Doepfer A-110-4 Quadrature VCO (8HP)

Full Description

Thru-Zero Quadrature VCO

The term 'Quadrature' refers to the operation of the VCO. It means that the oscillator outputs both sine and cosine waveforms simultaneously. 'Thru-Zero' is another operational description of the A-110-4. This basically means that the VCO is able to generate 'negative' frequencies. However, negative frequencies do not exist. What this is referring to is the module's ability to stop the sine and cosine waveforms when the linear control voltage reaches 0V. The waveforms then continue in the opposite direction as the linear CV becomes negative, and vice-versa.

Two Control Sections

Linear

The A-110-4 features a linear control section. This section consists of the LFrq control and the LFM input with a corresponding LFM attenuator. The linear CV is the sum of these two voltages. A dual-colour LED is used to display the polarity of the linear control voltage (red = positive, yellow = negative).

Exponential

The A-110-4 features an exponential control section. This section consists of the XTune control, the 1V/Oct input, and the XFM input with a corresponding XFM attenuator. The exponential CV is the sum of these three voltages.

Section Interaction

The pitch of the sine/cosine outputs is determined by the control voltages of both sections. The linear section is used to control the pitch in a linear manner. When the LFrq control (Linear Frequency Control) is fully clockwise, the module works like a normal Quadrature VCO and the LED will display a red light. 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). The 1V/Oct input is used for controlling the pitch using a 1V/Oct CV source. XFM is used to apply an exponential frequency modulation with adjustable depth, such as that from an LFO or another VCO. As the LFrq control is turned counter-clockwise from the fully clockwise position, the frequency is lowered in a linear manner until the sine/cosine waves (nearly) stop at the central position of the LFrq control. As the LFrq control is moved from the centre towards the fully counter-clockwise position, the wave starts again, but in the reverse direction, and the LED will display a yellow light. When the maximum counter-clockwise position of the LFrq control is reached, the module will again work like a regular Quadrature VCO. The LFM input can be used to modify the linear CV via an external CV. Linear modulation by another oscillator using thru-zero functions generates audio spectra that cannot be obtained from an oscillator without this technology. The reason is that a normal VCO will simply stop as the linear CV becomes 0 or negative, whilst a thru-zero VCO will start again with 'negative' frequencies as the linear CV also becomes negative.

Sine/Cosine Core

Many thru-zero VCOs use a different core design to the A-110-4. This is where Doepfer's VCO becomes advantageous. Sine/cosine waves are not derived from any other wave forms, such as sawtooth or triangle, by means of waveshaping. Instead, the sine and cosine waves are the core of the VCO, resulting in an extremely pure waveform output with minimal distortion and unwanted overtones.

New Edition With Higher Output Level

The new versions of the A-110-4 that were manufactured after October 2015 feature a new higher output level compared to the 3Vss of the older editions. These new editions are equipped with internal amplifiers that increase the output level to roughly 10Vss.

Specifications

• Width: 8HP/40.3mm
• Depth: 60mm (Measured from the rear side of the front panel)
• Current:
  • +12V: +90mA
  • -12V: -30mA