The SurfMan was designed to block out irritating, distracting noise
by creating the sound of rain, crashing surf, or unmodulated pink
noise.
It was designed by John Simonton and featured in the August 1992 issue
of "Radio Electronics combined with
Electronics Now" magazine.
Here is a very condensed summary that I derived from the original article about the SurfMan circuit.
The SurfMan uses the reverse biased base-emitter junction of a silicon transistor driven into avalanche to serve as a random noise generator. A 5532 op-amp is used to amplify the junction noise and drive a set of headphones.
One stage of a 74HC14 hex Schmitt trigger inverter is configured as an oscillator (about 40khz) to create a voltage doubler to drive the noise generating transistor. The other three stages are configured as low frequency oscillators (1 cycle every few seconds) running asynchronously to create the electronic approximation of surf sounds.
The combined oscillator outputs drive two voltage controlled filters made by controlling the effective impedance of two diodes that convert control voltages into a changing frequency spectrum. The audio filter consists of two "L" section circuits comprising two resistors, two capacitors, and the two diodes as the tuning elements.
SurfMan Updated
A visitor to the my Surfman web pages suggested replacing the 74HC14 ic with a CD / MC / HEF 40106 or a MC14584 ic that will work with power supply voltages up to 15 volts.
At the time I built this project I just added a 6 volt regulator to fix the problem with the 74HC14 ic getting fried and it didn't occur to me (?) that I might have a hex inverter ic in my old parts collection that I could substitute.
So after looking through my parts I found a MM74C14 which is dual
numbered CD40106 and a date code of 1984.
I removed the regulator ic, added an ic socket and a protection diode
in case I try to connect the battery backwards since I am changing
things anyway and now the SurfMan works fine.