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really? well, I thought TIM is a misguided description for slew rate limiting and attendant phase shifts which feedback isn’t the best cure of. Perhaps in some perverse circumstances more feedback reduces the ‘error’ signal sent through the amp sufficiently to avoid slew rate limits - BUT the issue usually occurs in the error amplifier itself where fbk ain’t gonna save you.
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One example of global negative feedback making things worse, is if the output transformer laminations are saturated (on either the positive swing or the negative swing; or even at low signal levels because the DC currents are badly un-balanced on a push pull output transformer).
In that case, the global negative feedback error correction signal will cause even more current to be pumped into the already saturated laminations.
Just a loosing battle.
Another example of negative feedback making things worse is if the circuit is in clipping, and either the circuit or the error correction "sticks". The slower response time causes a longer period until the amplifier recovers. Cacophony.
As I often say, if the amplifier is distorting, turn the volume down.
A lower volume with lower distortion, versus higher volume with gross distortion, is your choice for Hi Fi playback.
If you need more sound power for Hi Fi, build a more powerful amplifier, or get more efficient speakers.
For a Guitar amplifier, your choice may differ from the Hi Fi experience.
You may prefer the higher distortion.
Just my opinions.
In that case, the global negative feedback error correction signal will cause even more current to be pumped into the already saturated laminations.
Just a loosing battle.
Another example of negative feedback making things worse is if the circuit is in clipping, and either the circuit or the error correction "sticks". The slower response time causes a longer period until the amplifier recovers. Cacophony.
As I often say, if the amplifier is distorting, turn the volume down.
A lower volume with lower distortion, versus higher volume with gross distortion, is your choice for Hi Fi playback.
If you need more sound power for Hi Fi, build a more powerful amplifier, or get more efficient speakers.
For a Guitar amplifier, your choice may differ from the Hi Fi experience.
You may prefer the higher distortion.
Just my opinions.
There's a summary here, more detail in article linked to at the bottom Does negative feedback cause TIM? - PURIFI
Everything is so relative in electronics, here it says that TIM is caused by feedback .... and that is why tube amps have little TIM because they use little (tetrodes, pentodes) or no feedback (triodes) .....
?Realmente las valvulas suenan mejor? - Parte 2 - Arteaudio
Transient intermodulation distortion (TIM distortion)
" Any electronic component has a limited speed of response. When an electrical signal is introduced into a circuit, a delay is observed at the output. If this signal is fed back to the input, it is observed that the signals do not coincide. This creates a transient intermodulation distortion (TIM) made up of high-order harmonics. The problem is made worse by chaining feedback stages and by including global feedback. Of course the harmonic distortion (THD) decreases, but on the contrary the high order harmonics increase. Low order harmonics (2nd and 3rd) are hardly noticeable. However, it has been seen how the second harmonic adds richness and warmth to the music. The third is often frowned upon for being an odd harmonic. However, it is also a very present harmonic in nature. Like the second, it adds richness and spatiality to the music, although to a lesser extent. To understand it, one only has to turn to music theory: the third harmonic is the fifth (dominant) degree of the fundamental frequency. Without going any further, there are musical instruments that have the 3rd as their most relevant harmonic, such as the clarinet or the flute. Magnetic tape systems produce a much higher amount of 3rd harmonic distortion than 2nd harmonic, and no one would say they sound bad. However, the perception is getting worse as we increase the order of the harmonics. This is especially problematic for odd harmonics from the 7th. Returning to music theory, the 7th would be a major seventh, the 9th a major second and the 11th an augmented fourth. These notes would be out of tune with the root. In general, all high-order harmonics have a much greater impact on our perception than low-order ones. Even being attenuated by many orders of magnitude. These add noise and confusion to the mix, mask details, and increase listening fatigue. Tube amplifiers, in addition to having lower feedback rates, also have a faster response than transistor amplifiers. This is due to the good slew-rate or signal propagation characteristics in the valves. As a consequence TIM distortion is further reduced. In conclusion, we see how transistor amplifiers have lower THD (low-order harmonic) rates but a high content of higher-order harmonics. This has a great impact on subjective perception. The sound becomes sterile, fuzzy and in the long run increases fatigue. Of course, you don't have to be dogmatic or generalize with this. There are high-end transistor amplifiers that take all of this into account. Much progress has been made in the design, achieving very tube-like specifications, as well as greater power and better bass response. However, in more modest ranges all these problems are still seen and without a doubt the difference in sound is very noticeable. "
?Realmente las valvulas suenan mejor? - Parte 2 - Arteaudio
