Here is a typical scenario: Guitar player in local bar band is playing along through a song, and now it’s time for his/her lead. The player hits his stomp box or gain channel and POOF: Where did the guitar go? Instead of standing out, the guitar fails to cut through, and sounds like and angry beehive, lost in the mix.
This is not an uncommon occurrence. Players mistake gain for distortion, or expect to get more gain and just get more distortion. It’s understandable, as on amps and pedals the terms gain, volume, drive and boost all get used quite interchangeably. But generally speaking where you apply the gain in your signal chain will determine whether you are creating more volume, more distortion, or possibly just a bunch of mud.
In a simple non-master volume amplifier, the volume control increases gain at the preamp level. The power amp section is a fixed amount of gain. Whatever the preamp feeds it, the power amp section boosts it “X” amount. In this layout when the amp distorts, it’s the power amp tubes clipping. Unless your amp is 15 watts or less, this is pretty hard to do at reasonable volumes. This why some studio players like small low powered amps like the Fender Tweeds, old Supro’s, etc.
Master Volume amplifiers come in many shapes and sizes but most of them have some way of overloading a preamp tube (or tubes) and creating the distortion at the preamp level, and then using a second volume control (the master) to keep the overall volume level in check.
Any type of distortion causes clipping, which compresses the signal (reduces its dynamic range). The more distortion, the more the signal is compressed, producing a very even signal but with less ability to cut. Everyone has noticed how a clean guitar tone cuts through the band better than a heavily distorted one. The uncompressed dynamic range of a clean signal has a lot to do with it. Or if you use recording software, notice how much more peaky a clean guitar signal is than a distorted one? Clean guitar is much harder to track.
Let’s say you are on the dirty channel of your master volume amplifier, so you are already creating preamp distortion. If you hit a boost pedal feeding more signal into the amplifier, the effect is often to overload the preamp section even more, creating more clipping and compression. Distortion increases, but relative volume goes up very little or not at all.
Even if your “boost” switch is part of the guitar amplifier’s footpedal system, where the boost is applied will determine whether you get more volume (post preamp) or more distortion (in the preamp section). Pedals can do the same thing: If you pump a distorted pedal signal into a signal path that is already compressed, you are just layering distortion on distortion, further crushing dynamic range.
The concept of a “good pedal amplifier” is an amplifier that has enough headroom (clean gain capability) such that you can feed in boosted and distorted pedal signals without significantly overloading the amplifier. In essence the guitar amplifier is amplifying whatever you send in, but adding little or none of it’s own distortion.
A “bad” pedal amp would be a small Fender Tweed. They have so little headroom that any type of signal boosting device would just overload both sections of the amplifier, creating mush. At the other end, a Fender Twin or 100 watt Marshall can take a hot input signal without distorting, and have enough power to amplify that signal to very high decibel levels. If you listen to Angus riff on most AC/DC songs, it’s not heavily distorted, it’s just really loud. And it’s got great dynamics, bite and texture. Angus does not use any distortion pedals.
There are 15-30 watt amplifiers that are good pedal amps, and it has much to do with amplifier design, transformers, and tube selection. To generalize, a fixed bias amplifier tends to have a good amount of clean headroom (Blackface Fenders, many Mesa amplifiers) while a cathode bias amplifier may have great tone, but can be less forgiving to hot signals (Fender Tweeds, Vox, many Dr. Z EL-84 amplifiers).
Tubes matter too. While the 12AX7 preamp tube is by far the most common, the EF86 tube (some Dr. Z, 65 Amps, Bad Cat, etc.) has more gain and clean headroom potential. They also sound different than a 12AX7, but they handle pedals very well.
My own personal preference is to find a single channel amplifier with decent headroom and really good clean tone — pedals won’t make a bad amp sound good — and then go with pedals for overdrive and distortion. Real power amp distortion is awesome, but in a gigging situation where a lot of different tones/colors are needed, pedals are just more convenient and easy to modulate. If you are in a blues band and can put your Tweed on 10 and ride the guitar volume, it’s a great sound. But if you are in a wide-ranging cover band, the pedal-based format is more effective and flexible. For the record I don’t like feel or tone of attenuators, and feel it’s best to pick the right size amplifier for the job. Unless I’m outdoors I don’t play an amp bigger than about 20 watts.
You should also consider the order of your pedals. If your clean boost pedal is before your primary distortion pedal, it will increase distortion and some amount of volume. If it’s after your primary distortion pedal, it will increase volume more effectively with little increase in distortion. Arranging your pedals with an eye towards how they will interact can greatly increase their effectiveness.
If we go back to the hypothetical guitar player at the beginning of this post, think about some of your favorite blues and classic rock guitar leads. Quite often they are not wildly distorted, but there is a lot of texture, dynamics, and the personality of the guitar player comes through. Managing volume versus distortion can improve the quality of your lead work, and help it stand out better in the mix. I’m not talking about playing “clean” but that crushing amounts of pedal or preamp distortion can really suck the emotional life out of a guitar. Music is all about dynamics, and making sure your guitar does not vanish at that crucial moment can make or break the emotional impact of the song.