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  1. Bob Carver just sold another pair of INCREDIBLE Tube Amps on eBay~








    Here's the always interesting Q&A from the auction:

    Q: Hi Bob. I'm a little confused, perhaps you can straighten me out. In the first part of the description, you state that "I designed and wound a massive new and powerful output transformer." Later, you mention "Though I have become pretty good at winding them myself, it takes too long" and "I had the thought of getting a commercial transformer company to make them for me according to my plans, but the cost was too high." So,to clarify my clouded brain, are the transformers installed in the BLACK BEAUTY your own handiwork? Also, you mention that "A switch that changes the feedback from classical (vintage) to contemporary." Obviously, by 'vintage,' you must mean a Citation-like sound, right? But by 'contemporary' do you mean more like a current solid-state unit, e.g., Sunfire, or a modern vacuum tube unit, e.g., Audio Research? I'm using other manufacturers names for comparative purposes only; I'm certain that both positions represent the "heart and soul" of Bob Carver! Thanks! -Dave Mar-21-11

    A: Hi Dave, I can understand how you are confused because I'm confused myself. If I'm confused how could you possibly not be confused? Now you are making me think! Okay, here goes. I did teach myself how to wind them by copying the original units. Subsequently I changed the design from pie-wound to layer-wound, and have been more than pleased with the way they turned out. I used modern steel and segmented windings. Nobody wanted to pie-wind them - it takes too long, is very difficult, is too expensive and not necessary anyway. At this point in time the units in these Black Beauties are my own handiwork because I have not yet found a transformer house that will wind them for me (at least the way I want them wound), but I will soon. It's hard to wind output transformers - power transformers are easy - and I for one have developed a new-found respect and admiration for the handful of transformer guys on our planet who do it well. As for the feedback switch, "classical" refers to the amount of negative feedback = 20dB. "Contemporary" = 11dB. Modern tube amp designers often prefer less feedback than do vintage designers. That's mostly due to the fact that it's quite difficult to get substantial feedback around modern transformers (built with a rational budget in mind). Sometimes it seems that all the vintage units were designed as cost-no-object. Oh well, It's a good thing I love winding transformers! Hope I did not put you to sleep, Bob Carver

    Q: Hi Bob- Not a very exciting question here, but I'd love to see how you package one of these amps for shipment, and I'd like to know which shipper you prefer. I hope you'll be making these until I can afford a couple! Thanks, Clay Mar-21-11

    A: Hi Clay, Well, let's see. First I put some special soft cloths around each amp,then a plastic wrap around each one on top of the cloth. After that I put each amp in a box using foam corner blocks. After that, the box is then put inside a bigger box and lots more soft corner blocks plus bubble wrap is used to hold the inner box in place as well as to add extra cushioning. The whole big double box is finally taped closed and banded with nylon banding to hold the box together in case it's dropped down some stairs. Wow! At least I can describe the process faster than it takes to do it! Thanks for asking - I know lots of us want to know the answer to these important questions. I prefer UPS and the USPS. Bob Carver

    Q: Hi Bob, Have always truly admired your fine designs. Your tube amp is a beaut. I hope I can afford it. I do not know yet. I now am a proud owner of DOUBLE INFINITY IRS BETAS (2 woofer towers per side) and two main speakers per side as well. I intend to use them in a very large room. The issue of course since the main speakers are very low in impedance, would you recommend the tube amp connected in series (4 ohm tap) to the main speakers or would you still go parallel (they have very nasty impedance drops to the 1 ohm areas). As far as the woofer towers I am confident with solid state. Will be running one woofer tower facing front and another facing rear (omni) with two solid state amplifiers. Since the DC resistance of the towers are 3.2 ohms each could you recommend a stable amp of your own design (solid state again) that I can use for each tower --these will have their own acceleremoters of course... Could older Phase 400 be safe or should I use something else of yours? Mar-21-11

    A: H 'ster, I have owned a set of Betas - amazing speakers and one of Arnie Nudell's great and passionate works. The minimum impedance of three ohms or so is not difficult for almost any solid state amp, including any that I have ever designed. A Phase 400 would work great on the woofers. The mids and top with the Emits and ribbons are a different story though. Since they get down very low impedance-wise, we do need an amp that is happy with around an ohm. These Black Beauties will indeed make them sing. I have not actually hooked them up to a pair of Betas, but long ago I did hook up my Silver Sevens and the sound was STUNNING! I'm absolutely certain that results with these amps will be just as stunning, maybe even better. Take a leap of faith and bid happily away! Good query! Thanks for asking, Bob Carver

    Q: Hello Bob, First of all I would like to say congratulations on your design and on your longevity and passion for what you do. I have had various different full electrostatic speakers for the last 25 years and for nearly all of those years, I have depended on your amplifier designs to make them sing; Phase 700, Silver 7t, Silver 9t, Signature, Signature Series II. My current system is anchored with a pair of 20th Anniversary Martin Logan CLS's and a Sunfire Signature II small chassis (Architect Series). My question is a simple one. In your opinion, will these 400watt Black Beauties have the power and headroom to make my CLS' sing? Thanks in advance for the answer, Ray Mar-21-11

