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Bipolar Power Supply from 12Vac The triangle buffer shown above needs a bipolar power supply. We could go the fancy route, with fully regulated positive and negative power-supply rails. On the other hand, we could use a 12Vac wallwart. My reasoning is that since the triangle buffer shown runs a heavy idle current to maintain class-A amplifier push-pull operation, we could get away with something simpler Hybrid Phono Preamps Our goal is simple: use each technology where its strengths shine through.

With hybrid power amplifiers, the usual setup uses tube up front for signal gain, with the solid-state output devices following, delivering current gain. With a hybrid phono preamp, we reverse the order.

Solid-state offers low-noise amplification; tube-based circuits, lush sound and huge voltage swings. With a hybrid phono preamp, we don't want the tubes leading in front and the OpAmp following behind, as the tube's high noise will only get amplified Bi-Amped Phono Preamps In the previous hybrid designs, the OpAmp receives the signal from the phono cartridge and pass along the amplified signal to the tube-based circuit.

This is the obvious way to proceed. What if, on the other hand, we feed cartridge's signal to triode and the OpAmp at once, in parallel, so both can deliver amplified output signals? Okay, that is crazy enough an idea, but I can make it even crazier. What if we let the triode handle frequencies above Hz and the OpAmp handle frequencies below Hz, then we sum the two output signals into one? Of the four, I would say that Natalie Merchant is the best singer, but that has not precluded my listening to the other three.

Last week I realized that many years have passed since I last checked in on them. Streaming-music sources, such as Amazon Music and Tidal, however, make this an easy task. Better Facemask Since it appears that, much like the poor, facemasks will always be with us, why not design a better mask? I love asking such questions in front of some of my friends, as the gasps of near-lethal incredulity are delightful to behold. Am I a doctor? How dare I dare to presume to dare disturb the universe…?

I dare. If nothing else, why has no enterprising company sold facemasks with the bottom-half of our faces printed on the front? You send in a photo of your face and the masks arrive displaying your smile High-End Loudness Control Let us think back to happier times. When your father or grandfather wanted to play his new stereo-demo LP at a moderate sound level, he switched on the loudness switch on his receiver, filling the room with balanced sound, albeit at a lower volume level.

Today, we turn down the volume and resulting sound falls short, sounding thin and eviscerated. Why so? We do not have a loudness control. Somewhere around , audio puritans denounced the loudness control as being audio-impure, along with all other tone controls, which only mid-fi listeners would desire and use. A big mistake this was, as a high-quality loudness control would make for much more enjoyable listening. Too-Loud Loudness Compensation Not just Wallace Simpson aka Duchess of Windsor , but many hold to the belief that one can never be too thin or too rich.

Well, for many audiophiles, music playback can never be too loud. Indeed, for non-audiophiles, an audiophile is someone who is hard of hearing that happens to be also rich Music Recommendation: Estonian Incantations 1 I have listened to many albums with the Estonian Philharmonic Chamber Choir, but I have never sought out their albums in particular.

Recently, I did seek their albums out at Amazon Music. Plenty albums showed up for my sampling. I choose the album, Estonian Incantations 1. This is not your father's classical album, unless he listened to Leonard Bernstein's MASS —many did, in the early 70s, although it generally received bad reviews. What am I getting at? Speaker Diffraction Loss While writing my last post, and while looking at the first of the two passive RIAA equalization networks, the shelving network that boost the lows below 50Hz by 20dB and then fell off at 50Hz before flattening at Hz, I noticed an exact ratio between the two resistors in the shelving network This was not the case five years ago, when it seemed that all everyone was interested in was building a better DAC, usually with post tube sweetening Music Recommendation: Crime Of The Century While waiting in a local sandwich shop, I listen to music hits from the s pour from the ceiling speakers.

My pleasure restrained by my fear that the under-twenty workers must feel oppressed by this music, preferring as they must something more modern, something trendier. As I collect my roast-beef sandwich, I mention the music to the young man. He loves it; the radio station is his choice.

Amazingly enough, he revels in s music. Mind-boggling—well at least my mind boggled At the time, I owned bi-amped, home-built loudspeakers that held a Hz crossover frequency.

