Doepfer A-118-2 Noise / Random S&H

Noise & Random Voltage Generator for Eurorack

The module generates the signals white noise, coloured noise, continuous random voltage and stepped random voltage (derived from the continuous random voltage by means of a S & H / T & H unit).

The noise signal is generated 100% analog by amplification of the noise of a transistor. White and colored noise are usually used as audio sources. The random voltages are normally used as control voltages (eg for filter frequency or any other voltage controlled parameters).

The A-118-2 gives you the ability to mix the relative amounts of Red (low frequency component) and Blue noise (high frequency component) in the coloured noise output.

For the continuous random voltage the rate of change (rate) and amplitude (level) of the random voltage can be adjusted. The continuous random voltage is derived from the coloured noise signal by low pass filtering. Consequently the settings of the controls for the colored noise (Blue, Red) affect the behaviour of the random voltage! A dual colour LED (red = positive / yellow = negative output voltage) indicates the continuous random voltage.

The continuous random voltage is used as the source for the S & H / T & H unit. The type of operation can be set to S&H (sample and hold) or T&H (track and hold). When T&H is chosen the output signal follows the input signal (= continuous random voltage) as long as the clock input is “high”. As soon as the clock signal changes to “low” the last voltage is stored. When S&H is chosen the input signal (= continuous random voltage) is sampled at the rising edge of the clock signal.

For the clock signal a “digital” signal (eg clock, gate, rectangle output of an LFO) is required. It does not work with slowly changing continuous CV signals. Another dual colour LED (red = positive / yellow = negative output voltage) indicates the stepped random voltage.