    A: Hi 'gunn, Thanks for making my day - I am definitely happy that you have used my designs for all this time. It seems that together we are still in the arena, even after all these years. I have loved the way vacuum tube amps sound with electrostatics, and have spent countless hours optimizing these amps with CLS's. I continue: When Martin Logan was getting started long ago, I called the founder and asked for a set of CLS's. One thing led to another, and I helped Martin Logan with financing, as well as with some design work. In the process, we two did a lot of listening with his speakers and my amps, were both influenced substantially, and the end result has been amplifiers that work hand and glove with electrostatic speakers. These Black Beauties are perfect for your CLS's! You can even predetermine just the correct output voltage easily, and adjust the Black Beauties to match as well. Great question. Hope this helps, Bob Carver

    Q: hello Are you planing to built a preamplifier as good as your amps ? thanks for answering regards from France Mar-28-11

    A: Hi from France', I'm not saying. Oh what the heck - yes. But not until next year. When I do build a preamp I want it to be the best sounding, the best looking, and the best there is. I know I can do it - 14 tubes (!) in the phono section alone will give it the best sound and the quietest all-tube phono in the world. Of that there is no doubt. The line stage will be designed with the help of Stu Hegeman and Tim ( I hope) even if I have to travel all the way to another world and another place to work with them. A great preamp is a huge undertaking, pretty much requiring unending devotion day and night. No sleep, no play, no Disneyland,- it's a good thing I love designing preamps. There,I said it! Bob Carver

    Q: greetings do these amps produce a lot of heat? would placement/ventilation have to be a consideration thanks Mar-27-11

    A: Hi'ct, I am proud to say that these amps do NOT produce a lot of heat. It is relative of course, but as an example, most big amplifiers idle their output tubes at approximately 24 to 45 watts, with 35 watts being the average for a low distortion, wide bandwidth unit. It is the idle power associated with the output tubes that makes the amp get hot. Now for the best part: the DC restorer in these Black Beauties allows the distortion to go very low and yet have the idle power at 11 watts. The tubes are so cool we can hold them without getting burned, though it IS quite uncomfortable to do it. Still, and just the same, we should allways allow some ventilation for for any electroncs with tubes. Thanks for asking, Bob Carver

    Q: Hi im new to tube audio. I work alot with large sound systems and night club systems. I wanted to ask you if you worked with tube pre amps at all? I had an idea of building a tube pre amp that could have control on how much saturation or coloring the tubes would effect the sound. Do you think adding a tube pre amp will warm up the sound from CDs or computer based dj programs? Thanks Henry Mar-27-11

    A: Hi '53, I like your idea of including a "color saturation" conrol to your new preamp. You remind me of me in that department, because that's exactly the thing I would do left to my own thoughts. And yes, adding a tube preamp will tend to warm up the sound from a CD or computer based system.

    Q: Hello again Bob, This is Tim from Wilmington,DE.,last time we chatted you recomended me to salvage some old BOGEN amps for the quality of their transformers. While searching I came across a pair of BOGEN MO200A in good condition but had none of the 8417 tubes that they use. As you know 8417 tubes are very expensive and hard to come by especially since they require 8 8417's per amp. I know it is possible to run 6550's with a loss in power but wanted your opinion on what you would do with them if it was up to you.Would it run with KT88's or even the new KT120's. I would be very greatfull to hear your opinion. Warmest regards, Tim (mmmmcdowell@gmail.com) Mar-27-11

    A: Hi Tim, Good score on the Bogens! Actually the 6550's will deliver more power than the 8417. The reason is that they pull down better (by about 35 volts) than the 8417, though they do require about eight more peak drive volts. If you installed the KT120's you would achieve even more power, using the 16 ohm tap as the eight ohm tap, the eight ohm tap as the four ohm tap, and so on. You would have to modify the driver circuits to increase the drive voltage to the grids of the output tubes, though it should be pretty easy to do. If you wanted to use the Bogen circuit, just increase the B+ to the B+ side of the driver plate resistors by about 10 or 20 percent. Then let 'er rip! hope this helps, Bob Carver

    Q: How is the bias being adjusted? I see no bias pots. Mar-27-11

    A: Hi'tell, The bias is adjusted by a bias pot on the back of the amp. All we need to do is look at the front panel meter and turn the pot until it reads the desired current. All six output tubes are adjusted at once by the single pot. This is possible because of the DC restorer, the circuit that completely eliminates the need for tube matching. The desired bias current is not determined by the designer (me), rather by you and the sound you want from the amp. There is no OPTIMUM bias, rather a RANGE of possible currents, all "in the green". And the choice is yours. Of course I have my personal favorite bias current, and the operating manual that come with these Black Beauties tell us what it is and expands on the concept. Great query, Bob Carver

