AJH Synth Entropic Doom Eurorack Noise Oscillator Module (Silver)

The Entropic Doom takes noise and tuned noise to a whole new level, it can almost be described as an oscillator for noise, or Noisillator as we like to call it. Traditionally in modular synthesis we use either white or pink noise and then treat it through envelopes and filters to give various effects, however the Entropic Doom takes modular noise creation to places its never been before!

We have a CMOS Logic Gate based Noise Generator with Coarse and Fine tuning control along with a two, three and four pole low pass filter and a passband resonator within the noise loop itself. We have both Audio and Sync inputs, which can be mixed into the noise loop to add even greater variety to the sounds generated. We have both Bright and Dark Noise outputs, which are pre and post filter respectively, however because the noise and filter are in a feedback loop the Bright output responds to filter type and settings too.

There are CV inputs to allow voltage control of both Frequency and Resonance, and also an all important 1V/Oct input so that we can "play" the noise in tune from a keyboard or sequencer.

In addition we have a separate XOR based Ring Modulator and a Cmos gate based VCA sub modules. These can be used independently from and simultaneously with the Noisillator circuitry.

What is the Entropic Doom?

The Entropic Doom is a very unique module, we like to think of it as an oscillator for noise - a noisillator! It has a unique and unusual topology, featuring a cmos logic gate that is biased for use in the analogue region between logic zero and one. We use this for controlled noise generation, and it is in a closed loop circuit along with a variable pole low pass filter and VCA. The output of the filter is fed back into the input of the cmos logic gate, which generates noise that can be tuned depending upon the resonant loop gain, filter frequency and filter pole selection. We can take the output from two different points in the noise loop, either pre-filter (Bright Out) or Post filter (Dark Out). We can also mix an external audio signal into the noise loop with the Audio In jack and level control, and also use an audio sync signal (Sync IN) to reset the cmos gate and / or mix in adio to a different part of the noise loop. We also have included an XOR Ring Modulator and XOR VCA too, each of which is rather different in function from its regular analogue counterpart.

Usually in analogue synthesis we use a reverse biased transistor or Zener diode in avalanche mode as a noise source, however the Entropic Doom takes a different approach and uses a CMOS logic gate in a biased, analogue configuration as a noise generator - this is useful as we can also apply as Sync signal to the other input of this gate so that the noise generation is reset, in a similar way that Oscillator Sync works on an analogue VCO.

The Noise core itself is contained within a loop that also includes a low pass filter, which can be switched between 2 pole, 3 pole and 4 pole configurations, and the feedback from this filter is fed back into the noise core itself to create a resonant feedback loop. We have two noise outputs, the Bright output is taken directly from the Noise source itself, and the Dark Output is taken from the output of the filter.

External audio can be mixed into the pre-filter section of the noise loop using the Audio In jack and its associated Audio In level control.

There is also a Sync Input, to allow a signal to be fed into the other channel of the Cmos logic gate that is used as a noise generator - if a square or pulse waveform is used at a suitable frequency then this gates the noise source to give a similar effect to Oscillator sync in a VCO - the effect is subtle, and most obvious when using the Bright output. The sync signal is also mixed into the noise loop, so it serves as a second Audio input too.