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For example, Mischa Maisky is the cellist that can beat up your cellist, as he can thunder when needed Loudspeaker Crossovers with Polarized Capacitors Two events prompted to write on this topic.. Yes, I know it sounds like voodoo, but it is consistent voodoo. In addition, super expensive loudspeakers often hold a hidden battery pack or connection to a power supply, the latter often being used to power the built-in subwoofer Crowhurst Phase Splitter In the last post, we saw the article that Norman Crowhurst had written for audiocraft magazine in the s.
I thought that his careful explication of how each part value was derived was worth reading, as many falsely imagine that the values are either entirely arbitrary or are revealed only by inspiration. Of course, the truth is that an underlying logic dictates the part values Paraphase Phase Splitter While on the topic of the paraphase phase splitters, we should quickly look at the more conventional paraphase circuit.
I experimented with this phase splitter early on and quickly abandoned it, as it suffered from poor balance between outputs, differing frequency bandwidths, and poor PSRR The switch is a three-position toggle with an on-off-on structure. In the middle position, the off position, the amplifier sees a 1st-order Hz high-pass filter, which proves useful with subwoofers.
In the up position, the amplifier sees a DC connection to the signal source, allowing full bandwidth output. And in the down position, the amplifier is muted, which allows us to switch interconnects or line-stage amplifiers without having to shut-down the power amplifier Well, her new album, Blackbirds , is similar in that she eschews the Great American Songbook, preferring to reinterpret songs from the 50s and 60s, including classic rock songs Chapetta's OTL Ever since writing on the topic of two-stage amplifiers in post , a distant memory of an OTL amplifier made from two independent amplifier stages in cascade haunted my mind.
I remembered seeing it in a foreign magazine, probably an Italian or German audio magazine. Well, finding the magazine proved difficult, but I finally located it. Crowhurst In my quest for tube-related clipart in old electronics magazines, I found the following interesting article by the great Norman Crowhurst in an audiocraft magazine, October issue from His design incorporates two negative feedback loops between the driver stage and the output tubes' plates, along with a global negative feedback loop that includes the output transformer's secondary Aikido Mojo Push-Pull Frontend In the previous post on transformer-coupled circlotrons, I pointed out that making such an amplifier made more sense today than it did 70 years ago, as high-voltage, soft-recovery solid-state rectifiers are now available and as electrolytic capacitors are far superior to even the same capacitor from 20 years ago Frontend with Cathode-Driven Phase Splitter While I pondered possible frontends to the transformer-coupled circlotron, I remembered my cathode-driven phase splitter design from post The idea behind this phase splitter is that we deliver two input signals to a differential amplifier: one for the input triode's grid and one for the tied cathodes, the latter being half the former's magnitude Hybrid Cross-Coupled Amplifier I recently received an email from a reader, Kurt, who questioned the performance of a cross-coupled design from post I found what I was looking for and I found an interesting circuit that I didn't include in that post As I have been pointing out for over two decades now, the SPICE models of triodes are all fundamentally flawed, as they treat the triode as a variable current source, when in fact it is a variable resistance Hybrid Grounded-Grid Gain Stage The grounded-grid amplifier differs from a grounded-cathode amplifier in that we drive the cathode, not the grid, which is grounded.
The result is the input impedance is low, not high; the input signal is not phase inverted at the output, not inverted. In addition, the grid shields the cathode from Miller-effect capacitance, which results in a vastly improved high-frequency bandwidth.
The downside to the grounded-grid amplifier is that its input is not at ground potential and its input impedance is low, which throws a wrench into the volume control's audio taper. Insane-Gain Hybrid Grounded-Grid Amplifier Now that we have gotten use to the variations on the hybrid grounded-grid amplifier, we can move on to the insane-gain version.
Actually, the circuit is not exactly a grounded-grid amplifier, as the grid does see the input signal, albeit in an inverted and amplified form Music Recommendation: Antonio Lysy's South America I dimly remember reading about cellist Antonio Lysy a few years ago, but I never followed up with hunting down his recordings, a big mistake it turned out. I stumbled on his album, South America , at Amazon Music.
I sought background music, so I pressed play. I had no expectations, but just a few minutes in, I was sold. This was something special. Alternative Transformer-Coupled Output Stages Fasten your mental seatbelts, as things are not nearly as simple as you might imagine.
We are all so used to the conventional transformer-coupled push-pull output stage that we cannot recognize what an odd bird it is. For example, only in a push-pull class-A amplifier, which is astoundingly rare in spite of what glossy ads proclaim, do its output tubes see a constant load impedance; otherwise, the load impedance varies depending on whether both tubes are turned on or one is cutoff The same output transformer can be used in either topologies with the same output power.
The big difference in performance is that the cathode-follower output stage distortion and output impedance will be far lower. The price we pay for these enhanced attributes is a huge input signal is needed, as in hundreds of volts of input signal Transformer-Coupled Circlotrons The original circlotron circuit held an output transformer and two floating power supplies per channel; which was enough of a pain in the days of mono, but with the advent of stereo, the notion of a stereo power amplifier that required at least four tube rectifiers failed to appeal—big time.
In addition, we can use full-wave-bridge rectifier circuits that do not require a center-tap on the power transformer secondary. Moreover, today's power-supply reservoir capacitors are staggeringly superior those used 70 years ago. In short, a transformer-coupled circlotron makes more sense today than it did back in the s Much like the two-transformer version, the two-choke version uses the chokes ability to freely pass DC current and offer high impedance to AC signals Upon first hearing it, I thought, "Wow, this is the LP they should play in stereo stores to show off their equipment.
