lair in Charlotte, NC

Re: Interesting Reads: - Bob C / Carver / Sunfire

Post by treitz3 » Sat Aug 02, 2008 12:02 pm

Here's another on I ran across today....

AIG Talks with Bob Carver
Date posted: April 26, 1996 Category Tags: Bob Carver, interviews, Sunfire

Gordon Brockhouse talks to Sunfire’s Bob Carver

Few figures have engendered more controversy among audiophiles than Bob Carver. Virtually every product he developed at Carver Corporation, which he founded in 1978, contained an unusual feature with an impressive-sounding name. Supporters hailed these features as important innovations. Detractors dismissed them as gimmicks.

Carver preamplifiers had Sonic Holography, a fancy handle for interaural crosstalk cancellation. His amplifiers had Magnetic Field power supplies. His tuners and receivers had the Asymmetrical Charge-Coupled FM detector. And there were the infamous “t-mods,” affordable solid-state amplifiers modified to match the “transfer function” (and thus the sonic character) of ultra-expensive high-end amplifiers (a la Mark Levinson, Conrad Johnson and Carver’s own Silver Seven).

In 1994, Carver left the company following a long-standing dispute with his board of directors. “My idea was to stay our original course,” he recalls. “We would be allied with independent dealers with well-trained salespeople, and our products would be unique and aimed at people who historically bought my kind of products. The board’s idea was to expand distribution, then explode the product line. I felt this approach was doomed to failure, because success in the audio industry means being very focused. It was frustrating to watch, and so I left.”

Losing control of their companies is a common fate for entrepreneurs who take their companies public. “It’s an oft-told tale,” Carver agrees. “It’s painful, but it’s not unusual.”

At Sunfire Corporation, the company he founded after leaving Carver Corporation, Bob Carver continues to create innovative designs with high-fallutin’ names - and to create controversy. Sunfire’s first product was a power amplifier with a tracking power supply, dubbed “the tracking downconverter.” The next was a tiny 11-by-11-by-11-inch subwoofer said to deliver the same performance as much larger subs. The specified output of the True Subwoofer’s tiny amplifier - 2,700 watts - has raised more than a few eyebrows.

When asked to explain their products, many high-end designers break into a bullshit-baffles-brains monologue. Carver, by contrast, is lucid and down-to-earth, not what one would expect given the unabashed self-promotion in his companies’ advertising and literature. In person, what comes across is Carver’s gentlemanly demeanour, love of music and passion for audio - and his wonderfully creative approach to equipment design.

GB: One of the foundation technologies for Sunfire is the tracking downcoverter, which you use in your power amplifiers and subwoofers. What does it do?

BC: A regular amplifier has a power supply rail that’s parked up high in the sky. The audio signal varies under the power supply rail. The difference between the instantaneous value of the audio signal and the power supply rail is converted into heat - a great deal of heat. In the tracking downconverter amplifier, the power supply tracks the audio signal, so that the power supply rail is always six volts above the instantaneous value of the audio signal, rather than staying at 100 volts as in a regular amplifier.

The tracking downconverter was an idea I had about 18 years ago. It’s a generic form of a tracking power supply. I got a patent for it, but could not get it to work. It would always blow up. I gave up after a year of around-the-clock work, and decided to make the magnetic field amplifier instead. That is the product I used to start Carver Corporation, and it was very successful. A few years ago, I decided to have another go at the original circuit, and got it to work in spades. That was the basis of Carver Corporation’s Lightstar amplifier, and also the Sunfire amplifier.

GB: How did you get it to work?

BC: It’s so obvious now. I had to slow down the transition speed in the switching devices in the power supply. Engineers are always taught that the faster the switching, the more efficient the device. With the tracking downconverter, very rapid switching generates electromagnetic interference. That causes an electrostatic field inside the switching device, which causes a short circuit, and the part blows up.

It’s not the rep rate that causes the failure, it’s the transition rate. The rep rate is the frequency - how many times it switches per second. The transition speed is how long it takes to make the switch. Reducing the transition speed was the breakthrough. Once the transition speed was controlled, things stopped blowing up.

GB: In a conventional audio amplifier, you have AC coming in, then a power transformer to convert the line voltage to the voltages needed by the amplifier, followed by a bridge rectifier to convert to DC, storage capacitors to act as a reservoir and probably some power supply regulation to keep rail voltages steady. The audio circuitry functions as a tap, modulating the flow of energy from that big reservoir. How does your design differ from this model?

BC: Instead of feeding the amplifier directly, the reservoir after the bridge rectifier and power transformer feeds the input to the tracking downconverter. The output of the tracking downconverter feeds the amplifier. As far as I know, it’s the only tracking power supply in existence for home audio amplifiers. It may be the only tracking power supply in existence for anything.

With a tracking-power-supply amplifier, we can get the same performance as a regular amplifier, with reduced cost. Or, for the same cost, we can improve power output and the ability to drive low impedances by a factor of three or four. What we did was improve performance. The tracking downconverter is what gives the Sunfire amplifier its almost-magical ability to double its power continuously as impedance falls. You get 300 watts at eight ohms, 600 at four ohms, 1,200 at two ohms. And of course the amplifier doesn’t get hot.

A tracking power supply is a sort of holy grail of amplifier designers. Everyone worth his salt thinks, “If only I had a tracking power supply, my amplifier would have immense power and immense headroom. It wouldn’t get hot. It would be able to drive virtually any real-world load with ease without a huge heat sink and 100 output transistors.”

GB: Why have only you done it, and not all these others who dream of it?

BC: Once, when I was giving a talk at the Boston Audio Society, I was asked that very question. The founder of Analog Devices raised his hand and said, “I have an answer for that. Because it’s hard to do.”

