Voltage Controlled Low Frequency Oscillator

Constructional difficulty: Moderate. Some simple setting up required.


The suggested layout of the VC-LFO module in a 1U wide panel.

This is a versatile yet easy to use voltage controlled low frequency oscillator module that can also be used as an audio VCO over a useful range.

The unit features sinusoid, sawtooth, ramp, triangle and square outputs. All are available simultaneously. A sync input is available to reset the waveforms to a fixed point.

The module features two CV inputs. One is fixed at 1V/octave. The other CV input is controlled by a single pot on the front panel. When the pot is turned right of its central position, the pot acts as a normal attenuator; increasing the sensitivity of the CV input to a maximum of 0.5V/octave. Left of centre, the pot will act in inverting mode. Fully anti-clockwise the input will respond to -0.5V/octave.

A tricolour LED indicates the output status.

For DIY builders of this module it is possible to purchase the Sock8 circuit board which is available separately. This little board speeds up the wiring of the eight 1/4" sockets and reduces the chances of any wiring errors.

Power (+/-15V) is provided to the board either by our standard Oakley 4-way header or Synthesizers.com header. Current consumption is approximately 40mA per rail.

The board size is 104 mm (high) x 104mm (deep).

Specifications

The VC-LFO has an operating range of lower than 0.002Hz (one cycle every eight minutes) to over 14kHz from the front panel controls. The range can be extended with external CV inputs. The maximum frequency of the VC-LFO is well over 25kHz.

Range of Frequency control: 17 octaves

eg. When the fine control is central the frequency pot can vary the output from 0.016Hz (one cycle per minute) to 1.7kHz.

Range of Fine Frequency control: 6 octaves

eg. When the main frequency pot is central, the fine control will vary the rate from 1Hz to 64Hz.

These frequencies can be altered over a limited range by the onboard trimmer, or more significantly by a change in the master timing capacitor.

When used as an audio rate VCO the usable range that conforms to 1V/octave (to +/-2cents) is over six octaves from approximately 32Hz to 2kHz. This is none too shabby for a low frequency oscillator. For accurate musical use over 2kHz we recommend that you use the Oakley VCO.

Sync input requires a fast rising gate exceeding 4V when active, or at least 2V peak pulse or sawtooth waveform.

The Oakley VC-LFO board behind a natural finish Schaeffer panel. Note the use of the optional Sock-8 board to make wiring the socket field much easier. Contrary to what it says on the VC-LFO circuit board this is actually an issue 3 PCB.


Sound Samples

The following were made using the VC-LFO as an audio oscillator. Pitch was being controlled via the module's 1V/octave input.

Simple sequence being played while listening, in order, to the raw outputs of the saw, triangle, square and sine.

The same simple sequence being played using the sawtooth output but through a Superladder filter and a bit of effects to add ambience.

Sync sweep samples. Using the sawtooth output and syncing the VC-LFO with another VCO. The first set use an ADSR to sweep the VC-LFO's pitch, whilst the single note is manually swept with the coarse frequency pot.

Some more sync sample hits. This time using the other waveform outputs; square and then triangle.

The following sample set was obtained using the Oakley ring modulator using the VC-LFO as the modulator (Y-input). The first of the three sounds uses a stable sine output from an Oakley VCO as carrier whilst the VC-LFO's frequency is manually swept with the frequency pot - this shows the huge range of the frequency pot. The second sample processes the output of two mixed saw VCOs and sweeps the frequency of the VC-LFO from high to low. The final sample uses the same two saw VCOs but triggers the VC-LFO with the gate thus each new note always fades up from nothing.


Prices

Click here for how to order.

VC-LFO issue 3 PCB ...................................... 20GBP
Sock8 issue 2 PCB ............................................ 7GBP

VC-LFO issue 3 pot bracket kit ........................ 0.50GBP

1K +3000ppm/K temp co resistor .................... 1.50GBP
1K +3500ppm/K temp co resistor .................... 4GBP

You only need one temp co resistor, either the +3500ppm/K temp co or the +3000ppm/K temp co. The +3500ppm/K device offers greater temperature stability at an increased price. For standard LFO duties the +3000ppm/K device is good enough.

The optional Pot Bracket Kit contains the two 16mm Alpha pot brackets required to complete one module.

All other parts can normally be purchased from you usual electronic component supplier.

VC-LFO ready made modules are available from Krisp1.com.

All prices include VAT at UK rates. Shipping and postage is additional to these prices. See also the FAQ page.


Project Downloads

User Manual

Builder's Guide

Please note: Issue 3 boards are erroneously marked as issue 2. If you have a place for an HFT trimmer on your board then it is an issue 3 board.

Construction Guide Our handy guide to building Oakley DIY projects

Parts Guide Our handy guide to buying parts for Oakley DIY projects

Links to schematics are available to purchasers of the PCB or module and will be sent via e-mail when the board(s) are shipped.

Front Panel database

A Schaeffer front panel can be made for this module. The databases can be found by downloading the following links:

5U format in traditional black

5U format in natural silver

To read these files you will need a copy of 'Frontplatten designer' from Schaeffer. The program also features on-line ordering, so its now even easier to buy your panels from Scheaffer.

The company are based in Berlin in Germany and will send out panels to anywhere in the world. Delivery to the UK normally takes around ten days. For North American users you can also order your Schaeffer panels from Front Panel Express.


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Copyright: Tony Allgood.
Last revised: November 01, 2017.