Well, I just noticed that Amazon Music offers this classic album in bit, 96kHz format. Others will delight in the humor and puns for which Waits is famous Tubes glow. Tubes are forgiving. Tubes are intrinsically interesting. Tubes are anachronistic, yet persistently cool Dynaco Low-Power Design I have been hunting old schematics for designs that easily allowed their altering to accept a balanced input signal and that contained a negative feedback loop.
Ideally, we want to replace the shared ohm cathode resistor in the input stage with a constant-current source or a large-valued resistor, so we can apply the negative feedback to the other 12AX7's grid Balancing the Eico HF87 I remember when Eico power amplifiers were easily found at flea markets and garage sales.
Back in , Stu Hegeman departed from all previous tube amplifiers by using video pentodes rather than the usual triodes, such as the 6SN7 and 12AX7, in the input stage and phase splitter Circlotron Output Stages It's been a while since I have posted anything on the circlotron topology.
We certainly could build a two-amplifier cascade power amplifier using the circlotron as the output stage. Over the last two decades, I have come up with some amazing circlotron variations; for example, class-G circlotrons, many hybrid and pure solid-state circlotrons, current-out circlotrons, ultra-linear circlotrons, single-ended circlotrons, and single monopolar power supply circlotrons. Well, it's worth going back to Mr. Hall's original design, which used pentodes, not triodes as the output tubes.
In addition, he used an output transformer Constant-Cathode-to-Plate Voltage Circlotron Triodes require a high cathode-to-plate voltage to summon forth a flood of current. Solid-state devices pretty much don't.
In power-amplifier output stages, this puts tubes at a distinct disadvantage, as many amperes of output current flow are expected Crowhurst Anti-Blocking Technique I was looking through my collection of Audiocraft magazines, searching for cute tube-based clip-art with which to adorn my posts.
I ended up reading an interesting article by the great Norman H. No doubt, Harmonia Mundi has produced a few bad-sounding recordings, but I have never heard one. Instead, the sound has always proved first-rate Sep 14 Forward to Thanks to reader and patron, Paul Reid, for sending this my way. Paul has unearthed the first example of Aikido mojo Two-Stage Tube Amplifiers In the last post, we saw a unity-gain phase splitter that held its own negative feedback loop, which resulted in a fixed gain and lower output impedance—and with a dollop of Aikido mojo, improved PSRR.
This phase-splitter design was meant to fill in the hole left by the absence of a balanced input signals, such as those provided by the XLR jacks on the back of many DACs Partial Feedback Topology Another way to implement negative feedback is the partial feedback arrangement. See March of issue of the Tube CAD Journal and posts and and for more details on this form of negative feedback Many would find this power more than adequate.
My own single-ended power amplifier put out 10W, so 25W would make a hearable difference. A Hybrid Variation As you can see, there is no end to the possible variations.
The following design is coupling-capacitor-free effort by using a retrograde cascode made up of a triode and PNP transistor and collector resistor My guess is that a single transistor would have a hard time at it. We can use a single triode or a step-up transformer, but a single transistor is a lonely device Tube Equalizer Part-2 A quick recap: a balanced set of input signals feed two strings of resistors, terminating into ground; these resistors define two multi-step fixed attenuators; the output from each resistor connection, including the into ground, then travel to six position rotary switches, which then feed six equalization networks, whose outputs feed an inverting summing circuit, which mixes the equalization output signals with the inverted input signal.
If all the rotary switches are in their center position, a flat frequency results, as the inverted input signal just gets inverted again at the equalization output Not a Coffee-Cup Warmer I had fun last showing my latest project with a joke that it doubled as a coffee cup warmer. It was only a joke; it's never a good idea to place a hot cup atop hot electronic equipment Split-Load Balanced Headphone Amplifiers While on the topic of split-load phase splitters, I thought I should show the split-load phase splitter circuit can be used to drive low-impedance loads, such as headphones.
I mentioned this possibility several times before, but few can wrap their minds around the notion. My guess is that its reputation for dissimilar output impedances provokes a brain freeze Music Recommendation: Concurrence Iceland, in spite of being thinly populated and with only twice the population of my small Colorado city, fills a large portion of my consciousness. Prior Crossover Art A German reader, Thomas von Thaden , from Hamburg, wrote to me, pointing out that he had come up with the Broskie three-way series-shunt crossover in He's right I happened to have a pre-painted steel chassis from Hammond, 6 inch wide by 10 inch deep by 2 inch tall, which proved a perfect fit Attn Stepped Attenuator The Attn is a new stepped series attenuator that holds 11 resistors per channel and offers -6dB decrements, with a hard mute at the bottom twelfth position Tube-Based Equalizer Our recent incursion into the recording-studio circuits, such as a high-gain line-stage amplifier and signal mixers, appears to have gone over well with many readers.
Merlin Blencowe, the Valve-Wizard himself, recommends that we next look into tube-based equalizer circuits. Other readers have long asked for music amplifier and musician sound effects circuits Lowering Line-Stage Gain In contrast to designing phono preamp, where we usually seek to squeeze all the gain we can from a triode, when designing a line-stage amplifier we do not need very much gain.
My preference is for 12dB, which is a ratio of between signal and output signals Music Recommendation: Across The Universe Al Di Meola is one of those super talented musicians I use to listen regularly a few decades ago, but who I somehow lost track of—a big mistake it turns out. This year, Di Meola released a new album devoted exclusively to Beatle songs My OpAmp-free designs used discrete transistors in place of an OpAmp. Tube Mixers and Pan Pots Rare is the audiophile who has a need either for an audio signal mixer also known as a signal summer circuit or for a stereo pan-pot, which distributes an audio signal between left and right channels.
