Boosters and amps, my take on it.

[John Lyons]

Seems like this always comes up and is a bit confusing for folks

A booster pedal in front of a clean amp channel will make the volume jump up quite a lot but not
necessarily get you any overdrive/distortion.
It depends on the amp and how clean it is to start with.
A booster reacts to the amount of headroom or overdrive the amp already has. If the amp is very clean like a
fender twin reverb etc, the booster is basically a volume boost only. You will possibly get a little overdrive if you boost
the amp all the way, but not much.

Since an overdrive/fuzz/distortion pedal already has no real clean headroom left,
putting a boost in front of it will create more distortion and not boost the output level much if at all.
Distortion and fuzz produce clipping, clipping is the opposite of clean headroom.
When you boost an amp it will compress and clip. Clipping and compression are very similar in that the
output volume will not increase if you add more boost. Clipping and compression add sustain.

So by boosting an overdrive or a slightly dirty amp channel you increase sustain, compression and clipping.
At some point there is only so much clipping you can add before it will only add noise.

Some examples:
A booster in front of a slightly dirty amp = cool rock distortion/overdrive, with increased sustain.
Depends on how clean or dirty the amp is (how much headroom it has to start with)

A booster in front of a very clean amp = a big volume/level boost
(and possibly a little overdrive, depending on the amp again)

A booster in front of an overdrive = more clipping/compression and sustain. Basically intensifying the original sound adding some clipping.

A booster after an overdrive will make the volume of the overdrive much louder.
The overdrive sets the amount of clipping, compression and sustain, while the booster boosts the level of the signal.


So the moral of the story is:
It really depends on the amp and the pedals you use...and in what order you use them.
A booster only reacts to the amount of clean headroom in your amp of the pedal you use it in front of.
There are a few other factors in the equation here but in a nutshell this is what boosts do.

Hope this clears it up a little.
I'd like to hear some other opinions/explanations as well. I'm just a hack.

John

[Auke Haarsma]

Well said John.

One minor addition:

A booster after an overdrive will make the volume of the overdrive much louder.
The overdrive sets the amount of clipping, compression and sustain, while the booster boosts the level of the signal.

Of course, again the headroom of the amp limits the increased volume.
OD -> Booster -> Clean amp  => booster will increase volume
OD -> Booster -> Dirty amp  => booster will not increase volume, the dirt from the OD will mix with the dirt from the Amp.

[John Lyons]

Good point! I thought of that but forgot to type it. Even more variables!!

John

[Mark Hammer]

And since I can't resist the temptation to make it even more complicated, bear in mind that where a volume control is situated in the gain structure of the amp or pedal will determine the tonal outcome as well.  For instance, the Jordan Boss-Tone has a "sensitivity" control that pads down the input signal.  This is different than another pedal that might have a gain stage or two before any attenuation is applied.  Same thing goes for amplifiers.  Some have a volume pot very early in the signal path, and no master volume, such that aiming for lower output volume will necessarily maintain maximum headroom and only result in booster-related clipping if the boost is drastic (i.e., not your grandmother's puny 6db gain).  In other instances, the preamp itself is designed with enough headroom for the "normal" range of input signals that it will remain clean for most input signal levels, but because the volume control is situated so far downstream, there are several "unprotected" gain stages before it that can succumb to big boost.

The long and the short of it is that you need to consider all gain stages along the way, and the point/s at which any attenuation is inserted.  Indeed, that is often the very basis of why some of us like the amps or amp issues we do.  In one year of some classic amp, the volume control comes after a first low-ish gain stage and then goes to subsequent gain stages before the power stage. The following (or perhaps preceding) year, that same amp has the same number of gain stages but the volume (or tonestack, which also acts to attenuate signal, albeit selectively rather than universally) is bumped over a stage or so, such that the same nominal amp responds differently to pick attack.

[DougH]

A booster in front of an overdrive = more clipping/compression and sustain.

...And a lot more noise, usually.

[brett]

Hi
just to mix things up a bit further, I'm gonna suggest something that I've been thinking about for a while.

What if the loudness of an pedal/amp isn't just related to the volts it's putting out?  (and ignoring speaker efficiency etc)  Actually, we already know this because at low volume, midrange seems much louder than bass and treble. 

Anyway, I reckon that high gain signals (approximating square waves) sound much louder than low gain (sine waves) of the same power, especially at higher volumes.  It's probably caused by the mass and consequent inertia of various components in the ear. (ie if you accelerate them fast, as with a square wave, they might "overshoot" the clipping point, giving the impression of a more intense pressure wave).

Just a 2 bob theory.
cheers

[greigoroth]

What about a booster in an effects loop? (is it obvious that I don't have an effects loop?!!)

[drewl]

What about a booster in an effects loop? (is it obvious that I don't have an effects loop?!!)

well since most fx loops are after the preamps you'll be slamming the output section with a hotter/louder and or more distorted signal, UNLESS of course the amp in question has a master volume after the effects loop.

[greigoroth]

Okay, so this could in theory sound either like a boost in front of a clean channel, or it could sound like a boost in front of a dirt box?

[John Lyons]

Matt
Yeah, if the FX loop is post preamp then the booster will act as a clean amp does.
The booster will boost the volume level into the power section.
Once again, this depends on the amp and whetherit has a master volume as drew said.

With the booster in the FX loop the chain is like this:
guitar>amp input>preamp (distorted or clean)>booster> poweramp. Mostly, the booster will amplify level not OD/Compression etc. But there will be elements of all of those as you will be driving the power section and phase inverter (if it's a tube amp in push pull) as well as the input to the power tube(s).

John

[greigoroth]

Thanks John!

PS: love your woodwork!

[mac]

Anyway, I reckon that high gain signals (approximating square waves) sound much louder than low gain (sine waves) of the same power, especially at higher volumes.  It's probably caused by the mass and consequent inertia of various components in the ear. (ie if you accelerate them fast, as with a square wave, they might "overshoot" the clipping point, giving the impression of a more intense pressure wave).

If you plot a square wave and a sine wave of the same amplitude and frequency fo you'll see that the area below the square wave is larger than the sine wave. This excess area means more energy --> more pressure.
In terms of harmonics, the square wave can be obtained by adding the sine wave plus lots of sine waves of freq fn= n*fo, n integer.
Just generate in any audio software this two waves of the same freq and amplitude, and listen to the results.

mac