The MiniMod Dual LFO and VCA is a compact 10hp wide Eurorack format module. It comprises two independant LFO's with variable wave shapes and a DC coupled VCA. In addition LFO1 includes an extra low range and a Sync (reset) input.
The onboard VCA is normalised to the Triangle output of LFO 2 and this makes it a simple, one module solution for adding variable depth modulation to VCO's, VCF's etc. as the modulation amplitude (level) can be controlled by applying a control voltage (CV) of between 0 and +5 Volts to the VCA CV Input.
The VCA can also be used independantly from the two onboard LFO's, and it responds to CV voltages in a linear manner.
The "Triangle" output wave shape can be continuously varied from Sawtooth (Shape control fully anti clockwise) to triangle (Shape control at 12 o'clock) throught to Ramp (Shape control fully clockwise).
The "Square" output wave shape can be continuously varied from a duty cycle of 98% (Shape control fully anticlockwise) down to 2% (Shape control fully clockwise)
This module includes two completely independent modulation sources, LFO 1 and LFO 2. Each LFO has a "Triangle" and "Square" output, although the actual waveshape is determined by the setting of the associated "Shape" control (see below). These outputs are Bipolar, so the output varies between being a positive and negative voltage, and the amplitude is +/- 5V, or 10 Volts peak to peak.
The output wave shapes are continually variable with the Shape control, the following illustration shows resulting waveshapes from the "Triangle" and "Square" outputs , below a selection of "Shape" control knob positions.
The regular frequency range for LFO 1 and LFO 2 is:
Or expressed as time period:
The maximum frequency for LFO 1 & 2 is 25Hz with the Rate control fully clockwise and the Shape control set midway, but (usefully) if the Shape control is set to either fully clockwise or fully counterclockwise then the maximum frequency will go up into the audio range - to as high as 1 kHz. However, as the rate is reduced from maximum this Shape control non linearity reduces towards zero, so at Rates of 5Hz or less the setting of the Shape control has very little effect on the LFO rate. This behaviour is very useful, as it allows audio rate modulation to be achieved but still allows good resolution and fine control of rate without the need for course and fine Rate controls.
With the Slow switch down the rate of LFO 1 reduces to the following frequency range:
Or expressed as time period:
Do note that the Shape control still exhibits the same non linear behaviour towards the extremes of travel at higher rate settings (as noted above), however it is not particularly relevant (or useful) here as it is more beneficial to switch up to regular rate settings for higher frequencies, and there is a useful overlap between the Slow and regular frequency ranges with this in mind.
The Triangle and Square waveforms can be reset (restarted) from a sync waveform with a fast leading edge, such as a squarewave from LFO or an envelope generator set for fast attack. This can be particularly effective when using slower modulation speeds, when a gate or trigger (from a Midi to CV Converter for example) can be used to reset the start of the waveform on each new key press.
The VCA is DC coupled, and has a linear response curve, so it is ideal for using with modulation sources. The input of the VCA is normalised (connected by default) to the Triangle output of LFO 2, so by default the Triangle output from LFO 2 is automatically available from the output of the VCA, and it's output level is controlled by applying a Control Voltage to the CV input of between 0 Volts and 5 Volts, where 0 Volts will give complete attenuation of the VCA output and +5V will give unity gain, so in it's default state this would give between 0 and 100% output depending up on the CV Voltage applied - with no input or 0V the output will be zero, and with a +5V CV voltage the output will go up to 100%, which of course would be a +/- 5V signal level with the default connection of LFO2 to the VCA Input.
The CV input is safe to use with control voltages up to +12V, however it is only effective in the range of 0V to +5V, voltages between +5V and +12V will be clamped and treated internally by the VCA as +5V. Negative CV voltages are ignored, it is safe to apply CV voltages of up to -12V and they will not damage the module, they will simply be ignored as (like most VCA's) the CV input responds to positive voltages only.
If a signal is patched to the VCA Input socket ( for example lets say the Ramp waveform from a MiniMod VCO) then the output of LFO 2 will automatically be disconnected from the input of the VCA, and the signal patched to the VCA input jack (in this example the MiniMod VCO ramp waveform) would be routed through the VCA instead.
The onboard VCA is very useful, as it allows the modulation level of the LFO to be easily voltage controlled without the need for patching in other modules, a common application would be where a keyboard modulation wheel sends out a 0 to +5V voltage (Such as a Waldorf KB37 and many Midi to CV Converters), this can simply be patched to the Dual LFO CV In and the Modulation wheel would then control the level of modulation from the VCA Output between 0 and 100%
The relationship between the various inputs, outputs and controls of the Dual LFO / VCA is illustrated below.