Yet, Push-pull Auto-Cathode-Bias Output tubes are either biased with a negative grid voltage or with a positive cathode voltage. Making a cathode sit at some positive voltage is easy enough, as a cathode resistor or zener or constant-current source work well. The relatively high cathode voltages needed to cathode bias a tube creates a large enough voltage-window to run some interesting solid-state circuitry A few amplifiers hold both a nested local negative feedback loop and a global negative feedback loop Alas, tubes require far more voltage than a 24V switcher power supply delivers.
Since the triode-based cascode circuit was created to replace pentode gain stages as the two triodes in series offered equally high gain, but far less noise this topology was the obvious choice—but not the only choice Broskie Source Follower I always seek to exploit existing audio and electronic situations.
For example, I see that most standalone DACs offer a set of balanced outputs, which are seldom used. My mind puts these three observations together and wonders how all three could be utilized, i. What other audio device presents a fairly-low input impedance? Why is that important? The SRPP gain stage delivers its best push-pull output into a specific load impedance, which tend to be low Balanced Hybrid Headphone Amplifier Last time, we saw a split-load phase-splitter output stage used to drive high-impedance headphone drivers with balanced outputs.
A 6AS7 triode held ohm plate and cathode resistors, and the triode idled at 50mA. In spite of the beefy triode and high idle current, balanced driving ohm headphones was its limit. Well, what about driving low-impedance headphones, say those between ohms to ohms?
This is the impedance range where most planar headphones fall I had never heard of it, in spite of its fame. Its nickname is the "The Holy Grail" line-stage amplifier.
A gain of 46dB equal an amplification ratio of 1 to My guess is that Pull Out Rails For Cabinets Europe most recording studios would prefer something closer to 60dB 1 to 1, or more Music Recommendation: Not Music Podcasts are not music, even when the topic is music.
I get it. I am nine years older than Weinstein, but his story was amazingly similar to mine. Growing up, I had been hugely exposed to those inspired by the blues in rock and in jazz, but I didn't know much about the blues—and few if any of my friends did as well My existing two other 12Vac designs are big hits, as the volt AC sidesteps the wise fear of high-voltage I found something in post , written almost exactly 8 years ago.
Here are our assumptions: the two B output tubes are matched; the output transformer's primary impedance is ohms; the Bs idle at mA, which gives us the constant-current source amount of flow; the B require a cathode-to-grid voltage of V to establish a current flow of mA with a cathode-to-plate voltage of V; and the output transformers present a primary DCR of ohms and they hold secondary ohm and 8-ohm output taps Balanced Output Long-time reader, Pete, asked if the DarkVoice circuit could not be altered so that is provided a balanced output.
Pete had in mind using one 6SN7 and one 6AS7 per channel, with one 6SN7 triode functioning as a split-load phase splitter and with both 6AS7 triodes being used as cathode followers for one channel's output. All this is possible, but there is an easier route: we could use the 6AS7 triodes as split-load phase splitters The input coupling capacitor and DC servo erase the output's DC offset.
Well, this topology prompted me to remember a phono preamp design I came up with long ago, but failed to show here Lucky me. Her new album, Tie Me To You , is something.
I knew nothing about her, so I listened with unfiltered ears. By the third track, I was sold Well, at least this week's circuit continues the thread from my last post on cathode-follower output stages, but differs by being an OTL. The reader, Arief, who sent me the schematic had no knowledge of its source, but he heard that it was a headphone amplifier capable of delivering 1W into ohm headphones Well, I was half right.
The amplifier used four 6V6 output tubes, but the article mentioned using 6AS7s instead. Gilson and Russell Pavlat; and the article appeared in the May issue In addition, Kuldeep wishes to avoid source resistors. Much like a triode, a depletion-mode MOSFET conducts current in spite of its gate being negative relative to its source Music Recommendation: The Blues I have been listening to so much good music lately that I falsely concluded that only good music existed.
A big mistake. I felt much like General Manuel Noriega just before he was broken by music torture , the relentless, ceaseless, and merciless playing of heavy metal music Updating Error-Correction Schematic While writing my last post, I included a schematic from post The schematic showed how we could apply the Sandman error-takeoff scheme to a non-inverting power amplifier, not just the original inverting Knobs And Pulls For Bathroom Cabinets Lyrics amplifier.
As I looked over the schematic, something made my eyes itch, as something was wrong in the schematic Two-Position Auto-Bias Single-Ended OPS Everyone has seen the single-ended output stage that replaces the output tube's cathode resistor with a constant-current source.
The logic is compelling. The constant-current source auto-biases the output tube, making the idle current a fixed quantity, in spite of different tube brands or the same tube aging. Because a single-ended amplifier must—by necessity—be run in strict class-A mode, this simple technique works well Cathode-Follower Single-Ended Output Stage Output stages based on the cathode follower topology are rare, and reasons are not hard to find.
Cathode-follower operation offers low output impedance and low distortion, but requires huge grid-voltage swings to achieve full output Completed Project: New Headphone Amplifier I finally built something during this pandemic, another headphone amplifier. Before you get to say "Not another damn headphone amplifier," let me point out that this headphone amplifier is radically different.
How so? Unlike Music Recommendation: Kondonassis, Vieaux; Together Making this post's music recommendation was tough—not because I haven't been listening to new music, but because I have been listening to so much new music, the result of my one-month trial of Amazon Music.
