(pair of) SILVER-7 TUBE AMPs
Joined: Sun Jan 14, 2007 12:53 pm
Location: TN Native Languishing in MD
By John Atkinson • Posted: Feb 7, 2010 • Published: Feb 7, 1990
Although it was Thomas Edison who set the tone for technological development in the 20th century, with his intellectual sweatshop in New Jersey, it is the lone inventor who has always had a special place in the heart of the American public. Since the days of Samuel Colt, Eli Whitney, and Nikola Tesla, fortune and fame have awaited the genius tinkerer who emerges from his back yard with a better mousetrap, cotton gin, etc., etc.
Which brings me to 46-year-old Robert W. Carver: a physicist by training; the founder of two successful multi-million dollar consumer electronics companies, Phase Linear and Carver; the creative electronics engineer, termed a "genius" by some for his "Magnetic Field Power Amplifier," "Sonic Hologram Generator," "Digital Time Lens," "Asymmetric Charge-Coupled FM Detector," and "Auto-Correlation Noise Reduction System"; and an always controversial figure, with his "Carver Challenges" first tripping The Audio Critic magazine, then Stereophile, as Bob tried to show, with some subjective success, that at least with a hand-tweaked prototype, he could match the sound of one amplifier to that of another. "Transfer Function Matching" he called the process (footnote 1), and whether or not the Carver company could repeat the feat on the production line proved to be the crux of an intense public debate in these pages back in 1987 (footnote 2).
As Dick Olsher outlines in his review of Carver's Amazing Loudspeaker elsewhere in this issue, Bob Carver visited Santa Fe in September 1989 to carry out some urgent redesign on the product. I took the opportunity of his visit to try to pin him down over brunch both concerning the organizational changes that occurred last Summer at the company that bears his name, and about his design philosophy. My first question involved Bob's changing role at Carver following a severe drop in sales of almost $5 million to $20.5 million in 1988, a drop that led to a painful operating loss of $1.3 million (footnote 3).
Bob Carver: Since the inception of the Carver Corporation, I've been holding down two jobs, one by day and one by night. My daytime job has been president and chief executive officer, and my night-time job has been circuit designer. And inventor. The company has 275 people now, and the scope of both jobs has grown. I asked a friend of mine who's been on our board for many years to help me out and come take over my daytime job so that I could move my nighttime job up to the daytime. And to my great fortune he said yes, indeed he would do that.
John Atkinson: Basically, your role as administrator for a 275-strong workforce, coupled with the strategic running of the company, became a full-time job; it wasn't leaving you the time to devote yourself fully to product design.
Carver: That's right.
Atkinson: Last year you also hired Mark Friedman, one of the forces behind Onkyo's success in the US, to be your Vice President of Marketing and Product Development. I understand that Mark's feeling was that the Carver Corporation's problems basically stemmed from its product line suffering somewhat from staleness. The company had not adhered to the conventional consumer electronics "wisdom" of introducing a new line of products every year.
Carver: That's an understatement. Our products had gotten tremendously stale. For example, my 4000 preamplifier is over 15 years old. It was first introduced in 1974 as the Phase Linear preamp, and then resurrected when I formed Carver Corporation. It's been in our line ever since, and was only discontinued last year. That's a long time for a preamp to exist. And that's just one example. Over the years I've introduced new products with some special technology that the marketplace has liked a lot, but I stopped doing that about two years ago. With the result that we failed to bring out new products.
Atkinson: For a while in the early '80s, it seemed that every year there would be some new concept introduced which materialized as one or more Carver products. But couldn't you argue that, in fact, the 4000 preamp remaining in production all those years conformed to a good American tradition: "If it ain't broke, don't fix it."? Does a large company like Carver really need to introduce new products on a regular basis to retain its customers' interest?
Carver: I believe that all companies have to introduce new products to retain interest...new products and new technologies are the life blood of any company, and a failure to introduce new technologies is a failure to fulfill a company's destiny and, of course, the destinies of the people that make up the company.
I also became involved with loudspeaker design, and I'll tell you something about designing loudspeakers. It's worse than cocaine, in the sense that once you start it's hard to let go, and you end up working till two or three in the morning, ignoring life, ignoring family. It's almost a compulsive sickness. In the process of doing that, I didn't bring out the new products that I should have. So this last year I've made up for lost time and introduced 24 new products.
Atkinson: One of them, of course, was the C19 tube preamp. That's the second tube product we've seen from you, the first being the Silver Seven power amplifier. Does this represent a new-found passion, or have you always been interested in tubes?
