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The Tube Amp Book Aspen Pittman Pdf Temp
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\"The \"fizziness\" of clipping is determined by how \"hard\" the clipping is. There are three primary places that clipping occurs in a tube amp: the preamp tubes, the phase inverter and the power tube plates. Preamp tube clipping can range from soft to hard depending upon the design. Phase inverter (PI) clipping, which is actually the power tubes grids clipping, is very hard. Power tube clipping ranges from soft to hard depending upon the amount of negative feedback in the power amp. Preamp tube clipping is comprised of cutoff, which is soft, plus saturation, which tends to be hard. Actual saturation rarely occurs because most preamp stages are designed such that the grid clips before the tube enters saturation. Grid clipping is hard. Local negative feedback is used in the form of cathode caps to shape the response of a preamp stage. If there is no cathode cap then there is negative feedback at all frequencies which increases the hardness of the clipping. The last stage usually dominates the clipping. Some amps have no cathode cap on this stage, e.g. JCM800, and therefore have hard preamp clipping. The Axe-Fx II does not expose the negative feedback settings for the preamp stages to the user, these are hard-coded. Reducing the Triode Hardness parameter will soften the clipping more-or-less depending upon the particular amp model. In a typical tube amp the power tubes start to clip right about the same time the PI/grid clipping occurs. This is intentional so as to get the most power from the tubes. However some amps are intentionally mismatched as the designer's intent was to get more power tube clipping than PI clipping (i.e. Trainwrecks). The Transformer Match parameter adjusts the relative onset of power tube vs. PI/grid clipping. Lower values will cause the PI/grid clipping to occur before power tube clipping. Higher values will cause the power tubes to clip before the PI. Note that the power tube plates follow the impedance curve of the speaker so while the PI/grid may be designed to start clipping first, this only occurs in the midrange. At frequencies above 1 kHz or so the power tubes clip first since the voltage on the plates increases as a function of the speaker impedance. The first thing to clip tends to dominate as once you enter clipping the effect of clipping elsewhere is diminished. Negative feedback around the power amp attempts to linearize the transfer function. The more negative feedback the more the power amp is linearized. However this also causes the clipping to become harder. A power amp with no negative feedback will go into clipping softly. As you increase the negative feedback the \"knee\" gets sharper. The Damping parameter is the negative feedback control. Higher values give more feedback and harder clipping. Presence and Depth work by modifying the negative feedback. As you increase them the feedback gets less so by turning up the Presence you get softer clipping in the power amp. Therefore to decrease the hardness of the power amp clipping: reduce Damping, increase Presence, increase Transformer Match. To reduce preamp clipping hardness reduce Triode Hardness. There is no parameter exposed to adjust the PI hardness. HOWEVER, the relative hardness of clipping is not all that audible. You have to listen closely. The IR is far more important in the final result. Some IRs let through a lot more high frequencies and therefore sound more fizzy. Furthermore overanalyzing this is inadvisable. Many amps are specifically designed to clip hard as this gives a more aggressive tone that fits better in the mix. Some amps actually attempt to increase the hardness of the clipping as much as possible by using diode clipping or using very high values of negative feedback (i.e. Modded Marshalls, Camerons, 5150 III). Listening at low levels fools your ear. Our ears are more sensitive to midrange at low listening levels. This means we hear the clipping differently than when listening at the actual level the real amp would be generating.\" [71]
\"Noise isn't modeled. All preamp tubes have separate heating elements. This is called \"indirect heating\". Directly heated cathodes are no longer used except for rectifier tubes. Regardless direct or indirect heating has no effect on the noise floor. Noise is due to the random motion of electrons in a conductor. You can't \"reject\" it. You can lower the noise floor by keeping resistor values low (since noise is proportional to resistance) and by paralleling the input triode. No modeler models noise. The dominant source of noise in any amp, whether real or virtual, is usually your guitar (or rather its pickups). A 10K ohm pickup will have -114 dBv of noise at room temperature. Modern A/D converters, when properly designed, can exceed this so the dominant source of noise is your guitar. This noise is then amplified by the amp (that's why they call them amplifiers). If the amp has, say, 60 dB of gain then that noise is now -114 + 60 = -54 dBv. Gain it up another 20 dB with the power amp and now you're at -34 which can be quite audible. The situation gets worse as you roll off the volume in your guitar as you then introduce more resistance. A typical guitar pot is 500K ohms with an audio taper. If you roll the volume pot down to 8 or so you can easily introduce another 100K of resistance into the signal path. This will increase the noise to -94 dBv which becomes -14 after amplification. Really noticeable then. Bottom line: if you have too much noise you have too much gain. Learning to play with less gain will improve your technique and the quality of your tone. Gain just masks poor technique and reduces clarity, string separation and dynamics.\" [85]
\"The preamp modeling in 6.00 is the same as 5.xx except the parameters for the default tube type (12AX7A SYL) are different. The Sylvania 12AX7A is more nonlinear than other 12AX7As which results in more dynamics but will also result in more \"background\" distortion because the waveform is being distorted even when it isn't being clipped. The JJ version is more linear which will result in a tighter tone and less background distortion but less dynamics. For 6.01 I've also added back the old 12AX7B type which is the most linear of the types and clips hard. People who play with lots of gain tend to like this as it results in tighter tone and more aggressive harmonic content. There are two primary parameters associated with our preamp tube models. \"Preamp Hardness\" determines how abrupt the tube clips when it enters the saturation region. There is another parameter that determines how nonlinear the tube is between cutoff and saturation. This is currently not exposed to the user but I've been contemplating adding it. I've also changed the default type for British amps to the ECC83 model as these amps typically were equipped with ECC83s (duh). The ECC83 was the European equivalent of the 12AX7A and tended to be a bit more linear and clip a little harder.\" [173] 1e1e36bf2d