The non-linearity inherent in tubes means that there will always be small amounts of distortion introduced into the signal, even with a clean amp such as the Fender Twin. This is partly explains why a tube amp sounds warmer and has a more musical character than a solid-state amp. The sound of many great Rock ‘n’ Roll players such as Ritchie Valens, Buddy Holly and Chuck Berry were defined by amps with cathode follower preamp stages. Although the preamp section of these amps is relatively clean sounding, the power amp section generates significantly more signal distortion, especially when the amp is cranked up. The distortion is the result of several factors including:
- The power amp tubes entering the clipping region
- The rectifier tube voltage sagging
- The transformer core becoming saturated
- The speaker cone resonances and/or break-up
This subject, however, is outside the scope of this article – so let’s get back to the preamp section.