The speaker was a two-way design with an Audex 6-inch polypropylene woofer with a cast frame in an insanely over-built sealed enclosure, whose walls were 2. The motive is to exclude the resistor cathode from the AC signal path, which now includes only the output transformer, the output tube, and the bypass capacitor that completes the circle Music Recommendation: The Naxos classical-music label should be far better known and appreciated than it is.

Many, if not most, of their efforts are beautifully recorded and their CDs cost less than other more famous labels. Over the years, I have bought many of their box sets and have loved the music and the price.

Well, when I saw that Naxos had released a collection of hitherto unrecorded music by one of the composers that interests me greatly—Villa-Lobos, the Brazilian composer, conductor, cellist, and classical guitarist—I had to listen to it Loudspeakers Loudspeakers constantly come to mind—well, to my mind. Loudspeakers need the most help. With just cause, loudspeakers are identified as a stereo system's weakest link, not amplifiers or cables or DACs or equipment stands or power AC filters Crossover Thoughts If a loudspeaker holds more than one driver, it will need a passive crossover to divide the audio band of frequencies between the drivers.

As soon as I finished writing the previous sentence, I thought of exceptions; for example, we could use two fullrange drivers, one facing forward and one facing rearward for bi-pole design.

Even this design, however, would need a shared Zobel network. Three-Way Crossover Woes Textbooks inform us that three-way crossovers do not work—not even 1st-order three-way crossovers.

Neither the parallel nor the series 1st-order crossover yields a flat impedance or a flat frequency response Often, I am the sole source, which seems to trouble them, as a common viewpoint is that no new tube topology is possible, all topological development ending about 70 years ago The album bridges American jazz with African music, with a healthy dollop of church music mixed in. All the tracks are varied, some with singer accompaniment, including his own wife on the first track Thus, I set about making a SPICE curve tracer and I took the resulting plate curves and overlaid them upon a set of curves from an actual curve tracer Another Split-Load Phase Splitter Version After making my last post, I had this haunting feeling that I forgot to include another version of the split-load phase splitter that delivered equal and in-phase PSRR from both outputs.

I went hunting. If we include the SPICE circuits living on USB sticks and my main computer and the few hundred that I have lost due to hard-drive deaths, the total must be well over 5, Well, I found a more complicated version of what I sought.

Since the circuit is somewhat complicated, we will work our way up to it AnTec output Transformers Over the last two decades, I have bought many toroidal power transformers from AnTek ; and over the last three decades, I have bought many aluminum enclosures from AnTec's sister company, Metal. Fairly recently, AnTek has offered output transformers for tube-based power amplifiers, with push-pull output transformers that range from 10W to W and a 30W single-ended output transformer.

All are flat toroidal designs and the prices are more than reasonable. The transformers that interested me most are the 10W and 15W, as they offer the most extended high-frequency output I believe that this album was mention in a review of another album that was deemed to fall short of it; thus, my efforts to seek out the better album.

Domador de Huellas literally means "the tamer of the footprints. It worked. As far as I know, I had made all the solder joints. It certainly played loud enough. There was too much resistor noise for my taste, but the white-noise hiss is fairly easy to ignore.

Next week, the preamp will meet another system with an equally low-output moving coil phono cartridge This is a tad unfortunate, as the design is a very clever two-switch combination of stepped shunt and series attenuators that delivered 66 steps of attenuation, the result of using 6-position and position rotary switches.

What it didn't produce, however, was a flat input impedance, the result of using the shunt portion of the attenuator. Well, a potential customer asked when it would be back in stock. My answer was possibly never, as the new gold-contact Attn-2 stereo stepped attenuator works perfectly as a mono balanced stepped attenuator with 66 steps of attenuation A high CMRR ensures that signals shared in common are ignored; noise is usually a common-mode signal.

The two easy ways to achieve a high CMRR is to use either an input signal transformer or a constant-current source with a differential amplifier input stage Conclusion So, is this last circuit the best design? Remember, something is only best in relation to some goal or task. For example, an antiaircraft gun will kill a housefly, but it is not the best means of doing so. Using only two tubes per channel is a huge feature and offering a low differential output impedance is also a huge feature when it comes to driving high-impedance headphones Lateef was an amazing American jazz musician, composer, novelist, businessman, college professor, and purveyor of "World Music" before it had the name.