I think we are ready now, as the circuit probably seems familiar, no longer alien More DHT Heating I received an email from Rod Coleman, who pointed that the circuit I had attributed to him was an early effort and that his current design is entirely different.
He provided two links to PDFs associated with the current production of the kit Error Reduction Circuit While designing the DHT filament power supply shown above, my mind turned to an old idea I had at the turn of this century. I wrote about it back in post In a nutshell, the idea is that we can do more than just load a cathode follower or emitter-follower or source-follower with a constant-current source, as we could modulate the constant-current source's current flow slightly, just enough to force some error correction on the output signal Music Recommendation: Amazon Music A few months ago, Amazon sent me an email offering three months of free trial service of Amazon Music.
A friend who subscribed, however, complained about the service, stating that it wasn't nearly as good as Tidal, so I ignored the offer.
Well, I finally followed the link and that offer had expired, now reduced to just one free month. Well, I am only a few days into trying it and I quite like it I Measure Time in Albums During this deranged existence we are living, I hoped for the consolation of being able to hear more music.
Well, as I put this post together, I made a point to listen to as many albums as possible More Upside-Down Cascode Circuits You should consider my last post as the warm-up for this post, as the triode-PNP-transistor combination finds new uses in audio circuits.
In other words, my last post was meant to be twice as long, which would have been a mistake. We need a pause to digest. The important take away was that this gain structure had more than one application Current-Output Single-Ended Output Stage If we take the previous design and make a few modifications, we end up with the opposite of a voltage-output amplifier, a current-output amplifier.
Instead of a super-low output impedance we get a super-high output impedance; instead of a fixed output voltage swing, we get a fixed output current swing If the topic is new to you, I advise that you enter the following search phrase into Google, "shunt regulator site:tubecad.
At the risk of either embarrassing myself or losing my audiophile credential card, I must admit that I knew nothing about his design. In a way, this makes sense, for although I do own a few DHT tubes, none of my audio gear actually uses them For example, I have worn out at least three LPs of it over the last 40 years. Unlike so many jazz albums I enjoy, this album gets near universal acceptance from those who usually disdain jazz.
Well, I have discovered a jazz artist who also passes the spouse acceptance test, American saxophonist Stephen Riley I am well past my life's halfway age. No, what I am halfway to is to writing my post number 1,, and it has taken me 21 years to get to post Found Time I hope all of you have both found extra time and something with which to fill it. About two years later, when out of money, I opened the book and, like a gift from heaven, the bill tumbled onto my face.
Found money. What could be sweeter? Well, I have been waiting to find free time; in vain. The last thing I expected I knew what the cover looked like, so I was fairly confident that I would succeed, in spite the brain-dead approach Tidal applies to classical music Stuff My extra time hasn't arrived.
It turns out that when I can no longer go anywhere fun, I end up walking my dogs twice as much as normal. It turns out that email expands to fill the time allotted, as my in-box swells and swells. It turns out that my stay-at-home children are not as trouble-free as I had anticipated, as I must proctor their test taking and constantly feed them.
It turns out that I have not heard my loudspeakers in over a week, but my headphones get a daily workout Bipole-Dipole Loudspeaker After drawing the illustrations from my last post, I wondered how well a bipole loudspeaker would work in the mirror-reflected setup.
What's a bipole loudspeaker? Any speaker that shoots the sound out in two directions is a bipole. Most hold two sets of drivers at a degree opposition and are used in home-theater setups as side speakers. Klipsch makes a loudspeaker with an extra woofer and a tweeter on its top Two-Stage Negative-Feedback Pairs Often one grounded-cathode-amplifier gain stage is not enough, as more gain is needed. But two cascading grounded-cathode amplifiers is too much, as too much gain results.
The workaround for the two-stage arrangement is adding a negative feedback loop, which will lower the gain, distortion, and output impedance See my last post.
I noticed that Downes had a few videos at Tidal We love simple solutions. Wearing shoes is both simpler and more intellectually pleasing than covering the entire world with plush carpet. The possibly true, but probably apocryphal story of the too tall truck that got stuck in the too short overpass, only to be freed after the smartest consultants had been pestered by a boy, who asked why couldn't the air just be let out of the tires, is an example of a simple and beautiful solution Your listening room has been called your most important piece of audio gear.
I agree. I have heard luminous rooms, wherein all loudspeakers sounded fantastic. Conversely, I have heard rooms that no speaker could tame Music Recommendation: America Again by Lara Downes Working on the assumption that we can never have enough piano music, I went mining through Tidal's offering. I was lucky, as I rediscovered Lara Downes At its core, a grounded-grid amplifier DC coupled to a cathode-follower output stage.
The hybrid fanciness entered the picture at the input and the output More Phono Preamp Philosophy In post , I told the tale about my striving to build a phono preamp that actively achieved the inverse RIAA equalization, but with a constant negative feedback ratio across the audio bandwidth. We saw how OpAmps, when run open loop, i. Killing Time In my last post , I asked what we are all going to do with all the time, i. Well, I got my own answer this last weekend, which turned out to be my dealing with our broken water heater.
Late Friday night, a piercing alarm sounded, waking my family and me. At first, we could not locate the source, as the high-frequency seemed omnidirectional A Bi-Wire Answer A few weeks ago, I noted an email that asked if the reader's loudspeakers that sported bi-wire terminals couldn't be used bi-amp the speakers with a small tube amplifier for the tweeter and a big solid-state amplifier for the woofer Active Phono Equalization I was about to write "about 30 years ago," but the more I think about it, it was closer to 40 years ago that I came up with a radically different phono preamp design, but which I never successfully assembled, as I didn't have access to SPICE back then.