GB: With a signal that suddenly becomes louder, does slowing down the transition cause compression, or does your six-volt headroom prevent that?

BC: The power supply is slightly faster than the amplifier. The speed of the amplifier and power supply are related to bandwidth. The power supply has ever-so-slightly higher bandwidth than the amplifier itself. The amplifier is no slouch; it’s just under 100 kHz. The power supply is a little bit faster - actually it would be fine if it were just the same speed - and then it gets a six-volt head start. Between those two things, the amplifier tracks any transient you can blast into it, as long as it’s band-limited to 100 kHz.

GB: How do you plan to apply tracking downconverter technology in the future: to push performance higher, or to push price and amplifier size downward? It looks like you’ve been doing more of the former. Do you plan to do more of the latter?

BC: No. Not at all.

GB: Do you plan to license the technology to other companies?

BC: We’re doing that right now, but not in the high-end audio field. It’s being done for professional and subwoofer amplifier applications.

GB: Your power amplifiers have two sets of output terminals: one for current source and one for voltage source. What’s the point?

BC: The voltage source has very low output impedance like a solid-state amplifier, so it has the sound of a solid-state amp. The current source has output impedance like a vacuum-tube amp, so it sounds more like a vacuum-tube amplifier. With the current-source output, the output impedance is exactly one ohm. We did a survey of tube amps and they average about an ohm.

We recommend driving an electrostatic or ribbon loudspeaker with a current source, and driving the low-frequency driver with a voltage source. Most people who have panel loudspeakers bi-wire them using that suggestion, and they like it better. There’s a sweet glow to the midrange and a soft high end that you associate with tube amps; along with the tightly controlled bass you expect from a good transistor amplifier. When you hook the panel up to the voltage source, it sounds like a transistor amp. The midrange is a little laid back and doesn’t have that glow; and the highs are sometimes a little sibilant. GB: Does the difference between tube and solid-state sound come down just to output impedance?

BC: Not entirely, but almost entirely. Ninety per cent of the sound quality that we typically attribute to vacuum tubes comes from the output impedance.

GB: Many people think the output transformer, and associated factors like soft clipping and core saturation, create the tube sound. Does the transformer raise output impedance, and thus create tube sound?

BC: The forward impedance of the output tubes and the transformer together usually comes out at about 10 ohms. When you use 20 dB of feedback, it reduces it to around one ohm. That’s basically what a vacuum-tube amplifier is all about.

GB: If output impedance is what creates tube sound, why did you build the Silver Seven tube amplifiers at Carver? Why not just add a resistor to a conventional amplifier, as you’ve done with the Sunfire amps to generate the current-source output?

BC: Building a big tube amplifier was a dream I had carried with me since my childhood, when I saw a big McIntosh in a window. I went to college, went into the service, got married, had children. When I finally got around to building my dream amplifier, it got rave reviews by guys like Bascom King and Harry Pearson. Those guys love tubes in the first place.

GB: After you’ve designed an amplifier, does listening to it change the design?

BC: Not appreciably. But it changes some of the finishing touches. After I built the original Sunfire amplifier, I listened to it alongside a Silver Seven. The Silver Seven sounded like a tube amp and the Sunfire sounded like a solid-state amp. I modified the circuits slightly, so that the Sunfire sounded as close as I could possibly make it to the vacuum-tube amp. Part of that was putting in the one-ohm resistor; but there were other things we had to do to get the two amps to sound as much alike as possible. Essentially, this involved giving it the distortion profile of a tube amplifier - in the current-source setting.

GB: How audible are the differences between solid-state amplifiers?

BC: What I’m going to say will fly in the face of what most people believe. I believe that you can take two solid-state amplifiers, and provided neither one is overloaded in any fashion, they’ll sound identical. That’s a big if. Amplifiers are overloaded in three basic ways. They’re overloaded in amplitude; they’ve overloaded in current; they’re overloaded in speed. It’s very easy to do this if you don’t have a big juicy amplifier. Obviously a little Radio Shack amplifier is not going to be able to touch a big Jeff Rowland or a Mark Levinson or a Sunfire amplifier. Provided the amplifier has flat frequency response and sufficiently low distortion, both of which are trivial these days, and provided there are no interface problems, the differences will always be the subtle differences associated with overload, either momentarily, like slew-rate limiting or clipping, or just running out of drive current.

GB: So the main problem is overload, which you can overcome with brute force, i.e. a really big amplifier, or elegance, something like a tracking downconverter. Was the tracking downconverter what enabled you to build a very small subwoofer?

BC: Having left Carver I wanted to build a product that people would really notice. A very small subwoofer would certainly attract attention…provided it had performance. The smallest box I could fit a driver with a 10-inch basket into was 11 by 11 by 11inches.

GB: The power specification for the True Subwoofer - 2,700 watts - has been controversial.

BC: No one believes it, because the amp’s the size of a candy bar, albeit a big $2.25 Hershey bar. When Don Keele, a world-respected subwoofer scientist and reviewer, measured it, he measured 2,500 watts continuous for at least two minutes. And it’s capable of twice as much peak output - maybe 5,000 watts.

GB: Is it just raw power that enables you to get so much bass from so small a box?

BC: The True Subwoofer is a small box with a small driver that produces the same output and bass extension as a large box with a large driver. It has not been possible until now to build a small subwoofer with this kind of output. Conventional drivers are not very efficient at converting input power into motion. They operate close to “stall mode” where a lot of power is turned to heat. To get lots of output from a small box, we have to increase input power by a factor of 10 or more. Two hundred watts becomes 2,000 watts, and that burns out the voice coil. What was necessary was to make a driver that would remain highly efficient even in a small box. This requires a big magnet and lots of motion, which pulls the driver out of stall. When it’s out of stall, it’s efficient and there’s far less heat.

