One of the challenges in the implementation of my OKTAN6 Ultimate horn system has been the double-edge-knife that are the ultra high sensitivity compression drivers that I’m using. On one hand you hear every minute nuance and sound and on the other hand, you hear every minute nuance and sound. The drivers respond to the noise floor of the amps and any tube-rush-effects. While these may not be noticeable or an issue with drivers of conventional efficiency, with 118dB, 114dB, and 107dB sensitive drivers it becomes an issue.
The magic of Single Ended Triode - Directly Heated Triode amplification is their mojo, moxie, groove inducing sound and when the filaments are AC heated unfortunately they are not the quietest amplifiers at idle or during the lowest level passages. It’s typically a quandary to find a quiet and ultra low distortion amplifier. They are out there. In the SET/DHT arena my James Burgess, Sean Casper and Thomas Mayer amplifiers are some of the quietest of my amplifier.
In the game of low distortion, the lowest levels are usually achieved by the addition of feedback to the circuit. Negative feedback not only help lower the amplifiers output impedance but is used for output correction and thus lowering distortion figures/measurements. As a company from Australia named Halcro proved some years ago,THD and distortion numbers can be lowered to astonishingly low levels. The problem is that amps that typically implement feedback and have outstanding levels, in percentage, of Total Harmonic Distortion tend to sound cold, clinical, and devoid of that magic that SET amps produce and are known for. Some have even gone so far as to say that the microphonic tubes produce the best sound and that you want that little bit of added noise for that rich harmonic and euphoric sound.
I view all DIY’ers as chefs in the kitchen, all trying to design and build great sounding musical amps and preamps with a variety of ingredients. The great Radu Tarta has an engineering background but at this point relies more on his wealth of experience than on theory. Many of the great builders don’t come from a formal technical background or with an engineering education. Nevertheless that doesn’t limit them or stop them from producing some great sounding creations.
But I wondered what someone who has been in the commercial engineering world, with access to high-end oscilloscopes and signal generators and measurement tools could produce. Let’s be honest, my experience with great audio engineers with those that produce products like Halcro or Spectral, which I own and enjoy, which are good but will not be satisfying to those of use that crave the euphoric sound of the SET/DHT amplification. Most engineers understand the theory and can design circuits but we often lack that special sauce that great musicians have to deliver that hook that makes your toes tap and that sound that is less like a microscopic look at the sound, than the artisans that produce creations that let you get lost in the music.
What if there was someone who knows both sides of these worlds. Someone with a deep understanding of tubes and the elements at play in sound reproduction, but also possess the technical back ground of todays commercial/industrial electrical engineering world, with access to high-end oscilloscopes and audio signal generators and measurement tools and laboratory equipment? How good of an amplifier could someone like this design?
If you have been around the DIY Audio Community for some time, the name Pete Millett will be familiar to you. Pete has been around for decades and he shares his knowledge through his website, with forum postings, experts talks/panel participations and presentations at the European Triode Festival (ETF) every year, and perhaps most importantly through his audio DIY PCB kits and offerings on eBay. Pete knows his stuff. Pete is a true audio engineer and a subject matter experts with a ton of circuit designs and products designs and collaborations. Pete shares many of his designs on his website, obviously for non-commercial use, which unfortunately many have violated.
So after all those words, we finally get to the reason for my post today. A couple of months ago Pete came for a visit and I hosted him at my home. Pete doesn’t build amplifiers or audio components for others as builders like Thomas Mayer, Radu Tarta, Oliver Sayes do for example. Typically Pete develops a design and lets others build them, either in DIY form or through commercial collaboration, of which he has many like Arcturus Audio. But Pete does build amplifiers, preamplifier, headphone amplifiers, lab equipment, field-coil power supplies and other components but he builds them for himself, for his personal use and not for commercial offerings nor does he build anything upon request, I have tried to get him to build me some of his field-coil power supplies and I’m still waiting, not holding my breath on those.
As luck would have it, I had reached out to Pete to buy a couple of pairs of his tube panel meters for my Ultimate SET 300B amp and Ultimate DHT 171A preamp that Radu designed and built for me. Those tube panel meters look great. Too bad production has ended as I would have bought more for future projects. I have followed Pete for years, in terms of general awareness but had never heard one of his designs that I know of directly. So when I saw that Pete had built an elusive R120 amplifier it caught my attention. The Japanese have a certain fondness of the French R120 La Radiotechnique tubes. I reached out. Pete’s R120 amp is switchable and also can use PX4 as output tubes.
When Pete came to my house he also brought two other amplifiers that he wanted me to listen to. To be honest I was less excited about those two amps as they used transmitter tubes, not audio transmitter tubes like the 211/VT-4-C or 845, but radar and radio-frequency type transmitting tubes. And even worst these amps make use of feedback in their design. Boy was I in for a surprise. As they say, never judge a book by its cover. See not only does Pete know about how to properly implement electrical feedback, Pete knows a lot about distortions. Pete knows about odd and even harmonics and how to adjust them to taste. Pete can pump up the 2nd order distortion to sweeten the sound and produce that euphoric magical sound many of us crave. Pete’s amps have phenomenal low distortion for tube amps. I strongly encourage anyone interested, to read Pete’s white paper and PowerPoint presentation on audio distortions. Not all distortions are the same and different distortions have different implications. Pete also implements extremely large & heavy oversized output transformers on his amp builds which result in superb bass, both in terms of texture and extension.
One of the things that Pete and I both share is our interest in rare and exotic tubes. Pete and I are both interested in amps and preamps built around the less well known or used US and European tubes. I like to thank Pete for further opening my mind to the expert and judicious use of negative feedback, other operating modes and other circuit topologies other than strictly triode. There is potential for pearls and other hidden treasures beneath every unturned stone. This experience with listening to Pete’s amps has reminded me not to limit my explorations as you just never know what might be found and what great discoveries await. Just when you think you have experienced it all, you discover that there’s more to learn. And that’s exciting!