Here is the history: As a teenager, I had built several phono preamps based on circuits I found in electronic magazines. These were all solid-state designs, starting with discrete transistors and then with OpAmps Rejoice is a new jazz album at Tidal that delivers the high energy of African jazz, wherein the drumming propels the music.
Hugh Masekela, who died in , plays trumpet; and Tony Allen, the drums Self Quarantined Since we are all at home, we must find things to do. I assume that those not at home will not be reading this.
Normally, I have kits to put together, but I received only one new order in the last five days thanks Alex ; and when I am not filling little plastic bags with resistors and capacitors, I am shopping and driving my kids about, neither of which is needed now. For many, Netflix fills the void; for others, regular TV offers salvation More Phono Preamps The topic of phono gain stage circuits knows no limit, well at least none that I can see.
Each new circuit gives rise to others, which in turn give rise to others still. As soon as a new electronic device is invented, someone will try to make phono preamp using it Flat-Pack MC Phono Pre-Preamp A flat-pack design is one that makes use of a power supply built around a flat-pack power transformer with two separate primaries and secondaries, where none of windings sits atop another.
Hybrid 40dB Phono Preamp We can borrow the topology shown above in the first and second stages of a hybrid phono preamp with a final gain of 40dB that uses passive RIAA equalization in between gain stages Often sung with a cappella interludes, the music makes strong use dominant vocals and harmony and compelling rhythm. Both jazz and rock share Gospel music DNA. Wuhan Pandemic We await doom—well, at some of us do.
My old neighbor in his 70s , who has many health problems, is supremely indifferent to Wuhan Virus and makes no effort to avoid it More Flat-Pack-Power Supply Circuits Back in posts , , and , we saw many tube-based circuits that made good use of an interesting bipolar power supply that held a high-voltage positive terminal and a Vdc negative power-supply rail voltage.
The Vdc rail would power the heater elements and serves as a free voltage reference, assuming that the negative power-supply rail is regulated Hybrid Grounded-Grid Amplifier The grounded-grid amplifier offers the advantage of no phase inversion of the input signal at the output, unlike the grounded-cathode amplifier, which does invert the input signal at its output.
The big downside to the grounded-grid amplifier is its low input impedance. We must drive the cathode after all. The design uses only tree triodes and consists of a differential input stage DC coupling into a grounded-cathode amplifier.
The RIAA equalization is actively implemented Music Recommendation: Finzi's Intimation of Immortality I came by this post's music recommendation by an odd route. Class-G High-Voltage Regulator Part-2 I am back at it—it being my prevailing over design obstacles, obstacles both real and imaginary. But first a quick recap: our goal is a solid-state, variable-voltage, high-voltage power-supply with a regulated output that can sustain high output currents without overheating.
This regulator is not meant to be part of any audio gear; instead, it would be used in testing new tube-audio circuits, as it would replace the need to build up a working power supply for every new circuit.
Unlike my existing HP A high-voltage power supply, the new solid-state regulator must be able to deliver high current, say about mA The core feature of the adjustable high-voltage regulator is an implicit constant-current source operation. The constant-current operation of the OpAmp driving the pass MOSFET to maintain a fixed volt voltage drop across the 1k source resistor implies a constant-current flow of 10mA through the resistor, and, in turn, a constant-current 10mA flow through the series resistance below the 1k resistor I have seen the handheld, battery-powered oscilloscopes that power company sends out with their technicians.
Because the oscilloscope doesn't depend on the wall voltage for its juice, it can be used to evaluate problems with the wall voltage. Should an outlet be miss-wired, something more common than you would imagine, the self-contained power supply saves the scope from big sparks Resistor Decade Box If you have ever hunted in test-equipment catalogs for a decade-resistor box, you will be stunned by the high cost.
A decade-resistor box design is simple enough: an enclosure houses several position rotary switches and many resistors and two output terminals. That's it. In general, I like the old stuff, not the slick new, slick crossover country. Well, I am not alone. The biggest country music fan I have ever met was born and raised in New York. And I have read that Dolly Parton has many fans in Africa.
Hell, I have even read of Brit lovers of American country music, which I would have bet against Class-G High-Voltage Regulator Making any kind high-voltage regulator is tough, especially so with solid-state devices. I have owned several industrial-grade, tube-based, high-voltage regulators, with my favorite being my HP A high-voltage regulator I reread the post with mixed emotions.
Whenever I write any post, I always wish I had time to give it a proper rewrite—but I never have the free time. My first draft is my final draft. Thus, what I have just written always disappoints. Then something weird happens after a few years pass: I reread the old post and the disappointment transmutes into something closer to pride Hybrid Followers A cathode follower usually finds a resistor as its cathode load, but not always.
One sneaky possible load is an inductor with a high DCR. Or, we can use another triode as an active load, as in the ACF; or, we can use a pentode configured as a constant-current source. Happily, I was impressed by After the Darkness Super Triode with Pentode in past posts, we have seen many super-triode circuits that held a triode and either a MOSFET or a transistor—or even an IC power amplifier—but we could use a pentode instead.
In fact, post did show such a super-triode pairing of triode and pentode in a single-ended transformer-coupled amplifier. By the way, this post is worth rereading to get up to speed on the super-triode concept and its three pillars of operation. Cathode Followers with CCCS In my last post , I showed how an asymmetrical bipolar power supply could be made from a flat-pack power transformer.
The power supply offered a positive high-voltage and low-voltage power-supply rail voltages. The high-voltage portion used a voltage-doubler circuit one of the two primaries, while the low-voltage secondaries powered the low-voltage regulated negative power-supply rail voltage Five Fullrange Driver Loudspeaker After having mentioned the dipole loudspeakers that I built as teenager, I have been thinking about how I build the same speaker today.
