RO Hybrid 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, FB (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) dual triode preamp tube designed to work from a 12VDC supply, and two 6AK5W 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 (Q1), which can in turn overdrive the second triode, depending on the settings of the Input Gain and the Tube Fuzz 1 controls. Next, the signal goes through the Tube Drive control which feeds a 3-band Fender-style tone-stack, whose output goes to the Stack Sum control which feeds the first pentode (Q2), which in its turn can overdrive the second pentode (Q3). There is also a Feedback (FB) control in the pentode section, while the Volume control feeds an output buffer involving the second op-amp (OA2). The circuit is not intended to provide much gain, but is meant to provide a sound ranging from fairly clean, with low control settings, to highly distorted, with high control settings. Frequency range and maximum gain must be determined experimentally. Power-supply not shown. Requires a regulated single-polarity DC supply providing +12VDC @ >= 500 mA of current.