A-110-1 Standard VCO

The A-110-1 is Doepfer’s “standard” oscillator. The “standard” sounds a bit disrespectful, is that something like a “cheap VCO with economy sound”?

In terms of sound, the A-110-1 does not have to hide, not even from significantly more expensive oscillators! First of all, the waveforms on the oscilloscope don’t all look “exactly mathematical”, especially the triangle and sine, but also the somewhat “restless” sawtooth. Neither are they! But – and this is also a “philosophy” question – in my humble opinion they don’t have to be that with a musical instrument! The A-110-1 is certainly not a laboratory instrument for scientific experiments. But it is an excellent basis for a musical instrument that sounds very good!

How does this look on an oscilloscope?

A-110-1: Sawtooth
A-110-1: Triangle
A-110-1: Sine wave

The A-110 is based on a so-called “sawtooth core”, i.e. it basically generates a sawtooth oscillation and derives all other waveforms from it. For example, you can see a slight indentation in the triangle that results from this. A “real” triangle is produced by the VCOs of the “A-111 family”, i.e. the A-111-1, the A-111-2, the A-111-3, the A-111-4, the A-111-5 or the A-111-6 (“Triangle Core”).

Also the sine wave here looks a little “sharpened”, this is not quite a perfect sine wave. With the A-111-1 and even more so with the new A-111-2, this has been done much better, the sinus is also much more “shapely” with the A-110-4 or A-143-9. Of course, that says nothing about the perceived sound quality. However, there are also applications such as frequency modulation between oscillators, where a little “dirt” in the sine wave can lead to side effects, which one then again may like or – more commonly – dislike.

A-110-1: Square
A-110-1: Pulse

The rectangle and pulse appear strangely “incorrect” at first. Not really rectangular, but with “sloping roofs”. This is not a peculiarity of the A-110-1, but of many oscillators. Even good software synthesizers (for which it could be digital and therefore irrelevant) try to emulate this and produce very similar curves.

User interface

System bus:

The pitch of the A-110-1 can be controlled practically “invisibly” via the system bus, which has reserved its own line for this (each to the width of a backplane, which can be split into two parts per backplane via jumpers if necessary). Control via the system bus requires bus access, e.g. via the A-185-1 or A-185-2 module and is always useful when several VCOs are to be controlled simultaneously by the same source (sequencer, keyboard, etc.): A simple splitting of the control signal over multiples is no longer sufficient here, but would lead to voltage losses and thus to inaccurate intonation due to several “consumers”. But you are not “chained” to the system bus, the control voltage socket “CV1” is designed as a switching socket that controls the VCO independently of the bus if necessary.

Switching socket for disconnecting from the bus CV

The A-110-1 is the only Doepfer oscillator to have a “CV1” switching socket, which separates the VCO from the internal bus CV when a patch cord is plugged in. This is extremely useful if, for example, you normally control several A-110-1 VCOs via an A-182-1 (and thus via the bus), but sometimes want to make exceptions: Simply patch the corresponding control voltage into the “CV1” input and the module will work completely independently of the control voltages present on the bus.

In contrast to all other Doepfer VCOs, the factory connection to the bus does not have to be interrupted if it is not to be used (e.g. to avoid interference effects via the lines): As soon as the “CV1” input is used, the bus connection is cut.


  1. SYNC: Synchronisation with another oscillator.
  2. CV1: Control Voltage for modulation of the VCO frequency. Control characteristic is 1 V / octave.
  3. CV2: Like “CV1”, but with an attenuator (controller “CV2”) to reduce the applied voltage. “CV2” is not a switch socket.
  4. PW CV1: Control input for the pulse width of the pulse wave. A slowly-modulated pulse creates a floating sound that reminds of two slightly detuned oscillators. This is a popular trick to generate full sounds with only one VCO used by many lowcost polyphonic analog synthesizers (Polysix, etc.)
  5. PW CV2: Like “PW CV1”, but with an attenuator (controller “PW CV2”) to reduce the applied voltage.

Notes on SYNC and control voltage

SYNC – The synchronization with another oscillator. When the voltage at this input falls below a certain level (falling edge), the oscillation cycle of the oscillator is restarted. The square-wave output of another oscillator (“master”) is usually connected here. If it oscillates twice as fast, then our A-110-1 will be restarted as soon as it reaches the midpoint of its oscillation shape, which may change the sound of sine or triangle significantly, but much less with sawtooth or square wave. It also adopts the higher pitch of the master oscillator. And if the “master” has a lower frequency? Even then, the pitch of the master is always assumed, but depending on the frequency ratio, more complex oscillation forms occur: After a normal complete cycle, there is a partial cycle of the oscillation, then another complete cycle, etc., which can sound quite interesting (but usually not as “dramatic” as with a faster master).