    Q: Hello Bob: I have always been impressed with your products and designs. My question: can balanced inputs be installed in the amps? Thank you, S Mar-25-11

    A: Hi again my friend, Yes of course anything is possible, including balanced inputs. But I get great sound with the vintage, ubiquitous RCA inputs, and balanced does not add one bit of sonic improvement - only some convenience if you happen to have balanced cables. Balanced is extremely useful for long, professional, cable runs to help keep down hum and noise pick-up. However, for home systems, single-ended sounds best with far less complexity. A true balanced input requires an extra tube or an input transformer along with the ever-present possibility of compromising the sound because of the added complexity. Still, many folks have asked for balanced, so you are not alone. Hope this helps, Bob Carver

    Q: Great looking amps. Have you ever thought about making them in mirror imaged pairs? Thanks, Robert Mar-25-11

    A: Hi 'great, great name! Yes I did think of making them in mirrored pairs. Whenever I have a new idea, or don't have one and find myself stuck with my old idea, I make a mock-up of the second idea so I can try it on for size. Well, I mocked up a mirror image amplifier, put the two side-by-side, and did they ever look funny that way! At least they seemed that way to me! When two identical units were side-by-side, the whole system looked like a very serious arrangement. I liked the looks of the system better when they were the same. Great question - can't tell if I answered it though, but I gave it my best. Bob Carver Bob Carver

    Q: Hello Bob,I own a pair of modified Infinity RS1's with 9 EMIMS and 16 bi-pol EMITS a total of 32 per column. I use Beta Woofer Columns with the Beta Servo control unit. Mid/high columns I use Antique Sound Lab Hurricane tube amps at 100 Watt P and 200 T. Your previous amp had P/T feature, how do these differ and would this be a major upgrade across the board. Thanks for your response. Mar-24-11

    A: Hi - oops, I already answered this question. Read on. Bob

    Q: Hi Bob, last time I will annoy you. I was just studying your amps and thinking to myself, what an interesting look they would present with a yellow chassis and black transformers. A big ol pair of Bumblebees, if you will. Think about it. I'm in if you put together a pair like that. Sincerely, Timothy. Mar-24-11

    A: Hi '15k, Welcome back! Bumblebees - I like that! I used to build my model planes using that exact color scheme when I was a kid. Yellow wings and black fuselage. I got so stuck on a single color scheme that my little brother hid my yellow dope (model airplane paint). Well '15k, I'll probably build a yellow and black pair, but I promise not to make them HUMMMM and BUZZZZ like yellow and black bees when they are just sitting there (in hover). Thanks for writing, Bob Carver

    Q: Bob, First off, I, think your great and these thing are a work of art. I am a rookie when it comes to tubing and mono blocks, so please for give me if i sound at all skeptical. 1st off what is the purpose of the gauges are they for amps or output wattage and if they are for output shouldn't they read at least 300 ? 2nd is that picture of you winding these are the red pair you sold last month ? These look alot like the red pair that was suppose to be the only pair you had last month. I realize the red pair were only 180 watts. The reason I bring this up is that I am dying for a pair, built by Bob Carver even a better bonus, I just want correct info. If your going to build more I would just assume purchase a pair (through e-bay). Not trying to cut E-bay out by any means. Like I said, please forgive me for sounding skeptical but, when buying on line you like to see consistantcies in what your looking at. Tony Mar-24-11

    A: Hi '8rnks, The reasons my auctions seem inconsistent is because I have some character flaws. I procrastinate and I am often lazy. I procrastinate when it comes to taking new pictures sometimes, and so I just use the old ones - like me holding a brown amp with my new hat, or me winding the output transformers. The red units are indeed 180 watts, and the Black Beauties are 305 watts. Anyway, please don't be too sceptical - maybe just a little heathy bit. But it is really me. I can pinch myself to prove it! Ouch! It's me alright! Bob Carver

    Q: hello Bob, I would like to ask about Tubular Joe if I may. Your lengthy history in the audio world is well known, but I know very little about Joe or his backround. Are you able to shed some light on his involvement with this amp project? Mar-24-11

    A: Hi 'shin', Tubular Joe is a sound man here in the Pacific Northwest, is the best and most talented builder of all time I have ever met, does not like his picture taken, builds the amps on his kitchen table in the evenings and on weekends as a pure work of art and love, has a family and a beautiful young daughter named Corina. He sings solo and lead at night in the late night scene here in Seattle, and all the amps he uses on stage are tube amps. There's more, but that's it for now. Bob Carver

    Q: Hello Mr Carver... You have been building these amps for Ebay now for a couple years, and by the pricing of them, it would appear they have quite a following. Congratulations on that! My question is not so much about your most recent upgrade to 305wpc, as it is about future offerings. Are you planning other components to go with these amps, such as preamps and such? Also any plans for more powerful amps? Mar-24-11

    A: I'm not saying.

