Voltage Controlled Dual Sine Very Low Frequency Oscillator

I like slowly changing sound textures. This module provides two very low frequency oscillators - the main oscillator giving three sine waves down to 12 minutes per cycle, and an auxiliary single-output modulation oscillator going down to around 7 minutes per cycle.

• Main oscillator
  • 3 high-purity sine waves
  • 120 degees apart - 0°, 120°, 240°
  • 12 minutes per cycle up to 170Hz
• Auxiliary oscillator
  • Single sinewave output (diode-shaped triangle) - triangle available via component substitution.
  • 7 minutes per cycle up to 300Hz

• 100k input impedance
• short-circuit protected output buffers
• output levels ±5V

• operates from regulated ±15V supplies through 0.156" (3.96mm) 4-pin header (compatible with MOTM, Oakley)
• signal pads suitable for HE14 industrial connectors, dual-row 0.1" headers, or direct wire connection

• high quality fibreglass PCB, through-hole plated, soldermask, silkscreen legend, with full ground plane
• 80mm x 80mm (3.15" x 3.15") PCB with 70mm x 70mm (2.75" x 2.75") fixing centres

Sound Samples (MP3)

Coming soon.

Documentation

For interested parties the following documentation is provided.
Please note that all these documents are Copyright © 2009 Neil Johnson.

• Schematic
• PCB Layout
• Parts List

Build Options

• The integrating capacitors (C5, C6, C7 & C15) originally specified are big green Mylar 220n types, giving very low cycle times. You may choose to install different capacitors, and for this I have included standard 5mm-pitch holes as well.

• The auxiliary VCLFO is based on a triangle wave core. The triangle is then 'bent' by a diode ladder to produce a crude approximation to a sine wave. If you prefer to have a triangle wave then do not fit the diode ladder, replace R20 with a wire link and change R21 to 68k.

• The input CV offset voltage can be changed to provide other operating ranges. For example, changing the reference diode D16 from 2V7 to 3V3 will approximately shift the frequency ranges of both oscillators down by an octave.

• Similarly, increasing the input resistors will decrease the sensitivity. For example, changing R41 to 1M0 will provide a fine-tune input with 1/10 the range of the other input via R43 for the main oscillator.

Other notes:

• The white area near the power connector is for you to mark the board with some identifier (I usually write the date of completion).

• There is no setting up procedure - it is what it is. Any variations from the above specs will be due to component tolerances, making the characteristics of each module unique.

• Components marked 'DNF' are Do Not Fit - I put them in for experimentation (I find it easier to not fit a component rather than to bodge it on later if I change my mind). In particular, R36 sets the bias current in the VCAs. In this design I find the default behaviour (Class AB) is suitable.

Links

Here are some links to other people's work with this filter.

• Dave Brown's Dual VCLFO page describes his construction of this module. He presents three variations on MOTM-compatible front panels. Well worth reading.

Completed Module

Availability

This module is sold as a PCB only. The PCB costs £10 plus postage and packaging (£2.95 for UK, £3.95 for Europe/Rest of World).

Boards now available

Please Contact Me if you are interested in buying a PCB.

The only special component is the SSM2164P (DIL package version). This is available both from myself (see the Shop page) and from suppliers such as Farnell and Digikey.