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Boost pedal question: louder vs. more gain

jacoby75

Member
Messages
293
hey guys,

Quick question about boost pedals. In watching demos, how is it that some people use a boost just to get louder, and some are able to use it to add drive to their amp? I understand that in some instances, making it louder would bring the amp to drive. And I know if you put it before an OD pedal it will drive the OD harder. But in some videos I've seen, it doesn't really make the overall signal louder. Just drives the clean amp into breakup.

Is it about the amp impedence or something? I have a Fender HRD, which I play into the clean channel, and I've tried a boost after my OD, and all it does is make everything louder. Doesn't make it break up. Is it about a specific kind of boost pedal?

Thanks
 

JesterR

Member
Messages
2,616
Well, it depends. Boost can have some internal overdrive. But if we talking about same pedal, then it depends on amp. Some amps have more headroom (can stay clean more) and other goes into overdrive easily. And, most important thing is volume. If amp in video is just before break-up, then boost pedal would definitely overdrive it. And if your amp set on bedroom volume, boost just makes it louder. Overdrive means, that your amp stages can not handle so loud signals and starts do distort.
 

Rockerduck

Member
Messages
3,254
An OD compresses as it overdrives. That the key thing "compression". When boosting behind the OD, it distorts more, but not louder. Most musicians put a Low gain OD behind the OD and a boost after.
 

PatrickE_FenderADV

Silver Supporting Member
Messages
28,127
Two major components. Where the boost is located in relation to other dirt/ODs and is the amp set clean or dirty.
 
Messages
1,026
In the demos that you're watching, the dudes have probably dialed the amp in to be right on the verge of breaking up. The amp is just about out of headroom, or clean volume. When they hit it with a boost it dirties up the amp without much volume change.
 

jacoby75

Member
Messages
293
that's what I figured. Thanks. I know a lot of guys start with an already overdriven amp for the "clean sound" and then roll back on the guitar when they need to be cleaner, so then adding a boost is just more gain. But I heard one the other day where it sounded pretty clean and then got dirty with just a boost pedal. Thanks.
 

BoiceBox

Member
Messages
363
I think the amp and how it is designed plays a major roll here. My '69 Bassman pretty much just takes a moderate boost and stays clean unless the volume is very high. My 65amps London Pro is amazing at getting aggressive, overdriven sounds very quickly and then cleaning up with only a slight adjustment of the volume knob. Somehow they have designed that circuit so that the breaking point between clean vs breakup is only a tiny amount of extra volume. The boost that would do almost nothing to overdrive my Bassman will send the 65 into glorious distortion.
 

midwayfair

Member
Messages
2,046
Overdrive occurs when the signal size becomes too large for the power rails of the device.

First, forget using the term "gain" to describe "distortion." Gain is simply how much the circuit is able to amplify signal. Gain can be 100% completely clean ... until the device no longer has enough headroom to continue amplifying it.

As a general rule, you can get about 3dB of gain for every volt of power you're working with (at least, in a pedal), so a 9V pedal will be able to give you, at most, 27dB of clean gain. If it tries to make your signal any bigger than that, your signal will distort. If your guitar has hot pickups, it might create distortion earlier, too, depending on the devices used for amplification (certain types of transistors might distort more easily).

So that's the pedal side of things -- some boosts have their own distortion because they're trying to boost your signal more than a 9V circuit can handle it. (This is why some boost pedals run on higher voltage, by the way.)

Amps have similar limitations. Keep turning up the gain (this is the "volume" knob on most amps; the "master" knob on some amps is the output volume before the power tubes) and eventually it'll boost your signal enough to exceed even the much higher voltage of an amp. Most amps are actually designed to distort more easily, by not using every available bit of clean headroom they could.

Before we move on, there's something a lot of people don't realize: Once your signal exceeds the headroom of the circuit (amp or pedal), that's it -- it WILL NOT get louder. That's what "headroom" means. It will simply get more distorted and saturated.

So let's look at two situations (I'll use a rounder number of 20dB for the boost):

You run a pedal producing 20dB of completely clean gain into an amp that can handle a signal that large before distorting: You get a really big boost in volume. (Your signal will be about twice times as loud.)

You run a pedal producing 20dB of completely clean gain into an amp that CAN'T handle a signal that large before distorting: You get more distortion from the amp. Depending on how close to the saturation point the amp was before you hit it with the boost, you will get less than the full 20dB of boost.

In the above examples, you can replace "amp" with "an overdrive" and you'll have exactly the same thing going on, though obviously the overdrive will have far lower headroom than an amp.

So why isn't your Fender amp breaking up even when you hit it with a boost? Because it's still got more headroom. Fender amps are made to sound cleaner than something like a Marshall. If you haven't cranked your amp to the point where it's distorting on its own, a boost won't do a whole lot. If you CAN'T crank your amp to that point, a boost is the wrong tool for you if you want distortion (hence the popularity of distortion pedals).
 

ken374

Member
Messages
7,007
You could use the soul food pedal as a clean boost get a bit more gain out of the OCD. I use it to boost my Bogner blue. It thickens it some and increased gain/dynamics.
 

jacoby75

Member
Messages
293
Thanks for the very thorough lesson. : ) I think I've found the sweet spot for the clean channel on my HRD, but it's nowhere near breakup. So I'll probably be relying on OD pedals to get any sort of grit. And maybe a boost before the OD. Thanks.
 






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