Understanding Headroom

What is Headroom?

We always strive in our articles to be thorough without bombarding you with too much scientific jargon. After all, it's our hope that when you are done reading you will better understand the topic. In the spirit of keeping it simple,  the best way to understand headroom is to think of it as "clean volume." Basically in a nutshell, what we're talking about is how loud an amp can get before it begins to overdrive. As most of you are aware, one of the great things about tube amps is that they do begin to naturally compress or warm-up as you turn them up, and when they are really cranked they produce that harmonically rich overdrive that only a tube amp can deliver.  The problem is that the rate at which the amp begins to overdrive is going to be different for each amp. Different amps are going to have different levels of clean headroom.  There are a number of contributing factors, however, here are a few things that contribute significantly:

Wattage - As a general rule, there is a correlation between wattage and clean headroom. Overall, the higher the wattage, the higher the potential for clean headroom, at least as it relates to power tube overdrive. The reason for this is pretty simple. The harder you drive a tube, the more it is going to overdrive. Normally, as an amp increases in wattage, it also increases in the number of power tubes that it has, meaning that the "load" will be divided into smaller parts and each tube will not be driven as hard.

Voicing - Some amps are purposely voiced to yield more overdrive or more clean headroom, depending on the design. This can be done in a number of ways. One example of voicing an amp for more overdrive is when a designer purposefully makes the preamp section of the amplifier easy to overdrive by cascading the gain from one tube to the next in order to generate massive amounts of overdrive.  On the other hand, a designer may also choose to maximize clean headroom by either using lower-gain preamp components or even decreasing the amount of plate voltage on the power section of the amp.

Input - One of the reasons that headroom is such a difficult thing to quantify is that it's so highly dependent on the level of the signal going into the amp. Guitar pickups can vary wildly when it comes to output, and in turn, how hard they drive an amplifier. As the output of a pickup increases, the headroom typically decreases as the front-end (preamp) section of the amplifier will be driven harder and will yield more overdrive and compression.

How Much Weight to Give to Headroom?

When looking at any amp it's pretty important to have at least a general idea of how much headroom an amp has and how that will fit with your needs. Each player's needs are going to dictate the amount of clean headroom they prefer. There really is not a wrong or right direction. Every player's approach is going to be a little different. Some players are going to choose to get the vast majority of their overdrive from the amp itself and those players typically seek amps that have more gain naturally. For these players, large amounts of clean headroom is probably not all that important. On the other side, some players want a clean base-tone to work with. From there they will get any overdrive that they may need from a pedal or other source. Neither of these approaches is better than the other, however, in both camps the amount of headroom is pretty important for completely different reasons. It is probably safe to say that these two types of players could swap amps and be happy with each others rig, but what each are expecting from their amp is very different.  

It's hard to say exactly what will best serve your needs. Though we definitely want to help, that is a question ultimately you are going to have to answer. With that being said, here is a basic rule of thumb that may help if you are confused about how much headroom you may need. In most cases, we feel it is probably better to error on the side of more clean headroom than a player needs. The reason for this is it is a lot easier to find ways to overdrive an overly clean amp than to clean up one that has more gain than you would like. In general, we find it is just less of an uphill battle. It is also important to consider how loud you will typically be playing the amp. If you are only playing at home you may be okay with an amp with less headroom than you may need if you are trying to compete with a heavy handed drummer. Not that we've ever met any of those :).

Pedals and Headroom

Pedal users tend to pay a little more attention to headroom than other players, and for good reason. The relationship between the amp and pedals is pretty important. When assembled correctly, they augment one another. Headroom definitely plays an important role in this relationship. As we stated earlier, some players choose to use very clean amps as a platform for pedals. This is a very solid approach and a very popular one at that, but it is definitely not the only way to go about it. Another very popular approach is to use an amp that already has a moderate amount of gain and then further drive it with a boost or overdrive pedal. Proponents of this setup often claim that the overdrive achieved is richer and more natural, as the tubes are more engaged than when the amp is set to a clean setting.  Though it is hard to say if that is true or not, it seems like a sound theory. Anything you can do to get your amp and pedalboard to function more as a single unit rather than two separate components would seem like a good thing.