|John Broskie's Guide to Tube Circuit Analysis & Design|
14 October 2017 Post Number 399
One more to go before hitting post 400. At the RMAF, I was asked what creation of mine was I most proud of; the interrogator was thinking circuits, so I bet he was surprised by my answer—I know that I was. "I have posted 398 pieces, which are filled with my schematics and many hundreds of words; my last post came in at over 4,000 words. Eighteen years ago, I would bet that I would never hit post 100, as that would seem a very safe bet."
I like to say that I have written more than most ever read in a lifetime. Sadly, each passing year makes my statement more likely, but not just due to my having written more, but due to most reading less.
I face an odd problem of sorts, as my 300th post provoked a big response. Not so much due the big 300 number, but due to the topic I had chosen for post 300, Making Snazzy Schematics. I had tapped into an emotional stream, as many also bemoaned bad schematics. Many horror stories were emailed to me, detailing how bad schematic after another had been encountered. One EE professor wrote me, asking if he could print my effort up and hand it out to his students.
Mind you, drawing snazzy schematics does not necessarily entail tubes. Thus, post 400 might also be not tube-centric. I do not know yet what the topic will be, but I want it to be as popular as the 300th was.
Special Thanks to the Special 59
If you have been reading my posts, you know that my lifetime goal is reaching post number one thousand. I have 601 more to go. My second goal is to gather 1,000 patrons. I have 941 patrons to go. If you enjoyed reading this post from me for the last 18 years, then you might consider becoming one of my patrons at Patreon.com. It would make a big difference to me. Thanks.
John, you birdbrain, why do you keep saying "show" when it is a festival?
Sure it is a festival, just as much as Budweiser is the king of beers. In order to make a distinction, we need a difference. So what is the difference between the Rocky Mountain Audio Festival and any other generic audio show? Time's up. Sorry, having a different name and a different location do not prevail over an insufficiency of differences.
Returning to the bird metaphor, the woodpecker perspective eludes me the most at an audio show, at least when it comes to electronics, as schematics are seldom, if ever, given. Mechanical devices, such as speakers, turntables, and equipment stands, more easily give up their secrets. Occasionally, however, I encounter a designer of audio gear who has longed to find a willing audience to hear his detailed exposition on his latest design. And, on rare occasion, I come across an exemplary white paper of sorts, where the manufacturer spills the beans. One example from this show was the headphone maker's, Final, white paper on "Why Planar Magnetic Headphones with Air Film Damping System (AFDS)." I expected little from it, but as I was so taken by their E3000 $55 ear buds － and I do not like ear buds － that I had to buy them (thanks, Alex, for pointing them out to me), so I wanted to read what they had to say about their flagship headphones. It was a good read, filled as it was with long equations.
The hawk's perspective is also difficult to attain, as it requires a good memory and a lot of walking － alas, I cannot fly nor can I go over the Excel spreadsheet that reveals actual attendance and exhibitor numbers for this year and years past.
Imagine a sparrow trying to take a headcount of his fellow sparrows, in spite of their fluttering about from tree to tree, and make an audit of the number of trees in the forest, but not be able to fly above the treetops; and once having arrived at these two figures, he must be able to compare them to what he remembers from previous years' audits. He will never achieve the hawk's accuracy, but he can try nonetheless. So what did this wannabe hawk see?
I don't want to say that audio is dead, but I now know why undertakers are circling the block and morticians are leaving their business cards under the doormat. In short, it sure seemed like far fewer attendees and exhibitors. Someone walking by might mistake the crowd for the annual convention of bellybutton-fluff collectors, save for the fact that group would prove less old and less all-male.
But, John, isn't that what you said last year and the year before?
Indeed, it is and I was just as right those previous times. The long day wanes. The slow moon climbs… But like Tennyson's Ulysses, Audio although "made weak by time and fate, remains strong in will to strive, to seek, to find, and not to yield." In other words, I believe that Audio—the art, practice, and science of designing home-audio electronics—could call off the funeral and triumph again. What would such a long-awaited, long-anticipated triumphal resurrection look like?
Imagine a speaker system that provoked so intense an aural experience that grown men fainted like those teenage girls at The Beatles concerts of half a century ago. And why wouldn't a life-long audiophile swoon and lose consciousness upon hearing Diane Krall sing more clearly than she herself has ever heard?