This flies in the face of conventional driver design, because that type of driver generates vast amounts of back emf [back electromotive force, which results when the motion of the voice coil in the magnet gap generates a voltage]. The back emf prevents current from flowing through the voice coil, so there isn’t any output. To overcome the back emf, you need a special amplifier that can swing 100 volts, rather than 20 or 30 volts. When you compute the input power - 100 volts squared divided by four ohms, the resistance of the speaker - that’s over 2,000 watts. That’s what the amplifier would deliver if the load were purely resistive. But it’s not. It’s a loudspeaker load with high back emf. The real power delivered to the voice coil is only a few hundred watts.

GB: Is that the explanation of the controversial power specification of the True Subwoofer? That its amplifier delivers a few hundred watts into the resistive component of the load, but that it has to be capable of delivering far more power in order to deal with the reactive component of the load.

BC: You can think of it in those terms. That’s called “imaginary power.”

GB: I lose the ability to think when people start talking complex arithmetic and imaginary numbers.

BC: It’s hard. I’d forget about it at this point.

GB: What was the basic insight that led to the True Subwoofer?

BC: Necessity is the mother of invention. This woofer began two-and-a-half years ago with an eviction notice from my wife Diana. “Get this stuff out of the room,” she said. “If you want to have a big woofer in the room, it has to be invisible.” I began thinking of ways to do this. I’d think about when I was driving around, when I’d go to an opera, when I was going to sleep at night. Gradually, it occurred to me that one of the fundamental defining equations for efficiency, (Bl)2/re [where B is magnetic strength, l is voice-coil excursion, and re is voice-coil resistance], is true over all frequencies, not just for the midband as the equation is classically interpreted. It turns out I was right. That meant I could increase output and bass extension by using a big magnet and long-excursion driver.

GB: It sounds like a very unusual driver design.

BC: Oh yes. It requires careful attention to the suspension, surround and the magnetic geometry to keep it linear. They can’t collapse under the box pressures, which are around 150 pounds. So the rubber-rolled surround has to be sufficiently rigid so that it doesn’t cave in and act like a passive radiator in reverse.

GB: How do you obtain acceptable transient response with materials sufficiently massive to withstand these pressures and produce these excursions?

BC: Transient response is the mirror of frequency response. If you have good amplitude response, you have good transient response. If you have good transient response, you have good frequency response. The trick is to get the amplitude response correct, which is challenging enough. It requires good motor structure, good surround design, a good amplifier, the proper equalisation and so on.

GB: What about sensitivity?

BC: Sensitivity is so low it’s preposterous. It’s not so much the mass, although that does drive down sensitivity. The main thing is the back emf associated with the large magnet. The sensitivity is somewhere in the 60s or 70s [dB @ 1 watt @ 1 metre]. But it doesn’t matter because I’ve got this super amplifier to drive it.

GB: Isn’t distortion high with such a small box and driver?

BC: At full output, distortion is less than 10 per cent from 18 Hz upward. Most subwoofer manufacturers don’t specify distortion, because it’s very high: 10, 20 per cent or more. Even the Velodyne, which has a high-gain servo system, has one per cent distortion at low levels; but at full output, distortion is close to 10 per cent.

GB: How tolerant is human hearing of distortion at very low frequencies?

BC: Incredibly tolerant. It’s all but impossible to hear distortion at very low frequencies.

GB: Some speaker manufacturers maintain that distortion is important at those frequencies.

BC: Believing in low distortion is like believing in motherhood and apple pie. Low distortion is a good thing, and every manufacturer strives for ever-lower distortion. But it’s well-known how much distortion we can hear, and at what levels and under what circumstances we can hear it. If we apply those rules artfully, we can design products with vastly improved performance.

Take DVD as an example. DVD contains immense amounts of distortion as a result of the compression algorithms used for audio and video. A lot of information is thrown away. The components in the signal that are tossed out represent tremendously high distortion. But we don’t notice it because the designers know what’s important and what’s not.

Philosophically and conceptually, any audio product can be approached that way. It’s impossible to hear 20 per cent distortion if the thing’s operating at 9 Hz, because the first overtone is below the threshold of audibility unless it’s so loud that it’s hurting your ears � 130 dB or more.

GB: What about when you move higher in frequency?

BC: The thresholds change, but the rule still applies.

GB: In addition to the active driver, the True Subwoofer has a mass-driven unit that moves out when the active woofer moves out, and moves in when the active unit moves in. You’d expect the outward movement of the active unit to pull the mass-driven cone in, and vice-versa. How is the mass-driven woofer made to operate in phase with the active woofer?

BC: The force that moves the driven woofer is the electricity going through the voice coil. The force that moves the other woofer is the reaction force. To understand how this works, imagine standing on a chair and holding a Slinky in your hands. Pretend there’s a little weight on the other end of the Slinky. Your hand represents the voice-coil-driven woofer. The springs in the Slinky represent the spring of the air in the box, and the mass on the bottom represents the mass glued onto the other woofer. If you start moving that Slinky up and down with your hand, when your hand goes down, the bottom end of the Slinky comes up, and when your hand comes up, the bottom end of the Slinky goes down. It’s just the opposite of what you’d expect.

GB: That’s when the rate of movement is above the resonant frequency of the system.

BC: Correct.

GB: So you get this spring effect in the subwoofer whenever the input frequency is above the resonant frequency of the subwoofer, which, given the driver design, must be very low.

BC: It’s 18 Hz.

GB: Is the new 13-inch version of the True Subwoofer just a bigger cousin, with a little more output and lower extension?

