Overdrive II

Dual waveform modifiers produce overdrive & distortion

The Overdrive-II from Oakley Modular Systems and built by Lower West Side Studio features two different waveform modifiers to produce a wide range of overdriven and distortion sounds.

The first waveform modifier is a classic overdrive circuit which can produce a sound that is familiar to many guitarists. The original Overdrive 5U module contains just this part. The circuit has two basic modes selected by a switch. Hard is a raucous distortion type effect useful for grunging up your signal. Soft is a more subtle effect and produces a clean sounding overdriven amp sound.

Three front panel pots control the sound in this section. Drive controls the overall gain of the circuit’s 'pre-amplifier' stage and essentially determines the level of overdrive or distortion. Timbre is an effective tone control that cuts or accentuates the additional harmonics produced by the pre-amplifier stage. And the Blend pot is essentially a wet/dry mix control that allows you to add only as much of the effect as you want.

The second waveform modifier is a harmonic multiplier. This part of the module produces additional harmonics by folding over the input signal so that the tops and bottoms of the waveform are forced the wrong way. This produces strident changes in tone that are dependant on the signal level. Up to two stages of symmetrical folding are available and at the output there is a soft clipping circuit to prevent excessive folding at extreme input levels.

Two front panel pots affect the action of this circuit. Foldover adjusts the gain of the harmonic multiplier and controls the amount of folding the input signal will be subjected to. The Balance control is another wet/dry control so that you can mix the output of the overdrive circuit with the harmonic multiplier.

The input/blend switch selects whether the input to the harmonic multiplier comes directly from the input socket or the overdrive circuit. Thus the two modifiers in this module can be operated in series or in parallel. In conjunction with the blend and balance pots you can create a wide variety of different tones.

Voltage control is determined not within this unit, but as part of the signal chain placed before this module. Using a VCA to control the signal level that is fed into this unit will determine the strength of the overdrive, distortion or folding. Using a VCF to alter the timbre of the signal fed to this module will control the overall harmonic level far more than using a filter alone. In fact, hard sync type sounds can be easily obtained by simply sweeping the filter's cut-off frequency.

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