    Q: In your Sunfire Signature amps (have owned several of them) you were using massive torroidial transformers. I am curious as to why these transformers have little following in the design of tube amps. Are there any reasons for this? Mar-24-11

    A: Hi '1 again, Lots of people have asked me that, and the reason is simple. They are perfect up to the last volt-ampere product and beyond that they too quickly plunge headlong into overload oblivion. Non-toroidal transformers overload gracefully and far less abruptly, smoo-o-o-o-thing their way into overload. A very desirable characteristic with tube amps. Great question, Bob Carver

    Q: Hello Bob! I was wondering if you could shed some light on how the work of people like Stu and Tim have influenced your work. I know of the story of the 'coffee can' amp, but I am also curious as to what motivated you to go into the audio business to start with. It would seem a daunting task for someone just coming out of school to even being to think about, so I guess the question is who did you look up to in this field, and why? Mar-24-11

    A: Hi tropical',That's a tough question, but I'll do my best with it. It's complex but easy at the same time. Both Tim and Stu were my teachers and collaborators when it came to Tube amps. Stu as a ghost from the past when I studied his HUGE body of work, read everything I could get my hands on about him or written by him. Tim on the other hand, is my contemporary and I can still sit down over coffee with him and we can talk and talk. We have shared ideas, thinking and circuits. Both have influenced me a lot. I have to say though, when I first got out of high school, I had not yet met Tim - that had to wait until a dark and rainy night on a lonely, wet street in Germany outside of a Hi-Fi show. Stu Hegeman became one of my early heroes - the guy is like Albert Einstein - everything he did holds up to this day with not a single mistake. He knew how to listen, and he got it right! Nice questions - they make me think, Bob Carver

    A: Hi 'noon - that sounds funny - oh well, I have used Sprague Atoms, and they are amazing capacitors - no doubt about that. The main drawback here is that they are too big to fit inside my chassis if I want the energy storage I have designed for my amp. My "beast" - 305 watts rms - yeah - I guess it is! The E = 1/2CV^2 of the caps I have are actually quite superior to the Atoms in the narrow use I put them to. If there were a better cap with more performance, I would use it. The Atoms ARE preferred (for a variety of technical reasons) for guitar amps though. You are on the mark with that. There are few things more fun than building tube amps! Bob Carver

    Q: Hi ya, Bob! I'm kind of a doofus when it comes to some things, perhaps you won't mind explaining something about these amps for me. You say that "Power is an easy 305 watts rms with a power bandwidth from 24 Hz to 45 kHz, frequency response 2 Hz to 85 kHz, and distortion less than 0.15 % at 305 watts out." OK. I understand the 305 watts rms and distortion stuff, but what's the difference between power bandwidth and frequency response? Aren't they the same? If not, why not? And if they're not the same, how, if at all, would the difference at the low end affect my listening experience when driving full-range speakers, e.g., a pair of Carver Amazing Loudspeakers or similar? Thanks, Man! Nate Mar-24-11

    A: Hi again and welcome back! When I was first getting started as a baby inventor, I wondered about the same thing - power bandwidth vs frequency response. Power bandwidth refers to the amplifier's response at high output power just below clipping, whereas frequency response refers to the response at a lower level, usually (and by convention) -20dB. What we measure on the laboratory bench is power response, and when we listen we are listening to frequency response. Frequency response is what we hear - power response is what we measure. It's more complex (as usual)than that, but not much. Super question! Bob Carver

    Q: Hello Bob,I own a pair of modified Infinity RS1's with 9 EMIMS and 16 bi-pol EMITS a total of 32 per column. I use Beta Woofer Columns with the Beta Servo control unit. Mid/high columns I use Antique Sound Lab Hurricane tube amps at 100 Watt P and 200 T. Your previous amp had P/T feature, how do these differ and would this be a major upgrade across the board. Thanks for your response. Mar-24-11

    A: Hi 'blend, I remember taking a cab from Kennedy airport to Mike Kay's Lyric Hi-Fi in Manhatten, arriving on his doorstep with four large boxes under my arm. I wanted to show off my (then) brand new Silver Seven tube amps. I was traveling the country pitching my wares. Mike greeted me with his Greek accent - "Booby, lets hooook them up to the Big Infinitys, and see how they work." Well, Even though it was long ago, it seems like last week, and before long our faces were locked in ear-to-ear grins. Mike said, "Harry (Pearson) is going to looove them, let's call him." What happened later is another story, but before we left, we tried the amps up his RS1's. That was the first time in my life I had heard them, and I was amazed; the Silver Sevens together with Arnie's Beta towers were absolutely stunning. I won't forget it! These Black Beauties are my latest thinking, and if anything, will sound as good as that system so long ago. Probably even better. You will have the majestic power that is lacking in your existing amp, no matter how good it is - this would definitely be a very serious up-grade! Great speakers - Hope this helps, Bob Carver