BC: The Signature Subwoofer is the same system, but slightly larger. It has 6 dB more output, 116 dB as opposed to 110 dB, and it’s tuned to 16 Hz rather than 18 Hz. It uses the same amplifier, but larger drivers � equivalent to a 10 1/2-inch driver rather than eight inches.

GB: Your Theater Grand processor has some nifty ease-of-use features, such as the ability to set itself appropriately when you turn on a source. But it has a bunch of Carver-sque features as well. What does the video auto-correlator do?

BC: It’s mostly for video tapes. It’s a dynamic circuit that artificially extrapolates additional bandwidth that has been truncated by the VCR. It sort of reconstructs the signal. That is summed into the video circuits and presented to the CRT. If it’s done artfully, it gives all the appearance of a much more sharply delineated picture without ringing - that little bright line around objects that you get when you turn the sharpness control up. There’s a lot of what I call “psycho-optics” involved.

GB: What do you mean by psycho-optics?

BC: I mean fooling the eye into believing that there’s more definition on the screen than is actually present in the program material.

GB: What about the Holograph Generator and the Wall-to-Wall sound options?

BC: The Theater Grand has two kinds of music modes. Wall-to-Wall is a digital mode, which is similar to the jazz and arena and all that DSP-generated stuff we’re familiar with. Then we have an analog music mode, which is my Sonic Holography. I originally designed Sonic Holography for two-channel systems. On the Theater Grand it’s optimised for two-channel sources, except when it’s in the Theater mode. Then it’s optimised for home theatre. It takes care of the front hemisphere of the soundstage and adds some of the cues that allow front-to-back dimensionality, which usually disappears when you use three front speakers. Normally, three front speakers give a flat curtain of sound across the front stage. To get a sense of depth, you have to add time delay to the centre channel. With holography, that delay occurs in our ear-brain system because of the holographic image. The side channels fill in the rest of the room.

GB: For home theater where it’s not practical to have three identical to have identical speakers across the front, do you favour the use of centre-channel speakers?

BC: I don’t know. I’m such a two-channel fan. The illusion that can be created from a two-channel source by our ear-brain systems decoding the timing cues the spatial cues can be so incredibly beautiful and so deliciously three-dimensional, that it’s difficult to warm up to five speakers. Five speakers provide a nice sense of envelopment and immersion, but it’s different from the three-dimensionality that a good two-channel system can have. But for theatre, I believe a centre channel is better to lock the dialog in.

GB: Is sonic holography essentially crosstalk cancellation?

BC: Yes. The crosstalk cancellation has been adjusted to produce a realistic presentation on regular stereo recordings. Years ago, Harry Pearson wrote a wonderful series of articles on generating a soundstage with a stereo system. What you want is a sense of layered depth on a soundstage that extends behind the speakers and is wider than the speakers. I’ve adjusted Sonic Holography to really give a soundstage in spades using Harry Pearson’s treatise as a model.

In real life, for every sonic event we have two sound arrivals: one for the each ear. Every time I snap my fingers, you hear two sounds: one in your left ear, one in your right. In three-channel playback, every time I snap my fingers, you might hear six � one in each ear for each of the three speakers. Those unwanted sounds need to be cancelled if we’re to generate a replica of real life.

GB: But this reduces the sweet spot.

BC: Yes it does. It was one person wide when I started, and I managed to get it to be three people wide.

GB: What does the five- and seven-channel music mode do?

BC: It splits the soundfield into two hemispheres. The front hemisphere uses our latest thinking on Sonic Holography. The rear hemisphere gets a mix of L+R and L-R information. With a seven-speaker setup, more of the L+R information is apportioned to the forward position; and more of the L-R information to the rearward speakers. The Sonic Holography gives very precise imaging in the front hemisphere of the instruments within the soundfield. The rear hemisphere immerses one in the soundfield because it has a great deal of hall ambience, but very little precise imaging.

GB: You said you love two-channel and what it can do. Do you like this better than regular stereo?

BC: I don’t know yet.

GB: The Theater Grand does DTS as well as Dolby Digital decoding. What’s your view of DTS? Is it going to confuse the market?

BC: I hope not. DTS seems to be settling in to a peaceful coexistence with Dolby Digital in the marketplace, with DTS appealing mainly to a dedicated set of people. That’s our market really.

GB: Does it sound better?

BC: I can’t say.

GB: If it doesn’t sound better, what’s the point? It’s another system that does the same thing as Dolby Digital.

BC: We know off the bat that it has higher bit rate. Is that audible? I haven’t been exposed enough to it to know. But even if it isn’t today, it always has to hold the promise of being better because there’s more stuff there.

GB: What do you plan to do next at Sunfire?

BC: Right now, I’m working on my Cinema Ribbons. They’ll be sold as a set of five. Each speaker is a just a little bigger than your fist. But it goes down to 80 Hz and it puts out the same SPL as a big box with two eight-inch drivers and at least one centrally located tweeter.

GB: How do you get that kind of output from a small speaker?

BC: By applying the same back emf and high box pressure concept as my subwoofer. It uses a special ribbon driver with very long excursion and large magnet. That produces very high back emf and box pressures several times that of an ordinary speaker, which lets the speaker go down to 80 Hz and produce high SPLs.

I call it the world’s first fly-by-wire loudspeaker. The system includes a controller that goes between the processor/preamp and power amplifiers. It’s absolutely fundamental to the system. It has comprehensive speaker protection; a low-frequency excursion limiter, which I call the low-frequency auto-throttle; and a fixed excursion limiter for frequencies beginning around 200 Hz. It uses feedforward to reduce low-frequency distortion and make the frequency response nice and flat. It also performs active equalisation, with three positions for speaker location - in the corners, against walls or out in the room.