First, I would five identical fullrange drivers, as I want the Hz crossover to be as seamless as possible, which is only possible with identical drivers A rail-splitter circuit creates a virtual ground and bipolar power supply out of a mono-polar power supply, such as a battery or DC wallwart. Almost exactly two years ago, I devoted much of post to the topic of rail-splitters, which makes that post worth rereading Sorry for the Lag It's been a brutal month for me.
A thief in Egypt targeted my yahoo store with almost fraudulent credit-card transactions, as he tried to see if his stolen numbers were viable. It was a nightmare, as I had to catch him early on so I could to impose an IP-address filter on him, which forced him to switch to another account Tiny OTL? We all dream of owning a mammoth OTL—a hulking monster of an amplifier that causes the lights to dim when it powers up—as we weary of the output transformer wedged between the speaker and the tubes.
Indeed, as the transformer couples the low-impedance loudspeaker to the high-impedance tubes, we all know that it also gets in the way, imparting its own failings. True, no electronic device is perfect, but some are even further from perfection This came as a surprise, as the circuit is interesting. It uses a DC negative feedback loop to center the plate voltage on a target voltage Dissimilar Bipolar Power Supply I have made no secret my liking flat-pack transformers.
Unlike most transformers, the flat-pack transformer does not wrap windings atop other windings; instead, each primary and secondary gets its own bobbin. The far larger separation between windings results in far less capacitance coupling between windings Music Recommendation Hiromi's Spectrum Hiromi Uehara, the gifted Japanese jazz pianists, always impressed me, but seldom won my heart.
Well, she has turned forty and her new album, Spectrum , did win me over Mission Accomplished: Project Done Over the year-end holidays, I finished another tube-audio project: a small OTL headphone amplifier, a single-ended amplifier no less. Why, dear God, why another headphone amplifier?
True, I have built so many that I long ago lost count. But after having recently built so many headphone amplifiers, I have gained the knack of banging one together in recorded time In other words, both output tubes saw the same cathode-to-grid signal, but in opposing phase.
I pointed how this is the way to go, as the top output tube is not underdriven nor is the bottom output tube overdriven PNP Split-Load Phase Splitter If you read the last section, no doubt you didn't like the conclusion, as you dislike output coupling capacitors.
One workaround is to rearrange the way the output signal is returned to the split-load phase splitter and to couple the negative power-supply-rail noise to the splitter's plate resistor Of course, we can also get high gain from cascading two triode stages. Music Recommendation: Three Crowns We have all heard of crossover music, where country blends into pop or soul blends into pop or blues blend into pop.
Happy New Year! The month January and the word "janitor" derive from the Roman god Janus, the god of beginnings and ends, doors, gates, passages, transitions, and time itself, who—surprisingly enough and unlike most Roman gods—wasn't pinched from the Greeks He included a schematic, which is why I was happy to help him.
Not sending a schematic is like calling and not giving them your address. Looking over the schematic, which made my eyes hurt, I noted one huge topological mistake and four easily fixed problems A Safer OTL Fuse Setup My thoughts return to the example of the negative power-supply rail fuse blowing, but the top output tube still conducting.
What we need is dynamic circuit that shuts off the top output tube's current flow when the negative power-supply fuse blows. OTL Auto-Bias Pentode Input Stage Since the pentode input stage directly couples to the split-load phase splitter, getting the desired target voltages is essential, as missing the target voltages will lead to less power output In the Futterman patent, he cites 60dB negative feedback, which is amazing for a tube amplifier and impossible with an output transformer.
The way you get that much gain is to current starve the pentode input tube, so a plate resistor over 1M can be used. Here is the problem: pentodes are intrinsically noisier than triodes due to partition noise Music Recommendation: Indra Rios-Moore I began this post with a listing of those audio products that I enjoyed most this year.
Well, I was thinking of all the albums and performers I have recommended here. Which is the one that I return to most often? The answer came quickly: Indra Rios-Moore Merry Christmas! I so love this photo of Jane Greer that I look forward to each December.
Last night, I was telling my daughter about my best Christmas tree ever Single-Ended Electrostatic Headphone Amplifiers I like single-ended amplifiers, you like single-ended amplifiers, so why not build a single-ended amplifier that directly drives the electrostatic headphone's stators?
Yes, the idea sounds crazy, for what could be more intrinsically push-pull than electrostatic sound producer? Yet, the first electrostatic loudspeakers were, in fact, single-ended affairs, with only one stator Of course, we are not actually concerned with delivering real power into an electrostatic headphone; instead, our goal is huge voltage swings.
Hybrid Electrostatic Headphone Amplifier We return to the world of push-pull amplification. For many, which apparently includes Stax, using a tube-based output stage to drive electrostatic headphones is done more out of necessity than desire Thinking Outside the Conventions After looking over the last design, I wondered if it wasn't possible to move the OpAmps back up to ground potential, as that way we might eliminate the input coupling capacitors.
The solution I came up will take some setting the groundwork beforehand Winter Music Recommendations Perhaps you are like me in that most Christmas songs weary the ears and soul.
The more cutesy the song, the greater it irks. Santa Baby is a good example. Nonetheless, I do enjoy seasonal music Electrostatic Headphone Amplifier Update What follows are just a few quick observations. I wondered what NOS tubes would bring to the table, so I dug out a pair of Telefunken 12AX7 smooth plates and Sylvania 6SN7 black plates, which I believe are called tri-plates, as the plate structures are not situated in parallel.