    Q: Hey there Bob. Is that the expression I might find on my face if I tried to wind a transformer? I'm lucky if I can wind my watch. Oh, by the by, thanks for the tip on upgrading my Citation I. I think we got the noise thing figured out. Might have to touch base with you on the phono stage. Have not tried it out yet. Oh, gotta go, Rush "Working Man" playing....heading over to crank up the db's just enough to annoy my neighbor! Sincerely, Timothy. Mar-23-11

    A: Hi '15k again, welcome back. I know what you mean . . . I can wind a transformer, but not my wind-up flashlight. I'm glad the noise is figured out - let me know how you did it; play it soft. No, play it loud! Thanks for the heads-up, and may your listeners have fun tonight. Bob Carver

    Q: Hello Again Bob, Seems like youve outdone yourself once again. This one looks even more impressive than the last pair. is the difference power upgrade and tubes? If im understanding you correctly its not the tube the makes the great sound but the circuit designed around the tube that does? The kt120 i have never heard of could you tell us a bit about it and its sound qualities. Can other output tubes be used in this amplifier kt66 kt88s El34 etc. And finally why did audio manufactureres in the past use odball output tubes like 7027s 7581s 7868s 12by(hk) knowing they were going to be very hard to find and costly later on. quicksilver amps is one company that come to mind. Was it because they just wanted to be different than the rest? The same goes with preamp tubes amost everyone made them with 12ax7s 12au7s. thanks again. Mar-23-11

    A: Hi again '55, These Black Beauties have a bigger power transformer, a bigger output transformer, and the new Tung-Sol KT120's. To my ear, the KT120 sounds similar to the old Gold Lion KT88, except it can pull down a bit better (by about 40 volts because its plate inside that glass is huge), giving it a more "meaty" sound in the low end. And yes, any of the output tubes you mentioned can be used in these amps - all you have to do is plug them into the sockets, set the bias (using the front panel meter and the bias control), and let 'er rip! As to why did manufactures use oddball tubes? Those choices were made before my time, so I can only guess. My guess is that it was pretty much the individual designer's choice or a cost constraint. I'm almost certain they did not know which tubes would become hard to find 50 years later. For example, the 7027 was an RCA tube, developed by them to compete with the U.S. 6550 and the British KT88. They were VERY proud of that tube! It was also priced (for the amplifier manufactures) less expensively than any other big power tube. They hoped to encourage its use everywhere. And they succeeded! As for the 12BY7 used in the harman kardon amps, Stu Hegeman, the designer, wanted very wide bandwidth so he chose video output tubes. Only they had the high frequency response he wanted. He held the belief that the "Wider the band, the higher the Fi". 12AX7's were so ubiquitous that they stayed around to this day. And they are great tubes too! Hope I did not put you to sleep - if you are still awake, read on. Great questions, Bob Carver

    Q: Bob- I have a couple questions, I hope you don't mind. I believe the previous red amps were stated to be 180 watts rms. You say that these "BLACK BEAUTY" amps are 305 watts as a result of the "powerful" KT120 output tubes. Did changing the tubes require beefing up all the other components in the amp as well, for instance, the resistors, capacitors, etc.? Are any changes essentially only in the output stage? Power equals current times voltage in simple terms. Many amplifiers, including some previous Carver models, boast of high output current capability. What voltage/current is this amp capable of producing? Or is it not so critical when using output transformers instead of a direct coupled output like a solid-state amplifier would use? Thanks in advance for your answer! Chris Mar-22-11

    A: Hi 'ross8, Holey Moley Rollers! I love questions like this. Here goes - The extra high power comes from three things. One, the new output tubes, two, the new output transformer, and three, the new power supply. It takes all three to get the job done. The new tubes (KT120's) are much more powerful than the KT88's by half again as much. Mike Mathews (the owner of the Tung-Sol tube company) has wanted to build a wonderful tube like this for at least two decades, and he finally did it. This tube is nothing short of fabulous - it has lower distortion (about half as much), more power, and a higher dissipation rating than any other contemporary vacuum tube. I have never met Mike, yet I have known him by reputation for as long as I can remember, and I can tell that he has done everything humanly possible to make a great new tube. He must have a burning passion for output tubes. When I look inside his tube, I can easily see that the grid and screen wires are in tight, perfect alignment. I can also tell that they have been burned in for a long time in his quality control room. As for the output transformer, I changed the turns ratio to optimize the loading (the loading I wanted) for the new tubes, as well as to obtain the desired signal voltage output. I also designed a new power transformer that yields slightly more B+ voltage. All in all, the new transformers just barely fit inside their covers. The original power supply was so over-designed that I did not have to increase its capacity (except for the transformer). Back to voltage-current output: It can deliver 450 watts, and we can slice and dice this power any way we want. 30 amps and 30 volts peak into one ohm, or 10 amps and 70 volts peak into eight ohms. The output stage has a very wide power responce as have all my amps, solid state or tubes. for example, power into an eight ohm resistor is 305 watts, and ON THE SAME eight ohm tap, will deliver 450 watts into four ohms. This means it can drive almost anything.

