A square wave is a square wave and a sine a sine – right? Yes … but on the other hand – no, not quite. Even with classic analog VCOs, that output classic waveforms like saw, square, triangle and sine there can be significant differences in their circuits, structure and sound. And as VCOs usually are the basis for your sound it might be worth to think a bit about what a VCO can do for you and what character your VCOs should have. Writing about the different sound of VCOs is a bit difficult as it is a pretty subjective topic. Anyways here are some thoughts about analog VCOs that all have something special and add a nice trick or two to your rack.

VCOs lang

Classic Sound

The first two examples are special because of their history, quality and big vintage sound. The AJH MiniMod VCO is what you could call a real classic VCO, no fancy functions just good sound and solid engineering. And this is what makes this VCO so special. As it is designed after an earliest revision (Mk1) of the famous Minimoog the sound of these VCOs is classic, big and beautiful. The tracking has been improved and the built quality is excellent. What you get is the sound of the Minimoog, even with the special “sharktooth” wave, that was unique to this synthesizer and is now available in eurorack. The NTO is the most advanced VCO ever designed by Serge and the Random*Source – Serge New Timbral Oscillator (NTO) is an adaption for eurorack that has been developed in close cooperation with Serge. It features all the basics you would expect from a classic VCO and this it is – a VCO that has the word vintage written all over its sound. And with the NTO you buy a part of synth history, as the original design was first implemented in the famous TONTO synth that Stevie Wonder was using in the early 1970ies. The TONTO has been the most advanced polyphonic (modular) synthesizer that existed worldwide for a long time and the NTO was the most advanced VCO. The Random*Source version features excellent tracking and an output for the voltage controlled waveform.


Frequency Modulation

The Liivatera – Through-Zero VCO has its specialty already in its name. The Through-Zero term is related to a special behavior wenn frequency modulating the VCO. In a nutshell – it sounds better. The FM sounds are brighter and usually more pleasant to the ear. The technical side of things is a bit more complicated than in the usual FM circuitries and therefore not often implemented in VCOs. But the Liivatera VCO has another trick up its sleeves – the reversing sync input is something not to be found on many VCOs. The syncing behavior is switchable between rising, falling and rising & falling edges of a signal – plus: the trigger threshold is voltage controllable. With these options you get a lot of variety in sync-sounds. The Liivatera VCO is a very nicely engineered VCO for an excellent price point if you consider its functionality and quality. The through-zero technology you get with the Liivatera can also be found in the even more advanced Rubicon by Intellijel or the simpler Doepfer A-110-4.

The next VCO to be discussed is a unique design. The Berlin based artist and designer of electronic musical instruments Christian Günther has developed a special analog VCO with two sperate 1v/oct inputs that can be selected at audio rates – the CG Products – XR22 VCO (Finetune). This opens up new sonic territories as the two frequency control circuits can be switched and controlled in different ways. This adds a very wide range possibilities to an otherwise standard oscillator – this is a way more complex module than it appears. The description of the circuit seams to be easy to understand, but the complexity of the sound that comes out of this module is huge and demands some time to learn and experiment – but its worth it.


Different sizes

The next VCO is a future classic by Doepfer. The Doepfer A-111-4 Quad Precision VCO. The A-111-4 is a very interesting addition to the wide Doepfer range of products. What makes this one special is that its compiled of four individual precision VCOs and a mixing stage. This module is the perfect starting point for polyphonic setups or really massive analog mono voices. With the size of one more advanced VCO the A-111-4 maybe the most analog VCO per hp in eurorackland. With the mixing stage this VCO makes a great starting point for massive mono voices that only go through one filter/VCA … or tune the four VCOs to form a chord … or play a massive drone … a lot of interesting things can be done with four VCOs in such a small space!

The next VCO maybe the complete opposite of the Doepfer. It is huge. The Harmonic Oscillator by Verbos Electronics is as big as it gets when you look at single Oscillators. When you go through the features of the Harmonic Oscillator, and start on the left side – everything appears very common and “normal”. Different waveform outputs, tuning knobs, CV inputs. But right next to these basic features the interesting part of the Verbos VCO begins. The fader control the first eight harmonics of the fundamental tone – each with its own output, the level of which is controlled by the corresponding fader. Directly below the faders there are two sections for playing with the eight harmonic channels and their sum output. The first one scans through the harmonics from low to high or from high to low, by setting the width you can control the overall effect of this feature in an very intuitive way. Next to this function there is the spectral tilt section which lets you emphasize the low or high harmonics. The Harmonic Oscillator gives you a very interesting package of standard functions and functionality and playability that you won’t find elsewhere.


To create sound in a modular environment isn’t hard. Take an LFO, envelope or function generator, like a Befaco Rampage or Make Noise Maths and loop it fast enough – like this you get an audio oscillator and there are tons of other ways. But to have a dedicated module for this gives you more flexibility for frequency modulation, sync options, different waveform outputs and all the other little bits described above. Through-zero modulation, harmonic overtones, or a dual frequency modulation circuit – these are only some of the available options you will find in eurorack VCOs these days. And if you are searching for that special vintage and all-time classic sound, you are also able to find this in modern VCOs with classic and classy sound.

This is by no means a complete overview of available modules nor a full review of the discussed modules. The “what about…” texts are here to give you new ideas and maybe another perspective on things. All these modules offer more features than we have talked about in this post. For further information please click the provided links or – even better – visit the shop and ask the SchneidersLaden experts in the showroom.