His Ph. D dissertation was a comparative study of Western and Islamic music education. He played too many instruments to list, but was best known for his saxophone and flute playing. The first was a silkscreen error on the bottom of the PCB where the positive and negative sign on the heater pads are reversed.

This typo can cause a blown capacitor, as the heaters are shunted with a large, low-ESR capacitor. Fortunately, the fix was easy enough: just use a Q-tip dipped in acetone to remove the polarity signs Cynosure Resistor and Aikido Cascode The best way to achieve power-supply noise nulls is not with tight-tolerance capacitors, but with tight-tolerance resistors, as tight-tolerance resistors are both plentiful and cheap, whereas tight-tolerance capacitors are neither.

In addition, we can use a potentiometer, but not a variable capacitor. Here is an example of a 6DJ8-based Aikido cascode that uses two tight-tolerance capacitors Cynosure Split-Load Phase Splitter I am building a push-pull, tube-based, stereo integrated power amplifier, so phase splitters have been on my mind.

Unless a balanced input signal is provided, push-pull power tube-based amplifiers require a phase splitter to drive their output stages. This is true for both OTL and transformer-coupled push-pull tube-based power amplifiers My goal was to reduce the voltage differential between the input grounded-cathode amplifier's heater and the phase splitter's cathode, while still maintaining an equal and in-phase PSRR from both phase splitter outputs Cynosure Paraphase Phase Splitter The paraphase phase splitter is the pairing of a grounded-cathode amplifier and an anode follower, the latter of which is setup for unity-gain inverted output.

In England, it is known as the paraphrase phase splitter. It has made several appearances in previous posts, such as post and Last year during the pandemic, American female singer Morgan James created two albums with only her husband, Doug Wamble, playing acoustic guitar for accompaniment he sings with her on the Islands in the Stream track ; do not worry, as he is a gifted jazz guitarist MC Phono Preamp—Tube-Based After a month of thinking about tube-based moving-coil pre-preamps, I began to wonder if this trip was really necessary.

No, I wasn't thinking about step-up transformers or higher-output phono cartridges. Why not just build a phono preamp with enough gain to run a low-output MC cartridge, say, one with a gain of 60dB? This task would be easy enough with solid-state devices, but tubes require much more care and consideration If we pause to think about it, we soon realize that we ask an awful lot of the simple SRPP circuit, as it is expected to provide signal gain and phase splitting, and push-pull operation capable of delivering close to twice the idle current into an external load resistance.

Music Recommendation: High-Res Singers I was searching Amazon Music streaming service for high-resolution albums, when it hit me: I was doing it backwards. I should have been searching high-resolution music websites and finding the overlap between the website's catalog and Amazon Music's catalog.

I listened to a friend's MC cartridge with 40dB tube-based phono stage of mine. With the line-stage amplifier at full gain, the music played—played amazing well, in fact—but was too noisy.

Either a step-up transformer or an active pre-preamp with a 20dB would have made all the difference. Later that day, I filled out two pages in my sketchpad with circuits More Electrostatic Loudspeaker Ideas Post mentioned Harold Beveridge's amazing electrostatic loudspeaker design, which is unique in that he drove both the stators and the diaphragm, using two OTL amplifiers.

In the overwhelming majority of electrostatic speakers, the diaphragm passively sits between two driven stators, biased to a high-voltage through a many mega-ohm resistor, pushed forward and backward by the developing electrostatic forces Electrostatic Speakers with Wire Stators Be prepared to be mightily impressed. Mercy, doe she have amazing woodworking skills. Not only is Charlie a big advocate for wire stators, he has developed some truly interesting designs that use a segmented stators to tailor the high-frequency radiation, concentrating at the center of the tall diaphragm I don't, sadly.