Carver: I started designing amplifiers when I was in the 7th grade. Transistors hadn't arrived on the scene, so all my early work was designing vacuum-tube amplifiers. My first passion is vacuum-tube amplifiers, I grew up with vacuum-tube amplifiers. I love vacuum-tube amplifiers, I love them to pieces. I had a fantasy amplifier that I carried around in my mind all of these years; I dreamed about it, on and off, through my military career, through my children being born, through being married. I even purchased some Acrosound A-450 output transformers in the early '60s; I've carried those transformers with me all through my life, waiting some day for the moment to arrive to put them to use. The Silver Seven is that Fantasy Island amplifier, but I never really had the time to do it until now. The basic topology of the circuitry, however, was really hatched years ago.
A secondary reason for the development of the Silver Seven was that I really did want to endow an amplifier with everything that I could possibly think of, or anybody else could possibly think of, that would make it a wonderful, wonderful amplifier. And that included the silver wire and the Wondersolder, the gold connections inside...I've done a series of converging experiments, the results of which teach me that copper wire may well be equivalent to silver wire. But I'll tell you, in the case of the Silver Seven, if there was even the remotest possibility, unseen by me and undetectable by me, that silver would be better, I know one thing for sure: There's no better wire than silver wire!
Atkinson: Are there passive components where you have more definite feelings, where you have found that a more expensive construction or material does equate with better performance?
Carver: Absolutely. For example, if the power transformer is small and inexpensive, its performance won't be nearly as good in terms of thermal capacity, in terms of current capability, in terms of mechanical noise. But if it's a nice big one, expensively potted, vacuum impregnated, and so on, absolutely.
Atkinson: When you last visited Santa Fe, I remember you saying that output-transformer design is a black art. When you were conceiving the Silver Seven project, I understand you discussed transformers with people like David Hafler, who's been around since the golden age of tube amps.
Carver: David taught me how to design an output transformer. I had tried to design one myself and it had a bandwidth of 2kHz! Now, a successful audio output transformer requires a bandwidth of a quarter of a MHz if you want to close a feedback loop and make it stable. I talked to many people and I obtained examples of tube audio amplifiers, and I concluded that it was a lost art. Take a look at one of the nicest tube amplifiers around (save my own): the Jadis, say. Its output transformer is horrible at the high end—nothing to do with the way it sounds, but on a measurement basis—it's terribly flawed. I found out that the only guys that really seemed to know what was going on in output transformers were the guys that had been around for a long time: Bill Johnson, Sid Smith, David Hafler. It now seems to be coming back, however. The young guys are relearning how to make an output transformer for vacuum tubes because vacuum-tube amplifiers are very popular. I love vacuum-tube amplifiers. I really do.
Atkinson: Would it be fair to say that designing the Silver Seven output transformers was almost as obsessive an activity as getting involved in loudspeaker design?
Carver: Oh no, the loudspeaker design took over two-and-a-half years, the transformer design took a few weeks. But only because I talked to David and he taught me. If I had to dope it out myself, it probably could have been as obsessive a project. But, the transformer that I designed is basically the teachings of David Hafler with my own unique modern twists. Mostly just making it huge and winding it with silver wire. And I didn't run it ultralinear. I run my output stage with fixed screen potentials instead of an ultralinear biasing.
Atkinson: So it's a little bit like an older Audio Research design. They would run the screen grids at a constant high voltage, regulating it with a series-pass tube.
Carver: Must have been really old ones. The new ones have swinging screens.
Atkinson: Is Carver making many Silver Sevens?
Carver: It seems to me we're making a lot. I started out making one, then there was a demand—to my great surprise—for a $17,500 amplifier. So we made ten of them. And now this run I'm working on now is for 30 sets. (It takes four chassis each to make each pair.) I guess we're making about ten Silver Sevens per month.
Atkinson: To return to loudspeakers, it came as quite a shock when I saw that the first Carver speaker was a planar design. Have you always been attracted to planars?
Carver: I've been attracted to a particular kind of soundstage that was described brilliantly by Harry Pearson years ago in The Absolute Sound. It was a soundstage that had front-to-back depth, extended in a large arc behind and around the speakers, and from time to time could actually produce sound images outside of the limits of the loudspeaker edges. It seemed, when I read that essay, that that was so absolutely correct. That's the way a soundstage should be. And at that time, the loudspeakers that I was familiar with were unable to develop a soundstage that even came close to doing that. I found that mostly I would hear a flat curtain of sound strung between two loudspeakers.
