Poddwatt: Tube Amp With Mp3 In Mind


[Bruce] has designed a push-pull tube amp that has enough gain to connect to a portable audio player. The design is closely related to his OddWatt offering from a few years ago. The new amp has many redesigned circuits and the new hardware choices drop the price tag of the parts by about $50.

This little wonder pumps out 5-7 watts and [Bruce] is please with the end result. It doesn’t put out quite as much low-end as the KT88 amp we saw last year, but compared to some other iPod speaker solutions this provides stellar audio.

41 thoughts on “Poddwatt: Tube Amp With Mp3 In Mind

  1. Can someone explain to me why audiophiles that build these amps are totally cool with 0.5% distortions, when they could get more power, efficiency, and less distortion out of a single, cheaper IC?

    I just dont understand this tube culture.

  2. This is just a guess, but I believe that the distortion is of the agreeable type. Every tube amp owner I’ve know spoke highly of the “warm” sound that was produced. They aren’t “flat” response.

  3. Tube amps are the best cause there is nothing digital about music so therefore less digital the better. Im sorry that audio noobs dont get it. I have everything from the asus stx, creative fatal1ty and whatever else. Nothing comes close to a tube amp and pre. Sorry.

  4. I’m just saying this would make more sense if it was for a purely analog system, like a phonograph or audio tape. Pumping digitally-represented tunage through an analog amp seems like tubes for tubes’ sake at best, an exercise in futility at worst.

  5. I completely agree with a previous comment that feeding a lossy audio file through a DAC then into a tube amp is ridiculous. The only place tube amps make sense is with analog recordings. Tube amps do sound great with string instruments though, especially miked acoustic ones.

  6. I sit here with my HifiMan EF2 ($200) and Audio-Technica ATH700 ($140) connected to my PC and I’m enjoying great audio while I work. I switched from a Creative X-Fi and I have to say, unless you listened to the difference, you would not get it.
    The EF2 (available at head-direct dot com) is connected to my PC via USB and has no audio driver at all on my system so the MP3, WMA or better yet, FLAC files play on media monkey and out my USB as digital and are decoded on a Digital to Analg converter (DAC) inside the little amp. The DAC alone adds great value as it is much better quality than Creative uses in their process and it does not pick up system noise from being inside the PC. Then the sound goes through two vaccuum tubes and it amplified a bit and naturally picks up that warmth of sound that everyone who listens to tubes, enhjoys. Then it is boosted by an output section whhich gets it to the level and impedence of my headphones. So for under $400 I have sound which is in a lot of ways as easy on the ears and as rich and full in depth and soundstage as an expensive home system with regular speakers.
    If you get a chance, go visit head-fi DOT org and see all the different equipment the members have and talk about. It is an enjoyable site to learn about headphones and amps.

  7. let me tall you about experiment that many dome including myself, get the cheapest Chinese OPamp and connect it by data sheet schematics, HIDE IT, take a tube and connect only filament so it looks like working. Then ask audiofile what he think about sound quality, record all about warmth soul and etc on dictaphone than tell and show him truth by removing tube. I had busted audiophile in my university like this, and many have done same to theirs annoying buddies.
    And let me tell you about warmth, it nothing more than high frequencies you loses, the low frequency sound warmer and heavier/deeper than hi frequency so if you lose high frequency that what you get

  8. Being an audiophile is different to everybody. It’s all about getting exactly the sound you want. If you want precisely the sound that the producer and creator intended, then that’s what you should pursue. Same for if you are looking for something that does not have perfectly flat frequency response, but just that little something that works for you.

    If it is not your deal, then do your own thing.

    Great project anyhow, new technology is great, but the old stuff can be just as fun!

  9. Tube have distortion in the even harmonics while op-amp have it in the odd harmonics. Odd harmonics are those making a square wave, so they are ‘unpleasant’ to the ear. Even harmonics, on the other end, make for a softer sound. Tube also require less feedback, which is good.
    On the other end, using a tube amp to listen to digitally butchered music (aka MP3) doesn’t make much sense to me…

  10. I’m going to build a “tube” amp like this but put a cheap IC amp inside with a LPF to cut out the highs. It’ll sound the same to these tube-stricken “Audiophiles”, nice and “warm” – at least as long as it glows.

