ODC Diode Contour Overdrive

Op-Amp Diode Contour Overdrive

ODC is an overdrive, inspired by the revisions of the Fulltone™ OCD pedal*.
It is designed for musicians, who want a dynamic, amp-like overdrive that stays articulate from the lightest edge to full saturation.

Original pedal earned its reputation by doing something that sounds simple and is difficult to get right.

An op-amp gain stage feeds a MOSFET clipping stage (with additional Germanium-diode versions), which gives a more open and less abrasive character than conventional diode clipping, and a two-position HP/LP switch provides two distinct voicings in a single pedal.
That character belongs in the modern studio as much as on the pedalboard.

ODC extends the same touch-sensitive grit to guitars, synthesizers, bass and drum buses.

It can be placed anywhere in the signal chain. ODC refines the classic design with oversampling, Low Peak and High Peak filtering ahead of the clipping stage, three clipping modes and a Mono Frequency control.

• Main (MOSFET mode): The punchy, high-headroom classic configuration built around dual MOSFET transistors.
• Asymmetrical Germanium: Blends a Germanium diode into the clipping path for rich even-order harmonics and warmer, asymmetrical break-up.
• Symmetrical Germanium: Uses a matched pair of Germanium diodes alongside MOSFETs for an earlier, soft-knee saturation with vintage compression and sustain.

ODC executes all non-linear clipping math at an elevated internal sample rate, keeping top-end fizz silky, smooth, and analog-like even at maximum Drive settings.

ODC is a circuit-informed model built from published analysis of the pedal design. Fulltone™ and OCD™ are trademarks of their respective owners.

™: ODC is an original power-amp fx, developed by Turn2on. It is inspired by the circuit ideas, based on the original cranked amplifier. All product names, trademarks and registered trademarks are the property of their respective owners. All company & product names used are for identification purposes only. Use of these names, trademarks and brands does not imply endorsement_

MAIN CONTROLS:

DRIVE: Determines input gain fed into the non-linear clipping stage. Automatically compensated to preserve relative gain structure across settings.

MODE: Toggles between three Level-Matched clipping topologies:
- Main (MOSFET): Built around a dual 2N7000 MOSFET clipping stage. Yields direct,
punchy, symmetrical clipping—the standard high-headroom overdrive voice.
- Germanium Asymmetrical: Integrates a Germanium diode into one leg of the MOSFET
clipping path. The asymmetrical waveform clipping generates even-order harmonics for a
warmer, thicker, and more dynamic drive.
- Germanium Symmetrical: Pairs the MOSFET stage with a matched set of Germanium
diodes for both positive and negative wave halves. Saturation begins earlier with a softer
knee, yielding heavy compression and a smoother, vintage character.

VOLUME: Independent output trim, applied after Drive’s internal compensation. It has no effect on distortion character, only loudness.

TONE: Post-clipping high-frequency control. Adjusts overall brightness without altering distortion character. (Behavior adapts based on the HP/LP state).
- HP (High Peak): Boosts upper-mids and highs; increases gain and output volume for a
punchy, open tone.
- LP (Low Peak): Flattens the upper-mid response for a neutral, smooth, and full-bodied
sound with low-mid emphasis.

LOW PEAK: Controls the amount of low-end energy pushed into the distortion stage (eliminating low-frequency flub and mud). Attenuates low frequencies prior to clipping. High settings keep the distortion response tight and articulate.

HIGH PEAK: Manages the high-frequency content entering the clipping circuit (smoothing out harsh transients). Attenuates top-end content prior to clipping. Lower frequencies reduce
unwanted transient harshness at high drive levels.

OVERSAMPLING: Reduces aliasing artifacts from the clipping stage. Recommended ON, especially at higher Drive settings where signal edges get sharp and fast.
Turn off only if you need to save CPU and are working at lower Drive levels.

MONO FREQUENCY: Sets the crossover point below which stereo signals sum to mono, ensuring stable, phase-coherent low end on stereo buses and synths.

BYPASS: Relays hard bypass, passing input directly to output without processing

STUDIO APPLICATIONS:

• Transparent Clean Boost: Keep Drive low, boost Volume, select Main mode on HP. This pushes downstream hardware or amp simulators into natural tube breakdown without altering instrument timbre.

• Dynamic Lead Tracking: Use GE Symm on lead guitar or synth solos. The soft-knee compression smooths out aggressive peaks and lengthens sustain naturally.

• Tightening Rhythm Guitars: Select Main mode with HP enabled. Turn the rear-panel Low Cut up to ~120 Hz to clear space for the kick and bass while keeping palm mutes punchy.

• De-fizzing Saturated Signals: When working at extreme Drive settings, tame upper-harmonic harshness on the back panel using High Cut before touching the front-panel Tone knob.

• Drum & Bass Bus Glue: On stereo bass synth stems or drum buses, keep Low Cut low to retain fundamental sub-frequencies, and set Mono Frequency around 100 Hz to prevent low-end stereo phase issues.