GB: When DVD-Audio appears, with multiple channels and higher-resolution coding, what do you think it will do for music in the home? Will it be a repeat of the quadraphonic disaster, or are we smarter this time around?

BC: It should be able to work if it’s done properly. I would like it to be encoded in a stereo two-channel format for the front hemisphere, with some kind of crosstalk cancellation to give a more realistic presentation, and then use the additional channels as ambience fill for the back hemisphere, so that you can be immersed in sound.

GB: Do we need more than 16 bits and 44.1 kHz sampling? Will 96/24 sound better?

BC: I’m a great believer in being artful with existing technology. If you do a great job with what’s available, you can get something that’s absolutely superb. Ordinarily, when you make a change, you stumble for a while until the new technology is brought up to the level of the old one, even if the new technology has the capability of ultimately surpassing the old.

GB: We saw that with the transition from analog to digital.

BC: Absolutely. In spades.

GB: Can home audio reproduction get much better than it is now?

BC: It can get a lot better. Some day, your audio system is really going to fool you, so that you can close your eyes and believe you’re in the presence of a real live orchestra. Today even the best systems can’t do that.

GB: That sounds like getting the room to disappear. Some companies have spent a ton of money trying to do that, and haven’t succeeded.

BC: Either the room has to disappear, which is very difficult � maybe insurmountably difficult, or we have to make the room part of the acoustic venue, and work with the room. That would be my approach.

GB: But you listen to an orchestra in a hall hundreds of feet long and wide. The largest home listening rooms are tens of feet long and wide. How do you bridge that gap?

BC: Here’s one way to do it. Get two small speakers, like Cinema Ribbons, and put them at arms’ length in front of you in the middle of the room. Then use crosstalk cancellation, and make a special recording so that what we would hear is so much in the near field that the bounces from the room walls are insignificant. Or we could use a very large room with lots of sound absorbing material - lots of traps everywhere. Then use lots of speakers, or two speakers with Sonic Holography, or a combination of both.

Whatever technique we use, some day in the future there will be audio systems that can fool us. It probably won’t be in my lifetime, but we’ll have it.

Cool Runnings

Gordon Brockhouse Analyzes How The Sunfire Designs Work

The number-one enemy of virtually any electronic or electro-mechanical product is heat. Excess heat shortens the life of electronic parts - sometimes with dramatic abruptness. Designers often have to add weight and cost to the products to deal with heat issues; often they have to compromise performance as well.

Rather than getting rid of excess heat, Sunfire’s power amplifiers and subwoofers prevent heat from becoming a problem at all. Here, paraphrasing Bob Carver’s white papers on the True Subwoofer and Sunfire amplifier, is how they work.

The Tracking Downconverter

In a conventional amplifier, the voltage on the power supply rails is constant � typically 90 volts or so. Let’s imagine such an amplifier driving a four-ohm loudspeaker, which at a given moment in time (during a peak) is drawing 10 amperes. The output voltage will be 40 volts. Ten amperes are flowing through the output transistors; and there are 50 volts across the transistors (the difference between the 40 volts flowing to the loudspeaker and the 90 volts on the power supply rail). That means that 500 watts are not going to the output, but being turned into heat.

This example corresponds to 400 watts output power (assuming a purely resistive load). With the same amplifier putting 400 watts into an 8-ohm load, the output transistors produce 238 watts of heat. At 100 watts into a 4-ohm load, heat output is 350 watts. With an 8-ohm load, heat output is 218 watts. At 25 watts, heat output is 225 watts with a 4-ohm load and 134 watts with an 8-ohm load.

This has two consequences. First, large, heavy heat sinks are needed to conduct all this heat away from the output transistors. Secondly, the power supply must be large enough to drive the loudspeaker load and generate all that heat.

The 20-ampere output transistors commonly used in high-end and mainstream amplifiers are rated for 200 watts. That’s the amount of heat they can dissipate. That effectively limits the amount of current the transistors can produce. Going back to our first example, when there are 50 volts across the transistor, it can safely deliver 4 amperes into a 4-ohm load. When there are 70 volts across the transistor (as there would be at 100 watts output into a 4-ohm load), the device can deliver 3 amperes. To deal with low-impedance loads, several of these must be used in parallel. This drives up heat sinking and power supply requirements.

Sunfire amplifiers use a tracking power supply (the “tracking downconverter”). The voltage on the power supply rail is kept at a steady six volts above the output signal. That means that the voltage across the output transistors is always 6 volts. At 400 watts output into a 4-ohm resistive load, the output transistors generate 60 watts in heat. At 100 watts, they generate 30 watts. With heat output so low, there’s no need for heat sinking; and power supply requirements are dramatically reduced.

And because there are only 6 volts across the output transistors at all times, they can always deliver their rated 20 amperes. The Sunfire I uses 12 of these devices per channel, giving it peak-to-peak current capability of 240 amperes.

The True Subwoofer

To produce sound, you have to move air. To produce lots of deep bass, you have to move a lot of air. You can use a very large radiating surface with limited back-and-forth movement. Or you can use a smaller radiating surface that moves a lot.

Most subwoofers take the former approach. Sunfire’s takes the latter. Its two drivers (one active, one passive) have cone excursion of 2 1/2 inches. The diameter of the radiating surface is 8 inches. The combined air displacement is 251 cubic inches. According to Sunfire, this is comparable to three or four conventional 15-inch drivers installed in a large cabinet.

There is a linear relationship between cabinet volume and power requirements. If you want to reduce cabinet volume by half, you have to double input power to produce the same output. Moving from a two-foot cube to a one-foot cube, you have to increase amplifier power by a factor of eight to maintain the same output level.

