RO Experimental 3-Tube Fuzz III PUBLIC

RO Experimental 3-Tube Fuzz Circuit Version III

Richter Original experimental 3-tube preamp circuit, version 3, with 2-voice shunt-diode fuzz and 3-band Fender-style tone-stack. This is simply a modification of version 2. Changes include adding Presence control to Tone-Stack and adding Feedback control at the cathode of V2. Controls Include: Input Level, Bass, Mid, Treble, Presence, Feedback, Intensity, Fuzz 1 enable switch, Fuzz 1 symmetry switches, Fuzz 1 Depth, Fuzz 2 enable switch, Fuzz 2 symmetry switches, Fuzz 2 Depth, output Drive, and master Volume. The 12U7 twin-triode (not a starved 12AU7) was designed to provide the same gain (mu = 20) as a 12AU7 at high-voltage, though the 12U7 is at low-voltage. It was also engineered to sound the same. The 12DZ6 pentode (substitutes are 12AE6 and 12EK6, only), despite being a pentode, is reported to sound much like one triode of a 12AX7 twin-triode preamp-tube at high-voltage, though the 12DZ6 is also at low-voltage. Consequently, this project should sound like the preamp section of an American-made boutique guitar-amplifier that uses two 12AU7 and one 12AX7 tubes in its front-end, with the addition of a 2-voice diode-fuzz effect. Fuzz 1 is from standard silicon diodes and Fuzz 1 is from Schottky diodes. The symmetry switches set the harmonic content of the fuzz. Overall Frequency Range 22 Hz to 16 kHz. Suitable for 6/7/8-string guitar or 4/5/6-string bass. Overall Gain = +20 dBV (Vo/Vi = 10). The tubes are available at The Tube Store. https://www.thetubestore.com . Power-supply not shown. Requires a regulated single-polarity DC supply providing +12V @ 1A. Regulated wall-wart acceptable. Example: Triad brand; model WSU120-1000-R. DigiKey # 237-1456-ND. $8.45 each. https://www.digikey.com . Tube Sound Profiles: The 12U7 sounds like a 12AU7, very similar to a 12AX7 with a little less bass and more highs, but fairly identical mids. It is warm, smooth, and full-toned, with less harshness than a 12AX7, and provides harmonically-rich distortion when overdriven. The 12DZ6 sound is very close to that of a 12AX7, but cleaner, and with lower noise. Generally, it is articulate and highly responsive, with brighter upper-mids but more limited lows. Should be great at providing a vintage-style tube saturation for lead-guitar work. Rackmount implementation is recommended, with vibration damping mounts. And use pads on the tubes to mitigate vibrational noise.