Amplifier design / Bob Carver's thoughts

Here's an interesting article i ran across. For those that are interested in how devices work and the decisions that engineers make when designing a product, try taking a look at this article. It is an older interview with Bob Carver and gives background on the how's / why's of the Sunfire designs and why he chose the design attributes that he did. Obviously, the specific decisions made when designing any product are a matter of subjective preferences and some may not agree with Carver's personal designs / take on things. Having said that, the info provided here may help some of you that are less technically inclined understand how an amp works and what the various trade-offs are. Good reading, even if you don't like "Sideshow Bob". Sean

Design attributes of the Sunfire amplifier
Being a proud Carver Lightstar Reference owner, I appreciate
you digging up this article. I'm embarrassed to admit that I don't have a clue as to what all that technical stuff means. There is far more power than my e-stats can handle. All I know is that my music sounds great.
OK Sean, let me first thank you for the effort.I did
understand at least 40% of the information,but
not the technical part,He is talking that the sunfire
can produce limitless current.The bi wiring benefits.
Now you got me interested. The only problem. I dont
know who carried them, Use to be Columbia Audio Video,
sells them, but everytime I go there ,they are on the
HT set up, never set up correctly, And because of
that I was not impress at all.I wish you live close to
me.We are both from IL, but you are on the other side
of the city.Bob Carvers thought is very informative in
a lot a ways, made me feel this guy is a genius.I did
enjoy reading it though.

You know, that those who believe that shorter signal path is better cant still purchase 10W $25000 amps....
Great read Sean, thanks. That Carver guy's almost as smart as you.

Steakster: The Lightstar Reference is supposed to be slightly more neutral sounding than the Sunfire amps. Bob purposely built a slight dip into the upper midrange / lower treble of the Sunfire amps as he finds a small amount of euphonic colouration to sound better with most digital recordings. Having said that, this also works pretty well for most HT systems too, as it helps reduce the "shouty" characteristics found in most Hollywood productions.

As far as understanding what that article said, here's a brief run-down. Keeping the output voltage of the amplifier just above what it really needs allows the amp to deliver more current at any given time. This equates to increased dynamic potential and more driver control. Another benefit of this is that there isn't a lot of power wasted, so heat is drastically reduced. Efficiency is raised, so one can run a smaller power supply ( without penalty ) and with reduced heat-sink. This makes the amp less expensive to produce, easier to package and less expensive to transport. In effect, this type of design is a manufacturers dream and can be quite good sonically if properly implimented.

Jayc: Bob Carver is a genius, at least when it comes to manipulating electrical signals. Many audio "purists" discount his contributions to the world of audio as many of his circuit innovations are purposely designed to manipulate the signal i.e. "bells & whistles". This is done to achieve specific sonic goals that Bob finds worthwhile. Having said that, he's typically included the option of turning many of these "unnecessary devices" off or on as needed.

As a side note, many of these circuits / inventions came about as a way to address specific problems i.e. Bob was looking for a way to deal with specific situations in the average system operating under real world conditions. The Peak Unlimiter was a dynamic expansion circuit designed to deal with the limited dynamic range of highly compressed recordings. The Auto-Correlation circuit was designed to deal with surface noise as found on worn vinyl. Sonic Holography was designed to introduce a sense of spaciousness with more vivid imagery to compensate for poor recording techniques, etc... I think that you get the idea.

Marakanetz: Simpler circuits are cheap and easy to build, but hard to keep stable. Trying to resolve the stability issues may have one spending more time with a simpler design than just using more parts and making it a bit more complex. Then again, you already know this : )

Dave: I wish i was half as smart and a quarter as motivated as Mr Carver. Like him or not, he's responsible for quite a bit of the affordable technology & products that we have today. Sean
Thanks for this thread, Sean!