Imagine that the makers of the system soon discovered that room-acoustics are simply intractable, and that the average listener, whose median age was past the half-century mark, could not hear perfection, even if it could be delivered to his ears. Instead, the makers wisely bypass the room, bypass the listener's ears and, taking a page from Dr. Patrick Flanagan's neurophone, beam the musical information right into the listener's brain, bypassing the pinna, the ear canal, the tympanic membrane, malleus, incus and stapes, the cochlea, the auditory nerve, the cochlear nucleus in the brainstem; instead, modulated electron beams directly stimulate the inferior colliculus in the midbrain tectum, which integrates auditory input with other sensory input before relaying it on to the inferior colliculus, which then delivers the auditory signal to the medial geniculate nucleus, before the sonic information arrives, finally, at the primary auditory cortex in the temporal lobe.
No air compression or rarefaction was incurred in the making of this auditory experience.
Suddenly, we can all hear down to 1Hz and out to 100kHz—even retired heavy artillery gunners and members of The Who, even those born or made deaf, as working ears would no longer be needed. Indeed, the system would be so sophisticated that it would not let the droning of the dishwasher and roar of vacuum cleaner blight an otherwise flawless aural experience, so it would send out targeted electromagnetic pulses to purposely stun the inner-ear into forced quietude. What if the phone rings, the doorbell sounds, the baby wails?
The systems many microphones pick up these important audio events and evaluates them, and it deems them important enough, it allows you to hear them, just not with your ears, as the important outside signals are just mixed with Diane Krall's voice, so it sounds just the same as actually hearing the phone ring. Virtual hearing, it is soon called. And just as today many prefer pixel rendered sunsets, kittens, and naked women, many prefer virtual hearing to real hearing.
There's one catch, the cost of the virtual hearing system comes in at $25,000,000 and $40 more for the remote. Bill Gates and Warren Buffet love their virtual-hearing system, but you have no hope of ever hearing it, let alone buying one for yourself. Is this a triumph? Yes, of course, it is. It is a phenomenal technological triumph, a work of genius. But is it a societal triumph?
Imagine if the Henry Ford revolution of a car for every home never occurred, that cars remained playthings for the rich, so much so that many small towns held no cars, and even affluent neighborhoods held only one per block. Yes, yes, an ecological wet-dream, but would this be a societal triumph? Before you quickly answer, ponder this: would women's liberation have been possible without the car? Would the modern suburb be possible?
At this year's RMAF, I heard a seminar on the future of amplifier design. Wayne Colburn of Pass Labs remarked that Nelson Pass constantly reminded his employees that they work in the entertainment business. His utterance hit me like an icicle breaking free and falling down the back of my shirt. Entertainment business! Seriously? Later that night, at dinner, I told Wayne that I thought we were in the jewelry-for-men business. But the more I thought about it, the more I realized that Nelson was right. Just as cell phone makers are not in the radio or flat-screen business, but the communication/entertainment business, makers of audio gear are in the entertainment business. While listening to Tim Ferriss interview Sir Richard Branson (yes, the billionaire) and Branson said that early on he realized that his airline business was also partially in the entertainment business, not just the moving people about business.
Just as we consume food, we consume entertainment. Thus, even truly perfect sound for forever truly—at a truly reasonable price—might not prove sufficient to cancel the funeral and wake. Thus, a future triumphal return of Audio would, by necessity, entail a triumphal return of greater entertainment. Back in the 1980s, I boldly foretold an audio future that would wed the visual to the aural, and that just we were amazed that viewers could enjoy TV without color back in the 1950s, in a decade or so, we would be amazed by today's audiophiles who are satisfied to listen without the visuals, that MTV videos and opera recordings would lead the way, so that all future albums would have to hold visual content, which might just be a static slide show of nature or art gallery painting photographs to wide-screen video productions, with casts in the hundreds or computer-generated screen saver displays that followed the beat.
Indeed, I was sure that the CD-ROMs released by Microsoft and other companies that held music, such as Beethoven's 9th, and plenty of interactive extras would be the first step; and, when that didn't happen, I was sure the laser disc would be the true first step—hell, it even looked like an LP with a mirrored surface. I was wrong, although I owned many music laser discs at the time; When the DVD came out, I was convinced that now the time was ripe for the wedding of music to visuals. I was wrong again. Perhaps, this wedding need never occur, but some super enhancement of entertainment must occur. Remember when even movies were deemed insufficiently entertaining and they created Sensorama and Smell-O-Vision?
