RO 6-Stage RCA Tube Preamp PUBLIC

Richter Original 6-Stage Guitar Preamp Using RCA Circuits

Richter Original 6-stage real-tube guitar preamp using circuit topologies from the 1965 RCA Receiving Tube Manual # RC-24 (p. 544, 545); two "Low-Distortion Preamplifier", one "2-Stage Input Amplifier", and one "Bass and Treble Tone-Control Amplifier". Controls Include: Input Level, Bass, Mid-Center, Treble, Drive, Intensity, and Volume. Frequency Range 28 Hz to 16 kHz. Suitable for 6/7/8-string guitar or 4/5/6-string bass. Overall Gain <= +23 dBV (Vo/Vi = 14). Experimental circuitry. No simulation. Untested design. Build at own risk. Breadboard test before final soldering. House in a grounded metal enclosure. Power-supply not shown. Requires a regulated single-polarity DC supply providing +12V @ >= 1A. Example: 12V DC 1000mA (1A) Regulated Switching Power Adapter, Product ID: 798. $8.95. From the AdaFruit website. https://www.adafruit.com . Notes On The 12AC6: This is a space-charge pentode designed to operate with a +12V supply-voltage on heater AND plate. Its sound is warm, smooth, and neutral (i.e., no coloration), but with a slightly rounded tone, though not soft or mushy. Low-noise, with a stage-gain of 5, yet less bright than most high-voltage tubes. It was chosen to provide a clean input stage, difficult to overdrive. Notes On The 12U7: This is a space-charge twin-triode preamp-tube also designed to operate with a +12V supply-voltage on heaters AND plates. It is not a "starved" 12AU7, but is a different tube engineered to sound like a 12AU7 operated at high-voltage, and with the same gain (mu =20), though using a low-voltage supply. It was designed to sound the same as a 12AU7 (except when the 12AU7 is used in starved fashion with +12V supply), and therefore distorts the same when overdriven. Here, 12U7 triodes V2 and V3 can be overdriven, depending on the setting of the Input Level control, and triode V5 can be overdriven depending on the setting of the Drive control. Notes On The 12AF6: This is another space-charge pentode likewise made to work from a 12V supply-voltage on heater AND plate. Its characteristics are a bit different from those of the 12AC6, exhibiting brighter upper-mids, even crisp and edgy, but de-emphasizes the lows, yet providing warm soft-clipping, laden with even-order harmonics, when overdriven. It has less headroom than normal tubes, with less fullness, resulting in a tighter more controlled tone rather than lushness, but with faster responsiveness, described as "snappy". It was chosen to "colorize" the fuller sound of the 12U7 triodes by adding extra highs and overtones above their lows and mids. The final output of the preamp should therefore be broad-ranging, with controls providing an extensive number of voicings, a large distortion palate, and highly user-adjustable tonality.