Guitar effects pedal: Build your own guitar pedal | How to build your own Blue Tube guitar pedal

In 2004, Guitar & Bass introduced a kit for a valve overdrive emulator, Tube Bender. It was very successful – we still get mail from happy users. These kits weren't intended as regular business at the time, and after stocks ran out, the copyright reverted to Dinosaural, who had done most of the design and layout work (and still can sell you a finished Tube Bender). But people still call about TB kits, so we’ve decided to fill the gap with a new pedal, Blue Tube, which has a design agenda that includes feedback from users about the good qualities of the older pedal as well as some possible improvements.

What’s the difference?

The main one is that Blue Tube offers an expanded range of the popular clean/going-on-dirty tonality, with a switch that enables you to stay in a basically clean range or go to the grittier end of town. Having selected Smooth or Grit mode, the Drive pot can be adjusted to suit the requirements of a wide variety of guitars and music, from clean level/tone boost to squeezed’n’dirty Texas blues rock. We think Blue Tube’s dynamics emulate real valve amps more closely than most other pedals of this type, particularly in respect of the compressed bass (focus) caused in valve amps by output-transformer limiting.

We wired the tone network to cut or boost the top before the saturation stage, giving a smoother result with treble towards max, and working more like its counterpart in a valve circuit (in the Tube Bender it was wired across the output, which has some advantages for noise level, but filters the overdrive differently).

Blue Tube offers the kind of blues and blues-rock tones obtainable from the famous Ibanez TS series pedals, but we also recommend it for slide guitar to fill out the mids and get that howl on sustained notes. Lower Drive and higher Level settings give a clean boost with added mids and highs that you can control with the Tone pot (Tube Bender did this but over a narrower, harder-to-find range). The output can be set at instrument level, but has enough margin for use at line-level, enabling you to drive a power amp. Blue Tube gives great results with solid-state units, mixers and PA, or as a virtual DI box.Finally, by popular demand, there’s an ‘effect on’ LED pilot for those subtle settings that you can only distinguish otherwise by clicking the bypass.

How do we do it?

Junction-FET transistors behave differently to standard (bipolar) types, and amps have been designed around their saturation curve, which resembles that of a triode valve. FET amplifier stages only have this response over a restricted range, beyond which they copy the hard limiting behaviour of bipolars (more so in circuits where they have to produce similar gain). But with two FET stages in series, each designed for moderate gain, the effect is to extend the curved area, giving a truly valve-like transition into saturation. To get enough gain for overdrive we use a linear, i.e. clean, front-end amplifier.

The result is an easily-controlled balance of the right blend of harmonics. For more conventional overdrives, the Grit switch provides harder limiting with inverse-pair diodes across the output, as used in most of the well-known rock overdrivers. This setting is fully controllable by the Drive control and, just as importantly, by the guitar, but it’s more obviously distorted when played in band conditions (it can be hard to tell on the Smooth setting with single coils).