RO 12V 2-Tube Guitar Preamp PUBLIC

Richter Original 12V 2-Tube Guitar Preamp

Richter Original 12-volt 2-tube guitar preamp. Controls Include: Input Level, Fuzz enable switch, Fuzz symmetry switches, Fuzz Depth, Bass, Treble, Drive, Feedback, and Volume. Based on two proven circuits; Fender 5E1 Champ (input section) and the Garnet Herzog (output section), together with an output transformer that replaces the one in the Champ, to get the sound of an output transformer. Also includes a shunt-type Schottky-diode array (for fuzz) and a passive 2-band Baxandall tone-control. The design is meant to sound like a boutique single-ended tube-amp, though in a rackmount format, and using only a 12-volt supply voltage. The tubes, one 12U7 twin triode (not a 12AU7) and one 12AL8 triode + tetrode preamp tube, are space-charge types designed to operate using a single +12VDC supply-voltage on plates AND heaters (originally from a car battery). The 12U7 was created to work and sound like a 12AU7 at high-voltage, though the 12U7 is at low-voltage, while the 12AL8 was built for the triode to serve as a gain stage and the tetrode to serve as a power-amp driver, both of which are said to sound much like a 12AX7. Experimental circuitry. Untested design. No simulation. Frequency response and overall gain must be verified during breadboard testing. Calculated Frequency Range 20 Hz to 16 kHz with all controls at 50%. Calculated Overall Gain = +20 dBV (Vo/Vi = 10) with all controls at 50%. The tubes are available at The Tube Store. https://www.thetubestore.com . The transformer is available at DigiKey, part # HM4585-ND. https://www.digikey.com . The 8-ohm 10W resistor (standing in for a speaker load) is a Dayton DNR-8 wire-wound audio-grade 2%, available at Parts Express, part # OO4-C. https://www.parts-express.com . This circuit was intended as a rackmount project. Use vibration damping on the mounts and pads on the tubes, to help mitigate vibrational noise. Grounded and ventilated metal rackmount enclosure advised. Do not use any other supply voltage. Example Off-The-Shelf Supply: 12V DC 1000mA (1A) Regulated Switching Power Adapter, Product ID: 798. From the AdaFruit website. https://www.adafruit.com .