I have long predicted that future movies would get non-famous actors for the leading roles. Why? The leading role actors would wear face masks with a printed grid on its surface, so no need for a Brad Pit or Scarlet Johansson, as no one would ever see their faces. Whose faces would they see? The viewer's own faces, of course. Imagine that you watch the movie Casablanca, but with you in Humphrey Bogart's place and your wife in Ingrid Bergman's role. What could be more romantic, what could be more self-centered? Perfection.
The video player would scan your face and store the details to map upon the gridded, blank faces; indeed, it would search through your networks and phone for your childhood pictures and wedding photos. Of course, we would expect the porn industry to be at the vanguard of this development, so other photos might be added to the database. Cough. Cough.
Today, entertainment is cheap. For far less than $100 you can buy a decent smart phone and never receive or send a single phone call on it, yet be entertained by games, podcasts, music, videos, web surfing, taking notes, playing chess, gazing at Facebook or disrobed flesh for most of the evening—all made possible by WiFi and micro computing. Of course, the cell phone would be far less entertaining, if it cost $10,000 instead of $100. When it comes to bang per buck, a $100 cell phone is hard to beat.
As CPUs become ever faster and ever smaller, we might soon have an interactive audio system, where we can play the conductor and the virtual musicians heed our commands. Failing that, we might get something easier to pull off. I will quote myself from post 34 to lay the groundwork.
Well, sPecTAcuLaR is what we audiophiles crave—it is also what we need. So, let's amend the famous Stones song:
We crave, hanker, hunger, long, pine, and yearn for sPecTAcuLaR, but we face two problems. The first is that few recordings are sPecTAcuLaR. Why not? Most of the great music we older audiophiles, i.e. most audiophiles, enjoy listening to was recorded 30, 40, 50, 60 years ago. The Beatles' Sergeant Pepper's album is 50 years old. The recording technology at the time did not allow for sPecTAcuLaR, as it would either make LP grooves so wide that the cartridge flew off the LP or the cutting head would chatter or melt. In addition, line amplifiers clipped, tape saturated. The riding of the volume control was daily part of the recording engineer's job. I hear this all the time on recordings, as I can hear the hiss level modulate up and down with the music.
In other words, we have been listening to the inverse of sPecTAcuLaR for a long time.
Well, imagine that you sitting in your listening chair, laptop or tablet in hand, listening to your favorite album. You are no longer just a sonic passenger, sitting in the back seat, bemoaning not being behind the wheel. You have a tablet and the software lets you create sPecTAcuLaR playback. If the recording is out of phase, you flip the phase; if the recording holds too much stereo separation, a flaw that many 1960s albums hold, you narrow the image by blending the channels together a tad; if the highs fall off, you raise them; if the crescendo was unnaturally truncated, you expand the volume as needed.
In other words, this the exact opposite of the beginning of each Outer Limits TV episode:
With the tablet in hand, you can sit quietly, but not passively. You are in charge. You ride the volume up and down to your liking; you twist the frequency response to your liking. In other words, this is a dynamic, active listening session.
That's great, John, but it is also exhausting to even contemplate, as I cannot do this every time I play my stereo.
True enough, but who said anything about doing it every time. We live in the age of the CPU. We need only be in charge once, as the tablet will store your commands, so the next time you play your favorite Stones song, it will play just the way you liked it. Indeed, your previous riding of the volume and all the other settings playback with the song. Moreover, since we live in web-based society, we could share our sonic makeovers (takeovers) with others, so others could hear your take on Take Five. We would be, in a small way, artist ourselves, as what does an artist do but take the world he finds and alter its presentation to his liking.
The user-specified alteration the to sonic playback do not have to reside exclusively in digital processing, only the sequence of commands do. We could use motor-driven volume controls and stereo-width controls and tubes galore.
In conclusion, the only way out for Audio is to become more entertaining and, possibly, more social. I only presented one possible way, not the only way out of the cemetery.