The Balancer design offer gain and balanced outputs. This question, however, brought back memories from 30 years ago. A high-end audio company had major problems with a no-gain phase splitter that a genius tube guru had designed for them. My first question was why would anyone need a unity-gain phase splitter? More Crazy Speaker Ideas In the last post , we saw an electrodynamic planar loudspeaker that held no magnets, just a large solenoid.

Well, how about using electromagnets instead? The dynamic loudspeaker is almost years old invented in and most speakers back then held a field-coil to create an electromagnet—up until WWII, when lighter, powerful magnets were developed. The field-coil often doubled as the choke in the power amplifier's power supply. In other words, speakers with electromagnets are nothing new. What I am proposing is that planar speaker be built Bipole Electrostatic Speaker First, some electrostatic basics: electrostatic loudspeakers sandwich three key parts, the diaphragm in the center, and a stator on each side of the diaphragm.

The stators are electrically conductive and are acoustically porous due to holes or gaps in their surface: for example, perforated-sheet-metal or wire screen or many sheathed wires in parallel. Each stator receives a high-voltage audio signal, with the stators driven in anti-phase to each other Magnetostatic Electromagnetic Loudspeakers I hate the word, "magnetostatic," as it just confuses things.

I prefer the adjectives, "electromagnetic" or "electro-dynamic," when describing planar loudspeakers such as the famous Magnepan speakers, which hold many bar magnets and a low-resistance diaphragm More on MC Pre-preamp I have been giving some more thought to the idea of a tube-based moving-coil cartridge pre-preamp. For example, here is a variation with three 6DJ8 tubes per channel Music Recommendation: Offertorium The path I took to find this album was circuitous in the extreme, which is so typical of any music hunt at either Tidal or Amazon Music.

Just the other day, I asked my son if he knew the word, "divagate. Cummings poetry. Reading his poetry is difficult; listening to it being read, a delight.

The results were tiny, sadly. I did, however, find quite a bit of T. Eliot's poetry In addition, it allowed me to try out the new Attn-2 in an actual piece of audio gear. Hard Constant-Current Sources A constant-current source is a current limiter or current regulator that freely allows the flow of current, but only up to a set limit.

It is a practicable version of an ideal constant-current source, which would be something like a special battery that delivered a fixed current flow, not a fixed voltage; in other words, it would deliver a steady current flow regardless of the voltage-drop required. For example, an ideal 1mA constant-current source would develop 1kV across a 1M resistor and 1V across a 1k resistor and 1mV across a 1-ohm resistor.

In contrast, a battery strives to deliver a fixed DC voltage regardless of the current flow, be it only 1mA or 1A or 1kA He is not alone. Moving-coil cartridges are seldom plug-'n-play. I own a moving-coil cartridge, but it is a high-output Dynavector 10x5 Mk2 that delivers close to 3mV of output, so I have no problems using 40dB phono stages.

The only concession I had to make was using a 10k load resistor rather than 47k. Most of my friends who run low-output moving-coil cartridges use step-up transformers, not active pre-preamps, although most have tried active gain stages before. Does this mean that transformers are intrinsically better? No, not necessarily Yes, they do exist and they are well worth hearing. One example is Peter Sculthorpe, whose Requiem I found quite interesting and compelling.

I noticed Brett Dean's name on the lists of Australian composers worth checking out; justly so, it turns out Vinyl I have been spinning LPs. I needed to do so, as I was working on an old phono preamp of mine. As the LP filled the room with music, I could not fail to note how different the listening experience was to digital playback.

Records demand our attention. We must first perform the usual preparations, such as LP cleaning, neutralizing static, needle scouring, and lowering the tonearm.

Once the music emerges, we remain attentive to sound, listening for ticks, pops, and scratches—and something like live music More Infinite-Z Amplifiers In post , we saw two power amplifiers working in cascade—not in series, but one amplifier's output cascading into another through a resistor.

If the two amplifiers shared the same gain, not much would be accomplished—but with differing gains, magic takes place. The amplifier at the bottom of the cascade enjoys the amazing advantage, however, of not having to deliver any current into the loudspeaker; thus, the speaker's impedance effectively appears as infinite. Well, since writing that post, I have given the arrangement some more thought Infinite-Z Hybrid Headphone Amplifiers Since writing post , the idea of actually building a hybrid infinite-Z headphone amplifier has gripped me.