I have experience with LightStar amps, and can vouch that they offered fantastic value. The ability to wake the most demanding speakers that never gave me any glimpse of how they were capable of sounding with any other amp I mated with them earned my eternal respect. And, isn't that what an amplifier is supposed to do in the strictest sense? It's something that would need to be experienced to be truly understood.
I have always wanted a lightstar amp; I heard one years ago and never forgot it. I ended up buying an a760x which is a poor man's version of the lightstar, but reduced in its power and control. I never seem to have the money or I am always a little late on the rare occasions when one come up for sale. I wonder if I should break down an buy a sunfire. Except for its "voiceing" I think it is essentially the same design as the lightstar. Any thoughts? By the way in my opinion Bob Carver is a genius. The reason he is reviled by many audiophiles, is that he has no problems putting his name on junk. The thing is even his junk is still a pretty good deal for the price, just not up to audiophile standards. He doesn't have aproblem making compromises to design and manufacture to a price point. If you understand that, and appreciate his goals, you can realize tha he has brought good sound to many people who would have spent the same money for bad sound. If it isn't great sound, its still better then they likely would have attained form other components in the sam price range.
Rgcards: While i basically understand what you're saying and agree with you to a certain point, i also think that Bob gets hung up on bringing his ideas to fruition. As such, some of the fruits of his labor aren't implimented quite as well as they could be ( either in design or how that design is implimented in production ). Phase Linear products were a prime example along with the "cube", the later Carver corp products, etc... and even the early generation of Sunfire amps. In the earlier days, quality control / parts matching was not a primary concern. Those aspects of manufacturing can drastically increase time & labor costs, which isn't conducive to keeping prices low. Since Phase amps were the highest watt per dollar product on the market, there wasn't much overhead in the budget for high rejection ratios or time to gain match output devices.

As to how some of those design revisions of the Sunfire amps came about, suffice it to say that i had more than a few conversations with their Tech Support staff. After sharing ideas with them, i kept hearing "but you don't understand, this is not like other amps, you don't know how this design works". While i have no idea as to how influential some of my comments were, when all was said and done and the newer versions introduced, many of the comments and solutions that i had passed on ended up showing up in the newer revised models. Having said that, i know that notes were being taken during our discussions.

In terms of "bang for the buck", especially if you have a low impedance, low sensitivity speaker, they are hard to beat. There are more than a few folks on Agon using Sunfire's ( primarily Signature models ) to drive speakers that are well known for "chewing up and spitting out" high powered amplifiers. As i've commented before, my Sunfire's are not stock units and are being used in my HT system. While the mains are rated at 87 dB's and 4 ohms, they are probably closer to 85 - 86 dB's or so. My two channel Signature drives these with nary a problem in sight. Then again, with 1200+ cool running wpc available, it should : ) Sean
I just added a Sunfire Sig 2ch for my N802's and am amazed at what it brings out in these speakers...a new Sunfire convert!
Sean: I still have my Phase Linear 400 from 1971, still runs. Not much current for speakers less than 4 ohms, but works fine with anything else. I ran the PL 400 about 2 months ago with the Radians, a little lean on the high end, the bass response was surprising good, the midrange a little soft, a little gritty, edgy, but really not half bad either, though tiring after a hour or two.
The older Phase amps were very simple circuits, but due to poor implimentation and quality control, sounded worse than they should have. If one removed the current limiting circuit and matched the output transistors on these amps, you would get rid of a lot of the "grunge" and smearing that passes for treble response in these amps. It is this "grungy grit" that causes fatigue and makes everything sound harsh and veiled.

On top of all of that, these amps didn't overload very gracefully, partially due to the lack of matching in the output stages and the lack of power supply reserve. Once they started to clip, they went into hardcore saturation and smearing. Not only were the transistors being pushed, the power supply had given all that it had and was also trying to recover. Given the lack of power supply reserve to begin with, this happened more frequently than one might think. As such, many of the sonic problems with these amps under load was directly due to all of the voltage sag taking place during heavy demands. As such, increasing filter capacitance can make a VERY big difference with these amps, but the problem is, there just isn't much room to do this in these chassis. Kind of a "Catch 22" situation.

There are ways around this if one is resourceful, and these amps can be purchased quite cheaply. Quite honestly though, i can think of better candidates to work with if looking for powerful amps at or near the same price levels. As a spare amp "just in case" or something to provide "oomph" on the bottom end of an HT system, they don't work too bad though. I wouldn't want to run one in stock form powering the mains of a two channel rig though. As Shubertmaniac commented, they rank relatively high in the "sonic fatigue" department. Sean