The magic of Single Ended Triode - Directly Heated Triode amplification is their mojo, moxie, groove inducing sound and when the filaments are AC heated unfortunately they are not the quietest amplifiers at idle or during the lowest level passages. It’s typically a quandary to find a quiet and ultra low distortion amplifier. They are out there. In the SET/DHT arena my James Burgess, Sean Casper and Thomas Mayer amplifiers are some of the quietest of my amplifier.
In the game of low distortion, the lowest levels are usually achieved by the addition of feedback to the circuit. Negative feedback not only help lower the amplifiers output impedance but is used for output correction and thus lowering distortion figures/measurements. As a company from Australia named Halcro proved some years ago,THD and distortion numbers can be lowered to astonishingly low levels. The problem is that amps that typically implement feedback and have outstanding levels, in percentage, of Total Harmonic Distortion tend to sound cold, clinical, and devoid of that magic that SET amps produce and are known for. Some have even gone so far as to say that the microphonic tubes produce the best sound and that you want that little bit of added noise for that rich harmonic and euphoric sound.
I view all DIY’ers as chefs in the kitchen, all trying to design and build great sounding musical amps and preamps with a variety of ingredients. The great Radu Tarta has an engineering background but at this point relies more on his wealth of experience than on theory. Many of the great builders don’t come from a formal technical background or with an engineering education. Nevertheless that doesn’t limit them or stop them from producing some great sounding creations.
But I wondered what someone who has been in the commercial engineering world, with access to high-end oscilloscopes and signal generators and measurement tools could produce. Let’s be honest, my experience with great audio engineers with those that produce products like Halcro or Spectral, which I own and enjoy, which are good but will not be satisfying to those of use that crave the euphoric sound of the SET/DHT amplification. Most engineers understand the theory and can design circuits but we often lack that special sauce that great musicians have to deliver that hook that makes your toes tap and that sound that is less like a microscopic look at the sound, than the artisans that produce creations that let you get lost in the music.
What if there was someone who knows both sides of these worlds. Someone with a deep understanding of tubes and the elements at play in sound reproduction, but also possess the technical back ground of todays commercial/industrial electrical engineering world, with access to high-end oscilloscopes and audio signal generators and measurement tools and laboratory equipment? How good of an amplifier could someone like this design?
If you have been around the DIY Audio Community for some time, the name Pete Millett will be familiar to you. Pete has been around for decades and he shares his knowledge through his website, with forum postings, experts talks/panel participations and presentations at the European Triode Festival (ETF) every year, and perhaps most importantly through his audio DIY PCB kits and offerings on eBay. Pete knows his stuff. Pete is a true audio engineer and a subject matter experts with a ton of circuit designs and products designs and collaborations. Pete shares many of his designs on his website, obviously for non-commercial use, which unfortunately many have violated.
So after all those words, we finally get to the reason for my post today. A couple of months ago Pete came for a visit and I hosted him at my home. Pete doesn’t build amplifiers or audio components for others as builders like Thomas Mayer, Radu Tarta, Oliver Sayes do for example. Typically Pete develops a design and lets others build them, either in DIY form or through commercial collaboration, of which he has many like Arcturus Audio. But Pete does build amplifiers, preamplifier, headphone amplifiers, lab equipment, field-coil power supplies and other components but he builds them for himself, for his personal use and not for commercial offerings nor does he build anything upon request, I have tried to get him to build me some of his field-coil power supplies and I’m still waiting, not holding my breath on those.
As luck would have it, I had reached out to Pete to buy a couple of pairs of his tube panel meters for my Ultimate SET 300B amp and Ultimate DHT 171A preamp that Radu designed and built for me. Those tube panel meters look great. Too bad production has ended as I would have bought more for future projects. I have followed Pete for years, in terms of general awareness but had never heard one of his designs that I know of directly. So when I saw that Pete had built an elusive R120 amplifier it caught my attention. The Japanese have a certain fondness of the French R120 La Radiotechnique tubes. I reached out. Pete’s R120 amp is switchable and also can use PX4 as output tubes.
When Pete came to my house he also brought two other amplifiers that he wanted me to listen to. To be honest I was less excited about those two amps as they used transmitter tubes, not audio transmitter tubes like the 211/VT-4-C or 845, but radar and radio-frequency type transmitting tubes. And even worst these amps make use of feedback in their design. Boy was I in for a surprise. As they say, never judge a book by its cover. See not only does Pete know about how to properly implement electrical feedback, Pete knows a lot about distortions. Pete knows about odd and even harmonics and how to adjust them to taste. Pete can pump up the 2nd order distortion to sweeten the sound and produce that euphoric magical sound many of us crave. Pete’s amps have phenomenal low distortion for tube amps. I strongly encourage anyone interested, to read Pete’s white paper and PowerPoint presentation on audio distortions. Not all distortions are the same and different distortions have different implications. Pete also implements extremely large & heavy oversized output transformers on his amp builds which result in superb bass, both in terms of texture and extension.
One of the things that Pete and I both share is our interest in rare and exotic tubes. Pete and I are both interested in amps and preamps built around the less well known or used US and European tubes. I like to thank Pete for further opening my mind to the expert and judicious use of negative feedback, other operating modes and other circuit topologies other than strictly triode. There is potential for pearls and other hidden treasures beneath every unturned stone. This experience with listening to Pete’s amps has reminded me not to limit my explorations as you just never know what might be found and what great discoveries await. Just when you think you have experienced it all, you discover that there’s more to learn. And that’s exciting!
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