DD2 – LFO / DC Mixer
The DD2 is a dual module offering a simple Low Frequency Oscillator (LFO) and a polarizing DC Mixer
in a compact form. The new Rev.2 version adds switches to couple the LFO waveforms direct into the
DC Mixer so that you can achieve some interesting waveform combinations.
The LFO
has two ranges for slow or fast rates (total range c. 0.04 - 20 Hz) and is switchable between
Triangle or Square outputs (+/-5v buffered output signals).
The Skew control is used to shape the output – for Triangle output the signal is skewed from Ramp
Down through triangle to Ramp Up, while for Square output the pulse width is changed between Narrow
Pulse-On through 50/50 to Narrow Pulse-Off.
The DC Mixer
provides two inputs (DC-coupled) with polarizing controls using centre-detent pots –
turning a level control clockwise mixes a positive signal and turning it anti-clockwise mixes an inverted
signal, while in the centre position no signal is passed. This proves an extremely useful module for
mixing both audio and / or control signals. (the operation is basically the same as for the Bipolar
External mode of the CTL2 Joystick section)
There are two Couple switches which pass the LFO waveforms into the two channels of the DC mixer.
Not only does this allow you to combine, say, the LFO Tri-wave with some other modulation source, but
you could also combine the Tri & Sqr waveforms to generate some interesting waveforms - see the
scope shot images for some example waveforms.
Trimmers are provided to Null the centre detent point of the two DC Mixer channels. If adjustment is
needed, insert a VCO signal into one channel, turn the level control fully up and then back down to the
central position - now adjust the trimmer until absolutely no sound is heard at the output. Do the same
for the other input channel. There is always a little 'play' around the centre detent position but a little
wiggle should always allow you to find the true centre-off.
