What’s the difference between lowering Amp Gain and

simonp54

simonp54

Experienced
lowering input to the amp either by guitar volume pot or a volume block. The other night I was using the triple crown on standard settings with a volume block in almost the off position, and it was great for being responsive... just wondering if lowering the gain would be the same or is it a different thing?
 
The difference is dramatic. I look at the input gain as somewhat the distortion or drive level. Lowering or raising the gain however alters the tone and the gain (drive). The tone gets fuller as you raise the gain and brighter as you lower it.

I think the input trim acts more so in the manner you describe with an expression pedal.
 
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If I understand your question correct, the difference is the amp gain will respond just like it would on the real amp. It is dependent on the amp circuit modelled. Lowering your guitar volume or using a volume block before is controlling the level entering the amp block which will have different results.
 
The way I understand it is:

  • Gain - how much boosting / driving / distoring the preamp or drive circuit is doing to the signal coming in
  • Input Level/Trim - how much of the incoming signal there is

They can have similar effects (affecting the overall amount of gain/drive/dist/etc), but the main difference is where that happens.
 
The volume pot act as impedance divider... the trim as pure resistive... the gain as resistor in parallel with a capacitor. They affect the amp gain in 3 different ways.
 
The Gain control on most amps is after the input tube stage. The amount of signal at the amp's input determines how hard that input stage is driven regardless of how high the gain control is set. Input trim or a volume pedal would be before the amp input, so you're turning down the signal going into that first tube stage as opposed to immediately after it with the gain control.
 
Your guitar volume can often act as a treble cut when turned down as well, some guitars have a treble bleed circuit to help alleviate this.

A real volume pedal would also be electrically the same as that, and could do the same thing.

The volume block (unless it's modelling this same treble cut behavior, which I don't think it is) is just a flat level adjustment.

The input trim is also a flat level adjustment before the amp.

The amp block's gain/overdrive control is going to vary depending on the amp model (and therefore depending on the real amp schematic). If there's a bright cap, it will let some of the high end through even when it's down (why people say it sounds thinner and brighter when turned down). It also could have a number of other tone affecting behaviours as turned up and down.

So the gain knob will have a lot of character relating to how real amps were designed. The input trim and your volume block will instead be a totally flat signal level adjustment. Your guitar volume is also likely to change the sound as you roll it down because of how it couples to what it's plugged into. Also, lowering your guitar volume will give you a slightly worse signal to noise ratio since you're lowering the signal before it even gets to the Axe.
 
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