Articles for Audiophiles by Steve Deckert
AUDIO PAPER #001
The first dozen amps being made
A SINGLE ENDED TUBE AMP FOR THE MASSES
by Steve Deckert
This is an original design log that was written during the development of the
Original Zen Triode Amplifier
High Fidelity Engineering (Decware) has a clear focus that revolves around preserving
the forgotten past of hi-fi in the 1960s before it took a major step backwards from the perspective of sound quality. By that I mean that since the invention of non-discrete IC based solid-state receivers, overall sound quality has declined when compared to the older tube counterparts. Believing this gets harder and harder with each generation.
Kids don't know what records are, and they think tubes are light bulbs. And quite frankly, it is completely impossible to relate to the kind of sound quality I'm talking about unless you've been exposed to it. Kind of like a man trying to imagine what it must be like to be pregnant and give birth, something he'll never know... at least not in this lifetime.
If you're the average person with a stereo - even a fancy new surround-sound stereo then you enjoy the company of approximately 98% of all the people with stereos... and I'm sorry to say that presenting this amplifier in a way that you can grasp (because it goes against everything you know) may be no less complicated than a pregnant man.
The passion behind this idea for me comes from the desire to expose the common man owning the common stereo - to the magic of triodes, with a secondary objective of messing with the common audiophile who believes specifications are the 11th commandment. Someone should have done this long ago, but because of the unorthodox thinking required to pull off such a feat, I don't suppose other companies wanted to take the risk. For example, if I tried to market a 6 watt amplifier with around
10% distortion who would take it seriously?
An entry level " audiophile " amplifier that would be affordable to the masses has been my dream for many years now. To find a way to make it affordable and make it appeal to the average person is obviously the difficult part. The passion to do so comes from past personal frustrations of not being able to afford what I want and not being able to enjoy what I have because I've heard what I want! (been there haven't ya!) I can assure you most of us have a hard time justifying the crazy amount of money required to obtain a true high-fidelity system.
The general perception of an audio system to the masses is pretty much anything you could find at a " digital ready " electronics supermarket. Well guess what... the masses all have ears as good as any audiophile and the ability to appreciate the same things that result from high end listening. Those who've never been exposed to three-dimensional high fidelity can hardly be chastised for not appreciating the difference between the two, or for not being aware that there is a profound difference.
The science of sound and harmonic resonance is far and away the most complex and least understood science on earth, in my opinion. I would say that the monumental joint effort of all the people, and the equipment required to send up an Apollo mission would be simpler than building a perfect playback system. It takes significant effort in design and a significant quality in parts to achieve good sound. It should be pointed out that the HIGH-END audio market is oppressed with the monumental and expensive task of improving the high-fidelity playback system we commonly refer to as the " stereo " and that is why a respectable stereo system costs between 15 and $30,000.00 Gee, that's about the price of an automobile!
My objective with this design is to get the absolute highest quality… harmonically in-tact sound in the hands of the wanna be audiophiles. My research and experience over the years has taught me that tube circuits are the way to obtain this objective. If I were designing this on paper with specifications in mind I would have chosen solid-state circuits. I really prefer the natural sound of tubes and while I have heard some solid-state solid-state amplifiers that I could enjoy, they start at about $7500.00.
The market is SATURATED with solid-state gear, and as I said, I don't feel it is the format necessary to complete this goal.
Up until this summer, I have been building Class A1 push-pull tube amplifiers of various designs with the intention of marketing one as the entry level amplifier. The part I've been wrestling with (like all small manufacturers) is keeping the cost down and yielding terrific sound quality. Success usually seems to go to those who have achieved the correct balance of compromise (understanding of course that everything in audio is a balance of compromise).
The push-pull tube amp designs seem to be the most popular because they can be fairly inexpensive to build, have plenty of power, and sound quite good when compared to mid-fi solid state gear. I really thought the answer could be found in a push-pull design for those reasons.
This summer while playing with single ended tube amplifier designs for my own personal stereo, I stumbled into some results that forced me to take a real second look at exactly what are watts? You know you read these ads for those five watt triode amplifiers that start at around $5,000.00 and go way up from there and wonder why would anyone pay that much for such a thing if it only has a few watts?
Lets just say some enlightenment from the audio spirits came upon me, and it was enough to realize that at a normal listening level, most of the musical content can be found in the first magical watt of power. I then realized that the priority in high-fidelity reproduction should be focused on that first watt. I have been trying to truly understand this for some time now, and in particular, been trying to define in my own research the reason why solid-state watts seem less than tube watts to the ear, yet equipment measurements would indicate that they are capable of achieving the same amplitudes.
