nw2s::d0 hybrid overdrive
The nw2s::d0 is the smallest in a series of unique, hybrid overdrive, distortion, and wave shaper modules which are designed to range from subtle harmonics through mild break-up, and into full asymmetric clipping. Used creatively in a multi-tracking situation, in feedback loops, or in time-domain effects chains, some presence, warmth, or lo-fi grunge can easily be added to your patches. These are not for generating buzzsaw guitar pedal tones.
What's key about these modules is that they are extremely dynamic and responsive to the material. They can act as a wave shaper for a simple sine or triangle wave, or for more complicated signals such as drum tracks or sample output, they add a distinct tape deck tone. Instruments and voice as well can benefit from the playability of the circuit. Run them in series or parallel for even greater sonic options. Patch them in to your DAW as an insert on a parallel bus. Or, my favorite - run your reverbs through this on a warm, slightly overdriven sound and bask in the glory.
This block diagram illustrates the signal flow. The input buffer provides a consistent high input impedance and drives the first two clipper circuits. The drive potentiometer controls how much signal is routed to two symmetric green LEDs. When fully counterclockwise, the LEDs have almost no effect. When fully clockwise, the entire signal is "clipped" by the LEDs. Since green LEDs have a very slow onset and a relatively high forward voltage, the result is a very tube-like rounding-off of the tops of the waveforms.
The second phase is an asymmetric diode clipper based on a 1n4148 silicon diode. Just as with the drive control, the asym control moves from zero impact on the signal to full negative clipping. Since the silicon diodes have a faster onset with lower forward voltage, this results in a buzzier sound.
After the clippers is a 12dB per octave Sallen-Key filter with a fixed peak of a few dB at the corner frequency. This has the effect of both rolling off some of the top of the signal while giving the signal more presence at the corner frequency. I find these types of filters very appealing in the upper mid-range of travel. The filter knob operates such that the filter is completely open in the clockwise direction. The range of the filter is about 500Hz to 5000Hz.
After the filter is a 600Ω audio transformer with a fairly limited bandwidth of about 8kHz. These types of transformers were typically used in telephonic circuits in days of old. In this case, the transformer is significantly under powered, so in addition to limiting the bandwidth, it adds a fair amount of a specific kind of magnetic distortion and hysteresis. A bias control adds a DC bias to the primary of the transformer, bringing it closer to saturation, causing thin bass frequencies and pushed mids.
Finally, the level control adjusts the output gain by about 10dB to both make up for the signal loss through clipping and to allow you do overdrive whatever module may be next in your signal chain. This stage is not intended to add distortion in and of itself, but should allow you to set the gain staging properly depending on the desired impact downstream from this module.