I expected magic, and I thought I was hearing magic—at first Considering the three big attributes—low distortion, high PSRR, and low output impedance—the price of four triodes doesn't seem excessive. Still, if we can get away with fewer triodes, we would welcome the savings It was a grand ride while it lasted Electrostatic Headphone Amplifier After listening to my latest Aikido push-pull headphone amplifier , I noted that the sound took on what I deemed electrostatic delicacy, as micro details surfaced that I had never heard from my Sennheiser HD headphones before.
To be frank, I do not know what aspect of the design deserves the credit Class-A Push-Pull IMC for Headphones In the last post, we saw several single-ended IMCs designed to present ohm loads to the tube-based headphone amplifier that had been optimized for a ohm load. All single-ended output stages run in strict class-A, where the idle current equals the maximum peak output current swing Just imagine 36W of B power I hear a big Beatles influnce along with Bob Dylan on this album, which is quite mellow compared to some of his other albums Well, all the software downloads are half price today to Monday.
Happy shopping Variations on a headphone Amplifier My latest project, the octal Aikido headphone amplifier created a small stir.
My answer took the yes-no branching Driving Low-Impedance Headphones My octal Aikido headphone amplifier was designed to drive ohm loads, which is great for my Sennheiser headphones, but not so good from Audioquest, Final, and Grado headphones.
With the 6SN7 or 12SN7 output tubes, about 20mA is the biggest current we can reasonably expect, given the V voltage drop across each triode Solid-State Solutions Silicon is cheap. A handful of transistors cost less than one good vacuum tube. In addition, low-voltages and DC coupling at the output and a solid-state workaround commend themselves to us.
At the same time, we want to tubes to do some work in driving the low-impedance headphones, other than just providing amplified signal. This leads us to my impedance-multiplier circuit IMC Founded in , this choir has garnered an excellent reputation. A great choir is a thing of supreme beauty My Latest Audio Project I have mixed emotions about describing my latest tube-based headphone amplifier.
I made more than a few mistakes. So many, in fact that I almost abandoned the project. Let me lay out my design goals A two-resistor negative feedback loop sets the gain. A coupling capacitor blocks the large DC offset voltage at the output Binary Capacitance for Phono Cartridges Speaking of switches, how do you get fifteen increments of pF of capacitance with only four capacitors? Answer: you use a BCD binary position rotary switch.
Strictly speaking, BCD means 10 positions, from 0 to 9, but Grayhill makes a position rotary switch that delivers the full 4-bit range.
Capacitors add together when in parallel, unlike resistors, which decrease in resistance when placed in parallel We could use two batteries to create a bipolar power supply, but I would prefer a monopolar power supply Bastode MC Pre-Preamp While on the topic of monopolar power supplies, the following is a circuit that may not make sense, as it seems to be missing a negative power-supply rail Ground-Grid Amplifier MC Pre-Preamp I am sure that I must have shown this topology before, but just in case I haven't… Normally, a grounded-grid amplifier presents too low an input impedance to be of use in must audio applications, but moving-coil cartridges, along with current-out DACs, are the exception Bettye LaVette is usually classified as a soul singer, which is mostly correct.
I, however, would file this album under jazz singers. Good jazz transforms just-okay songs into great art PCBs Arrive! It's been a long time coming, but they are here. All are now available at my GlassWare-Yahoo store Tube Dream If you are like me, then you get countless emails in your in-box and many paper flyers and catalogs in your mail box from the mail-order company, Parts Express.
I am not complaining; in fact, I enjoy going through their catalogs, while eating breakfast A Different Differential Input Stage An OTL power amplifier's output tubes are often arranged in a totem-pole layout, with one output tube atop the other. This is the arrangement used in all the Futterman OTL amplifiers Ultimate Tube Headphone Amplifier A few months ago, I was pondering how add another sonic control to an ultimate tube-based headphone amplifier.
My goal was to use a knob to switch from balanced to slightly unbalanced push-pull operation. The tradeoff would be less potential output power He stated that he needed about 12dB more gain Music Recommendation: Reality Audio Sony has released a new audio media variant: Reality Audio , which is used with headphone listening Crossover Epiphany Let's start with the word, "epiphany," which labels the sudden manifestation, perception, intuitive grasp, illuminating discovery, realization, or disclosure of the essential nature meaning of something or some event.
I believe that it was James Joyce who high-jacked the word from Christian theology and it now flourishes in the artistic and scientific spheres Single-Ended Output Stage with CCS Mojo A single-ended output tube can be auto-biased by using a constant-current source in place of the cathode resistor. This is an obvious and simple solution. Since a constant-current source, much like a high-inductance choke, can also shield the audio circuitry from the power-supply noise, why not get twice the benefits from the constant-current source?
In other words, our goal should be not only to auto-bias the output tube but to improve greatly the amplifier's PSRR I recounted this story back in post , which was devoted to class-A designs. I was fascinated by class-A amplifiers at the time and afriend had bought one, one made by Pioneer no less.
Inductor-Loaded Push-Pull Class-A The British magazine, Electronics World , back in November of , almost 20 years ago, they published an interesting article by Richard Burfoot on his class-A amplifier that ran off of a car battery.
If you have access to the old issue, I recommend that you read his article, as it is a fun and informative read Music Recommendation: Mujeres del Tango I discovered this album on Tidal and I am glad that I did, as it is an excellent collection of female tango singers.
The recordings range from very good to stellar. First of all, tango is not just a dance, as it is a music genre as well.
