LFO Low Frequency Oscillator ~30Hz Sine

A project log for Dalek / Cybermen voice changer

A simple ring-modulator circuit which can change your voice to sound like a Dalek or Cybermen from Doctor Who

sproketSproket 02/03/2021 at 10:240 Comments

Since this ring modulator project started I have not found an ideal solution for generating low frequency sine waves. This is particularly due to wanting a sub-audio 30Hz sine which most circuits can't quite manage. I have tried Wien bridge oscillators (with and without light bulbs), multivibrators, quadrature amplifiers, and various logic circuits.

Clean signals from a Wien bridge oscillator broke down nearer the lower frequencies and often reached the limits of being able to 'self start' reliably.

Most logic based circuits suffer from asymmetric threshold voltages which is compounded by how quickly a capacitor can discharge compared to charge.

A solution?

I may compromise and use a triangle-wave, which arguably has the same relationship with a rectifier circuit (or ring-modulator) as a sine-wave would have. Harmonics generated by a triangle-wave are not desirable as they will effect the overall sound, a solution may be to partially shape the output by adding some capacitance.

The current go-to commercial device is a Moog Minifooger MF Ring modulator, which reportedly generates a shaped triangle-wave when you select sine. So if it's good enough for the pro's...

555, anyone?