Boost = Gain = Volume = Level Increase (Why Does My Boost Pedal Add Gain)
Lets first clarify a few terms. Boost=Gain=Volume Gain=Volume addition or whatever else you may wish to call it.
You’ll understand later why the word ‘GAIN’ is commonly associated with amount of distortion but it should be clarified here that the word GAIN only means Addition of Volume in a technical sense. It is a commonly misunderstood term and I get a lot of questions such as ‘will this pedal add ‘GAIN’ to my signal.. Well if it didn’t (as Gain=Boost) you’d be wasting your money, might as well just get an empty box with 2 jacks so that it looks cool.
But I make it clear here that out booster adds boost/gain/volume/signal level CLEANLY and does not add distortion to the signal by itself. What goes in comes out the same but LOUDER!
Lets imagine we have a clean guitar signal in BLUE. (we’ll use a basic sine wave signal for simplicity although in practise your guitar signal will be a lot more complex)
You wish to raise the level of your guitar so you add a bit of boost/volume gain.
The signal goes up and it now looks like the GREEN wave. (you can see that it has more gain as it is larger. It looks nice and round (sine wave) so it’s still clean just louder than the original blue signal)
What happens if we just keep raising the signal level?
Say we’re using our Booster. The booster can keep boosting some more. We boost/add more gain to the signal and end up with the RED wave. As we can see it is still clean when it EXITS the booster.
But here we can run into something interesting. Various amplifiers have various limits on how loud of a signal they can RECEIVE on their preamp before they start to distort. We will call this clean HEADROOM.
HEADROOM=amount of clean signal an amplifier (or pre-amp) can faithfully reproduce without distorting
So if we exceed this amount of headroom, what happens is that bits of our RED wave are now outside the pre-amp’s limits and can no longer be reproduced cleanly. They hit the ceiling and are either cut off (fig) or more likely gently squashed down(fig 4).
How your amp handles this excess depends on it’s design. Tube amplifers do this gently and can sound really good and warm when they do. This then becomes a very useful feature of the booster as you can run the amp very HOT to get a tube overdrive at lower dB levels and not make your ears bleed (or your neighbours)
Where this headroom sits also depends on your amp’s design. It would be impossible for me to know each set up and how the booster would behave in it as there are too many variables which start with how hot your pickups are and what else you use in the signal chain to either boost or attenuate the signal.
You can now see why the word GAIN is commonly associated with distortion. As you add more boost/gain you can distort the following stage in your signal. Distortion pedals make a good use of this principal by ‘limiting’ the headroom of the pedal right after the gain stage by using diodes for example or something similar. As you raise the gain to start pushing the diodes hot and and up with distortion coming out of them. (the signal going into them is clean usually)
In the next article we will explain the uses of boost pedals with ‘drive’ channels on some amps, how they behave, and possible set ups to get the sound you want.
Written by Brian of Boo Instruments
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