However, the loudspeakers where sound could also go out the back, the dipole speakers and the bipole speakers, made a soundstage that approximated the description that Harry Pearson had enunciated in his essay. I thought that was wonderful. The speakers that made the big soundstage were the Magnepans, the Bose 901s, the Dahlquist DQ10s; and if you think for a moment about the speakers that have lasted through the years relatively unchanged, the classic speakers all have had sound going out the back, bouncing off the rear wall to make a special use of room acoustics to help generate a large, three-dimensional soundstage. Those are the guys that have longevity. And I think it's because there's something particularly sumptuous, realistic, loveable, and believable about the soundstage that those speakers present. Naturally, I fell in love with the dipole speaker.
After reading Harry's essay, following his teachings, and trying to replicate that soundstage, I found that there were many components associated with that soundfield that had to work just right to make it believable deep into our ear-brain hearing system. One of the basic requirements was that the early arrivals be pristine and uncluttered. Which meant that early reflections, sidewall reflections, needed to be eliminated. Floor reflections, ceiling reflections, all of those things had to be eliminated to allow the first arrivals to arrive uncluttered so that the ear-brain can process both the amplitude and the timing cues associated with those wavefront arrivals.
The way to do that turned out to be by using a line-source driver. Like a ribbon. Because a ribbon does not radiate down, and it doesn't radiate up. And it doesn't radiate to the side very much. It radiates straight ahead and straight back. So there are no early-arrival reflections to muddle up the sound. Our ears hear the first arrivals, latch onto them, and build in our mind's eye a picture that has space and breadth and believability. Then the special use of room acoustics comes in about six milliseconds later. These are the longer-term reflections. If the loudspeakers are three feet from the back wall, by bouncing the sound off of the back wall, a multiplicity of arrivals occurs at our brain and our ears 6ms after the first arrivals and further enhances that lush, big soundstage that I wanted to achieve. That's why I chose a ribbon over anything else. And it works. It works. It can build an incredibly believable, beautiful, fun to listen to, spectacular soundstage with a planar ribbon loudspeaker.
Atkinson: But then you had to choose whether the line-source ribbon would be electromagnetically or electrostatically driven. Were you at all tempted toward electrostatics?
Carver: Well, when I first decided to do the loudspeaker, I actually built electrostatic ribbons and electromagnetic ribbons. There are two ways to make a diaphragm move: electrostatically or electromagnetically. The universe gives us those two choices. Maybe some day we'll have gravity-driven speakers. (Some theoretical work has to be done before we can harness the forces of gravity.) I built some electrostatic ribbons, and they worked fine. I also built the magnetic ribbons. They also worked fine. I ended up choosing the magnetic ribbon because at the time it seemed that it would be less problematical and less expensive to attain the equivalent results.
Atkinson: And did you discover along the way why magnetically driven ribbons are not very popular drive-units?
Carver: Yes I did! It's a lot harder than I thought to make a ribbon really work right. Ribbons don't look very good on paper. Even a perfect ribbon on paper has an erratic frequency response, due to the physics of the wavelaunch acoustics. A practical ribbon is even worse than that. It has resonances, buzzes, power-handling capacity problems, it has longevity problems. It's a very difficult design to get right. But amazingly enough, as rotten as a ribbon might look theoretically on paper—and, by comparison, even an inexpensive Radio Shack tweeter looks magnificent—when you put a ribbon in a living room and fire it off, some magic happens. There's a seamlessness, the voices are just pristine, just beautiful. That's the part that I worked on the hardest. Getting voices right.
When I started the design, the closest ribbon that would do it all was the Apogee ribbon. It's a wonderful ribbon, just a fabulous design. However, it has to be rolled off beginning at about 800Hz and its sensitivity—excuse me, its efficiency—is approximately one quarter to one eighth of the efficiency that I thought the marketplace would accept. That's proven to be true. When I first came out with the Amazing Loudspeaker, my ribbon was four times less efficient than it is now. And the marketplace wouldn't accept it. I mean, I sold Amazing Loudspeakers all right, but not nearly as many as I wanted to.
Even my own amplifiers had troubles driving them, to be honest. You know, if you'd wail on an original Amazing Loudspeaker with one of my amplifiers, which had enough power, sometimes it'd run out of thermal capacity and would go "Click!" The thermal switch would turn it off.
Atkinson: One difference between the Apogee treble ribbon and yours is that you tension the ribbon from all four sides, whereas the Apogee just has it lying floppily in the magnetic field. Does that give you sensitivity advantages?