The Sunfire True Subwoofer’s cabinet is very small - 11 by 11 by 11 inches. To get lots of deep bass from a cabinet this small requires a very powerful amplifier. Sunfire rates its subwoofer amplifier at 2,700 watts!

The driver design that displaces so much air also prevents it from burning up. Conventional moving coil speakers are inefficient at turning input power into cone motion. To move the cone, they require a lot of current passing through the voice coil. This produces heat. More input power means more heat.

You can increase driver efficiency by using a more powerful magnet and longer voice-coil excursion. Normally, this is completely impractical. This combination results in high amounts of back electromotive force (emf). The motion of the voice coil in the magnet gap produces a voltage. If the amplifier cannot overcome the voltage produced by the motion of the speaker, no current can flow into the voice coil, and there is no sound.

For such a driver to work, you need an amplifier capable of very wide voltage swings. The tracking downconverter amplifier used in the Sunfire subwoofer can swing over 100 volts. Because of heating problems and space limitations, it would be impossible to use a conventional amplifier that could swing 100 volts into a four-ohm load. But because a tracking downcoverter amplifier runs cool, does not require heat sinking or a large power supply, it can be made small enough to work in this application.

With this kind of amplifier, back emf becomes an asset. The Sunfire sub’s long driver excursion and huge magnet (225 ounces) produce large amounts of back emf, which prevents damaging amounts of current from flowing into the voice coil. Consequently, the voice coil does not burn out. The huge magnet enables the long excursion even though the amount of current flowing in the voice coil is small.

Only a small portion of the output from the True Subwoofer’s unusual amplifier flows into the voice coil as current. Most of it is used to overcome the huge back emf produced by its unusual driver.
In search of accurate reproduction of music. Real sound is my reference and while perfection may not be attainable? If I chase it, I might just catch excellence.

The best way to enjoy digital music reproduction is to never listen to a good analogue reproduction.

User avatar
Toy Maker
Puppet Master
Posts: 6875
Joined: Wed Oct 08, 2003 1:26 am

Re: Interesting Reads: - Bob C / Carver / Sunfire

Post by Toy Maker » Sat Aug 02, 2008 12:52 pm

When you guys find good shit worth posting, PLEASE COPY AND PASTE the text onto the forum as well...
If the original page ever vanishes, at least we'll have a backup copy !!! Link to them as well...

User avatar
Posts: 580
Joined: Sat Jul 12, 2008 3:29 pm
Location: Montevideo, Uruguay

Re: Interesting Reads: - Bob C / Carver / Sunfire

Post by brit01 » Sat Aug 02, 2008 2:07 pm

This may be of some interest to members here:

Sunfire Corporation
No email adres available
Carver official website
5210 Bickford Avenue, Snohomish, WA 98290, USA
+1 (425) 335-1978
No fax number available

Carver web site (April 2001): Message from Bob Carver, Date unknown As you may know, I lost control of the Board of Carver many long years ago – 1987 to be exact. I became only a figurehead at the company I founded, and after watching the actions of the Board from up close (more on this later), I decided enough frustration was enough and I left. Since then I’ve watched from afar as a once proud company has gone down. As the years trolled by and the company’s valuation trickled away, I made it clear that I was always available to help. I repeatedly asserted that I could stanch the losses in excess of $3,000,000 per year and put the company on solid footing. I shared my plan, yet the Board wanted nothing to do with me. I was persona non grata. I was the Evil Founder. In the meantime, I founded a new company, Sunfire, salted it with two inventions and a small capital infusion, and off it took.

Sunfire’s growth has been strong, with sales revenue nearly doubling each year. Ditto for earnings. If all goes well, and that’s a big if, I intend to combine Sunfire and Carver approximately 15 months from now, thus forging a larger and stronger public company. (Sunfire is at this time privately held.)

Back to Carver. By the end of 1998, Carver had spent all its money and then some. Carver Corporation reminded me of the 1950’s science fiction movie in which an H-bomb has been dropped on New York. What used to be a beautiful city was shown with only the wind blowing through a dusty and empty town, and only the occasional tumbleweed rolling along deserted streets. No cars, people, or anything. Empty! This was the state of affairs at Carver when the Board of Directors finally called me. Carver Corporation literally had a mere seventeen dollars in the bank. They had managed to develop a negative net worth of over $1,000,000. I visited Carver and found nobody home. The assembly line had been shut down and the workers had gone. Carver hadn’t been able to pay salaries. There were empty desks, empty cubicles, blackboards with writing on them, and no one around. It was as if everyone had just left on a moment's notice. My Carver was a thriving, bustling place. This was surreal.

I was witnessing the complete and unmanaged collapse of the company, like an imploding star, into an uninhabited black hole. Carver had no money, no employees, no plan, no technology, and no manufacturing. Carver did have roughly $1 million in lawsuits, $1.6 million in unpaid bills, and a practically nonexistent Dealer network. Through a series of disastrous sales and marketing tactics, Carver had angered its Dealers, who had resigned the line in droves. Carver retained a few factory Representatives in name, but these were ineffective and without action. The primary lending bank had informed Carver it would seize all remaining assets unless the outstanding loan balance was immediately paid in full. I was informed the landlord was in the process of acquiring a court order allowing him to padlock the building. I knew Carver didn’t have a legal leg to stand on, and the landlord would indeed prevail and shut the doors. The Board asked me to step in and save Carver. I jumped at the chance, and put my years of passion and experience to the task.

