A-110-1 Standard VCO

The A-110-1 is the “standard”-oscillator by Doepfer. “Standard” sounds a little condescending, is this something like a “low cost VCO with saving sound”?

The sound of the A-110-1 is on par with even significantly more expensive oscillators! When viewed with an oscilloscope, the waveforms do not look too precise or “mathematical” – notably triangle and sine, but also the bit “restless” sawtooth. But – and this is somehow a question of “philosophy” – in a musical context, mathematical exactness may not be relevant at all! The A-110-1 is no laboratory instrument for scientific experiments. But it is an excellent basis for a musical instrument that sounds very good!

How does this look like on an oscilloscope?

A-110: Sawtooth
A-110: Triangle
A-110: Sinus

The A-110-1 is built on a “Sawtooth-Core”, i.e. it basically generates a sawtooth waveform and all other waveformes are derived from it. You can see a little notch on top of the triangle which results from this. “Real” triangle waves are generated by e.g. A-111-1 or A-111-5 (“Triangle Core”).

The sinewave looks somewhat “sharpened”, so this is not a perfect waveform. The A-111-1 or the new A-111-2, A-110-4 or A-143-9 manage to create more precise shapes. Sure enough, this does not say anything about the perceived acoustic quality. However, there are some applications like frequency modulation between oscillators, where some “dirt” in the sinewave may lead to side effects (which you may like or probably do not like).

A-110: Square
A-110: Pulse

Rectangle and pulse are in a strange way “incorrect”. They are not really rectangular, but with “sloping roofs”. However, this is not a characteristic of the A-110 alone, but of many analog oscillators. By the way: Even good software synthesizers (which are digital and could easily create the exact waveforms) try to recreate this and produce very similar raw waveforms.


System bus:

Virtually “invisible”, the pitch of the A-110-1 can be controlled by the Doepfer system bus. One of the current lines is reserved for this on each bus circuit board and may be splitted into two independent lines by means of a jumper. Using the system bus requires a dedicated connection to this part of the bus, e.g. with a A-185-1 or A-185-2 module. We may use this when we want to control several VCOs with one single source, like a sequencer or a keyboard. Splitting up the control voltage with a simple multiples module will not be sufficient, since the usage of several consumer units will lead to slight voltage losses and thus to incorrect intonation. However, we are not “bound” to the system bus, since the »CV1« input jack is built as a switch jack which can control the VCO independently from the bus whenever necessary.

Switch Jack and Bus-CV

The A-110-1 is the only VCO by Doepfer with a switch jack which disconnects the oscillator from the internal bus CV when a plug is connected. Other VCOs usually add the bus CV and the CV from the control input jack. When you usually control several VCOs with a single A-182-1 (and the bus) and just want to make exceptions from this, the switch jack is quite useful. Just patch the control voltage into the »CV1« input and the VCO will operate completely independent from any control voltages on the bus.



Remarks to SYNC and control voltages

SYNC – For synchronization with another oscillator. The waveform of the oscillator will restart when the sync input falls below of a certain voltage (falling edge). Usually you will feed this input with the rectangle output of another oscillator (“master”). When the master VCO oscillates twice as fast, then our A-110-1 will restart its waveforms at their mid-points: This will change the sound of a sine or triangle wave much more than the sound of a sawtooth or rectangle wave. Moreover, the synced oscillator will adopt the frequency of the master oscillator. What will happen if the master has a lower frequency than the synced VCO? In principle, the master’s frequency will be adapted, too, but some more complex waveforms will result, depending on the frequency ratio of the two VCOs: After a normal cycle with a complete waveform we get a partial cycle and a restart of the waveform, etc. This may sound quite interesting but will usually not be as “dramatic” as with a faster master VCO.

The Control Voltage on the CV1 and CV2 inputs is used for modulation of the VCO frequency. The control characteristic is 1 V / octave. Here you may connect a keyboard, sequencer, slow oscillators (so called LFOs – low frequency oscillators) and so on: Anything that should control the pitch. If you connect another VCO with significantly different frequency, you will get quite metallic sounding FM sounds (FM for frequency modulation). The frequency resulting from modulation here is always exponentially related to the applied voltage, i.e. 1 V addition increases the frequency by 1 octave (i.e. to the double frequency), 2 V increase the frequency by 2 octaves (fourfold frequency), 3V then to 3 octaves (eightfold frequency). Other oscillators, such as for example the A-111 allow also a modulation of pitch linear to the applied voltage: 1 V increases in the frequency by e.g. 500 Hz, 2V then by 1000 Hz. Such linear frequency-modulated oscillators can be very interesting for tonally playable FM sounds. The reason is that with linear FM the perceived fundamental frequency of the modulated oscillator remains the same – with exponential FM it does not. This is thus perceived as “tonally not correct”. The input “CV1” is built as switching socket: The internal connection to the system bus control voltage can be interrupted here and replaced with a different power source.





Temperature compensation

The A-110 uses quite a classical design from the end of the 1970s in which temperature compensation has been integrated for the first time in a circuit. Moog used this design for example in the Rogue Synthesizer (1981).

Patch examples

A first simple synthesizer

The control voltage of a keyboard or sequencer is used for the control input “CV1”, one of the audio outputs is sent into a filter (either directly or via mixer together with other VCOs) and then into a VCA. If needed, you may modulate the pulse width with a rather slow LFO or an envelope generator, possibly also the pitch via the input “CV2” with a slightly faster LFO (but severely weakened: We want some slight vibrato and no yowls, at least for the moment).

Mixing two VCOs before sending their outputs to a filter and a VCA is some kind of “standard” for many synthesizers: Some detuning between the oscillators provides nice motion and a lively sound. Unfortunately there is some mutual extinction between two VCOs, depending on the phase shift of the signals (i.e. “mountain” plus “valley” of the two waveforms at the same time sums up to something near “zero”, a moment later there may be two “mountains” resulting in an increased amplitude again).

In order to mitigate this (or at least to make it less predictable), the use of a third VCOs can be useful. (Say hello to Minimoog!) A small modular synthesizer could look like this:

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

Mixed waveforms

Mixing the waveforms.

You may try to mix the individual outputs of an A-110, ideally with a polarising mixier (e.g. A-138 (c)), which allows for example the “subtraction” of a pulse wave from a sawtooth. You will receive additional waveforms that are not accessible by filters.

Switch socket for the separation of the bus-CV

The A-110-1 is the only oscillator by Doepfer offering a switching Jack “CV1” that separates the VCO from the internal bus-CV when a patchcord is inserted. This is extremely handy if you want to control for example several A-110-1 VCOs with an A-182-1 (and thus via the bus) but want to be able to allow exceptions: Just patch the corresponding control voltage into the “CV1” socket and the module will operate completely independently of control voltages that are on the bus.

A VCO modulates itself

A frequency modulated VCO.

The output signals of VCOs are only voltages. There is no fundamental difference to control voltages. This means you may of course use VCO output to modulate other VCOs, VCFs, VCAs, and so on.

When you modulate the pitch of a VCOs by his own output signal (pulse, sine, and so on), you get quite expressive, “wild” spectra.

Modulated sync master

An LFO modulates the sync master VCO.

When using SYNC between VCOs, modulate the frequency of the master VCO with an LFO or an ADSR generator – you will get very moving sounds.

Cutoff frequency modulation and amplitude modulation with the VCO

Sine waves from a VCO modulate a VCA.

Modulate filters or amplifiers with the VCO – this way, even an amplifier can strongly colorize the sound!


Width10 HP
Depth55 mm
Power consumption90 mA (+12V) / -20 mA (-12V)