Doepfer A-106-6 VCF

Doepfer A-106-6 XP Filter

The Doepfer A-106-6 VCF is a multimode voltage controlled filter based on the filter design in the Oberheim Xpander. Like the Oberheim synthesizer the A-106-6 has 15 filter modes. In the analogue filter architecture different poles build up a filter, where every pole attenuates frequencies above or below (depending on filter type) the cut off frequency with 6 dB per octave. So, for low pass filters a 1-pole, or a 6 dB per octave, filter attenuates less high frequencies than a 4-pole, 24 dB per octave, filter does. By that means different filter architectures creates different sounds when they attenuate different amounts of undesired frequencies. Of the 15 filter modes provided by the A-106-6 8 filters are available simultaneously. The filters are paired to one output, and a switch selects group of filters.

There are 11 symmetrical filters:
– one-, two-, three- and four-pole low pass
– one-, two and three-pole high pass
– two- and four-pole band pass
– two-pole notch
– three-pole phase shift or all pass as Doepfer calls it
And 4 asymmetrical filters:
– two- and three-pole high pass plus one-pole low pass
– two-pole notch plus one-pole low pass
– three-pole phase shift (all pass) plus one-pole low pass

As usual the Doepfer layout is perspicuous, even if the row of filter outputs might appear a bit mazy at a first glance. Build quality and knob feeling are very nice. As for all Doepfer modules the A-106-6 VCF comes in bubble wrap with the mounting screws in a zip bag. For once, at least in the writing moment, there’s no manual to download at the Doepfer web site. The A-106-6 VCF is 12 HP and is easily mounted with the two supplied mounting screws. The filter has one signal input, with attenuation, two CV inputs for the cut off frequency whereof one with attenuation, controls for cut off frequency and resonance (called Q), one CV input with attenuation for the resonance, a switch to select the left or the right filter group, and 8 filter outputs (the two-pole high pass plus one-pole low pass filter mode has one output in each filter group).

The filter sounds absolutely great, creating any sound you could ever dream of. No, it will not substitute your craving for a MiniMoog, or your avidity for a TB-303. However, the A-106-6 will always fill your need for a voltage controlled filter and it will do that with its own sound, maybe with some flavor of the Oberheim Xpander and who could really ask for more?

The filter goes nicely into self-oscillation, and the control scale for the cut off frequency is good enough to use this VCF as a voltage controlled sine wave oscillator. The resonance sounds great, and adds extra power to the cutoff frequency while attenuating frequencies around, giving rather nice 303-ish acidic sounds if desired. A great feature that I often miss in other VCFs, is the possibility to voltage control the resonance. With the A-106-6 you can add some growl to your sound whenever you want to, and then go back to a more subtle sound again. This makes this multimode filter design even more usable. A nice thing to try out is using a mixer between your sound source and the VCF input, and rerouting one of the outputs (for example the one-pole low pass) to the mixer, giving some feed back to the signal path, for even more interesting sounds.

However, the multimode design, the 15 filter types, and the 8 outputs might make the VCF less intuitive since not all filter types are available at the same time. You also need to understand and remember Doepfer’s abbreviations, like 3A1L and 2N1L, and in turn how the cut off frequency control affects all filter modes. A slight drawback with the A-106-6 filter design is that the outputs have slightly different levels and noise floor. This is caused by the different internal amplifications and numbers of stages that are required to generate the different filter modes. The noise is not very prominent and the different output levels are, according to me, not a big problem, it rather gives the filter a true analogue feeling.

To summarize, the A-106-6 VCF is a great VCF. Its many filter modes and fantastic sound makes it, in my opinion, a must buy. But maybe, it’s not that suitable as the first VCF for the more inexperienced modular geek.

