Doepfer A-111-1 User Manual

doepfer

CV 2

CV 1

A-111

High End VCO

CV 2

Range

System A - 100

1. Introduction

Module A-111 (VCO 2) is a voltage controlled oscil-

.

lator

The VCO has a range of about 12 octaves, and
produces four waveforms simultaneously: pulse
(rectangle), sawtooth, triangle and sine waves.

VCO 2 A-111

Lin. FM

PCV

Lin. FM

PCV

H-Sync

S-Sync

Saw Sine Tri Puls e

Tune

Fine

PW

The VCO's frequency is determined by the position of
the range switch, tune and fine tune controls, and the
voltage at the two pitch CV inputs, CV 1 and CV 2.

Footage

(the octave of the fundamental) is set by the
Range control, which has seven octave steps. The
Tune control is used for coarse tuning, and the Fine
control for

fine tuning

of the VCO pitch.

The A-111 can be modulated by both exponential and

linear FM (frequency modulation).

You can control the

pulse width

of the square wave
either by hand, or by voltage control - Pulse Width
Modulation, or PWM for short.

The A-111 has inputs for Hard Sync and Soft Sync.

1

A-111

VCO 2

System A - 100

doepfer

2. VCO 2 - Overview

A-111

HIGH END VOLTAGE CONTR. OSCILLATOR

➊

➋

➌

➍

➏

➎

CV 1

CV 2

Lin. FM

H-Sync PCV

S-Sync Pulse Saw Triangle Sine

-3

Octave

0

+4

CV 2

10

0

Lin. FM

10

0

VCO 2

0

0

0

0

Tune

10

10

10

10

Fine

PW

PCV

➁

➀

➂

➃

➄

➆

➅

Controls:

Range

1

Tune : Control for coarse tuning

2

3 Fine : Control for fine tuning

CV 2

4

PW : Manual control for pulse width

5

PCV

6

Lin. FM : Attenuator for voltage at linear FM

7

: 7-position switch for octave selection

: Attenuator for pitch CV at input

"

: Attenuator for PWM voltage at PCV

input §

In- / Outputs:

! CV 1 : Pitch control input (1 V/oct.)

"

Lin. FM : CV input for linear FM

§

$ H-Sync : Input for hard synchronisation

%

PCV : Input for pulse width modulation CV

&

/, (, ), = : VCO outputs

: ditto, level adjustable with

CV 2

S-Sync

: Input for soft synchronisation

4

&

➐

➑➒➓

2

doepfer

System A - 100

VCO 2 A-111

3. Basics

3.1 Waveforms

Module A-111 puts out four waveforms simulta­neously. All these signals have the same pitch, since
all are controlled by the same CVs at inputs ! and " .

Sawtooth

The VCO’s sawtooth waveform is available at output
/. It has a ‘cutting’ sound, rich in overtones. All the
harmonics of the fundamental are present, with a
linear reduction in intensity as the harmonic series
progresses - so that the second harmonic is half as
strong, the third is one third, the fourth a quarter, etc.
(see Fig. 1).

Sawtooth waves are ideal for synthesizing sounds
which are rich in harmonics, such as percussion, brass
or vocal timbres, and as the carrier input to a vocoder.

Pulse wave

The VCO produces a square / rectangle wave at
output =. You can alter its pulse width (see Fig. 2) by
hand or by voltage control (
or PWM for short).

pulse width modulation

100 %

0%

f1f

f3f4f

2

f6f7f8ff

5

Harmo n ics

9

➨

Fig. 1: Harmonic spectrum of a sawtooth

A symmetrical pulse wave (ie. an exact square
wave, with a pulse width of 50%) has only odd harmo­nics of its fundamental (see Fig. 3) and produces a
typically hollow sound.

c

a

1/f 1/f

b

Fig. 2: Rectangle waves with different pulse widths

3

A-111

VCO 2

System A - 100

doepfer

100%

0%

f1f

2

f3f4f

f

6

5

Harmonics

f7f8ff

9

➨

Fig. 3: Harmonic spectrum of a true square wave

The further the pulse width deviates from 50% (see
Fig. 2, b and c), the weaker the lower harmonics
become, and the more the sound gets thin and nasal.

Pulse waves are often used as a sound source in
subtractive (filtered) synthesis, because of their rich
overtones, and are good at producing woodwind-like
timbres.

Triangle wave

A triangle wave (output )) is poor in upper harmonics,
and sounds softer and more mellow. It only contains
odd harmonics, whose strength decreases exponenti-

ally - the third harmonic is a ninth as strong, the fifth
1/25, and so on.

100%

0%

f1f

2

f3f4f

f

6

5

Harmonics

f7f8ff

9

➨

Fig. 4: Harmonic spectrum of a triangle wave

Because of their soft, rounded timbre, triangle waves
are ideal for synthesizing timbres like flute, organ and
vibes. Because of the comparative weakness of the
upper harmonics, they are not ideal for treating with a
low pass filter, in subtractive synthesis.

4

doepfer

System A - 100

VCO 2 A-111

Sine wave

Sine waves are pure waves: they just contain the
fundamental, without any harmonics (see Fig. 5).
They are thus not suitable for subtractive synthesis
(shaping sound with a filter) - as there’s nothing to take
away!

100%

0%

f1f

2

f3f4f

f

f7f8ff

6

5

Harmonics

9

➨

Fig. 5: Spectrum of a sine wave

3.2 Frequency Modulation (FM)

Since the frequency of the VCOs can be voltage
controlled, that of course makes frequency modula-
tion (FM) possible. The frequency changes conti-

nuously, depending on the incoming voltages at CV1
and CV2. In contrast with the standard VCO module
(A-110), the A-111 provides two types of frequency
modulation.

For

exponential FM

(like on the A-110) you simply

input a modulation signal via the normal CV inputs, !
or ". For linear FM there is a dedicated CV input §,
complete with attenuator.

If the modulation signal is in the sub-audio range (for
instance modulation with a slow LFO), there’ll be no
real difference noticeable between the two types. The
result in both cases is a typical vibrato (see Fig. 6).

Fig. 6: Frequency modulation with a slow LFO

(vibrato)

5