Transient intermodulation distortion (TIM distortion)
" Any electronic component has a limited speed of response. When an electrical signal is introduced into a circuit, a delay is observed at the output. If this signal is fed back to the input, it is observed that the signals do not coincide. This creates a transient intermodulation distortion (TIM) made up of high-order harmonics. The problem is made worse by chaining feedback stages and by including global feedback. Of course the harmonic distortion (THD) decreases, but on the contrary the high order harmonics increase. Low order harmonics (2nd and 3rd) are hardly noticeable. However, it has been seen how the second harmonic adds richness and warmth to the music. The third is often frowned upon for being an odd harmonic. However, it is also a very present harmonic in nature. Like the second, it adds richness and spatiality to the music, although to a lesser extent. To understand it, one only has to turn to music theory: the third harmonic is the fifth (dominant) degree of the fundamental frequency. Without going any further, there are musical instruments that have the 3rd as their most relevant harmonic, such as the clarinet or the flute. Magnetic tape systems produce a much higher amount of 3rd harmonic distortion than 2nd harmonic, and no one would say they sound bad. However, the perception is getting worse as we increase the order of the harmonics. This is especially problematic for odd harmonics from the 7th. Returning to music theory, the 7th would be a major seventh, the 9th a major second and the 11th an augmented fourth. These notes would be out of tune with the root. In general, all high-order harmonics have a much greater impact on our perception than low-order ones. Even being attenuated by many orders of magnitude. These add noise and confusion to the mix, mask details, and increase listening fatigue. Tube amplifiers, in addition to having lower feedback rates, also have a faster response than transistor amplifiers. This is due to the good slew-rate or signal propagation characteristics in the valves. As a consequence TIM distortion is further reduced. In conclusion, we see how transistor amplifiers have lower THD (low-order harmonic) rates but a high content of higher-order harmonics. This has a great impact on subjective perception. The sound becomes sterile, fuzzy and in the long run increases fatigue. Of course, you don't have to be dogmatic or generalize with this. There are high-end transistor amplifiers that take all of this into account. Much progress has been made in the design, achieving very tube-like specifications, as well as greater power and better bass response. However, in more modest ranges all these problems are still seen and without a doubt the difference in sound is very noticeable. "
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And here we have (to add to the confusion .....) why in the PS some designs (and especially by Diy's audiophiles) are still using a rectifier valve instead of diodes.
?Realmente las valvulas suenan mejor? - Parte 2 - Arteaudio
" Power supply
Finally, we must highlight the impact of the power supply on 100% tube amplifiers. That is, the amplifiers that have a rectifier valve in the power supply.
The function of this valve is to convert the alternating current from the power supply transformer into direct current, which is the current at which the amplifier will work. In solid state designs, this valve is replaced by infinitely smaller, cheaper, faster and more stable rectifier diodes. Solid state sources are much better regulated and provide large current spikes without flinching. The drawbacks of tube grinders are once again well regarded by guitarists. The large internal impedance of these valves causes a voltage drop that changes with current demands. That is, in the event of a strong attack from the strings, the voltage of the power supply will drop. How does this affect the sound? After the voltage drop, and as the note sound fades, the source voltage is restored. This increase in turn causes an increase in the gain of the amplifier, and therefore the volume. As a consequence the note is held for longer. I mean, we just increased the sustain. We can say that the rectifier valve has the effect of a natural compressor pedal."
?Realmente las valvulas suenan mejor? - Parte 2 - Arteaudio
" Power supply
Finally, we must highlight the impact of the power supply on 100% tube amplifiers. That is, the amplifiers that have a rectifier valve in the power supply.
The function of this valve is to convert the alternating current from the power supply transformer into direct current, which is the current at which the amplifier will work. In solid state designs, this valve is replaced by infinitely smaller, cheaper, faster and more stable rectifier diodes. Solid state sources are much better regulated and provide large current spikes without flinching. The drawbacks of tube grinders are once again well regarded by guitarists. The large internal impedance of these valves causes a voltage drop that changes with current demands. That is, in the event of a strong attack from the strings, the voltage of the power supply will drop. How does this affect the sound? After the voltage drop, and as the note sound fades, the source voltage is restored. This increase in turn causes an increase in the gain of the amplifier, and therefore the volume. As a consequence the note is held for longer. I mean, we just increased the sustain. We can say that the rectifier valve has the effect of a natural compressor pedal."
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