Carver: Not sensitivity advantages. It does gives me a low-frequency performance advantage. To make the ribbon work right, I felt I wanted it to be perfectly seamless, perfectly crossoverless. I didn't want to put a crossover in the system. To do that required response down to 100Hz and to achieve 100Hz response requires a lot of air area. My ribbon design is therefore a large-area ribbon. As a matter of fact, there's as much area as a 12" driver.
The big problem has been that it's my first serious loudspeaker design. And it's been a lot more difficult than I thought. Once the drivers, the woofer system and the ribbon system, were working properly, just getting the tonal balance right was fraught with difficulties. That drives everybody crazy, not just me, because there is no right or wrong. It's not like a direct radiator system where you can measure it one meter on-axis and make it flat and that's the end of the discussion. Because of the acoustic radiation geometries associated with the ribbon wavelaunch, the tonal balance changes with distance. So you either have to have a way to compensate for that or you have to pick one and hope that your listener agrees with you.
Atkinson: Voicing a loudspeaker is not a trivial affair when it comes to a planar design.
Carver: It's easier with an electrostatic with a wide panel. It's much more difficult with a line source. Yet a line source is the more perfect transducer.
Atkinson: Once you had the concept of the ribbon going down to 100Hz, did you try other methods of matching it to a subwoofer before you went with your current one where you use high-Q bass drivers to compensate for the finite-baffle rolloff?
Carver: The first thing I tried was just a normal subwoofer. I couldn't integrate it.
Atkinson: Is that because of the mismatch between the omnidirectional radiation pattern of the subwoofer at crossover and the dipole one of the ribbon?
Carver: I honestly don't know. I just didn't care for it. I then tried dipole woofers; at the time I hadn't yet figured out how to make them have flat response without a lot of equalization. So I hooked up my panel to a normal low-Q woofer and EQed it till it was flat, and listened to it: it integrated seamlessly with the ribbon. I thought, "Am I imagining this?" So I hauled out a Quad, which of course is seamless in the crossover region at 100Hz—it doesn't have a crossover. I measured the phase response and acoustic response of the Quad, and compared it with my speaker, paying particular attention in the crossover region: the two curves literally fell on top of each other. And I concluded from that experiment that the dipole woofer was a perfect match to the dipole ribbon, and was definitely the way to go.
Subsequently, I found that there were many advantages, the biggest one being that the response can be extended down to 20Hz and below without the severe efficiency penalty. The woofers are also cheap, because their magnets are tiny.
Atkinson: If you use purely electronic equalization to flatten the response, then you would have to use significantly expensive drive-units.
Carver: Expensive drive-units plus the electronics to equalize them.
Atkinson: From this weekend's experience, there would still seem to be some minor problems with the speaker which have been irritating you for some time.
Carver: I've been hacking away at the problems for two years. And they're down to residual problems right now.
Atkinson: I felt that with the low-frequency ribbon resonance suppressed, the sibilance emphasis seemed to become more audible. Is it fair to say that, as soon as you've solved one problem, that leaves another slightly more exposed?
Carver: I'll never be happy with my speaker design. There will always be problems to pursue and always problems to solve. That's why I love being an audio designer. I love it with a passion. If the problems went away, it wouldn't be fun.
In the case of the ribbon, the remaining problems involve controlling resonances. So what else is new? Controlling resonances is always a problem in loudspeaker design. A never-ending one. The time-domain performance of the ribbon emerges very naturally by its design, however, so I didn't have to work very hard for that.
Atkinson: As well as the smaller Silver Edition, I understand that one day you might introduce a twice-the-size version of the Platinum.
Carver: I'm working on the "Great Amazing" right now. Which will be a killer system. It'll be right up there in performance with the Silver Seven tube amplifier. I haven't prototyped it, but as we speak, the cabinets are being fabricated. When I get back home, I'll be assembling it and firing it off for the first time. I can hardly wait! And it'll undoubtedly teach me things during the development that I'll be able to apply to the current Amazings.
Atkinson: Do you have many other engineers working with you at Lynnwood?
Carver: I wish. There are only two engineers: myself and Vic Richardson, who's been with me eight or nine years. Since right after the inception of the Carver Corporation.
Atkinson: That's not many creative people for a $25 million company.
Carver: Yeah. We should have more.
Atkinson: A change of subject: The last time you appeared in Stereophile's pages was in response to the amplifier challenge. What was the legacy of that whole business?
Carver: When I started that transfer-function emulation project and then subsequently designed an amplifier with that transfer function, I thought I was being a powerful force for good and doing something worthwhile.
Atkinson: By allowing people to get what in effect was the same sound at a significantly lower cost?
Carver: What, in fact, I ended up doing was just pissing everybody around me off. I angered my dealers, I angered so many people, that I wish I could hop in my time machine, go back in time, and not do it.
