No gain. As it has a very diy wood overlay for wire shelving yield background noise it's great for recording. Music Recommendation: Not Music Podcasts are not music, even when the topic is music. Like true quality heirloom instruments, Blueridge guitars aren't overbuilt; they're crafted to be light and resonant. 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. Which is the one that I return to most often? Does this mean that transformers are intrinsically better?

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Here are some pointers to give you an idea of who we are:. In fact, I usually test with an OpAmp that is both slow and cheap first; then, I progressively upgrade the OpAmp until I encounter problems. I, too, had bought some badly warped LPs, mostly Jamaican reggae imports, but I was sure he was exaggerating, as only one in twenty LPs was egregiously warped, not the half he claimed.

When I saw his cartridge and tonearm undergo seizures, however, over the slightest departure from perfect flat, I understood what was going on instantly. I pointed either he needed either a different cartridge or a different tonearm, as his combination was completely incompatible, as high-compliance cartridges like his demanded light tonearms, not massive ones like his.

Of course, he thought I was completely wrong, crazy wrong, as both cartridge and tonearm had gotten rave reviews I was hunting through my old SPICE circuits for a certain phono stage and I found a circuit I created long ago that just too interesting not to share. My goal in designing this phono stage was a relatively low plate voltage, not rumble filtering.

No totem-pole or cascode structures. No large valued plate resistor values. The solution was found in the two-triode feedback pair, with each triode loaded by constant-current source Music Recommendation: Totem No doubt many have discerned my love of Euro Jazz, which often sounds like American Jazz infused with the European classical-music tradition.

Well, Italian bassist and composer Ferdinando Romano furthers blurring the line that separates jazz from classical music in his album Totem Everyone says, "Thank God is over. Since I have more posts to create, I have to get to work Hybrid HPA with Howland Current Pump I ended my last post on a bi-amped amplifier with the observation that electrodynamic planar loudspeakers and headphones, due to their ruler-flat impedance, would make the best fit with a hybrid amplifier that used a conventional voltage-out amplifier, either a tube-based or solid-state design, along with a solid-state Howland current pump circuit to provide most of the current delivery What was missing was a bottom plate and four rubber feet.

No more. Since this SRPP hybrid headphone amplifier doesn't generate all that much heat compared to my many other tube-based headphone amplifiers, one of which required a fan , I decided not to perforate the bottom panel Transformer-Coupled MOSFET Output Stages After writing about how class-D amplifiers could be built into a tube-based power amplifier in my last post, I wondered about an alternative approach, one that exploited the existing high-voltage power supply used by the tube-based output stage.

In other words, rather than use two power supplies, a high-voltage one for the tubes and a low-voltage one for the class-D amplifier, we could use just the single high-voltage power supply with a MOSFET-based power amplifier Music Recommendation: Quietly There Alison Neale plays a wonderfully delicate alto saxophone on this album, reminding me of the jazz greats from the s and s, such as Art Pepper and Paul Desmond.

This is an album that those who don't like jazz will still like. I discovered it when Amazon Music recommended it as being the sort of music I seem to like. They were right I was right, I could—only because so much of it was already assembled. In the last post , we saw the solid-state headphone amplifier that James had sent me Bi-Amped Amplifiers?

We are going full Gedankenexperiment, i. In other words, I can offer no absolute solution or design, only my deliberations and reflections. By the way before we get started, let's review some history. Although Albert Einstein made the word "Gedankenexperiment" deservedly famous, he wasn't the first to use the word A sentence I never thought that I would write.

Nothing sticks into your ears, yet a big sound results. If I actually wore sunglasses, I might even think about buying them. If you haven't heard them, you should give them a listen I called it in March!

Dogs that do not bark. Note that Africa, with a huge Chinese presence and the weakest health-care systems, has gone relatively virus free. How's that possible? I remember seeing a map of the populations with the highest amount of Neanderthal genes Music Recommendation: Grace We tend to use up singers; I know that I have, so I am always on the search for new singers to hear. I had heard of the 40 year-old singer Lizz Wright, but I had never heard her sing.

This failing was righted recently. Wow, really impressive. Her voice is often likened to Norah Jones'. Well, maybe, but I don't hear it. To me, her powerful voice drips of spiritual s, gospel, church choirs, and the South.

Nina Simone would seem a better match than Jones. SRPP Harmonic Restoration Circuit The world's favorite tube circuit finds a new application: harmonic restoration, the purposeful introduction of harmonic distortion to enrich thin or odd-ordered tonality.

Not all distortion counts, only the right sort. For example, we won't accept any hum or buzz or hiss, only the natural linear cascade of harmonics produced so famously by single-end and class-A, push-pull amplifiers. The goal is to undo some of Diy Wood Overlay For Wire Shelving Install the thinning and washing-out effects of signal processing More No-Gain, No Pain Just a few decades ago, high gain was considered a feature in a line-stage amplifier, with tube-based line amplifiers routinely boasting as much as 30dB of gain Today, however, most signal sources put out more than enough output signal to drive most power amplifiers to full power output, as most power amplifiers require no more than 1Vpk to achieve full output and most DACs put out 2Vpk.