  2. Someone asked for it, so here goes:

    Before/After Review:

    I guess I'd have to say the main difference is CLARITY. Cymbals are crystal-clear; the "edge" of instruments shows through--saxaphone, trumpet, etc. Stringed instruments& awesome voices sound so good on great recordings it could just make your cry. The closest I can call it is a "graininess" that was there before & now isn't. Before, if I played at moderately loud levels, it would sound better after about 30 minutes, but never as good as now. My guess is the caps & in-line passive crossover components were aged & in need of replacement. If I had all new passive crossovers, PERHAPS the difference between passive & active wouldn't be as great. Too late to tell for certain now~

    On top of that, a lot more headroom is available from the amplifiers; I give a conservative estimate that roughly 40% of available power was wasted on the passive crossover components.

    I can't think of a single thing that's suffered (other than simplicity) from the upgrade. I highly recommend it! Just don't skimp on active crossover components, & get the most for your dollar there.

  3. I'm planning a gathering of Carverphiles, with a few sprinklings of Polkies, Klipschers, and possibly even AudioKarmites:

    * On or about March 12, 2011 (Sat), noon-ish to whenever (will firm up in the next couple of weeks)

    * At my place in Lusby, MD

    * PM me for contact info/address & to screen out any particularly annoying or crazy jerkwads wink.gif

    A select few are exempt from the last requirement--you know who you are~ [:D]

  4. I found symmetrical leading aircraft wing edges available in balsa wood for SUPER cheap ($2 each) & ordered several in both 1/2" & 3/4" sizes to build my waveform guides. \:D/ I'll shape to fit & paint them black to match the ribbons:

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    I'll post pics when I get them done!

  5. I know this thread is old but I'm in e process of bi-amping my AL-IIIs and wanted to know if you ever completed the physical wave guide form mod? I have a Rane XO on it's way, a C-1 preamp, a TFM-35x and M1.0t. As a first step I planned to bypass the passive XO for high and low and leave the notch filter connected (I'm not quite ready to tackle the active notch - I will have enough trouble adjusting the gains with these amps). After reading many threads on this topic it appears that I can get rid of all the passive components entirely! This is, of course, I can successfully mod the area around the ribbon to eliminate the need for any band stop. The problem is that I haven't seen this in action. Any insight would be appreciated! BTW - impressive documentation of your mods! It's inspired me to keep going.

    No, I've not done that yet. Realize the room will probably add more peaks & dips than anything in the electronic chain....

    I still plan to do the mod, just have had other priorities of late~

  6. Two outstanding discs for revealing dynamic range are:

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    For all around outstanding recording, clean, deep bass:

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    I actually prefer "Temptation" from The Girl In The Other Room by Dianna Krall, and Norah Jones' "Not Too Late" is much better than Come On Over"....FWIW

  7. Thingy update: I found it still stuck to the head of the porcelain cat. Either she's not seen it there or is tired of the game.

    Testing that theory, I moved it to the door of the microwave. She uses the microwave daily to either warm her coffee or something.

    Update?? (I'm bored)~

  8. Combined Unbalanced and Balanced Inputs

    Very often both unbalanced and balanced inputs are required, and it
    is extremely convenient if it can be arranged so that no switching
    between them is required — switches cost money. A handy way to do this
    is shown in Figure 20.9, which for clarity omits most of the extra
    components required for practical use that are referred to above. For
    balanced use, simply connect to the balanced input and leave the
    unbalanced input unterminated. For an unbalanced input, simply connect
    to the unbalanced input and leave the balanced input unterminated. No
    mode switch is required. These unterminated inputs sound as though they
    would cause a lot of extra noise, but in fact the circuit works very
    well and I have used it with success in high-end equipment.
    As described above, in the world of hi-fi, balanced signals are at
    twice the level of the equivalent unbalanced signals, and so the
    balanced input must have a gain of 0.5 or —6 dB relative to the
    unbalanced input to keep the same system gain by either path. This is
    done here by increasing the value of R1 and R3 to 20 kQ. The balanced
    gain of this circuit can be made either greater or less than unity, but
    the gain via the unbalanced input is always unity. The differential gain
    of the amplifier and the constraints on the component values for
    balanced operation are shown in Figure 20.5, and are not repeated in the
    text to save space. This applies to the rest of the balanced inputs in
    this chapter.

