If the amplifier doesn't have an effects loop or using it is inconvenient, but there's still a need for it, don't worry! A similar setup can be constructed using gain pedals, so that you get your delay/reverb -effects after the heavier distortions, allowing them to sound as you require.
The easiest way to understand and change your own gain stages is to think of your amp’s preamp as an overdrive or distortion effect pedal. High gain (hard clipping) tube preamp distortion looks virtually the same in an audio analyzer as the transistor- and/or diode-based distortion produced by a pedal.
If a high-gain amp’s preamp can be compared to a distortion pedal then a mildly overdriving (soft clipping) tube amp preamp could be seen as an overdrive pedal.
Using a transparent transistor-based preamp completely clean is close to plugging your guitar straight into the amp’s power amplifier at line level, even though there’s a certain amount of preamp boosting and equalization.
For the dullest and most one-dimensional sound possible, you can connect a guitar with hot pickups straight into a high-gain amp’s preamp with the gain turned to full. What you get is that your amplifier's first 12AX7 tube will be overly saturated. As a result sound is compressed to the point that there are practically no way of controlling anything with your playing dynamics.
Many young and inexperienced players take this route, because it is very easy to play with this kind of sound. Simply hit any note and it will come out of the amp in an easy-to-predict way. You could argue that this type of sound is ideal for metal music, but in reality it is also something of a dead end road, as there are many more ways to sculpt interesting, multi-faceted overdrive tones.
If an amplifier has originally been designed with the clean tone as the main focus, chances are its overdrive channel does not inspire you as much. A good example could be many of Fender’s various designs over the decades.
The reverse can be said about many high-gain amps, who often tend to include somewhat unispiring clean channels. This category includes some Marshalls, but also the newer Mesa Boogie models, Peavey’s 5150, and many others. The amp designer has put all his energy and knowledge into designing the crunching high gain channel, with the clean channel often added as a mere afterthought, because you “have to have one”.
It is a hard task to design a great-sounding high-gain channel, which is why you can also find so many bad amps, aside from the classics named above. I have encountered many different modern amps, whose high-gain sounds were almost self-oscillating and which sounded like a table saw at full tilt.
An easy way for altering your sound would be to use the high-gain amp’s clean channel with a distortion pedal. Depending on how well your amp has been designed the resulting sound may even be better than using the lead channel on its own.
Many professional session players prioritize their clean sounds so they use a great-sounding clean amplifier as the foundation of their sound. This is also the reason why many guitarists have such large pedalboards. If your clean sound is important to you, and you have chosen your amplifier accordingly, adding different shades of gain and distortion to your signal is very easy. At least it’s much easier than trying to find a healthy-sounding clean tone and various dynamic overdrive stages using a substandard multi-channel amp.
In many affordable high-gain amps the moderately-gained second channel (often labelled Crunch or OD1) sounds much more organic than the high-gain lead channel. If you combine this channel with the signal coming from an overdrive pedal, you will get the amount of gain you’ve been looking for, but with a much more desirable tone than you’d get from just the amplifiers high-gain channel on its own.
If you worry that your clean sound is not clean enough, remember that when you’re part of the band, clean sound doesn’t necessarily have to be as clean as you would imagine whenever you’re playing by yourself. In a live situation minimal tube saturation will disappear beneath the drummer’s cymbals and the reflections of the venue, but this type of clean will sound much livelier and contain more upper harmonics, which in turn will make the guitar tone stand out better.
Should your guitar amp feature several different channels and if it's high-gain tones leave you a bit wanting, you can try the following:
This type of setup mimics the behaviour of an FX loop but gives you way more alternatives to controlling your sound. You can adjust the behaviour of your modulation- and delay- and reverb-effects placed between the gain stages in three different ways:
This way you have added two additional gain stages in front of your amp. If we remember that a high-gain preamp often contains up to five internal gain stages, viewing the second overdrive pedal as part of the amp’s preamp will bring you closer to the basic principle behind a high-gain amplifier’s circuit, but with external add-ons.
Using this method moves the 1st gain stage closer to the guitar so that you can place pedals between your gain stages. A signal path like this leaves plenty of scope for playing dynamics and the use of the guitar’s volume control. Your effects will have a clearer sound and offer more possibilties for adjustment.
And if you have chosen your gear well, you could take this analogy further and try to build your gain even more gradually. As a result you could achieve a little power amp warmth, output transformer saturation and a bit of speaker distortion. The resulting sounds are often significantly juicier, more open and more dynamic than when you’re relying solely on your amplifiers preamp for your distorted sound.
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