Dang, Every Room Sounds Good
My guesses are that the noise level went way up and everyone compensated by cranking up the volume; the wall voltage got more contaminated; and filling an already small room with extra people just robs the room of air volume. The Marriott hotel has gotten a major facelift and it looks far more attractive as a result, but many of the rooms were made smaller, alas. Not good for bass or imaging or comfort or...
My recommendation is to find a different venue next year, in spite of the facelift. Imagine hunting for a new car to buy and encountering a car dealership that only lets you test drive the car in the showroom's garage.
It Sounds Bad, Good, Great
My rule at an audio show is: If it sounds good, it is good; if it sounds bad, it is...who knows, might be bad, might be great.
The Missing Audio Measurement
My ultimate test for headphones (and headphone amplifiers) is how long can I listen to them in hours, minutes, and seconds, before I have to rip them off my head. This is hard number, just like THD. When new movies are about to be released, movie studios perform careful prescreening, where they monitor every yawn and glance at he wristwatch. We could do the same with audio gear by noting how a varied group of audiophiles can listen to an amplifier or headphone or speaker before switching it off.
The Most Important Thing to Bring to a Show
The next room performed better, far better. The next room was less pleasing... so it went. I was astounded to be so underwhelmed by some $2,500 headphones and $4,000 headphone amplifier, as I had heard so much more sonic information on my far less expensive HD-650s and the small hybrid amplifier I was testing at home. Before you imagine a crowded room, teaming with yakking audiophiles, don't. I was alone in a silent room. I have heard those exact same headphones wow me, two years ago, at the Can Jam with Alex Cavelli's top-of-the-line headphone amplifier, so I must blame either the amplifier or the DAC or the laptop server or bad luck.
Without my own well-known music, how would I know whether the system or the music was off? I wouldn't.
Speaking of music being off, in one room, the fearless sales rep played an LP by PJ Harvey.
If you don't know her, you might check her out. Her musical output gets classified under: alternative rock, punk blues, art rock, indie rock, folk rock, and experimental rock. Basically, she sings her guts and soul out. If you subscribe to Tidal, try out her album, Dry, about which one reviewer said, "Polly dredges these sounds from the pit of her dissected soul and drags them out of her mouth with clenched fists." If you are a Patti Smith and Amy Winehouse fan, you will get her. If she doesn't move you, then try Fenne Lily, her antimatter sister.
I used the adjective "fearless" due to the intentional distortion recorded on the LP. Someone walking into the room might think that the tip of the needle had broken off and the rep too deaf to hear it. Mind you, he did repeatedly tell his audience, "The distortion is supposed to be there."
Speaking of Tidal
Back in the early 1980s, I was reading about the future launch of the CD. I told my friends about it and they all asked the same question: "Can you record onto it?"
If nothing else, Tidal allows you to hear music that you might like, without having to take the risk of buying before you hear. God knows that I have done that far too many times. If you like the music, then hunt down the high-res download or buy the 16-bit CD or 180gm LP of it. If Tidal saves you from just one bad purchase, it has paid for itself that month. Here is an example, I like to do search for all the covers of a famous song and then listen to all 30 of them. I was listening to Moonlight in Vermont, when I heard the Spanish singer Beàs sing it. At first I thought it was just a gimmick song that wouldn't age well. But I kept returning to over and over.
I then let Tidal play her entire album, Stolen Diamonds, for me. Dang, I love it. So much so that I bought the high-res files from HDTracks.com. Her's were some of the tracks that I bought on my thumb drive. Each time her songs played, I was enthusiastically asked who was singing. Definitely my favorite album of 2017 and an excellent audio-show-off album. If you subscribe to Tidal, check her album out—mind you, you have to type "Beàs" to find her, not Beas, try "Stolen Diamonds," instead. I just love her mild Spanish accent as she sings "dream," but says "drem." Cute and lovely.
Okay, I admit that Tidal is not perfect, not even close. I long for classical and jazz versions of Tidal, which will be free of Jay Z and Tee Grizzly and Taylor Swift. Until that happy day, the first thing Tidal must do is improve their search engine. In the early days of eBay, I bought a bunch of classical CDs for a $1 each because the seller had misspelled Beethoven or Shostakovich (I have seen at least three different spellings of his name); today, this is not possible, as the eBay search engine looks for sounds-like spellings. In other words, if you type "Lynyrd Skynyrd" but replace all the 'Y"s with "i"s you should still find Lynyrd Skynyrd. And if you type "Beas," you should still find Beàs.