  11. I wasn’t assuming this is an audiophile thing. I figure it’s just a funny hack. Nobody will seriously use this, just like nobody will seriously use the toilet twitterer.

    If it were for music production, like an amp for a guitar, it’s well-known that tube distortion is generally better-liked than transistor distortion. There’s a reason why a lot of effort has gone into making transistor amps that model tube properties, with varying degrees of success.

    1. Actually he nailed it pretty well .
      Even harmonics aka – 2 , 4 , 6 ect is the same type of harmonics produced by
      acoustic instruments example acoustic guitar .
      If acoustic guitar ( or other instruments likevise ) had Uneven distortion as highest then
      they will sound harch and NOT good .
      The even harmonics distrotion is the dominating distortion source in tubes , that
      make tubes sound much more plesent and warm even with higher distortion than
      the solid state do .

      Solid state amplifiers on the other hand have most Un even harmonics distortion due
      to the charecteristics of the transistors , that mean they also have to be driven with as
      little distortion as possible to not sound harch ( that typically unplesant distortion typically
      in higher frequencies )

      If you drive the solid state with same amount of distortion as a tube amp then it
      WILL sound hard and harch and you easy get hearing fatigue after too long time listen .
      ( some type of mosfet transistors produce more even than uneven harmonics distortion
      and that bring them closer to tube sound )

      Thats why I ONLY use mosfet in my solid state amps .
      I prefer tube amps but due to my travels with my studion trough the past years I
      only have tube guitar amps .
      But when I have a better place to settle down and rebuild my studio then I will again build
      tube amplifiers , after all they sound great and you can build them with very low distortion .

      Another thing is when driven hard then a solidstate have a much more hard clipping and
      both sound really bad when it happen and most likely will blow speaker parts ( typically tweeters )
      The tube amp on the other hand will sound ‘ softer ‘ when clippind due to the fully magnetic field in the
      transformers and speakers better survive it because it by nature work a little like compression .

      But I disagree with him about mpg3 … all digital sources can benefit from tubes just like analogue.
      When thats said … true analogue sound better and more ‘ natural ‘ than digital .
      You can’t chop up a signal into steps and then take those steps and truely recreate the pure analogue
      curve . Thats why thy try to solve this by using different types of filters after the d/a converter .
      there will always be something ‘ missing ‘
      but its close enough that the average person can not hear the difference …

      I CAN HEAR THE DIFFERENCE – but my hearing is NOT average .

  12. @ riazap–
    You are not being fair to @Serge747. He is essentially correct. The “warmth” attributed to vacuum tube amplifiers and audio gear stems from the type of distortion they tend to introduce. If you know anything about music theory, you know that doubling the frequency of a tone brings you up one musical octave. So, for example, if your fundamental is 440 Hz (an “A”), and distorion causes even harmonic content at 880 Hz, it still sounds good, because the harmonic is pleasantly and musically-related to the fundamental. This is true for all of the even harmonics.

    Tubes are not the only pieces of audio equipment that exhibit this tendency. For years, studio engineers ran their tape decks “hot,” purposefully recording above the recommended 0db level so as to introduce even harmonics that “fattened” the sound.

    Solid state gear tends to produce odd harmonics. These harmonics are *not* musically related to the fundamental, but are instead dissonant. Distortion with odd harmonic content tends to sound harsh.

    An exception to this is FET circuitry. FETs are voltage-controlled devices, as are tubes, and if they’re set up right, and driven into distortion the right way, they can have remarkably tube-like audio qualities.

    Another thing that @Serge747 touched on is the idea of feedback. Modern amp design usually involves building an amplifier with huge amounts of gain, then taming that gain with negative feedback. The benefit, among other things, is improved bandwidth. Vintage tube audio tended not to have a great deal of negative feedback. If you feed both types of amplifiers with percussive, narrow-pulse audio (as might be found in a snare crack, or the ting of a ride cymbal) audible differences appear due to the time constants associated with the feedback network in the solid state amp.