Born in Argentina in the s, tango songs are like poetry inspired blues songs Aikido PH-2 and Tube Rectifier A few weeks ago, I received an email that bemoaned my going for dual and separate heater regulators for the Aikido PH-2 phono stage where each channel gets its own separate heater regulator , as it prohibited the use of a Janus shunt regulator to power the phono stage, as the Janus holds only one heater regulator More Adventures in Class-A Last time out, we saw that class-A output stages are certainly massive and hot, but not necessarily more complicated; in fact, they offer the advantage of easily being auto-biased, unlike class-AB output stages which demand extra effort, especially solid-state output stages; fortunately, tubes are more forgiving I found the following power buffer I had devised for driving low-impedance headphones with no signal gain—the assumption was that a tube-based line-stage amplifier would be used for that task The danger of thermal runaway is just too great with optimal idle current flow Class-A with Compound Output Stages One advantage to the compound arrangement is that the driver transistors control the current flow through the output transistors.
The driver transistors should experience a fairly constant temperature, so their base-to-emitter voltages should remain also fairly constant; thus, the idle current through the output transistors should also remain fairly constant, in spite of big temperature chang Amazing stuff, both the CD and the speakers. The CD held a tapestry of sonic landscape, strange and bewildering Scott Adams, the creator of the Dilbert comic, says that when he watches the news he is sometimes surprised to discover that he is part of the news.
Apparently, he had heard a cable demonstration earlier and now he realized that that it was settled audiophile science that nothing was more important than wire, expensive wire, wire whose making required either an advance degree in particle physics or, at the other extreme, the Stradivarius-like talent for careful weaving and assembling tuneful cords of conductive metal. The poor fellow was crestfallen to hear the professional recording engineer tell him that those truly in the know just laughed at him and his fellow followers of fulsome flexes, finding them foolish and pitiful in the extreme Class-A A reader spotted my nametag and we briefly spoke during our elevator ride.
Embarrassingly enough, I cannot remember his name; sorry, if you are reading this. He told me of his many audio projects and his goal of one day being able to build class-A amplifiers, which seemed beyond his abilities due to their added complexity. This complaint is one I have heard many times More Crossovers I know that I have promised no more crossovers, but my mind refuses to let go of the topic.
After seeing and hearing several self-powered loudspeaker at the last RMAF, I grow ever surer that in the near future most high-end loudspeakers will hold internal active crossovers and power amplifiers. Music Recommendation: Ode To Billy Joe Since much of this post has a remembrance of RMAF just past quality, I will give a quick of what I told Larry Owens, Patron and friend, that I just rediscovered Bobbie Gentry and she was amazing; every is about was amazing, her fierce guitar strumming, her stunning beauty, her voice, which could purr and roar, her boldness, and her disappearance from the public stage when she was at her peak popularity RMAF Here is an outlandish idea: imagine having to compare an orange bought today to an apple bought last year.
Where to begin? Their huge advantage is that they are cheap, readily available, and come pre-built, which nicely sidesteps the problem of dealing with wall voltages and assembling power supplies.
Each year, switcher power supplies improve in quality; in addition, we can buy medical-grade switchers, which usually offer increased performance and certainly greater safety I will post afterwards, as usual, but so that ye be not Pull Out Rails For Cabinets Guide troubled I wanted to get something out beforehand These designs were not that different from tube-based split-load phase splitters, differing in that tubes do not come in the P flavor More Dang Crossovers I planned on giving crossovers, both active and passive a good, long, rest.
At the same time, I knew that topic was nowhere near exhausted. For example, we saw Yamanaka and Baekgaard crossovers with filler drivers and 2nd-order and 3rd-order crossover slopes for the woofer and tweeter, but what about a 4th-oder for the woofer and tweeter, with a 1st-order slope for the filler driver?
Was that possible? It is Music Recommendation: Harp vs. Harp Only a few new albums instantly thrill me. Harp , is one of the few. The idea behind this at first silly sounding, but ultimately truly cool album is why not combine a stringed harp and harmonica aka a harp so these gifted musicians can produce latin-flavored jazz.
Errata My last post held a schematic typo, a wrong part value. Here is the corrected schematic Odd Experience I put on my headphones and hit the play button. Soon enough, I realized that it wasn't happening. A few days ago, I played the same album, the same signal source, at the same time of day, with the same headphones—and it was happening then, but not now.
The SRPP is the world's favorite tube circuit—at least that is what I must conclude based on my seeing it everywhere and it filling my incoming email. More Phase-Flat Crossover Designs Throughout my long life, I have run into weirdoes—or at least to me seemingly weird people. How were they weird? They didn't care for expensive audio systems in the least, vastly preferring the sound from their table radio or car radio.
They were not indifferent to music, just the opposite, as they were often the type of music lover who knew all the lyrics and who would sing along to songs; indeed, many could read music and play an instrument, neither of which I can do Problems with the Yamanaka and Baekgaard Crossovers While these phase-flat crossover grant some real benefits, they also present some problems.
The first is that they do not deliver a flat impedance plot across the audio bandwidth, as they all dip at the crossover frequency Active Yamanaka Crossovers First of all, let me admit the idea of using three power amplifiers for what is ostensibly a two-way loudspeaker system does seem crazy.
Fortunately, it's not the craziest idea I have heard in audio circles Released in and produced by Linda Ronstadt, Warm You Heart , perfectly showcases Neville's amazing voice and the recording engineer's art. If you do not include all of the above information, it may invalidate your notification or cause a delay of the processing of the DMCA notification. Please note that, under Section f of the Copyright Act, any person who knowingly materially misrepresents that material or activity is infringing may be subject to liability.
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