Second, Tidal must allow users to customize their Tidal environment, so I can never see Jay Z and Tee Grizzly and Taylor Swift names again, while someone else can never see Johnny Hartman and Beethoven and Shostakovich names.
Third, Tidal must understand sub-genres. For example, the blues comprise at least twenty sub-genres, such as acid blues, African blues, blues rock, boogie-woogie, British blues, Canadian blues, Chicago blues, country blues... You get the picture. Once you hit the blues button, all of those sub-genres should be listed, then you can go deeper.
Where Are the Damn Audio Gear Previews?
Consistency is what I encountered. The all big Wilson Audio speakers, which included their new Alexia, sounded great, as did the Sanders electrostatics and Magico;s Model Q7, and so, too, did the Acoustic Zen speakers and the new flagship from Vandersteen. And they dang well better sound great, as they all cost more than the average car, save for the Acoustic Zen speakers, as their Crescendo Mk. II models is cheap at only $18k. All of these speakers are big. I wanted to use a Ferrari analogy, but they are all closer to a hulking SUV. Well, I believe the Raidho Acoustics D-4.1 might have to be added to that list, although it being so much more slender that the Ferrari analogy can be applied to them. How much? A mere $119,000–$138,000.
Returning to the planet Earth, once again I was stunned by how great the Harbeth loudspeakers sound and image in the Vinnie Rossi Room. They always do, year after year. Of course, Vinnie's ultra-radical electronics must take half the credit, possibly more than half. Rossi started by making battery-powered gear with his Red Wine Audio company, but he has moved on to capacitor-powered gear with his new brand, Vinnie Rossi. The problem is I know Vinnie and like him a great deal, as he one of the nicest and brightest guys in audio today. This is problem in that as much as I would like to rave about the great sound he consistently gets, I can't. Why not? We always talk at shows, but this year I called him up asked for his advice, which he generously gave. This changes things from an ethical standpoint and now precludes me from giving his fine products a full review. So, check out this link, Incredible LIO & Harbeth Synergy! I am glad that someone else has said this, as it needs saying.
At the budget-end of the spectrum, the two self-powered speakers made Vanatoo are amazing. They start at $359 the pair and top at $584 the pair. If you have a son or nephew that you would like to start down the path of audiophilia, buy him a pair of Vanatoo speakers as a graduate present. All he needs is a smart phone or an iPod or laptop with Bluetooth and he is off and addicted in no time.
The speakers hold 60W amplifiers and one must be plugged into the wall (the other r speaker is driven by its partner). You can use either a 3.5mm headphone plug cable or USB or Toslink optical or coax cable or Chromecast Audio puck to send them their signals. Let's say you are not that generous, well then buy yourself a pair of Transparent Zero wee tiny speakers for $359 and use them in the bedroom or as computer speakers.
Unlike their big brothers, these speakers use a 24Vdc wallwart to power their four 48W direct-digital class-D amplifiers. Yes, the speakers are bi-amped and use DSP to realize the crossover. Yes, they only cost $359 the pair. No, I am not a decade off the price. In fact, the prices are even lower, for if you use their RMAF promo code of RMAF2017 at their web store, the Zeros cost $319. If you could take them with you in a time machine and go back twenty years ago, they would assume that these little speakers must cost $3,190, not $319.
By the way, I do not get any kickback or life-time loan of the speakers—I just think they are amazing and a staggering bargain.
Here is the description from theirwebsite:
Embarrassingly enough, I never listened to it. When Jason and I get together it's circuit talk 110% of the time. So, I will have to trust my friend's, Jim, enthusiastic endorsement, until I get a chance to try it out.
I often ask audiophiles that I meet what would they most like to be added to their systems. Two items come up all the time: tone controls and a balance control. For a lousy $149 with a 15-day money back guarantee on a product that is made in the USA, what is not to like?
More Expensive Tube Gear
I meant to mention them last year, but I forgot to do so. (I will have to start bringing a notepad with with, just like a real journalist, but I refuse to take up smoking.) Raven Audio's tube equipment are beautifully made and heavy. Metal, lots of metal. I cannot comment on the sound, as I tried to hear them twice and both times I could not stand the music being played, so I left both times; alas, I didn't try third time.