Ratings (1 = poor, 5 = excellent)
Build quality: 4
Functionality: 4
Audio quality (if applicable): 5
Ease of use: 3
Cost/Bang for your buck: 4

Comparison chart
Category: Filters
Controls: 1x Input level, 1x Cut off frequency, 1x Attenuator for cut off frequency CV 2, 1x Resonance, 1x Attenuator for resonance CV, 1x Switch for filter group.
Inputs: 1x in, 2x Frequency CV in, 1x Resonance CV in.
Outputs: 16x filter type outputs.
Size: Width: 12 HP, Depth: 50 mm
Power consumption: +12 V = 50 mA, -12 V = not specified, +5 V = not specified
Price: 150.00 € / $245.00

Doepfer A-124 VCF

Doepfer A-124 Wasp Filter

The Wasp was a black and yellow quirky little synthesizer manufactured by EDP (Electronic Dream Plant) in the UK between 1978 and 1981. The peculiar synth had a great sounding filter with high pass, low pass, and band pass options. The Doepfer A-124 Wasp filter is a voltage controlled multimode filter based on the filter in the Wasp, and likewise treats digital inverters like analog operational amplifiers. This misuse of the digital circuits is what creates the rather unique distorted filter sound. But, when the Wasp was impudent yellow, the Doepfer is boringly gray. A bit dull maybe, but the layout is nevertheless easy to understand and work with. However, I’m not going to compare the Wasp and the Doepfer filter further in this review.

All input and output jacks are located to the left with the control knobs on the right. Personally I would prefer to have all jacks at the bottom and controls above, since the patch cables might interfere with knob tweaking and live adjustments. Even though the VCF is rather cheep, the feeling of the knobs and the build quality are great. The A-124 VCF comes in bubble wrap with the mounting screws in a zip bag, not very sexy but efficient enough. A manual can be downloaded from the Doepfer web site.

The A-124 VCF is 8 HP and mounts easily with the two supplied mounting screws. The filter has one signal input, with attenuation, two CV inputs for the cut off frequency whereof one with attenuation, controls for cut off frequency and resonance, a mix control between low pass mode and high pass mode, and two outputs: one for band pass and one for the mix between low pass and high pass. The filter setup makes sure of easy patching and good flexibility. The mix control outputs, in the leftmost position only the low passed filtered sound and in the rightmost position only the high passed filtered sound. When adjusting the mix control different notch-filter settings, symmetrical as well as asymmetrical, are obtained.

The filter sounds great, creating superb bass sounds, screaming lead sounds, and clacking synth sounds. The control scale for the cut off frequency is not very precise. However, this is not a big problem since the filter won’t go into self-oscillation, and you can’t use the VCF as a sinusoid signal source. The resonance sounds good but distorts the filter, too much and in a not very musical way, at maximum setting. The resonance is also affected of the input level, and sounds better when driven with a slightly lower level.

To summarize, the A-124 VCF is a low price but great sounding VCF. Its multimode options, offering low pass, band pass, notch, and high pass filter modes, makes it a competent and useful filter at a very affordable price.

Ratings (1 = poor, 5 = excellent)
Build quality: 4
Functionality: 4
Audio quality (if applicable): 4
Ease of use: 4
Cost/Bang for your buck: 4

Comparison chart
Category: Filters
Controls: 1x Input level, 1x Cut off frequency, 1x Attenuator for cut off frequency CV 2, 1x Resonance, 1x Mix (Low pass and High pass).
Inputs: 1x In, 2x FSrequency CV in.
Outputs: 1x Band pass out, 1x Low pass/High pass out.
Size: Width: 8 HP, Depth: 45 mm
Power consumption: +12 V = 30 mA, -12 V = not specified, +5 V = not specified
Price: 75.00 € / $110.00

Doepfer A-156 Quantizer

Doepfer A-156 Dual Quantizer

The Doepfer A-156 Quantizer comes in bubble wrap with the mounting screws in a zip bag. As usual with Doepfer modules the manual is not included, but downloadable from Doepfer’s web site. At the first glance the module looks a bit dull, almost boring; nine jacks and three switches on an anodized aluminum face plate. However, the layout is easy to follow and makes patching a simple pleasure. As for all other Doepfer modules the A-156 feels sturdy enough, with good build quality.

