Diode Clipping Test Circuit PUBLIC

Multiple-Diode Clipping-Test Circuit

Circuit designed for making comparison tests of the sound of different diode types used for causing clipping of guitar signals to make a fuzz effect. Controls Include: Gain, Drive, Fuzz Switches, two Fuzz Depth controls, and Volume. There are two diode matrices; a Feedback Matrix and a Shunt Matrix. Each Matrix has four diode arrays with one enable switch and two symmetry switches. This allows for comparisons between eight arrays involving four different diode types; four in feedback loop (called a "hard-clipping" arrangement) and four in a shunt circuit (called a "hard-clipping" circuit, where the diodes are between the signal-path and ground). The diode types are also referred to as giving "hard" or "soft" fuzz. The diode types used here are; Schottky (soft), Germanium (soft), Standard Silicon (hard), and Zener (hard). Comparisons can thus be made between diodes in the same Matrix or those in the two different Matrices. With no fuzz enabled, the op-amps have a range between 49 Hz and 6.3 kHz, and a maximum gain of +24.7 dBV @ 250 Hz, with the controls at 50%. But with controls at 100%, maximum gain is +45.2 dBV @ 250 Hz, and the range extends from 22 Hz to > 20 kHz. Yet, the diodes do not greatly affect gain. The switch arrangement in the schematic indicates that for which clipping levels are very close across the board, so adjustment of the Volume control is minimized during comparison tests, and the enable switches allow for selection either of one array at a time or multiple arrays simultaneously. The symmetry switches set the harmonic content of the fuzz, and may have the most noticeable effect on sound. Note: Schottky arrays have the most effect on gain, but it amounts to no more than a 1.4 dBV cut. This circuit is designed as an experimentation project and could therefore remain as a breadboarded effort only. But if permanent soldering is desired, rack-mounting is recommended due to the number of switches, and to avoid bending over to make changes if floor-mounted. Power-supply not shown. Requires a regulated dual-polarity DC supply providing +-9VDC or +-12VDC or +-15VDC at >= 20 mA of current. Note: Higher supply voltage results in lower op-amp noise.