The control voltage at the inputs CV1 and CV2 is used to influence the frequency of the VCO. Control characteristic is 1 V / octave. Keyboard, sequencer, etc. are connected here to control the pitch, but also slow oscillators (so-called LFOs – Low Frequency Oscillators) to generate vibrato, for example. If you control with oscillators in the audio range, you often get very metallic FM (frequency modulation) sounds. The modulation of the pitch is always exponential to the applied voltage, i.e. 1 V additionally (not attenuated) increases the tone by 1 octave (i.e. to twice the frequency), 2V additionally increase the tone by 2 octaves (i.e. already four times the frequency), 3V then by 3 octaves to eight times the frequency. Other oscillators, such as the A-111-1, also allow the pitch to be modulated linearly with the applied voltage: 1 V increases the frequency by e.g. 500 Hz, 2V then by 1000 Hz. Such linear frequency modulated oscillators can be used very well for tonal playing. The reason is that with linear FM the perceived fundamental frequency of the modulated oscillator does not change, but with exponential FM it does (and thus the sound is no longer “right”). The “CV1” input is designed as a switching socket: A control voltage applied to the system bus can be interrupted here and replaced by another voltage source.


  1. There are separate outputs for sawtooth, pulse, triangle and sine. When mixing a sine with e.g. sawtooth or pulse, bass frequencies will be enhanced. But also a mix of square and sawtooth yields interesting sounds. Or a triangle mixed after filtering to compensate for the bass loss that occurs sometimes with high filter resonance.


  1. Range: Rotary switch for the preselection of the octave. The switch is labeled with +/- 2 octaves but is even working beyond this (higher octaves).
  2. Tune: Controller for fine-tuning the pitch (approximately +/- 1/2 octave).
  3. Attenuator for the CV2 control input.
  4. Manual adjustment of the pulse width PW: Unlike some other VCOs, the A-110-1 allows a pulse width in the full range of 0% to 100% – the zwo extremes “0%” and “100%” are of course no longer audible. This is quite useful for interesting automatic sequences where the VCO can be “switched off” via pulse width modulation at full range.
  5. Attenuator for the PW CV2 control input.

Temperature compensation

The A-110-1 evolved from a very classic design from the late 1970s, in which temperature compensation was integrated into the circuit for the first time. Ein kleines „Heizelement” sorgt dafür, dass die temperaturkritischen Bauteile immer mit einer konstanten Temperatur oberhalb der Raumtemperatur, aber unterhalb zerstörerischer Hitze versorgt werden. For example, Moog used it in their Rogue (1981).

Patch examples

A very simple synthesizer

The control voltage of a keyboard or sequencer is used for the “CV1” control input, one of the audio outputs is routed (directly or via a mixer together with other VCOs) to a filter and then to a VCA. If necessary, you can modulate the pulse width with a rather slow LFO or envelope generator, and possibly also the pitch via the “CV2” input with a slightly faster LFO (albeit much weakened so that it results in vibrato and no howling).

Two VCOs mixed into the filter and VCA are “standard” for many synthesizers: Slight detuning between the oscillators ensures beautiful beats and a lively sound. Unfortunately, two VCOs sometimes cancel each other out – depending on the phase relationship of the signals to each other (i.e. “peak” plus “valley” at the same time in the two oscillations results in cancellation, and a moment later there is amplification again).

To mitigate this, the use of a third VCO can be useful. (Minimoog says hello…!) A small modular synthesizer might look like this:

2 VCOs, a VCF, a VCA, plus a mixer and ADSR = simple synthesizer!

Mixing of waveforms

Mixing of waveforms.

Try mixing the individual outputs of the A-110-1, ideally with a polarizing mixer (e.g. A-138c), which also allows, for example, the “subtraction” of a pulse wave from a sawtooth. You get additional waveforms that are not achievable through filters. You get additional waveforms that are not achievable through filters.

A VCO modulates itself

A VCO modulates itself in frequency.

The output signals of a VCO are also only voltages – so you can also use it to modulate other VCOs, VCFs, VCAs etc.

Wenn Sie die Tonhöhe eines VCOs durch sein eigenes Ausgangssignal (Puls, Sinus usw.) modulieren, erhalten Sie recht ausdrucksstarke, »wilde« Spektren.

Modulated master at sync

An LFO modulates the sync master VCO.

When using SYNC, modulate the frequency of the master VCO with an LFO or ADSR generator, for example – you get very dynamic sounds.

Cutoff-frequency modulation and amplitude modulation by the VCO

Modulation of the VCA with the sine output of the VCO.

Modulate downstream filters or amplifiers with the VCO – even an amplifier can strongly color the sound in this way!

Technical specifications

Width10 HP
Depth55 mm
Power requirements90 mA (+12V) / -20 mA (-12V)