RO 12V Hybrid Guitar Preamp PUBLIC

Richter Original Hybrid Op-Amp + Tube Preamp for Guitar

Richter Original experimental hybrid op-amp + tube guitar-preamp circuit. Controls Include: Input Gain, Tube Fuzz 1, Tube Drive, Bass, Mid, Treble, Stack Sum, Tube Fuzz 2, Intensity, Feedback, and Volume. Intended for 6-string electric guitar. Involves one OPA2134PA dual FET-input op-amp IC chosen to ensure clean op-amp operation at all control settings, one 12U7 (not 12AU7) space-charge type twin triode tube designed to work from a +12VDC supply, and two 12DZ6 space-charge pentodes also designed to work from a +12VDC supply. The Input Stage involves one op-amp (OA1) which can overdrive the first triode in the preamp tube (V1a), which can in turn overdrive the second triode (V1b), depending on the settings of the Input Gain and the Tube Fuzz 1 controls. Next, the Tube Drive control feeds a 3-band Fender-style tone-stack whose output goes to the Stack Sum control, which then feeds the first pentode (V2), which can overdrive the second pentode (V3). There is also a Feedback control in the pentode section, while the Volume control feeds an output buffer involving the second op-amp (OA2). Overall gain is +20 dBV (Vo/Vi = 10). Frequency Range 10 Hz to 16 kHz. [Note: Pins 2 and 7 on the 12DZ6s are interchanged in the diagram, but since they are connected to each other anyway, this will not affect circuit performance.] Power-supply not shown. Requires a regulated single-polarity DC supply providing +12VDC @ >= 500 mA of current. Example: 12V DC 1000 mA Regulated Switching Power Adapter, Product ID: 798. $8.95 each. https://www.adafruit.com . Notes On The 12U7: The 12U7 was intentionally engineered to work and sound like a 12AU7 preamp tube, but operated with +12V on heaters AND plates (originally intended to be from a car battery). It is not a "starved" 12AU7, but an entirely different tube made to sound like a 12AU7 operated at high voltage, and with just as much gain (mu = 20). Notes On The 12DZ6: Comparable to a 12AT7 in tone, but with softer highs. Its sound is warm and full‑bodied. Less harshness in the mids, and with more openness in the upper mids, than high-voltage tubes. Less dynamic range than high‑voltage tubes, making it sound more compressed when overdriven, and with a pleasant vintage‑style smoothness.