DOEPFER / A-110-6 Trapezoid Thru Zero Quad VCO

Variations

This module is made by the German synthesizer manufacturer Doepfer. It features a quadrature VCO and enables linear through-zero frequency modulation.

The A-110-6 is a trapezoid core through-zero quadrature VCO. This module is based on Donald Tillman's 2003 idea but has been revised to use modern electronics (without OTA/CA3280). While its unique trapezoidal core sets it apart from other VCOs, this isn't its only feature. It's a quadrature VCO, enabling linear through-zero frequency modulation.

The term ""quadrature"" means the oscillator outputs two trapezoidal waves with a 90-degree phase shift, similar to standard quadrature oscillators like the A-110-4 and A-143-9. These waveforms are called TRASIN (trapezoidal sine) and TRACOS (trapezoidal cosine).

""Thru Zero"" implies the generation of negative frequencies; however, this is misleading, as negative frequencies are not actually present. Negative means that when this connection reaches 0V, the sine/cosine wave stops, and when the linear CV moves in the opposite direction, the sine/cosine wave becomes out of phase.

This module has two control sections: linear and exponential. The exponential section consists of an XTune control, a 1V/Oct input, an XFM input, and an XFM attenuator. The exponential CV is the sum of these three voltages.

The linear section consists of an LFrq control, an LFM input, and an LFM attenuator. The linear CV is the sum of these two voltages. A dual-color LED indicates the polarity of the linear CV. The pitch of all outputs is determined by the CVs in both sections.

The linear section is used to control the pitch linearly. When the LFrq control (LFrq stands for Linear Frequency Control) is fully clockwise, the module behaves like a normal VCO and the LED lights up red. Pitch is controlled by the manual control XTune in the exponential section and the exponential frequency control inputs 1V/Oct and XFM. 1V/Oct is used to control the pitch via a CV source (e.g., a sequencer or MIDI/USB-CV interface). XFM is used for exponential frequency modulation (e.g., from an LFO or other VCO) with adjustable depth.

Starting from the fully clockwise position and rotating counterclockwise, the frequency of TRASIN/TRACOS decreases linearly until it stops at the LFrq center position (when there is almost no LFM signal). Moving the LFrq control from the center towards the counterclockwise position, the waveform moves again but in the opposite direction and the LED turns yellow. When LFrq reaches the fully counterclockwise position, the module operates like a normal VCO again. However, modulating linear CV with an external CV (usually another VCO) using the LFM input yields very exciting results. Linear modulation by another oscillator using the through-zero function in combination with a trapezoid waveform produces an audio spectrum that cannot be obtained from other oscillators without the through-zero function. This is because when the linear CV is zero or negative, the ""normal"" VCO simply stops. However, when the linear CV becomes negative, the VCO starts moving again with a negative VCO.
In addition to the trapezoid waveform, a total of five types are available: triangle wave, sine wave, square wave, and sawtooth wave. All five waveforms are available as quadrature pairs (pairs with a 90-degree phase shift).

■Width: 12HP
■Depth: 55mm
■Current Consumption
+12V: 80mA
-12V: 70mA