    There are a few compromises in
    this scheme. The noise performance in the unbalanced input mode is worse
    than for the sort of dedicated unbalanced input circuitry described
    earlier in this chapter
    , because R2 remains effectively in the
    signal path in unbalanced mode. Also, the input impedance of the
    unbalanced input cannot be very high because it is determined by the
    value of R4, and if this is raised all the resistances around the op-amp
    must be increased proportionally and the noise performance is markedly
    worsened. A vital point is that only one input cable should be connected
    at a time. If an unterminated cable is left connected to an unused
    input, then the extra cable capacitance to ground will cause
    frequency-response anomalies and can in bad cases cause HF oscillation. A
    warning on the back panel is a very good idea.
    There, how's that for info overload?? [:P]
  9. More from "Audio Power amplifier design handbook" Douglas Self

    Common-Mode Rejection Ratio

    Figure 20.4 shows a balanced interconnection reduced to its bare
    essentials: two source resistances, and a standard differential
    amplifier. The balanced output in the source equipment is assumed to
    have two exactly equal output resistances Rout + and Rout -, and the
    balanced input in the receiving equipment has two exactly equal input
    resistances R1, R2. The balanced input amplifier senses voltage
    difference between the points marked In-+ (hot) and In— (cold) and
    ideally completely ignores common-mode voltages that are present on

    The amount by which discriminates is called the common-mode
    rejection ratio or CMRR, and is usually measured in dB. Supposes
    differential voltage input between In + and In— gives an output voltage
    of 0dB; then reconnect the input so that In+ and In— are joined together
    and the same voltage is applied between the two of them and ground.
    Ideally the result would be zero output, but in this imperfect world it
    won't be, and in real life the output could be anywhere between —20 dB
    (for a had balanced interconnect: and —140 dB (for a very good one). The
    CMRR when plotted may have a flat section at low frequencies, but it
    commonly degrades at high audio frequencies (more on this later).
    one respect balanced audio connections have it easy. The common-mode
    signal is normally well below the level of the unwanted signal, and so
    the common-mode range of the input is not an issue.

    The extremely simplified circuit of Figure 20.4, with a little
    SPICE simulation, demonstrates the need to get these resistor values
    right for good CMRR, before you even consider the rest of the circuitry.
    The differential voltage sources Vout+,Vout- that represent the actual
    balanced output are set to zero, and Vcm, which represents the
    common-mode voltage drop down the cable ground, is set to 1V to give a
    convenient result in dBv. The output resulting from the presence of this
    voltage source is measured by a mathematical subtraction of the
    voltages at In+ and In— so there is no actual input amplifier to confuse
    the results with its non-ideal performance.

    Let us start out
    with Rout+, Rout_ = 100 ohm and R1, R2 = 10k, which are plausible values
    and nice round figures. When all four resistances are exactly at their
    nominal value, the CMRR is infinite, which on my simulator rather
    worryingly appears to be exactly —400 dB (presumably that is the
    mathematical 'noise floor'). If one of the output resistors or one of
    the input resistors is then altered in value by 1%, then the CMRR drops
    like a stone to —80dB. If the deviation is 10%, things are predictably
    worse and the CMRR degrades to —60dB, as shown in Table 20.2. That would
    be quite a good figure in real use, but since we have not begun to
    consider op-amp imperfections or other circuit imbalances, and have only
    altered one resistance out of the four that will in real circuitry all
    have their own tolerances, it's a bit unsettling. Clearly we need to
    understand how to improve things at this theoretical level before we
    start to complicate the circuitry.

    The essence of the problem is that we have two resistive
    dividers, and we want them to have exactly the same attenuation. If we
    increase the ratio between the output and input resistors, by reducing
    the former or increasing the latter, the attenuation gets closer to
    unity and variations in either resistor have less effect on it. If we
    increase the input impedance to 100k, putting aside the technical
    implications of doing this for the moment, things get 10 times better,
    as the Rin/Rout ratio has improved from 100 to 1000 times. We now get
    —100 dB for a l % resistance deviation and —80dB for a 10% deviation. An
    even higher input impedance of 1 Mohm, if it can be managed, raises
    Rin/Rout to 10,000, and gives —120 dB for a 1% resistance deviation and
    —100 dB for a 10% deviation.

    As another angle of attack, we can reduce the output impedances
    to 1052, ignoring 'for the moment the need to secure against HF
    instability caused by line capacitance, and return to an input impedance
    of 100k. This again yields, as you have probably guessed, —120 dB for a
    1% deviation and —100 dB for a 10% deviation.
    In practical circuits, the combination of 68 ohm output resistors
    and a 20 kohm input impedance is often encountered; the 68 ohm resistors
    are about as low as you want to go with conventional circuitry, to
    avoid HF instability. The 20kohm input impedance is what you get if you
    make a basic balanced input amplifier with four 10 kohm resistors. I
    strongly suspect that this value is chosen because it looks as if it
    gives standard 10kohm input impedances — in fact it does nothing of the
    sort, and the common-mode input impedance, which is what matters here,
    is 20 kohm on each leg (more on this later). It turns out that 68ohm
    output resistors and a 20 kohm input impedance give a CMRR of —89.5 dB
    for a 1% deviation which is not at all bad. All these results are
    summarized in Table 20.2.

