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 12DZ6 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 to sound fairly clean with low control settings and go highly distorted with high control settings. Frequency range should be measured experimentally but should work for 6-string electric guitar, while maximum total voltage-gain should be around 21. 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 .