Those years have taught me that at a minimum, a Board of Directors owes a company a capable and competent leader. In my opinion, Carver’s Board failed miserably in this regard by repeatedly appointing leaders with absolutely no audio industry experience. As incredible as it seems, after each CEO would in turn fail at the job, he was then given a seat on the Board of Directors! Ultimately, the Board was almost entirely comprised of former failed Carver CEOs! Decisions at the very top of the ladder were being made by men who had failed to pull the company out of its downward spiral. Unbelievable! All I could do was watch from afar as decisions made in ignorance and arrogance relentlessly hammered your company into the ground. Forgive me, for I digress…

To begin, I quickly cut a deal with the bank, paid off the debt, and effectively became the secured creditor for everything Carver owned. Every computer. Every table. Every pen and pencil. Indeed, every roller track, power tool, assembly line, jig, fixture, copy machine, all assets including the patents, trade marks, and the very name of the company. We got word that the landlord had received his court order, effective on the first of the coming month – just days away. My Sunfire employees and I rented trucks, leased numerous storage sites throughout the area, and cleared space at Sunfire in preparation for a very hurried move. During the course of several arduous days and nights, we loaded everything up and moved it all out. You can believe that Carver again has a responsive leader, and one who truly cares. I’m back. Carver now has a fighting chance.

Prior to doing all this, I signed an agreement with the Board of Directors (see "The Operating Agreement"). Inked just prior to the Consumer Electronics Show, this agreement galvanized Sunfire’s engineering department. We designed five new products, including two brand new technologies and one clearly in a class by itself through the use of existing Sunfire technology. We worked around the clock – from the crack of dawn to late in the morning – night after night, day after day, and finished just in time to go to the show. We showcased five new products sporting the Carver Logo. Our goal was to generate excitement for the New Carver Corporation, and to sign up 100 new retail Dealers. It was also our intention to sign up 18 new factory Representatives at the top level of the new revitalized sales network for Carver products.

As we all know, trust is something that is earned slowly and is difficult or impossible to regain once lost through an unfaithful act. When a company is placed in what I call ‘the penalty box’ for such a loss of trust, it often remains there indefinitely. At best, it’s very difficult to get out of this ‘box.’ We fully expected the Dealers would be extremely wary of the Carver brand. We’re proud of the trust Sunfire Dealers have in us, and we knew that they would at least listen. Carver had lost the trust of its dealers, and in turn lost its way. We had much work to do.

We asked Dealers to look at the new products and talk with us. To our great pleasure, the Dealers loved the products. On the basis of the new products and my personal commitment to the Dealers (most of whom I’ve known for many years), their wary attitudes faded significantly. I gave them a solemn pledge, "Even though Carver used to be bad, it will now be good." One by one, we managed to sign up 100 Dealers – exactly our goal. We also signed up an entire factory Representative network. This new network of Dealers and Representatives is simply waiting for the new designs to be finished, put into production, and distributed.

We’ve replaced Carver’s dysfunctional infrastructure with the healthy corporate systems in place at Sunfire. We have an exceptional sales force, a world-class engineering department, and above all, new technologies. Sunfire has assumed all the functional and operational elements for the Company. Everett Audio Repair, an independent repair shop in Everett, Washington, has assumed responsibility for warranty service. Things are looking up for Carver. Carver now has Dealers and factory Representatives who are firmly committed. Carver now has new technology, and hope to go with it.

It’s been a wild ride for all of us. We’re packed to the gills with twenty years worth of Carver stuff sitting around everywhere. It's like a submarine ready to put out to sea; one can’t even walk through the isles because there are so many stores, provisions and other gear. Carver was once following a death spiral to its doom, and now it isn’t. We have a chance. That’s where we are today.

Sincerely, Bob Carver

SNOHOMISH, Wash - Feb. 1, 2000 - Carver Corporation today announced that it has executed an agreement with Robert W. Carver, its founder, Chief Executive Officer and Chairman of its Board of Directors, and with Mr. Carver's privately-held Sunfire Corporation for Sunfire to:

(I) direct the development, manufacturing, marketing and distribution of a new line of products for the home and car under the "Carver" brand name that incorporates certain new technologies,
(ii) establish a new manufacturer's representative and independent dealer network, in order to rebuild Carver Corporation as a dominant force in the USA as a manufacturer of consumer audio electronics, and
(iii) for Mr. Carver to assume full operational control of the Company pursuant to the operating agreement.

As consideration for such services, Mr. Carver will be granted an 80% ownership interest in Carver Corporation, subject to shareholder final approval. In addition, a repurchase option will be granted to the Company, which may be executed under certain specified conditions. As previously announced, the Company and Sunfire may merge within 18 months, again, subject to certain criteria and Mr. Carver's discretion. The shareholders of Carver Corporation would retain a 20% ownership interest in the combined entity following such a merger. The terms of the operating agreement and granting of ownership interest to Mr. Carver are subject to shareholder approval, and shall be presented in a proxy package in advance of a shareholder meeting to be scheduled as soon as practicable in early 1999.

In response to the execution of this operating agreement, Mr. Carver stated, "I am very excited to have this opportunity to rebuild the Company I founded so long ago, and am confident that the independent dealers will be receptive to Carver Corporation's new products. Sunfire and Carver products serve distinct segments of the market, and should complement each other extremely well. The Board of Directors and I share a desire to maximize value for all shareholders, and believe that the opportunity presented in my business plan will evidence this upon receipt of the proxy package that will be distributed to them"

From a Canadian distribution standpoint, Mr. Saxe Brickenden, president of the Evolution Group, a division of AC Simmonds & Sons, Carver's Canadian Distributor says, "I'm delighted with the outcome of the Carver & Sunfire negotiations." Mr. Brickenden says his 20-year association with Bob Carver, since the inception of Carver Corporation in 1978, has been a positive and prosperous one. "Bob Carver is an outside-the-box thinker and this situation is a classic example of what happens when a visionary is lost. And with the new deal, they have found the vision and direction again. I'm really looking forward launching our new products".

