Doepfer A1101 Standard VCO
NoiseBug Price : $197.00
Manufacturer Description:
Module A1101 is a voltagecontrolled oscillator. This VCO's frequency range is about eight octaves (ca. 15Hz ... 8kHz). It can produce four waveforms simultaneously: rectangle, sawtooth, triangle, and sine wave (triangle and sine shapes are not perfect, see remark below). The output levels are typically 8Vpp for saw and rectangle, and 10Vpp for triangle and sine. The frequency or pitch of the VCO is determined by the position of the octave (Range) switch and tuning (Tune) knob, and by the voltage present at the CV inputs. Frequency modulation (FM) of the VCO is therefore a possibility. Footage (the octave of the fundamental) is set by the Range control in five steps, and Fine tuning controlled by the Tune knob. The tune knob range is about +/1 semitone for older modules. Since about middle of 2015 the value has been increased to about+/ 1/2 octave. In the A110 service manual is described how to modify the range.
You can control the pulse width of the square wave either by hand, or by voltage control  Pulse Width Modulation or PWM.
In addition the A110 service manual is available as an example for the A100 service manual that is available at extra charges. This document describes also how to modify the sensitivity of the tune control (changing the value of the resistor R5), how to readjust the 1V/octave scale and the frequency offset (i.e. the absolute pitch). Such modifications should be carried out by experienced users only !
Technical remarks:
The core of the A1101 is a sawtooth oscillator (in contrast to the A1111, which is based on a triangle oscillator). The other waveforms are derived from the sawtooth by internal waveform converters. As the sawtooth reset (i.e. the backtozero slope) is not infinite fast but takes a little bit of time the derived waveforms triangle and sine are not perfect ! At the top of the waveform they have a small glitch or notch that is caused by the sawtooth reset and cannot be eliminated by the waveform converters. The sine is derived from the triangle by a simple diodebased converter and the sine shape is not perfect (only a rounded triangle). To obtain a nearly perfect sine signal the triangletosine converter module A1842 is recommended. It includes also a voltage controlled crossfader to fade between two waveforms.
If a perfect triangle is required the A1111 or A1112 is recommended. For a perfect sine wave the thru zero quadrature VCO A1104 or the quadrature LFO/VCO A1439 is recommended.
The sawtooth output of the A1101 has a falling (or negative) slope as shown on the front panel.
A simpler VCO (without sine, without rotary switch, but with linear FM input) is the module A1102.
Width: 10TE / 10HP / 50.5 mm
Depth: 55 mm (measured from the rear side of the front panel)
Current: +90mA (+12V) / 20mA (12V)