Thus, I have made my recommendation of just 12dB worth of gain for most line-stage amplifiers The negative power-supply rail would power both the DC servo and heat the triode's heater. I also envisioned making use of the regulated Vdc power-supply rail voltage as a free voltage reference Having long ago exhausted all his novels save for Ada , whose list of hundreds of Russian names seemed just too daunting and his books of lectures and autobiography, I have been thirsting for more Vladimir Nabokov for many years now.

Amazon was kind enough to point out that a recent collection of his uncollected essays, reviews, interviews, and letters to the editor was out, titled, Think, Write, Speak As far as I know, this was where class-H amplifiers began.

Cathode-follower operation means several things: low distortion, low output impedance, and huge input signals How cheap? The stereo amplifier runs off a 36V switcher power supply. In contrast, high-quality loudspeaker crossover inductors and capacitors needed for a woofer crossover cost far more More Passive Crossovers Loudspeaker crossovers not only divide frequencies, but they themselves divide into several categories.

The most obvious topological division is between parallel and series crossovers Sadly, this was Svensson's last album prior to his death in a diving accident in Class-G and Class-H Spies, Soviet spies in particular, were given to interpretation, the analysis and appraisal of what their espionage uncovered.

This habit drove their controllers back in Moscow crazy My son recently asked who is the current best Beethoven-piano interpreters. My list included Lewis, which prompted me to see what Amazon Music streaming service had to offer Although I made that post last February, my memory said it must be years older.

No doubt, many also feel as I do that this year—paradoxically enough—has gone on forever and that it hasn't actually begun yet. As I looked the circuit over, I saw much that needs updating If you run a square-wave or a tone burst through a 1st-order crossover, then a square-wave or a tone burst comes out, due to the crossover's phase-flat output.

The only problem is getting away with it, as the 1st-order's attenuation slopes are relatively weak, coming in at only -6dB per octave and dB per decade Four-Way 1st-Order Crossovers A four driver loudspeaker offers an easy solution to the problem of sluggish woofers and frail tweeters, as we can cascade the filters so both the woofer and tweeter see slopes that begin as -6dB-per-octave then increase to dB-per-octave, while the two middle drivers see 1st-order slopes throughout Five-Way Crossovers Yes, five-way loudspeakers are rare; but if we include four-way loudspeakers that use a separate subwoofer, they are less rare.

Many possible arrangements come to mind. We could cascade entirely in favor of the tweeter or entirely in favor of the woofer—a choice between tweeter safety and midrange clarity. The arrangement that appeals to me most is the one wherein both the woofer and tweeter receive cascaded crossover slopes, while the remaining middle drivers all see 1st-order slopes throughout.

Let's start with no cascading crossover frequencies Six-Way Crossovers Five crossover frequencies does seem excessive. In fact, although I am sure that six-way loudspeakers are made, I don't remember seeing any. If we start at a low enough frequency, however, we can get five crossover frequencies that seem to make sense.

What tickles me about a six-way loudspeaker is all the various possible crossover configurations A dang pity, as it is a fun listen. I have used thier album, In Love , as a test CD since it came out. The test is interesting: I listen to solid-state amplifiers try to produce an unanoying reproduction when playing it. Most fail. Some spectatcularily so. In contrast, tube amplifers from the s have passed the test beautifully. About 35 years ago, he was kind enough to indulge my interrogation for over an hour, between the talks he was giving at a high-end audio salon Here is the quick summery from Analog Devices Yes, the primary will experience huge voltage swings, but as the output stage runs in strict class-A, the average voltage drop equals the idle voltage drop IMC for Headphones A few months ago, I received a request from a long-time reader, Dan, for an IMC impedance-multiplier circuit for his Aikido-based headphone amplifier that was setup to drive ohm headphones.

Dan wanted to drive some lower-impedance headphones, such as the ohm types made by Grado and others. He had seen the discrete-transistor design post and wondered if an OpAmp could not be used instead Music Recommendation: Linn Records I remember being thrilled by the sound quality of recordings from Linn Records , as they were often showcased in demo rooms at audio salons and audio shows. I wondered if Amazon Music HD streaming service offered any of them, although I was fairly confident that they wouldn't.

I was, happily, wrong. Sidewinder Hybrid Power Amplifier I was going through a box filled with old and odd loose sheets of paper. Most of it was old advertising material, the type that used to be mailed out to those in the electronics industry. For most of my life, I had Diy Wood Projects For Garage 95 a love, hate, hate, hate relationship with junk mail, as I enjoyed getting about a fourth of it. I like reading white-papers on new IC designs; and fat catalogs filled with electronic components were even more interesting to me than the occasional Victoria Secret flyer.

In the foot-tall pile, I found a Xerox i. Polarized 4th-Order Crossover In my last post, we saw how to polarize the capacitors in a speaker's crossover. I showed 1st, 2nd, and 3rd order crossovers, but failed to show a polarized 4th-order crossover First of all, the LR crossover alignment only applies to even-order crossovers; thus, there are no 1st or 3rd order LR crossovers.

The 4th-order LR crossover functions much like the 2nd-order LR crossover, as both drivers are down -6dB at the crossover frequency, so they sum to unity; it differs in that it requires that both drivers are in phase Each brought his or her own signature to playing the cello. 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 Diy Wood Gifts For Dad Off 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 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 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.

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