    The bottom line is this: It seems to me that a lot of what passes for “audiophile quality” equipment and accessories really boils down to an “I-have-a-bigger-d*ck-than-you” type argument. In other words, it’s BS. I’m not convinced that a $10,000 amplifier is 100 times better than a $100 amplifier, and the way most people use them, you would never hear the difference.

    However, that doesn’t change the fact that there *is* a difference between the way tubes and solid state devices process sound, and there are legit reasons why one would purposefully choose tubes.

    One final comment. There is no such thing as “reproducing” music. Why? Because no snare drum in the real world sounds like the snare drums you hear in pop music. Those drums are gated, filtered, and usually processed with one or more types of reverb. A real electric guitar doesn’t “sound” like much of anything at all. In fact, an electric guitar is really a kind of analog synth, because it uses the vibration of steel wires in a magnetic field to produce disturbances in a coil of wire. The signal that comes out of that is amplified, compressed, gated, clipped, and processed with chorus, delays, reverb, and who knows what else. Even the singing you hear in a recording is *not* how a real-life singer sounds, unless you are used to having people sing full-blast within 4 inches of your ear.

    My point is that music, from the moment of creation, is really a *subjective* expression. When that recording is later played on your ipod, a car stereo, a boom box, or whatever, it is further altered and modified, intentionally or not, by your space, your equipment, and your settings.

    The ambiance of the space between your ear-buds and your ear drum, or in the passenger compartment of your Nissan, is not the same as the ambiance in Carnegie Hall. Even if it was, *nobody* can seem to keep their hands off the bass and treble controls. Then there are those numb-nuts who drive down the street with the volume so high that their own eardrums are being driven into distortion. Accurate “reproduction” my *ss!

    Music, from creation to delivery is entirely subjective in nature.

  13. @samurai

    Power and efficiency are irrelevant at experiencing music. Some people pay insane amounts of money to listen 1kW+ power amplifiers on 80dB/W or less efficient loudspeakers. Other people make 3-5W power amplifiers and use them on 90dB/W or more efficient loudspeakers. Truth is the human ears can’t listen music louder more than 85dB for long periods of time without suffering permanent damage.

    Distortion level (THD) is number that describes level (amount) of distortion, nothing more. It does not describe how brain perceives distortion, so it is more a number for the magazines than guidance for the pleasure.

    Hearing is believing, and goes double blind-folded for audio.

  14. FLAC still goes through a DAC. I still say if you want the full sonic spectrum, you need a completely analog system. FLAC is good, but it’s not analog. Anyone who tells you the amplifier (transitor or tubes) is the most important aspect of maintaining sound quality is full of crap.

  15. I dare you to find a single person that can tell the difference between a FLAC rip done from a mint vinyl record, and the vinyl record itself, given the exact same full-analog setup (after the point of phono-preamping or flac->dac).

    I guarantee any properly-sized trial will yield no better than random (.50/.50) at picking out the source of audio.

  16. I’m going to have to come back later on to us fresh eyes to understand this design, for some reason it’s confusing the hell out of me. Certainly the constructing a duplicate should be straight forward for anyone experianced with constructing electronic project by using a schematic. The final result of this construction looks fine.

    I can understand those who use hollow state before solid state came into being put off by the sound of solid state that doesn’t contain the distortion that the tube equipment has. I do suspect a learned snobbish element on the young bucks cut their teeth on solid state, then again HiFi has has a tinge of snobbery from the beginning. Can’t for get some do find the distortion added by electric guitars agreeable. I too wonder to what degree of the desired sound of tube amplifiers is lost when playing mp3 files. At the very beginning of the digital recording process digital is only an approximation of what any human ears at the scene may be hearing. Will the person listen to the playback of the recording on their own equipment know that something might be missing? Probably not, most may not be able to note any difference when given an opportunity to listen to pure analog recording of the same event. May not worth the time noting the differences, much less arguing about them. Last one at the pub buys the beer.

