What makes high gain amps to have higher voltage gain thus higher peak dB gain?

[R.G.]

@thinkingchicken:
Just like gain is not distortion, sustain is not gain.

Sustain comes from the net balance of energy into and out of the string, if it's real sustain. There are fake sustain methods, generally used in pedals.

Let's start with a vibrating string, and reverse the question. When you pluck a guitar string, you introduce a pulse of energy into a resonating spring and mass. The string vibrates at the resonant frequency of the spring tension and mass of the string. The reversed question is this: why does it ever >stop< vibrating?

The general answer is that each vibration loses a bit of the initial pluck's energy as sound into the air and as heat in flexing the string material, and as leaks into the supports on the ends of the string. Each flex back and forth uses up some of the energy, and eventually there is zero energy left and the vibration stops. Exactly the same explanation holds for things like why bells stop ringing and why pendulums stop swinging. How long it takes for any of these to stop ringing depends on the energy balance: how much energy gets fed into the string/bell/pendulum and how fast it bleeds out of the ringing. This is sustain, how long a note keeps ringing.

Infinite sustain requires that at least as much energy is fed back into the string/bell/pendulum as it's losing. Pendulums, as used in old-time grandfather clocks, can be fed a little "kick" each swing. This is usually done by a weight-and-pulley scheme, or a wound-up spring. In a guitar, sustain can be made "infinite" by feeding in energy acoustically, by holding the guitar up to speakers, or magnetically, using what amounts to a reverse-pickup: a pickup that uses magnetic fields to drive the string not to pick up the vibrations.

Fake infinite sustain can be done by using a modestly-advanced electronic circuit called a phase-locked-loop (PLL) which is an electronic oscillator that is made to synchronize to the frequency of a signal (in this case, the string's frequency), then can be made to hold that frequency for a long time. It won't really go forever, but is a good enough fake for guitar work. Pedals exist that can do the magnetic drive thing with special reverse pickups, and also to do the fake sustain.

Notice that gain isn't really involved, except in a very minor role. Amplifier gain is needed to drive speakers to loud enough to re-vibrate the strings acoustically. Really, this is "loud enough" rather than "enough gain". Notice that this is related to my previous note that simply increasing gain gets noisier and more prone to vibration. It's a recognized truism in electrical engineering that every circuit will oscillate if you keep adding gain. You may or may not want acoustic feedback; this is why some public address systems squeal when the volume is turned up.

Understanding this more completely requires a high-school or freshman-college course in physics, and possibly other courses.

[thinkingchicken]

@thinkingchicken:
Just like gain is not distortion, sustain is not gain.

Sustain comes from the net balance of energy into and out of the string, if it's real sustain. There are fake sustain methods, generally used in pedals.

Let's start with a vibrating string, and reverse the question. When you pluck a guitar string, you introduce a pulse of energy into a resonating spring and mass. The string vibrates at the resonant frequency of the spring tension and mass of the string. The reversed question is this: why does it ever >stop< vibrating?

The general answer is that each vibration loses a bit of the initial pluck's energy as sound into the air and as heat in flexing the string material, and as leaks into the supports on the ends of the string. Each flex back and forth uses up some of the energy, and eventually there is zero energy left and the vibration stops. Exactly the same explanation holds for things like why bells stop ringing and why pendulums stop swinging. How long it takes for any of these to stop ringing depends on the energy balance: how much energy gets fed into the string/bell/pendulum and how fast it bleeds out of the ringing. This is sustain, how long a note keeps ringing.

Infinite sustain requires that at least as much energy is fed back into the string/bell/pendulum as it's losing. Pendulums, as used in old-time grandfather clocks, can be fed a little "kick" each swing. This is usually done by a weight-and-pulley scheme, or a wound-up spring. In a guitar, sustain can be made "infinite" by feeding in energy acoustically, by holding the guitar up to speakers, or magnetically, using what amounts to a reverse-pickup: a pickup that uses magnetic fields to drive the string not to pick up the vibrations.

Fake infinite sustain can be done by using a modestly-advanced electronic circuit called a phase-locked-loop (PLL) which is an electronic oscillator that is made to synchronize to the frequency of a signal (in this case, the string's frequency), then can be made to hold that frequency for a long time. It won't really go forever, but is a good enough fake for guitar work. Pedals exist that can do the magnetic drive thing with special reverse pickups, and also to do the fake sustain.

Notice that gain isn't really involved, except in a very minor role. Amplifier gain is needed to drive speakers to loud enough to re-vibrate the strings acoustically. Really, this is "loud enough" rather than "enough gain". Notice that this is related to my previous note that simply increasing gain gets noisier and more prone to vibration. It's a recognized truism in electrical engineering that every circuit will oscillate if you keep adding gain. You may or may not want acoustic feedback; this is why some public address systems squeal when the volume is turned up.

Understanding this more completely requires a high-school or freshman-college course in physics, and possibly other courses.

Thanks, RG. Appreciate your detailed response, and of course I'll re-read it from time to time.

If the electricity in my hood was powered by a hydroelectric dam, and I keep holding my guitar in front of a loud amp to let it continue to sustain indefinitely, it will sustain as long as the hydroelectric dam keep functioning. We understand that hydroelectric dams can last for 100 years. Hmm... Amazing

Sometimes I want more gain because more gain equal to more brutal or aggressive in my opinion as someone who played metal and harsh "music". Also, like the previous poster said, higher gain will give us longer sustain but also make our tapped notes to be much louder so we don't have to tap with too much force on the frets. Thus, somehow higher gain make our instruments to be more touch-sensitive. Thanks to yours and others explanations, what are the most important for some people who like "MORE GAIN is better" are higher inherent amplification factor/gain of the amplifying component and lower power supply to give lower headroom.

[thetragichero]

Also, like the previous poster said, higher gain will give us longer sustain but also make our tapped notes to be much louder so we don't have to tap with too much force on the frets. Thus, somehow higher gain make our instruments to be more touch-sensitive.

not so fast. in your example, increased gain is bringing the lower level signal (tapping) to be around the same volume level as the higher level signal (plucked string). this is compression, which is the exact opposite of the oft-used "touch sensitive"