The Company also announced that its Chief Operating Officer, Fred Grund and one of its directors, James McCullough have resigned. Prior to Mr. Carver's arrival, the Company had previously announced certain other operating strategies, including distribution of products through the Internet, but was forced to seek alternatives due in principal to a lack of operating capital and a lack of new products and technologies.

Bob Carver recently introduced a number of new Carver-branded products including a 200-watt per channel five channel Dolby Digital/DTS receiver, a high pressure, high back-emf subwoofer for home theater, a 300-watt miniature (the size of a pack of cigarettes) amplifier for automobile subwoofers and two companion subwoofers. These were shown at the Consumer Electronics Show that was held in Las Vegas, Nevada earlier this month. Brickenden comments, "our demonstrations were dropping jaws throughout the Consumer electronics show. Bob's magic is back at Carver Corporation." Each of the products contains new technology; an exception is the receiver, and it stands alone in the marketplace as the most powerful five-channel receiver there is.

Forward Looking Statement Statements in this news release looking forward in time, including those concerning development and delivery of new products, are forward-looking statements which involve known and unknown risks, uncertainties and other expressed or implied by such statements. These risks include the effect of changing economic conditions, trends in the audio components market, product demand and market acceptance risks, and other risks including those described from time to time in the company's Securities and Exchange Commission filings and other communications.

SOURCE Carver Corporation /CONTACT: Sara Potgieter of Carver Corporation, 425-335-1978/ (CAVR) [Copyright 1999, PR Newswire]

SEATTLE, WA – May 19, 1999 -- Carver Corporation today announced that on Wednesday, May 12, 1999 it filed a voluntary petition under Chapter 11, in United States Bankruptcy Court for the Western District of Washington. The case number is 99-05793.

The cause of the filing was an accumulation of unpaid debt and resulting legal actions filed by creditors. These actions created the prospect of an inequitable distribution of payment to creditors and prevented the Company from being able to operate as a functioning business entity. In October of 1998, the Company ran out of working capital and laid off the remainder of its workforce. Subsequently, at the invitation of the Board of Directors, Robert W. Carver, the founder of the Company and former CEO, stepped in to take over.

The Board of Carver Corporation found it necessary to seek protection under federal bankruptcy laws in order for the Company to move ahead and reestablish itself as a viable entity in the marketplace. The Company intends to reorganize for the long-term success of the Carver brand name, profitability for shareholders and quality audio product for its faithful customers.

CONTACT: Carver Corporation, Bob Carver, (425) 335-1978

Robert H.Lever (November 2001): Contact Carver Service (now a part of Sunfire Corporation, Bob Carver's new Company at +1 (425)335-4748. They can provide service or schematics on most ol Carver Models, even some Phase Linear.

Brand History site (July 2002): Carver started out in about 1986 making ”The Amazing Loudspeakers, and at the time the design blew people away. (2) 30” ”full range ribbon drivers” and (4) freeair 12” subs. The ribbon design was what sold the speakers. To this day, the Carver ribbon drivers are still a hard full range speaker to beat! When Carver introduced TAL, the ribbon drivers used a dual strand Kapton membrane.

After about 3 years in production, Carver came out with the new ”Platinum” and ”Silver” ALS's. In these models, the new single 60” ribbons for the ”Platinum's” were 1st seen, as well as the new 48” ribbon for the ”Silvers” In the new designs, a few crossover changes came about, and the Kapton now had (4) aluminum strands on it, and was crimped to slow down the response to where they needed it to be.

In 1992, the AL-III ”Amazing Loudspeakers 3” were introduced. This new speaker design used the 48” ribbon driver and a new 10” ported subwoofer. In these speakers, they stooped crimping the Kapton, because they realized that in crimping the membrane, it was adding that much more material to be allowed to stretch, so in the AL-III's the ribbon is smooth. Either way it can't be seen on the AL-III's, unless you take the ribbon out of the speaker.

1995 brought on the AL-III Plus. Same basic speaker as the AL-III, with a few mods...

Questions and Answers

Add a question

Woofer repair/replacement for Platinum I (John Humphries)
Clearview Crossover for Carver Ribbons (James Darwin)

go to the questions and answers listWoofer repair/replacement for Platinum I by John Humphries (March 22, 2006): I have a pair of Carver Platinum IV speakers that have 3 damaged woofers as a result of an accident. Two woofers have distorted cones and one has only a damaged foam surround. Ideas?

Please click here if you can provide an answer.

go to the questions and answers listClearview Crossover for Carver Ribbons by James Darwin (May 11, 2004): Hi,

I know this is a long shot, but... in 1998 I bought some 60" carver ribbons,
some NHT 1259 bass speakers, and a Clearveiw Active Crossover. I build the
appropiate boxs/pannels and the system worked fine for a couple of years,
then the crossover had some problems, so the system is now in storage.

I am looking to try and get my cross-over fixed or replace. I have lost my
contact for Clearview. Do you have any ideas how to find them?



go to the questions and answers listAnswer by Steven A. (January 29, 2005): Hi James,
You can find Rudi Blondia at

Rudi just gotthe website up and will be offering the Clearview active crossovers again.


Please click here if you can provide an additional answer.

External links

Carver Audio Stereo Repair Information [Everett Audio Repair] Fort Myers, Florida
Carver Corporation
Carver Repair.Com New and refurbished Carver Amazing's ribbons, crossovers, woofers and panels. Platinum Silver and ALIII series. Refurbished Speakers Platinum, Silver and ALIII's
Carver Ribbon Project #2 by Gary Sanford
TFM-55, CT-3, Klipsch F-1, Rotel RCD 930AX

Post Reply

Return to “Bob Carver, the Myth, the Legend”