MATRIXSYNTH: Slightly Nasty 4U Modular

Saturday, May 22, 2021

Slightly Nasty 4U Modular

This one was spotted and sent in via Martin Gn├Ągi.


Slightly Nasty Modular, Roland MKS-7, and Akai S3000XL
Slightly Nasty Modular - Cinematic Jam
Slightly Nasty Modular - Techno Jam
Five Video Game Covers in Five Minutes
The Model 1011 Discrete VCO
Slightly Nasty Modular Jam
Pit Bull DM-1S - Metal Demo
Slightly Nasty Modular - 8 bar sequence jam
Slightly Nasty modular - dirty cyberpunk bass

Current module line-up via

Model 1011 Discrete Oscillator

The Slightly Nasty Model 1011 is a voltage controlled oscillator that’s a little bit different. Despite featuring a host of functionality including four mixable waveshapes, suboctave, linear and logarithmic FM, pulse width modulation, and oscillator sync, inside it you won’t find a single IC opamp or OTA. What you will find is no less than 41 discrete transistors flying in close formation, doing their best to output useable musical tones.

The Model 1011 has been designed from the ground up to use modern “jellybean” components that can be cheaply and easily obtained from most electronics suppliers. Despite the unusual implementation, the architecture is actually a very traditional sawtooth-core design that will be familiar to most people who have worked on VCOs before.

Three outputs provide mixable sine-triangle, saw-pulse-suboctave, and suboctave square respectively, the pulse wave also featuring both manual and CV-controlled symmetry (pulse width). Aside from the usual 1V/Octave input, there are also separate inputs for both linear and logarithmic FM, each with input attenuators, as well as a hard sync input. The exponential converter is temperature compensated for better thermal stability and the sawtooth core features high-frequency compensation for better pitch tracking.

The Model 1011 uses the Loudest Warning 4U format for the front panel, and follows Eurorack electrical and power standards. All front panel components are PCB mounted for easy wiring-free construction. The front panel is available in two finishes – satin anodised and gloss white powdercoat.

Model 2231 Asymmetric Slew Limiter

The Slightly Nasty Model 2231 Asymmetric Slew Limiter is a versatile signal generator and signal processor based on the principle of the Universal Slope Generator originally found on Serge synthesisers. This style of module is often seen as one of the defining elements of the “West Coast” school of synthesiser design, with its emphasis on open-ended versatility and functional abstraction.

Essentially the Model 2231 is a voltage-controlled integrator, with a few additional circuits that allow it to be used for a number of other functions. The basic principle behind the module is that the there are actually quite a few synthesiser circuits that are based internally around some kind of integrator – the Model 2231 takes this central core and presents it in a way that allows it to be used in these different configurations.

There are three operating modes on the Model 2231. “SLEW” takes the incoming signal and slews it according to the rise and fall rates set by the panel controls and CVs. At longer slew times, this can be used as either a traditional slew processor for portamento effects, or to add attack and release times to a gate signal like an AR envelope generator. At higher (audio) rates, the 2231 can operate as a voltage controlled lowpass filter, with the added trick of being able to have different cutoff frequencies for the rising and falling parts of the waveform. This can yield an interesting combination of filtering and waveshaping.

“ENV” turns the 2231 into a voltage-controllable AD envelope generator, triggered by the positive edge of a gate signal. The envelope is auto-completing and retriggerable, and is great for generating percussion envelopes.

“CYCLE” turns the 2231 into an oscillator (or LFO) with a range of around 0-1kHz, with independently controllable rise and fall rates allowing for some interesting waveshape and pitch modulation. Using one subunit of the 2231 as an LFO to modulate the other allows for some interesting rhythmic effects and is an easy way to add movement to a patch.

The slope times have a logarithmic response extending from “As slow as you trim it” to 1 millisecond for a -5v to +5v swing. “ENV” mode outputs a 0-5v signal, and “CYCLE” a +/-5v waveform (10v peak-to-peak). The gate input features a internal comparator that ensures gate signals are always converted to a 0-5v signal before reaching the slew processor, to ensure that sub-5v gate signals still generate a 0-5v output when the module is used as an AR envelope generator.

Model 2251 Multiband Filter

The Slightly Nasty Model 2251 Multiband Filter is a versatile multimode 12dB Oct state-variable filter that provides four simultaneous filter outputs: lowpass, highpass, bandpass, and notch. Both cutoff frequency and resonance are CV-controllable, with attenuverters provided for both. A dedicated audio FM knob allows add extra texture to be added without tying up an external mixer. In addition, one of the unused LM13700 OTA stages is used to implement a bonus utility VCA that operates independently of the filter.

The 2251 was designed to provide very controlled and consistent resonance across the operating range, so that very dynamic CV control of the resonance within a patch would always result in controlled and predictable signal amplitudes without excessive distortion or clipping. The resulting character of the filter is quite smooth, while still providing a satisfyingly big analogue filter sound suitable for basses, leads, and general sound design. Despite this self-limiting resonance, the filter still self-oscillates and can be “pinged” by setting the resonance on the threshold of oscillation and hitting the audio input with a transient signal.

