There are many methods of generating distortion with pedals, one of the earliest being to saturate the first stage of the amp with boosted guitar signal. The pedal market reflects the variety of personal preferences in overdrive sound, and perhaps the difficulty of finding amps with controllable and pleasingly distortion. Of course, many valve amps have dedicated overdrive channels for improved flexibility. The key advantage of push-pull valve power stages, though, is, as we’ve tried to show, the balance of harmonics they can achieve under the right conditions – this is difficult to copy with single-ended triode preamp stages that spend much of their overdrive cycle in cut-off.
Some drive pedals, though, can achieve this balance. The Ibanez TS series with its soft-clip circuitry based on diodes in a feedback loop around an integrated circuit op-amp has become the first call for bluesy, semi-distorted guitar sound. Another example is our upcoming Blue Tube kit pedal project, whose overdrive curvature (Fig. 6a) results from a balance of low harmonics (Fig. 6b) that a valve amp achieves only at certain levels. It's is aimed specifically at helping lower-cost amps achieve a valve-like overdriven sound with easy control.
With DSP (Digital Signal Processing), the guitar signal is used as data entry, then conditioned by software programmed with the waveforms of classic amps at all driven levels. DSP is versatile and, yes, can be convincing. After a recent gig where the guitarist was blowing nine bells out of a JCM800 with a Les Paul; he showed Guitar & Bass the DSP unit that he'd patched through the PA – educational stuff. DSP is only limited by its programming quality and the mindset of the analogue-oriented guitarist. Processing speed and touch response is improving, and it's a matter of time before it seems just like the real thing to the player – as it already does to most of the audience. The future of guitar amps may will be decided by how entrenched we are in our nostalgic attachment to the glories of the past.
Read about how a guitar overdrive pedal works with an Amp. Use our in-depth guide to see how transistors act in an Amp
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How too: Read how a transistor fuctions in a guitar amp