Gain vs volume vs master volume: what each one does

What gain does

Gain is the amount of amplification in the preamp, the first stage the guitar signal meets. Low settings leave the signal clean. As it rises, the preamp is pushed past what it can pass cleanly and starts to clip, which is distortion, along with more compression and sustain.

Past a point gain stops making the amp much louder, because a clipping stage cannot get much bigger. It keeps adding saturation, noise and a softer attack instead, which is why a high-gain sound needs less gain than people expect.

What volume and master do

On a master-volume amp the preamp's output goes through a level control before the power section, and that control sets how loud the amp is without changing how distorted it sounds. On a two-channel amp each channel usually has its own Volume, used to balance one channel against the other, and a Master sets the level of the whole amp for the room.

Some amps have no master at all. On a Fender Deluxe Reverb or Princeton Reverb, the Volume knob is the only level control: it sets how hard the preamp is driven and how loud the amp is at once, so breakup arrives only when the amp is loud.

The same two jobs under other names

Amps name these controls differently. A Marshall JCM800 2203 calls them Preamp Volume and Master Volume. A Peavey 6505+ calls them Pre Gain and Post Gain. A Roland Jazz Chorus has a Distortion knob beside its Volume. Whatever the label, one control sets the drive and the other sets the loudness.

On a modelling amp such as a Boss Katana, the channel Volume is stored with each saved sound and the Master is not, so Volume balances your sounds and Master sets the room.

Power amp distortion

On a valve amp, turning the master up far enough also drives the power valves, which adds a looser, more compressed kind of distortion than the preamp makes. That is why an old amp with no master, turned up loud, sounds different from a high-gain preamp played quietly.

Power reduction exists to get that feel at a lower volume. The Blackstar HT Club 40 MkII switches its output stage down to 10% power, and the Boss Katana's Power Control switch does the same job on a solid-state amp.

Settings to start from

Clean: Gain 2 to 3 and Master wherever the room needs it. Crunch: Gain 5 to 6. High gain: Gain 6 to 7, rarely 10, with the low end kept in check. Change the Gain for the sound and the Master for the level, and do not use one to fix the other.

On an amp with no master, the Volume knob sets both. Low settings stay clean, and the breakup starts somewhere past halfway depending on the amp and your pickups, so find that point at the volume you will actually play at. When a song's settings were written for a different kind of amp, Tonelify translates the gain and volume positions to yours.

Gain vs volume on a mixer or microphone

The same split applies outside guitar amps. On a mixer or an audio interface, Gain sets the input level into the preamp and the fader or volume control sets how loud that channel is in the mix. Set the gain for a healthy level that never clips, then do the balancing with the faders.