Neil Johnson
Three Pole Voltage Controlled LFO Module

 

I built the voltage controlled low frequency oscillator PCB from Neil Johnson which uses the Analog Devices SSM2164 quad VCA.

 

VC-LFO Mouser part number list

  VC-LFO Modifications:

  1. LEDs on each LFO output to indicate rate and polarity (green indicating positive output and red indicating negative output)

  2. An Aux LFO switch to select between a sine and triangle output

  3. Rate control for each LFO.  I set the upper limit to 7.5 volts which produces an upper frequency of ~60 Hz.

VC-LFO panel controls and LED schematics

 

 

Panel

I created three 1U concept designs for the module.  The main LFO has both a rate and FM attenuator.  The Aux LFO has a FM input but no attenuator and both a triangle and sine output.  I had to compress the jack spacing to fit 7 on a 1U panel.

The center panel uses small potentiometers which allows both a Rate and FM control for each LFO.  I eliminated the 7th jack by using a switch to select between a triangle and sine output. 

The right panel is standard MOTM spacing.  The main LFO has both a rate and FM attenuator.  The Aux LFO has a FM input but no attenuator and a switch to select between sine and triangle output.  I chose this design and made a panel out of 1/8" aluminum with a paper overlay.  I use spray adhesive to mount a full size laser print of the FrontPanelExpress file and then cover it with a couple of coats of lacquer for texture and sheen.  This is my third module using this type of panel and they seem to hold up reasonably well.

                             

Sine and triangle VC-LFO FrontPanelExpress design file (left)

Dual control VC-LFO FrontPanelExpress design file (center)

Standard MOTM-style VC-LVO FrontPanelExpress design file (right)

 

 

Construction

I made a PCB bracket out of aluminum and used  P260P potentiometers from BI Technologies, and potentiometer chiclets from John Loffink.

 

 

 I added the additional LED op amp on top of IC5.  The LED for the main oscillator indicates the polarity of phase 1 (0).

 

 

Waveforms

These scope images show the three phase sine waves from the main LFO and the sine or triangle wave from the aux LFO.  The diode waveshaping produces a reasonable sine wave.

 

 

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