Solid-state stereo gear has a tendency to sound thin, and quickly run out of headroom (clip) when pushed. Tube amps are very different. If you compare a 40 watt tube amp with a 100 watt solid state amp or receiver, the tube amp will put more music in the room, and get louder every time. You will find that at nominal listening levels, the loudness button is needed to get the solid-state amp to sound full-bodied, yet the tube amplifier sounded warm and full with a dead flat signal. This is a great example of how " watts " are not " watts " and a prelude to a secret only the most advanced audio gurus will share, and that is that specs in audio gear mean nothing.
Why is it that a 10 watt musical instrument amplifier such as a guitar amp will in real life (and on stage) get loud enough to split your brain in half, yet it seems to take mega bucks and major stereo gear with 100's of watts to reproduce the same sound in your living room, a room that remains a fraction of the size of a live performance? Perhaps it's because everyone is going about it wrong, confusing convenience with performance.
Enough rattling on... Two weeks ago I completed prototyping the circuit for a single ended low power tube amplifier and have been listening to it ever since. The schematic is at the top of this page. At this stage I have already decided that this will be the chosen design for the project. The actual cost will decided by the cost of the output transformers. One of the main reasons single ended tube amps are so much higher in cost than their push-pull counter parts is that the output transformers are completely different. In a single ended design, the output transformer must be designed to handle the DC current at the bias point, so a special transformer must be used. It features an air gap that optimizes the coupling at low frequencies and the DC current that serves to lower the permeability of the core. Without the air gap, the iron will saturate under too little DC bias to accommodate the needs for a single ended triode. Too much gap will reduce primary inductance so that the lowest frequencies will not pass without attenuation.
All other things being equal, the output transformers (or IRON as I call it) has the final say in the resulting sound quality. When you're looking at different iron for a design, you find that the standard push-pull output transformers range in price between $75. and $400.00 ea. (per channel.) and you find the single ended output transformers range in price from $150. to 1200.00 ea. That BTW is why the single-ended stuff is so expensive.
I have a 50 watt (ea. channel) tube amplifier that I built up to a reasonably impractical extreme, and I have been using that as my personal reference piece. It powers an efficient pair of speakers in my main listening room (over 90dB) and in all honesty (with feedback off) sounds better than any other push pull amplifier I have compared it to. In fact, a version of it was my original idea for this project, and has been for years because I liked the sound so well…
My specific design goal has wavered a bit in the past months as I get ready to do this. If I am going to market a tube amp to people who have never had the joy of listening to one, and given the solid state, cranked up with the loudness on and tone controls engaged listening habits of those people, how should it sound? Do I go for power so it will stomp their past systems, or do I go for pleasure so it will reveal to them the inner levels of music? In other words, do I give them what they already have but just a lot better, or do I give them an opportunity to discover a magic in music that they are unaware of. It really gets into a psychology issue, one that I have pondered for almost 10 years now. From a business standpoint, I would make more money with the prior.
This is what happened... to completely solidify the decision. My new little single ended amplifier will run in either Pentode or Triode mode. In Pentode it benches 5.7 watts, and in Triode, it does 1.8 watts RMS pure class A per channel. Because of the front end, and additional gain stage in the design it is possible to get louder than you could ever believe is possible with 5.7 watts. Anyway, ever since I switched the little guy over to triode mode, I have not had any desire to switch it back. It is the most natural real sound I have ever heard in this house. And the eerie thing is that it achieves a nominal listening level high enough to be exactly the same listening level I have been accustomed to. That’s 1.8 watts Vs. 50 watts which is the same as a hundred watts or more in a solid-state receiver. The enormous improvement in quality has made this new little amp my full time personal listening amp. My good ol’ favorite just got bumped. As for the psychology issue, I will be going for the magic.
In my observations over the years the reason people turn the volume up to the levels they do, is to gain the effect of physically feeling the music. This effect is the motivating reason for turning it on, and this effect is the ONLY effect that the quality of equipment has to offer so it's no wonder. Once you have spent an evening with premium gear like this little triode amp, you find that the physical effect you were accustomed to happens sooner and at lower volumes because the even order harmonics are in-tact and free of odd order harmonics found in solid-state circuits. Then the big one hits you, another more profound EFFECT happens in addition to the physical effect -- emotional effect. So you have one that strokes your body, and one that caresses your inner self adding a new found joy to the experience of listening to your stereo.
Having my strongest talent in speaker design I have thought long and hard about the statement: "Your speakers have the most effect on how your stereo will sound - replacing your speakers first gets the most improvement." Being a speaker designer the temptation to accept that has always been strong, however I have been slowly and consistently disproving that to myself year after year.
It is my opinion that the amplifier makes the most difference in the sound of your stereo and then your other electronics. I can safely say that your speakers are probably the least contributors to the sound rather than the most if your listening to good tube gear. If you gave me a choice of a good tube amp and a pair of Bose speakers or a mid fi solid state amp and a $24000.00 pair of speakers, I would choose the Bose and the tube amp because it would sound better.