Atkinson: Purely because of the social aspects rather than the engineering?
Carver: I just didn't like having my feelings hurt so much. It's my own fault. I didn't understand at the time that that's what would happen.
Atkinson: It certainly provided a lot of editorial copy for The Audio Critic, The Absolute Sound, and Stereophile. How do you see the relationship between a company like yours and the high-end hi-fi magazines? Do you see your company and the magazines as basically being in an adversarial position? Or as working toward the same end?
Carver: I see us all working toward the same end. As a matter of fact, in the case of Stereophile, it was a horrible slap in the face that hurt me tremendously editorially. But you know what? It really got me off my duff and it got me busy designing some new things. Some important and significant new products. That was the silver lining for me, personally and professionally.
Atkinson: One of the comments that I thought rang true was from Larry Archibald, when he said that he would be much more interested in seeing what you, Bob Carver, would be capable of doing as a creative engineer if you had no limits imposed.
Carver: Well, in part it was because of Larry's feelings that I started on the Silver Seven. Now I'm not going to say I did it to say, "Ah! I showed you, Larry Archibald! I can design a great amp too!" But probably at some subconscious level, there was a little of that going on. It did result in a world-reference-class amplifier; the Silver Seven's unquestionably the best amplifier in the world. And it gave me a new transfer function; this time it was my own transfer function! And I've done the best job I can to put that transfer function in my Silver Seven-t. It's not exactly the same. It's not an infinite null, but it's as close as I can possibly make it.
Atkinson: In production?
Carver: Both in production and on the lab bench.
Atkinson: Because one of the things which came out of that whole business for me was how unstable the null was. If you breathed near the amplifiers, the depth of the null would change and the position of the null would change.
Carver: If you let the sunlight shine on an amplifier that's sitting there with a 70dB null, the null will go higher. Or deeper. Less null.
Atkinson: This is the crux of the matter...
Carver: A 70dB null is a very steep null. It's really down to the roots of the universe and things like that. 70dB nulls aren't possible to achieve in production.
Atkinson: What is your target null between the Silver Seven-t and the original Silver Seven?
Carver: About 36dB. When you play music, the null will typically hover around the 36dB area. So it's not a perfect null. No question about it.
Atkinson: It's 98.5% the same...
Carver: It's not a bad null.
Atkinson: ...and there is a significant price difference.
Carver: Yeah. The only way to get a 100dB null is to buy the Silver Seven.
Atkinson: You were saying last night that one legacy of the Carver challenge was that it made you realize that, in fact, high-end magazines have significant readership among retail-store staff. The people who actually sell the equipment. Do you think that that is as important as the effect they have on audiophiles?
Carver: To the extent that the magazines enhance people's understanding of this wonderful, fun art of ours. Store salesmen are audiophiles.
Atkinson: Do you think that magazines, a) realize that, and b) take their craft seriously enough?
Carver: I don't think that magazines understand the power they have. You've heard the expression "the power of the press"? It's amazing. Part of being human is not believing that you can control the world. Why would a normal human being have that belief? And why, indeed, would a magazine have that belief? The reality, however, is that there is a tremendous, tremendous amount of power inherent in the press. Probably way more than any member of the press thinks or believes. That's been my impression from talking to editors for 20 years.
Atkinson: So even a casual remark, if it's in print, may have a significant effect, either up or down, on sales for a company like yours?
Carver: Absolutely. A tremendous effect.
Atkinson: How then could magazines do a better job in acting responsibly?
Carver: [laughs] I think the answer is very easy. Be open, be honest, be receptive to fresh ideas, particularly being receptive to different religions.
Carver: Religions. There are several religions that exist in our audio community. Magazine editors should practice religious tolerance. If you can be honest, if you can be truthful, if you can put your scientific hat on, be scientific when you need be, put your subjective hat on, be a subjectivist when you need be, and always be open-minded, never be defensive, that's what I believe a magazine should strive for.
Now, it's part of being human to be defensive, to have a tad of religious intolerance. That's okay; it's part of your humanity, it's part of my humanity. But I feel that magazine editors will do their job better if from time to time they step back, survey the scene from above, and question themselves as to their religious tolerance. Other than that, be honest and truthful. And the manufacturers have to respond in kind. They have to have the same fundamental, philosophical approach. Nobody's exempt from that. And I think that in the end the magazines play an incredibly important role in advancing the state of our audio art, both in the effect they have of getting manufacturers to do a better job, and also in their constant questioning "What if?," "What could be?"
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
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.