If you want to learn more about pre gain vs post gain and what that means in the context of guitar amplification, you’ve come to the right post!
Understanding Guitar Amps
Before I jump into the matter, we should just cover some of the basics of guitar amps. As you know, there’s no point in using an electric guitar without some sort of amplification. However, amps aren’t these simple speaker boxes that you just plug into your wall outlet and get a sound out of them.
An amplifier consists of a preamp section and a power amp section. The preamp takes the signal from your guitar’s pickups and amplifies it enough to be processed.
The power amp then takes it from there and further amplifies the signal. The whole point of a power amp is to make it strong enough to drive the speakers. As you may already know, an amp can come with integrated speakers or have a separate speaker cabinet.
For the most part, guitar amps can be solid-state or tube-driven. However, this may be a bit of an outdated division. A lot of solid-state amps come with digital modeling units that emulate different amps. And, of course, you have modeling units these days that can completely replace amps.
Be that as it may, most amps gravitate towards the tone of tube-driven amps. Although it’s an older technology, it brings the most pleasing kind of tone.
The Preamp Section
For this guide, we want to focus on the preamp section. As I mentioned, this is the first section that takes the signal. However, it does more than just amplifying the initial signal.
In fact, the preamp section is what shapes your guitar tone the most. Firstly, all the EQ controls are on it. The only exception is the presence control, in case your amp has one. It’s technically an EQ control since it tweaks the higher mids. But it’s a part of the power amp section.
Then we have the distortion. Be it mild or high-gain, all or most of the distortion comes from the preamp section. A power amp section of a tube amp may also add some distortion. Certain settings also allow you to get distortion predominantly from the power amp. However, this will get you those warm saturated tones rather than harsher-sounding distortion.
Pre-Gain Vs Post-Gain: What’s the Deal?
And then we get to the issue of pre-gain and post-gain controls. What’s interesting is that you don’t see these particular controls on most guitar amps. However, technically, a lot of amps have them. It’s just about how they’re named.
So what’s the deal here? Well, the answer isn’t that complicated. The pre-gain and post-gain controls technically do the same thing. However, they do it in different parts of the signal’s path.
Sure, it sounds weird. But it makes a difference and I’ll discuss it all in more detail. What you need to know first is that pre-gain adjust the signal level right when it enters the amp. It’s the first control of the signal’s path. The post-gain, on the other hand, adjusts the signal level right before it goes out of the preamp section.
As I said, you won’t see these exact control names on most amps. However, if your amp has more detailed preamp controls, they’re probably on it with different names. The pre-gain control is what most amps have labeled as just gain. And the post-gain control is just the independent preamp channel output volume.
So don’t get too confused by some weird-sounding control labels. Although different in their tone and some features, all guitar amps pretty much work the same way.
Headroom and Clipping
To understand this better, I’ll have to explain a few other things as well. Pre-gain and post-gain controls will affect the tone in different ways. So we need to explain headroom and clipping.
Headroom is essentially how much an amplifier can handle before reaching its limits, or, in other words, how strong of a signal can get through it before clipping.
So then we get to another issue, and that’s clipping. And clipping, obviously, happens when the signal is too strong for the amp to handle. This may seem a bit confusing, but let me explain it with a couple of graphs.
Firstly, here we have a graphic representation of a regular guitar signal. I could say that this is how a clean guitar signal looks like.
As you can notice, the clean signal is like a continuous sine curve. Then we also have these two parallel thicker lines below and above the sine curve. As noted, this is the amp’s headroom. It’s the amp’s limitation.
The graph below shows what happens if you amplify the signal. Or, in other words, you increase its amplitude.
And the clipping occurs when the signal hits the amp’s headroom. And, as you can see, it gets clipped. In simple terms, headroom cuts off the ends of the sine curve.
Generally speaking, clipping is an undesirable thing for most audio equipment. However, with guitar players, it’s mostly a desirable trait. It’s how you get distortion in the first place.
How Pre-Gain Control Affects Your Tone
The pre-gain control will increase the amplitude of the signal. And using this knob, you’ll also be able to achieve clipping within the preamp section. To some extent, you’ll also make the output louder. But the moment you start getting that distorted tone, the increase in volume stops.
So let’s go back to the graphs that I shared above. With the pre-gain controls (or gain on most amps), you’ll reach the headroom more easily. This means that you’ll achieve distortion.
If you’re playing through a tube amp or a hybrid amp that has a tube in the preamp section, you’ll even get some distortion on a clean channel. To most fans of tube amps, this is a favorable trait.
How Post-Gain Control Affects Your Tone
The post-gain control essentially works in the same way. It increases the amplitude of the signal within the preamp. However, it does that at the very end of the signal’s path. You tweak the input gain and EQ. And the post-gain control (or the channel volume) adjusts this processed signal.
In a practical sense, the post-gain control can also adjust the headroom to some extent. If you increase the post-gain level to a certain extent, you get a louder but clean tone. If you lower it down but increase the pre-gain control, you’ll get a dirtier tone.
However, if you’re using a tube amp, this control can do more than that. Increasing the post-gain control too much, and you’ll drive the power amp. You’ll increase the signal coming out of the preamp. And the tubes in the power section will do some heavy lifting.
The distortion that you create this way is a bit different. You won’t exactly get the same type of clipping as you get in the preamp. However, you’ll get that midrange punch with some smoother saturation to it.
If we’re talking about a solid-state amp, then the post-gain control will just increase the volume. This may change if the amp has some special digital modeling presets that emulate tube amps.
Pre Gain Vs Post Gain: Conclusion
I hope this article has helped clarify this topic.
And feel free to leave a message in the comments below if you have questions about this or another guitar-related topic!
Lastly, if you want to learn more about guitar amplification, check out the gain vs drive article on this blog!