Woo Audio makes a lot of tube gear for driving headphones, but nothing prepared me for seeing their WA8 portable battery-operated headphone amplifier & DAC, something that I wanted to do for the last twenty years.
Tiny and heavy, if I had the cash to burn, I would have ordered one on the spot.
Audio Hungary showed some beautifully retro chic tube gear.
Nothing looks so cool as a phalanx of hot tubes.
Another new company, well at least new to me, was Whammerdyne. You have to check out their website, as the pictures say more than I can ever say about how retro- industrial -cool their 2A3 amplifiers look. If you want a tube amplifier that looks like no solid-state ever made, this is the place to go. I love their model names. "Damn Good Amplifier," "Damn Great Amplifier," "Damn Awesome Amplifier," and "Truth."
Best Sound at the Show
I own one of her CDs, Blue Mind, which is great for showing off your stereo system and soothing your soul.
Well, live music is a gorgous thing to hear. Mind you, her delicate voice was no match for the piano, which sounded more pianoFORTE than usual. My guess is that she enjoyed playing it so much that she didn't want to restain the piano; if you ever take a Maserati for a test drive, are you going to obey the posted speed limits? I wouldn't.
More FET Designs
And it this circuit that reader, Sergey, called me out on it. As he sees it, rightly I might add, the biasing will be tricky, so we have no guarantee that the output will center at half the B+ voltage, as it could slam to either ground or some voltage near the B+ voltage. Point taken. What is missing is a DC negative feedback loop that will align the DC voltages for us. I took an old SPICE circuit and tweaked it until this circuit was born, which holds both an AC and DC feedback loop along with some of my Aikido mojo. The P-channel FET is a J177. (By the way, the FET's source attaches to the triode's cathode and the FET drain is grounded.)
The result, at least in SPICE simulations, is impressive with its gain of +20dB and bandwidth out to 1.8MHz; the PSRR was exemplary for a tube circuit. If I actually built this design, which I am sorely tempted to do, I would split the 20M resistor into two 10M resistors, with a decoupling capacitor in between. Here is the Fourier graph for 1Vpk at 1kHz.
Even if reality lets us down by adding +20dB to each harmonic, the results are amazing. Actually, the one thing that did bother me was the PSRR, as the deep null occurred at 1,400HZ with the 2.2F capacitor. I then replaced it with a 150µF capacitor and the following SPICE-generated graph resulted.
Ideally, we would the notch to center at 120Hz here in The States; 100Hz in Europe. Nonetheless, not bad.
The second FET-related email asked if FETs couldn't be used to make a fine harmonic restoration circuit, as the FET's curvature was much closer to that of the triode. The answer is yes. All I had to do was not any distortion reducing tricks. Here is the schematic.
Still, there is a lot going here, as I threw differential handing of an unbalanced signal; see post 357 for more details. I also added some Aikido mojo. Note that the 1kµF capacitor does not terminate into the negative power-supply rail, but ground; this induces a countervailing ripple current through 1k resistor at the output, which nulls at the output, assuming that both rail voltage hold equal and output phase ripple.
Here is the resulting harmonic enrichment.
The THD is a tad over 1%. Note the even cascade of harmonics. Very single-ended. Also note the low bipolar power-supply rail voltages. This would be a fun project to try on a perf-board. Perhaps the resulting sound would prove too ripe, but then I have seen men swoon over 10% single-ended amplifier, so it might prove not ripe enough.
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User Guides for GlassWare Software
For those of you who still have old computers running Windows XP (32-bit) or any other Windows 32-bit OS, I have setup the download availability of my old old standards: Tube CAD, SE Amp CAD, and Audio Gadgets. The downloads are at the GlassWare-Yahoo store and the price is only $9.95 for each program.
So many have asked that I had to do it.
WARNING: THESE THREE PROGRAMS WILL NOT RUN UNDER VISTA 64-Bit or WINDOWS 7 & 8 or any other 64-bit OS.
I do plan on remaking all of these programs into 64-bit versions, but it will be a huge ordeal, as programming requires vast chunks of noise-free time, something very rare with children running about. Ideally, I would love to come out with versions that run on iPads and Android-OS tablets.
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