The Audio FM knob allows for some additional dirt and texture to be easily added by modulating the cutoff frequency with the input signal, which results in a sound somewhere between soft distortion and harmonic FM. The extra VCA is ideal as a final envelope/output VCA, meaning that a single oscillator and 2251 filter can provide a complete signal path for basic subtractive synth sounds.

Model 1411 Discrete Mixer

The Slightly Nasty Model 1411 Dual Discrete Mixer is a basic mixer module that provides two independent 3:1 mixers, with switchable soft-clipping overdrive distortion and both inverting and non-inverting inputs.

The circuitry in each half of the 1411 is based around a pair of discrete opamp-type circuits that operate as summing amplifiers – providing signal isolation between the inputs. Additionally, when in “Linear” mode, input C is inverted, allowing for more CV mixing and phase cancellation options.

Inputs A and B can also be fine-trimmed to have better unity gain when turned up to maximum – which is useful when mixing pitch CVs that require accurate scaling.

The “Distortion” mode engages a soft-clipping diode circuit with an asymmetric high-frequency response, to emulate the sort of distortions found in some early synthesiser mixers. This is useful for adding just a touch of saturation and overdrive to sounds like bass percussion that might otherwise struggle to be heard in a mix, as well as providing a nice aggression to detuned oscillators.

Because the Model 1411 is a true summing mixer (inputs are added together rather than averaged), the distortion may be overdriven further by bridging the inputs together, thus amplifying the input signal by a factor of three, Additionally, feeding the output back to one of the inputs creates a more aggressive disortion, going into self-oscillating feedback at higher levels. Experimenting with different modules in the feedback path opens up a whole world of interesting distortion timbres and feedback effects.

Model 2111 Random Voltage Source

The Slightly Nasty Model 2111 Random Voltage Source allows you to easily incorporate elements of randomness and chance into your modular patches, either clocked to some sort of external trigger (such as a clock or gate pulses), or free-running via the internal voltage-controlled clock. It provides three different flavours of noise signal, three random voltage outputs plus a slewed variant, random logic, clock output and a clock-synced ramp output.

The noise is available in White, Dark, and Light variants – White is flat across the spectrum, Dark emphasises low frequencies and rolls off the top end, and Light rolls off the bass frequencies and emphasises the high frequencies. This is particularly useful for making multiple percussion voices, as well as allowing noise to be directly mixed into a patch without tying up a filter.

The random voltages are generated by feeding random voltages into the input of a shift register and then generating the outputs via two scrambled 6-bit resistor-ladder DACs to create one of 64 possible output voltages. Outputs A and B are mostly independent from one another, output “A-B” is the difference between the two and has a somewhat different (more centre-weighted) distribution, as well as being available in a linearly-slewed variant for smooth random modulation.

The Voltage-Controlled Clock increases the versatility of the module by providing useful timing functionality, and the ability to create interesting random timing signals by feeding the unit’s random outputs back into its own Clock Rate input. The timing core of the clock is broken out to the RAMP output as a 0-5v ramp signal that allows for interesting synchronised modulation when using the 2111 as a master clock (Note that this output will always follow the internal clock, even when using an external clock source). The Clock can run into audio rates as well, to create interesting voltage-controllable noise effects.

The two logic outputs on the 2111 are the Clock output, which is self explanatory, and the Random Logic output – which follows the first bit of the shift register and is useful as a random two-state modulation source, a random gate/trigger signal for envelopes etc., or an Atari 2600-style digital noise signal.

Due to the use of an 8-bit shift register to convert the noise signal into clockable static voltages, the randomness of the 2111 is somewhat unusual. While it is impossible to predict exactly what the next value will be, the fact that each clock pulse introduces only one new binary bit into the register means that any given output value can only be followed by one of two possible subsequent values. This means that certain patterns will reappear as similar bit strings travel through the register on different occasions.

In Development:

Model 2411 Voltage Processor

(In development) A versatile voltage processor with dual units, each featuring two attenuverters – one switchable to +5v input for offsets, as well as a 3-1 mixer output and comparator output. Additionally the bottom of the panel provides a convenient unipolar-to-bipolar / bipolar-to-unipolar converter.

Model 1221 Discrete Lowpass Amplifier

(In development) A cross between a traditional discrete VCA and the Moog ladder filter, this module can operate in either VCA or Lowpass Amplifier modes. The slope in LPA mode is 12dB/Oct.

Model 2201 8-Band Resonant Filterbank

(In development) An 8-band filterbank with bands capable of going into self-oscillation, or ringing at lower amplitudes. Separate inputs and outputs are available for odd and even numbered filter bands.

Model 2211 Transfer Processor

(In development) A four-stage voltage-controlled wavefolder / distortion unit.

1 comment:

  1. Really nice performance with a great command of building things up.
    Melodies over sequences - Wonderful!


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