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Thread: Comparing the Nonlinearity of a Triode and a Bipolar Junction Transistor

  1. #36
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    Where did that even and low order harmonic thing come from?
    If you take a bottom E on your git and call it 82 Hz and look at the harmonic distortion products. Hz values below are rounded a bit.


    1 - E Fundamental = 82 Hz
    X2 - 164 Hz is an E an Octave Up
    X3 - 246 Hz is a B which fits an E Chord - that is it is muscially related
    X4 - 328 Hz is another E an ocatve up again
    X5 - 410 Hz is a G# also part of an E Chord, musically related
    X6 - 492 Hz is another B
    X7 - 574Hz - 1/2 way between a C# and a D - Musically unrelated
    X8 - 656Hz - another E
    X9 - 738Hz is an F# but doesnt fit an E Chord
    X10 - 820Hz - 1/2 way between a G and a G# - Musically unrelated
    X11 - 902Hz - Halfway bwtween a A and an A# - Musically unrelated

    The first 6 harmonics are musically related.
    Those musically un-related harmonic products are called "Quint" and you don't want them produced.
    So avoid 7th, 9th, 10th, 11th and higher harmonics.

    It is the higher odd order ones which sound objectionable.

    Cheers,
    Ian
    soundmasterg, pdf64 and tubeswell like this.

  2. #37
    Senior Member Malcolm Irving's Avatar
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    Modern music uses the ‘equal tempered scale’. This means that all octaves are exact, while all other intervals are a bit ‘out’ from the harmonic series. The scale is listed here:

    https://pages.mtu.edu/~suits/notefreqs.html

    For example, E2 is 82.41 Hz and its 3rd harmonic is 247.23 while the nearest note on the scale is a B which is 246.94. Obviously, that is pretty close. But for higher harmonics the situation gets worse, e.g. the 5th harmonic is 412.05 while the G# on the scale is 415.3
    pdf64 and Jazz P Bass like this.

  3. #38
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    I think that a key difference between tube and ss stages is that the tube stage has significant distortion even below the clipping level, especially if the level is so high that clipping occurs during part of the guitar waveform. BJT has little distortion below clipping because, as has been shown here, the transconductance is so high that feedback (within a stage, around several, or both) must be used to control the gain. It usually is used in JFET circuits as well, but it appears that it could be avoided with the right design.

    The sound of a signal is a result of the harmonic content. If a stage is used near clipping, or especially above clipping part of the time, then the tone should be a function of the harmonics produced (below clipping). This would mean that tubes and ss should sound different even if you make the clipping responses similar.

  4. #39
    Supporting Member loudthud's Avatar
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    Consider the various tube/solid state hybrid offerings. A 12AX7 front end on a bass amp is somewhat common. It sweetens the sound but being at the beginning of the signal chain doesn't contribute much to hard clipping. The only guitar amp I can think of with a tube front end was something called a Legend(?) from the 80's. Never played or worked on one, I think it had two 12AX7s.

    Then there is MusicMan. First version had a full tube power amp with opamp preamp. Didn't sound horrible but a little on the cold side. Second version got rid of the tube phase inverter. Not an upgrade in my opinion. A little colder sounding. Final version kept the same power amp but added a tube distortion generator. That made the amp somewhat usable, better distorted tones available. When overdriven the opamp preamp generates mostly odd order harmonics. The tube phase inverter (1st gen) might have generated some even order harmonics if it was driven hard enough. The distortion generator tube (3rd gen) also contributed some even order harmonics. None of these really sounded like an all tube amp under all conditions. Nobody is building clones of these amps.
    Justin Thomas likes this.
    WARNING! Musical Instrument amplifiers contain lethal voltages and can retain them even when unplugged. Refer service to qualified personel.

  5. #40
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    Had a Legend for a while, 3x12AX7. Played several MusicMans, currently trying to unload a Peavey Deuce VT. All of these fall short compared to my Fenders. The Legend I consider different from the "tube preamp" hybrids of today, because they just stick a single preamp tube in with SS for the rest. The Super Champ XD I find "passable" at best, when put up against a real Champ with a couple pedals - you just can't dial the digital out, and I tried lots of speakers.

    Even for bass I prefer an all-tube amp, and more so in the power amp. I tried a Fender TV Bassman a few years back, the top-shelf one. Putting that $1300 hybrid against that crusty old Bassman 100 in the corner for $400, no comparison.

    And even my little Spitfire clone powering a 4x10 homemade crap-speaker column that my buddy got for $20 on CL being fed by my friend singing into an SM-57 elicited this response from our dobro player when our singer asked me to turn up his vocals a bit: "Oh, hey - I didn't even notice you were singing through a Mic. I just thought you were singing loud!"

    I support tubes for pretty much everything... it may not be 20-20k, but it's warmer and easier on the ears to me.

    Justin
    "Are you practicing in the lobby of the municipal library? It's still a guitar amp and it SHOULD make some noise (!!!)" - Chuck H. -
    "When receiving a shock I emit a strange loud high pitched girlish squeak." - Alex R -
    "All I ever managed to do with that amp was... kill small rodents within a 50 yard radius of my practice building." - Tone Meister -

  6. #41
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    Quote Originally Posted by loudthud View Post
    Consider the various tube/solid state hybrid offerings. A 12AX7 front end on a bass amp is somewhat common. It sweetens the sound but being at the beginning of the signal chain doesn't contribute much to hard clipping. The only guitar amp I can think of with a tube front end was something called a Legend(?) from the 80's. Never played or worked on one, I think it had two 12AX7s.

    Then there is MusicMan. First version had a full tube power amp with opamp preamp. Didn't sound horrible but a little on the cold side. Second version got rid of the tube phase inverter. Not an upgrade in my opinion. A little colder sounding. Final version kept the same power amp but added a tube distortion generator. That made the amp somewhat usable, better distorted tones available. When overdriven the opamp preamp generates mostly odd order harmonics. The tube phase inverter (1st gen) might have generated some even order harmonics if it was driven hard enough. The distortion generator tube (3rd gen) also contributed some even order harmonics. None of these really sounded like an all tube amp under all conditions. Nobody is building clones of these amps.
    There were also the Vox hybrid amps from the 60's, the UL 7120/4120 and 730/430. They were and are very rare amps but that is the sound of Revolver from the Beatles and that's a pretty good sound. A little more noticeably harsh then the all tube stuff but better than an all solid state amp.

    I wonder if those new vacuum channel transistors might have any audio applications down the road? The last update I saw from them was back in April and they had posted curves that looked a lot like a triode.

    Greg

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