One subtlety that I failed to consider was the importance of the output impedance, i. Infinite-Z Amplifier Meets Triadtron While pondering how to achieve the lowest output impedance from a tube-based headphone amplifier, one topology that came to mind that offered an intrinsically-low output impedance was the Triadtron The huge advantage to using two identical amplifiers is that they both share identical frequency and phase responses He probably would have won it, had he not won the award in for his album, The Offense of the Drum Subwoofer Ideas As a teenager, I owned and built several subwoofers.

Some were surprisingly good, which was primarily due to their cabinets, robust and super-thick-walled, never less than 1. In addition, my brother and I bought wood screws by the Great Gross a dozen gross, i. Single Subwoofers with Two Amplifiers Since class-D stereo power amplifiers are both readily available and cheap, why not use one in a powered subwoofer? We could double up on big 4-ohm woofers, so the subwoofer's maximum SPL would increase by 6dB.

Something less obvious might be to create a bi-amped subwoofer, which would hold two woofers, say, a inch and an 8-inch driver Subwoofers in the Corners I once saw an ad for a subwoofer that made the claim that the best location for a subwoofer is the corner of the room.

The ad claimed that the corner not only permits the greatest coupling of the subwoofer to air, but ensures that the wave-front leaving the subwoofer hits our ears first before its reflections arrive Differential Amplifiers and Crossovers In post , we saw Richard Small's outline of an active four-way crossover that cascaded three low-pass filters and then used three differential amplifiers to extract the top three signal outputs Music Recommendation: Dreamers This was an easy recommendation to make, as the album delivers both artistic content and sonic splendor.

Thus, the album straddles the two genres of Jazz and Classical Small on the topic of crossover design. I had only distant and faint memories of this article, which was a dang tragedy, albeit a small tragedy, as his paper could have saved me much recent mental effort Shifting Loudspeaker Crossovers Shifting is fun. Well, what if loudspeaker crossovers allowed shifting?

What would we shift? Two possibilities are frequency and slope I found it at Amazon Music Service. Oh yeah, this is one fine album. The recording is first-rate and Will Liverman's baritone singing is exemplary Is there a compelling reason for not pursuing this?

Regulators and Resistor Band-Aids Here is a topic seldom seen: adding a power resistor to either a series or shunt regulator to soak up excess dissipation Pure-Tube Shunt Regulator Many view solid-state and hybrid designs with disdain. Indeed, many view indirectly heated cathodes as cheating.

Well, we can build an all-tube high-voltage shunt regulator. What all voltage regulators require is a voltage reference, a negative feedback mechanism, and a pass device.

Hybrid Shunt Regulator Hybrid designs hope to realize the best of the two technologies: the vacuum tube's robustness in the face of high-voltage and the solid-state device's low noise and high gain. 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.

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It does not have the most intuitive of workflows, but the company is young and rapidly evolving. Raptor maps does not currently have publicly available pricing.

Maps Made Easy and DroneDeploy have been among the top contenders for ease-of-use and low barrier to entry. Initially Maps Made Easy was the preferred of the the two due to its seemingly more accurate stitching algorithm and more reliable app. DroneDeploy has recently made some big changes to their workflow and now seems to have surpassed Maps Made Easy as far as ease of use and functionality. The big plus that Maps Made Easy has going for it is the per-acre pricing , which is great for occasional users who do not want to sign up for yet another month-to-month subscription service.

Ease of use, some great options under the free package. Also, pay-as-you-go means you are not stuck in a month-to-month contract like you are with some of the others. Also great for processing massive jobs allows for upload of up to images!

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These two apps go together. DataMapper is used to process the data from these flights into useable data. One of the earliest and key players in the UAV industry, PrecisionHawk has made quite a name for itself in the agricultural sector thanks to its trademark PrecisionMapper feature that is not available in other drone mapping software. The software also provides specialized metrics for monitoring and analyzing crop health as well as volumetric measurement. Thanks to all these features, this software is excellent for large-scale operations that require intensive and careful monitoring like farming, real-estate, and energy.