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A-110-4 is a Trapezoid Thru Zero Quadrature VCO. The module is based on an idea by Donald Tillmann but is realized with modern electronic circuits (Don’s original design from 2003 used the obsolete CA3280). Because of it’s unique trapezoid core it’s totally different compared to other VCOs. But the trapezoid core is not the only specialty: it is also a quadrature VCO and features linear thru zero frequency modulation.
The term “quadrature” means in this connection that the oscillator outputs two trapezoid waves with 90 degrees phase shift. The same as sine and cosine of a standard quadrature oscillator. These waveforms are called TRASIN (trapezoid sine) and TRACOS (trapezoid cosine).
The term “Thru-Zero” means that even “negative” frequencies are generated. But this a bit a misleading term as negative frequencies do not really exist. “Negative” means in this connection simply that the TRASIN/TRACOS waves will stop when the linear control voltage reaches 0V and continue with the opposite directions as the linear control voltage becomes negative and vice versa.
The module has two control sections: linear and exponential. The exponential section consists of the XTune control, the 1V/Oct input and the XFM input with the corresponding attenuator XFM. The exponential control voltage is the sum of these three voltages. The linear section consists of the LFrq control and the LFM input with the corresponding attenuator LFM. The linear control voltage is the sum of these two voltages. A dual color LED is used to display the polarity of the linear control voltage. The pitch of all outputs is determined by the control voltages of both sections. When the LFrq control (LFrq means Linear Frequency Control) is fully CW the module works like a normal VCO and the LED lights blue. The pitch is then controlled by the exponential section with the manual Tune control XTune and the exponential frequency control inputs 1V/Oct and XFM. XFM is used to apply an exponential frequency modulation with adjustable depth (e.g. from an LFO or another VCO).
Other waveforms like triangle, sawtooth, rectangle and sine can be obtained very easily from the TRASIN/TRACOS signals (triangle e.g. simply by subtracting TRISIN and TRICOS). And all waveforms will be available as quadrature pairs (i.e. with 90 degrees phase shift).
That’s why we think to add all these waveform outputs to the module in the final version – or alternatively a about a breakout module which makes all 10 waveforms available (trapezoid, triangle, sine, sawtooth, rectangle – all as quadrature pairs).
Latest news (as of October 2016):
We decided to add all waveform outputs to the final version of the module rather that offering a separate breakout module. The new picture on the left shows the arrangement of the additional sockets. We also added an LED that displays the signal of the TRASIN output (in addition to the LED that displays the thru zero function). By means of 2 internal jumpers the module can be converted into a VCLFO.
Specifications
Width: 12hp
Depth: 61mm
Power: +80mA, -70mA
Manufacturer product page here.