Tubulation I Distortion PUBLIC

Tubulation I MOSFET + Op-Amp Distortion Circuit

Tubulation I MOSFET + Op-Amp distortion circuit for electric guitar. Uses two dual op-amp ICs and one dual MOSFET device to produce distortion similar to that of a 12AX7A dual-triode tube. Controls Include: Input Gain, Clean Bass, Clean Mid, Clean Treble, Clean Level, Distortion 1 Gain, Distortion 2 Drive, Distortion 2 Gain, Distortion Tone, Distortion Attenuation, and Output Gain. The input signal is boosted by an FET-input op-amp and sent to a Fender-style tone-stack and to the Driver Stage of the distortion circuitry. Only the clean signal goes through the Tone Stack. The signal from the Tone Stack goes to the Output Stage through the Direct Level control. One BJT op-amp, which provides additional tube-like distortion when overdriven, serves as the Driver for the rest of the distortion circuitry, and is controlled by the Distortion 1 Gain pot. However, Distortion 1 itself is from a matched pair of depletion-mode MOSFETs (aka D-MOSFETs) whose output is boosted by another BJT op-amp gain-stage whose input can be overdriven to produce Distortion 2. The final distorted signal has a simple tone-control that only cuts highs. The clean and distorted signals are summed in the Output Stage, whose level is set by the Output Gain control. The overall Frequency Range is 20 Hz to 40 kHz with all controls at 50%. Suitable for 6/7/8-string guitar or 4/5/6-string bass. Maximum Gain = +21 dBV @ 1 kHz with all controls at 50%, or > twice that with all controls at 100%. [Do not use the circuit with all controls at 100% except as a brief worst-case scenario while breadboard testing.] Rackmount implementation is recommended. The batteries can be replaced by a regulated single-polarity +12VDC power-supply providing >= 60 mA of total current. Special Substitution: The Distortion Section will accept a 12AU7A dual-triode preamp-tube as a direct substitute for IC3, with instructions at the bottom of the diagram. The lower section was based on Craig Anderton's "Real Tube Distortion" circuit (Guitar Player mag., Oct. 1981), which used a 12AU7 tube instead of MOSFETs. This circuit, however, was designed to accept either type of device, with the circuit shown as-is verified by CircuitLab's Frequency Domain Simulation. However, while verified, the design must be considered experimental regardless of whether IC3 or a 12AU7A tube is used. Breadboard test before committing to a soldered build. And house completed project in a grounded metal enclosure to prevent EMF interference.