The A-156 Quantizer is 8 HP and is easy to mount with the two supplied mounting screws. The module is divided in two parts: Quantizer 1 and Quantizer 2. Patching it up is easy, with four jacks for Quantizer 1 at the top, four jacks and three switches for Quantizer 2 below, and an additional transpose jack controlling both quantizers located at the bottom left corner.

By default Quantizer 1 is in chromatic scale (or All as Doepfer calls it). That means that Quantizer 1 will adjust all CVs to the nearest semitone according to the chromatic scale (i.e. voltage steps of 1/12 V). However, by moving a jumper (J1) on the circuit board Quantizer 1 can be controlled by the same three switches as Quantizer 2. The first of these three switches is the Scale switch: All (Chromatic), Major, or Minor. In the All setting all 12 semitones in the octave is used, in Major only the tones in the major scale is used, and in Minor the minor scale is used. This is really handy since it will help you set the right pitch CV for your track. If the Scale switch is set to All, the second and third switch have no function.

The second switch, Mode, selects the output mode: Scale, Chord, Fundamental & fifth. In the Scale mode the quantizer outputs all pitch CVs (tones) within the scale set by the Scale switch (major or minor), in the Chord mode the quantizer outputs only the three tones that build up the chord (major or minor depending on the scale switch, e.g. C E G for a C major chord, and C Eb G for a C minor chord), and in the Fundamental & fifth mode the quantizer outputs only the fundamental and the fifth tone (e.g. C and G, if the fundamental tone is a C). If the Mode switch is set to Scale the third switch has no function. The third switch, Sixth/Seventh enables the addition of a sixth or seventh tone to the output CV. In position “-” this function is disabled.

The trigger input sets when the quantizer should read and quantize an incoming CV. If no external trigger source is provided incoming CV will be quantized at the internal rate of 500Hz. The trigger out outputs a trigger pulse of 10ms every time a quantization takes place, i.e. every time the output CV changes. This trigger signal might be used to trigger other modules, e.g. an envelope generator, with every note change from the quantizer.

Transposing the quantized CV is easy to do by applying a CV at the Transpose CV in. The CV will be quantized to the nearest correct semitone and then both quantizers will be transposed. It might be worth mentioning that it is only possible to transpose upwards since you can only add a positive voltage, and up to maximum output CV of +10V. If you add +0.0833V you’ll transpose one semitone (1/12V), if you add +1.0V to the transpose input you’ll shift the quantizers one octave up. There are ways of working around the limitation of positive transpose voltages. You could, for example, start with adding +1.0V to the transpose CV input and tune your VCO to the right octave, if you then decrease the voltage at the transpose CV input you’ll transpose to a lower tone than the original one. So, if you would like to change chord from Bb major to C major this is easily done by adding +0.166V (two semitones) to the transpose input. However, if you then want to go to a G minor a transpose change is not enough but you need to switch Scale from major to minor as well. Then you need to switch back to Major and add another CV to the transpose to go to F major. After a while you’ll wish for CV control of the Scale, Mode, and Sixth/Seventh switches.

A small problem I’ve noticed is, if your pitch CV is too far away from a “real” note you’ll get some artifacts from the quantizer. It might be due to it is shifting very fast between two semitones or some kind of aliasing effects, resulting in a poor CV signal which creates a growling sound from the VCO. The VCO will be in tune but sound harsh. If this is the case you need to adjust your CV source to be closer to the correct voltage to avoid this.