    The conclusion is simple: we want to have the lowest possible
    output impedances and the highest possible input impedances to get the
    maximum common-mode rejection. This is highly convenient because low
    output impedances are already needed to drive multiple amplifier inputs
    and cable capacitance, and high input impedances are needed to minimize
    loading and maximize the number of amplifiers that can be driven.
  10. THE Right Way

    Balanced Interconnections

    Balanced inputs on power amplifiers are used to prevent noise and
    crosstalk from affecting the input signal, especially in applications
    where long interconnections are used. They are standard on professional
    amplification equipment, and are steadily becoming more common in the
    world of hi-fi. A balanced input amplifier is sometimes called a line
    receiver. The basic principle of interconnection is to get the signal
    you want by subtraction, using a three-wire connection. In some cases a
    balanced input is driven by a balanced output, with two anti-phase
    output signals, one signal wire (the hot or in-phase) sensing the
    in-phase output of the sending unit, while the other senses the
    anti-phase output.

    In other cases, when a balanced input is driven by an unbalanced output,
    as shown in Figure 20.3, one signal wire (the hot or in-phase) senses
    the single output of the sending unit, while the other the cold or
    phase-inverted) senses the unit's output-socket ground, and once again
    the difference between them gives the wanted signal. In either of these
    two cases, any noise voltages that appear identically on both lines
    (i.e. common-mode signals) are in theory completely canceled by the
    subtraction. In real life the subtraction falls short of perfection, as
    the gains via the hot and cold inputs will not be precisely the same,
    and the degree of discrimination actually achieved is called the
    common-mode rejection ratio (CMRR), of which more later.

    It is tedious to keep referring to non-inverting and inverting
    inputs, and so these are usually abbreviated to 'hot' and 'cold'
    respectively, though this does not necessarily mean that the hot
    terminal carries more signal voltage than the cold one. For a true
    balanced connection, the voltages will be equal. The 'hot' and 'cold'
    terminals are also often referred to as In+ and In—, and this latter
    convention has been followed in the diagrams here.

    The subject of balanced interconnections is a large and subtle one, and a
    big fat book could be written on this topic alone. A classic paper on
    the subject is by Muncy. To keep it to a reasonable length, this section
    has to concentrate on the areas most relevant to power amplifier


    • Balanced interconnections discriminate against noise and
      crosstalk, whether they result from ground currents, or electrostatic or
      magnetic coupling to signal conductors.
    • Balanced connections make ground loops much less intrusive, and
      usually inaudible, so people are less tempted to start 'lifting grounds'
      to break the loop. This tactic is only acceptable if the equipment has a
      dedicated ground-lift switch that leaves the external metalwork firmly
      connected to mains safety earth. in the absence of this facility, the
      optimistic will remove the mains earth (not quite so easy now that
      molded mains plugs are standard) and this practice is of course
      dangerous, as a short-circuit from mains to the equipment chassis will
      result in live metalwork. A balanced interconnection incorporating a
      true balanced output gives 6 dB more signal level on the line, which
      should give 6 dB more dynamic range. However, this is true only with
      respect to external noise — as the section below describes, the electronics of a standard balanced input is more than 6dB noisier than the electronics of an unbalanced input.
    • Balanced connections are usually made with XLR connectors. These
      are a professional three-pin format, and are a much superior connector
      to the phono (RCA) type normally used for unbalanced connections (more
      on this below).


    • Balanced inputs are inherently noisier than unbalanced inputs by a large margin,
      in terms of the noise generated by the input circuitry itself rather
      than external noise. This may appear paradoxical but it is all too true,
      and the reasons will be fully explained in this chapter.
    • More hardware means more cost. Small-signal electronics is
      relatively cheap; unless you are using a sophisticated low-noise input
      stage (of which more later), most of the extra cost is likely to be in
      the balanced input connectors.
    • Balanced connections may not provide much protection against RF
      intrusion — both legs of the balanced input would have to demodulate the
      RF in equal measure for common-mode cancelation to occur. This is not
      very likely, and it is important to provide the usual input RF filtering
      to avoid EMC difficulties.
    • There are more possibilities for error when wiring up. For
      example, it is easy to introduce an unwanted phase inversion by
      confusing hot and cold in a connector, and this can go undiscovered for
      some time. The same mistake on an unbalanced system interrupts the audio
  11. Perhaps I'm mistaken about what you're talking about, but when you brought up XLRs, realize you're talking apples & oranges. AC power & what is being transmitted via XLR interconnects are two separate things.

    The XLR connections have:

    Hot -a positive version of the audio signal

    Cold - a Negative version of the same signal (out of phase 180 degrees)

    Ground - normal ground

    When the signal arrives at the next component, the negative is inverted (cancelling any noise picked up on the way) & summed into one signal.

    Connecting any other way is erroneous. Balanced connection are also at a different dB level than unbalanced connections.

    This is completely different than the three wires on the A/C signal.

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