Dream Machine

Holidays in COVID-19 times: many people stay at home or in their own country, while the bravest among us dare to fly to Majorca or Ibiza. A sea voyage on a cruise ship? Well, better not . But don't worry: here, we present you a DIY sea sound generator, with which you can transform your bedroom into a cabin on a luxury cruise ship!

How can we simulate sea noise (or, more accurately, the sound of the surf)? Actually, it is a noise that slowly swells and dies out again at a regular rate. And armed with that knowledge, we can put together a "shopping list" of what we need: a noise generator, a sawtooth generator for the swelling and dying out, and an audio amplifier plus a loudspeaker. The result is sketched in Figure 1.

Figure 1

The sawtooth generator is built around the op-amp IC1 connected as a comparator — well, it is not a "real" sawtooth because the output voltage (read: the voltage across capacitor C1) does not increase and decrease linearly but follows the charge/discharge curve of the capacitor. But that does not matter here. Resistor R3 provides sufficient hysteresis so that we find about C1 and pseudo-sawtooth with a decent amplitude (about 5 V). The ratio between swelling and decay time can be set with P1.

The noise is provided by transistor T2, which is "misused" as a reverse diode. Due to the relatively high supply voltage, this diode flashes without breaking the transistor: R6 limits the current.

Such a pulsating transistor makes a noise that it is a delight. Op-amp IC2 amplifies this noise enough to drive a loudspeaker. With FET T1, we have transformed this amplifier into a kind of voltage-controlled amplifier (VCA): the gain increases and decreases at the rate of our sawtooth.

Constructing the circuit (with "classic" parts on a pinhole board) is not difficult. Have a pleasant cruise!