To summarize, apart from the problem with the sometimes harsh CV output and the wish for more CV controllable options, the A-156 works very nicely, adjusting CVs from sequencers to warmed up tuned VCOs creating beautiful music.
Ratings (1 = poor, 5 = excellent)
Build quality: 4
Functionality: 3
Audio quality (if applicable): –
Ease of use: 3
Cost/Bang for your buck: 3

Comparison chart
Category: Utility
Controls: 1x Scale (3-position switch: Chromatic, Major, Minor), 1x Mode (3-position switch: Scale, Chord, Fundamental & Fifth), 1x Sixth/Seventh (3-position switch: None, Sixth, Seventh).
Inputs: 2x CV in, 2x Trigger in, 1x Transpose CV in.
Outputs: 2x CV out, 2x Trigger out.
Size: Width: 8 HP, Depth: 55 mm
Power consumption: +12 V = 50mA, -12 V = not specified, +5 V = not specified
Price: 120.00 € / $175.00

Doepfer A-110-1 VCO

Deopfer A-110-1 Standard VCO

Deopfer A-110-1 Standard VCO

As for all other Doepfer modules I’ve bought, the A-110 VCO comes in cheap bubble wrap with the mounting screws in a small zip bag. No manual is included, but a decent manual is downloadable as a pdf from Doepfer’s web site. The A-110 has a very sober layout, maybe a tad towards too neat-German-precise-engineering-sober, but never the less it’s a simple and understandable layout. The front panel is anodized aluminum with black text and Doepfer-grey knobs. Inputs are placed on the left side, controls on the right side, and outputs at the bottom. To me this makes a clearly arranged and lucid layout. However, the position of the input jacks makes the VCO a bit less easy to work with, since the input patch cables might be in the way for easy knob tweaking. Despite the fact that the A-110 VCO is a cheap VCO the module feels great, robust and sturdy. The controls have a good feeling, even if the 5-position Range rotary switch rather has 10 positions (feature or failure?).

The A-110 VCO is 10 HP and is easy to mount with the two supplied mounting screws. Patching it up is easy enough, with inputs on the left and outputs at the bottom. There are two CV-inputs for frequency control (CV1 and CV2), two PWM-inputs (PW CV1 and PW CV2), and one Sync-input (Sync) for hard sync. Additionally there is the (supposed to be) 5-position octave switch (Range), a fine tune control (Tune) that covers about +/- six half tones, a pulse width control (PW) with a range from 0 to 10, an attenuator for CV2 and an attenuator for PW CV2. The outputs are for Sawtooth, Square wave, Triangle wave, and Sine wave, and all of these can be used simultaneously.

According to the Doepfer manual the A-110 VCO might need up to 20 minutes of warm up time before fully stable. The oscillator is then stable over (about) four octaves. This is certainly not great, but good enough for most applications. It is worth mentioning that due to the sawtooth core of the VCO, neither the square wave nor the triangle wave is perfect, neither the sine wave is good but rather a rounded triangle. Furthermore, I do miss the possibility to choose between linear and logarithmic frequency modulation. The A-110 has exponential frequency modulation that, besides changing the harmonic content of the sound, also affects the fundamental frequency of the tone in an (probably) unwanted way. Additionally, the A-110 VCO lacks the possibility to choose between hard and soft sync. The A-110 has hard sync, which completely resets the slave waveform when the master waveform completes a cycle.

To summarize, the A-110 VCO is a low price but nevertheless rather competent VCO with many enough functions that make it a good buy to be the workhorse in a modular system. But for the high end applications there are more advanced and expensive VCOs.

Ratings (1 = poor, 5 = excellent)
Build quality: 4
Functionality: 3
Audio quality (if applicable): 3
Ease of use: 3
Cost/Bang for your buck: 4

Comparison chart
Category: Sound sources
Controls: 1x Range (rotary switch), 1x Tune, 1x CV 2 (attenuator), 1x PW, 1x PW CV 2 (attenuator).
Inputs: 1x Sync in, 2x frequency CV in, 2x pulse width CV in.
Outputs: 1x Sawtooth out, 1x Square wave out, 1x Triangle wave out, 1x Sine wave out.
Size: Width: 10 HP, Depth: 55 mm
Power consumption: +12 V = 70mA, -12 V = not specified, +5 V = 0mA
Price: 140.00 € / $199.00