  17. @ RandomPrecision I believe person named Carver was acknowledge with duplicating the sound of tube audio amplifiers with transistor amplifiers. He’s know dummy, where there are few who want to buy transistor amps that sound like tube amps he manufactures high end expensive tube amps as well. Used to anyway it’s been a long time since I pay close attention to the audio entertainment world. My 30 year old Radio Shack system still works well.

  18. I came up with a rather simple rule, many years ago, after working in a high-end stereo shop for a while and having people come in who basically wanted to buy equipment that distorted music in some particular way that they claimed to ‘like.’

    Whether it was JBL speakers with the once-popular ‘west coast sound’ (basically pumped-up midrange) or Empire phono cartridges with certain definite frequency limitations, or even people who wanted to use equalizers to minimize trumpets or whatever, my rule came to be “get equipment that reproduces as accurately as you can afford, and if you don’t like what you hear, then you need to listen to different music.”

  19. I agree with kedavis. (And I’m also late to the audiophile blaming)

    The storage format has absolutely nothing to do with the distortion of the amplifier, so yes, it’s perfectly valid to use a tube amp with crappy mp3s, there’s still a difference.
    A polished turd rolled in glitter is still better than a polished turd without glitter.

    Lossless storage of AF waveforms is lossless storage of AF waveforms, it has been scientifically demonstrated that your ears can’t tell the difference between lossless codecs at 24/48 and perfect analog signals, and the few differences there are, actually make analog worse.

    I’m an audio engineer (with actual engineering and audiology knowledge, not “corner bar sound dude”), and here on the production side of things, the sound of music _is_ treated objectively. We calibrate the monitors (SPL-linearized speakers with room correction on an already neutral room) to the operator’s ears and then apply the standard weighting curve, so as to replace the error in the operator’s ears with an averaged error, which makes the sound of music (when reproduced through perfectly linear equipment), for every person, as close as realistically possible to what he hears. The artist is trying to communicate a message, after all, and we want listeners to get the same message the artist composed, wether it’s good or bad.

    So trust me, if music was really better with some particular sound or coloration or whatever, the artist would have already applied it in production. In fact, most mastering engineers run the music through tube amps. Some things can give the illusion of sounding better, such as compression, or happy-face EQ, but it’s just an illusion that will end up getting tiresome, and at the end, if you don’t like how it sounds on the equipment that only tells the truth, then you don’t really like the artist – just as kedavis said, you need to listen to different music.

    The truth is the truth, regardless of if you’re happy with it or not. Distorting your music to be happy with it is like using drugs to fly, instead of building an airplane.

    Hope nobody minds the long rant, this is an outdated thread after all :-)

  20. Thanks for the backup, Whoever.

    It was also said at the time I worked at the audio shop that many recordings were being mixed using 6×9 car speakers since that’s how they wound up being heard by many people. I don’t know if that was really true or not, but either way it helps to illustrate the point I was making before. Especially back then when personalized distortion seemed to be the rage.

    If you really don’t like trumpets, don’t buy Herb Alpert albums plus an expensive equalizer.

    Another guy at that shop used to record tapes for his car, and he would boost the recording level on the right side and slightly lower it on the left, to make the ‘stereo’ effect sound more ‘balanced’ from his position in the driver’s seat while keeping the balance control on his car stereo at the middle, rather than record them ‘straight’ and then make whatever adjustments he wanted in the car. Same kind of thing. And it also made his tapes ‘wrong’ for him to play at home, or even in other people’s car for that matter. Plus that it would sound ‘wrong’ to anyone/everyone else in the car with him.

    There was also another place – not the one I worked at – that sold Magnepan speakers among other brands. I think they sold the same set of Magnepan speakers over and over, because someone would hear them in the store and think ‘wow, that’s really something!’ but after living with them and listening to them for extended periods of time they traded them for something else after they realized that ‘really something!’ wasn’t the same as GOOD.

    And when I went to OSU, the Bookstore had a perpetual “truckload sale” on Pioneer going, each year a few kids would blow a bunch of their own money or financial aid money on some big setup that would rattle their windows for a few days but then they didn’t seem to want to hear it any more. And it wasn’t because they were busy studying.

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