Theory behind a distortion channel

[Dman]

I'm a little new to building/designing guitar amps so this question might be common sense, but either way it hasn't come together in my brain yet. So here is my question.

"What is the difference between the design of a clean channel as opposed to the design of a crunch/distortion channel in a tube guitar amp? How do you achieve distortion, good desirable distortion?"

Thanks in advance!

[cbarrow7625]

The biggest difference is carefully controlling the gain, i.e., how hard you hit successive stages. The key is to control the signal so that the distortion builds gradually. You want to create nice sounding harmonics in the earlier stages and really only hit the last stage hard.

There are other tricks to it, like limiting the low frequencies and controlling oscillations, but for GOOD SOUNDING distortion nothing is more important than a gradual build up of gain. It's the difference between a buzzy pile o'crap and smooth, touch sensitive distortion.

Check out the current Dumble videos at guitargear.org for an example of a really well constructed preamp based distortion sound. Not a shill for the site - the sound clips in the videos just blew me away.

[defaced]

Cascaded gain stages are the most popular method, which is the gradual build up of distortion cbarrow talks about. Usually, three stages will get you a nice what I'll call "medium" level distortion (AC/DC), four stages will get you full on saturated distortion depending on how it's designed (almost every metal band on the planet). More stages are used at times (Peavey 5150), but aren't necessarly needed to get full blown saturated distortion.

I consider a pedal out in front a gain stage. It's not the purest in the sense of "tube" distortion, but it all works toward the same general goal which is gradual build up of clipping. For example alot of bands (Slayer with a JCM800 or Killswitch Engage with a Recto, Machine Head with a 5150) will use a Tube Screamer out in front of the amp to get a particular sound.