The MiniStorm almost completed and fully functional

This synthesizer is specially designed to be used with a wind controller and to produce single wind/brass instrument type sounds. With the Berglund Instruments NuEVI you can control the synth with analog control voltages. This avoids the drawbacks with a digital control system, like MIDI.
I wanted to make this synth as small and portable as possible but still include as many features as possible that are useful for wind/brass instrument type sounds. It is slightly smaller than an A4 page (but obviously thicker). As an afterthought, it also has functions for playing plucked-type sounds and in that mode the breath signal is replaced by key velocity.

The MiniStorm uses three AMORE modules. It's the Woodwind VCO, the Minimoog VCF/VCA mkII and the Wind VCAD (to be announced). Additionally, it has a small custom piggyback board and a power supply board (visible in the picture below). Apart from these boards, all circuitry is on the front panel board, where all pots and switches are soldered.

You can tilt the front panel, like on a Minimoog. The panel can flip over 180 degrees. This gives access to the innards, for trimming, service etc. By disconnecting a single connector and unscrewing one of the sides, you can remove the front panel completely.

There will be schematics, circuit board layouts, sound clips and more in due course. These take time to do and aren't done yet.
In the section below, we have look at the functions in detail.

Synth functions and features

The MiniStorm has several functions you won't find on other synths. I started by simulating the synth topology and functions on the Nord Modular G2. This way, I could evaluate which features were useful and which were not, without building and testing every idea in hardware.
Instead of a block diagram, I include a render of the front panel, which clearly indicates the synth structure. Then I explain the functions module for module.

The front panel

The modules


This is the woodwind VCO of my own design. It is based on a core that is similar to the Minimoog's. This has a very good tuning stability.
The VCO offers sawtooth, variable triangle, pulse and double pulse. The triangle has controls for pulse width up and down. These also control the pulse waves. Note that the pulse widths don't change with the VCO's frequency. This means that the width can be set to longer that the wave period. For the up width, this causes the frequency to be divided down.
A fixed pulse width will mimic the formants on wind instruments. However, if you set note tracking to full (+5), the pulse width will vary, to remain constant relative to the wave cycle. Then it works (almost) like a traditional synth pulse wave.

The VCO has two outputs. Both has switches with off and two different volumes. The normal output is routed to the VCF and additionally, there is an output directly to the BPF for the variable triangle. This is in antiphase to the VCF output, so setting both to high volume will not necessarily result in a louder sound. The variable triangle output has a fixed 5 kHz 24 dB/oct lowpass filter to remove the buzz.

An LFO is integrated on the VCO module. It generates a triangle wave only. This can be routed to the up pulse width or down pulse width or both, with the toggle switch. In the latter case, the LFO is fed in antiphase to up and down pulse width, so when one increases, the other decreases. The LFO is also available at the VCA, for a tremolo effect. There is no control for LFO vibrato, since you're supposed to do vibrato manually on the wind controller. But there is a trimmer at the left panel edge that can add LFO vibrato. This can of course be substituted by a panel mounted pot, if you wnt.

The sub + noise

This module actually consists of several. It offers two suboctaves, derived from the VCO saw plus noise. You can select square waves one or two octaves down. If you select both, there will be a 25% duty rate pulse two octaves down. The noise has two levels plus off. The preset noise levels can be adjusted with trimmers at the edge of the board.

The noise and/or suboctaves are fed to a dedicated VCA which is controlled by the EG and/or breath pressure. The output of this VCA is sent to two fixed 24 dB/oct lowpass filters – one with 100 Hz and the other with 500 Hz cutoff. With the out-switch, you can select to send output from either filter to VCF FM or the signal (unfiltered) to the VCF input.


This is a Minimoog clone voltage controlled filter with 24 dB/oct lowpass output. Emphasis is Moog-speak for resonance. There are knobs for cutoff frequency modulation from note, breath pressure, break and EG. This means that you can mix these modulations anyway you want. The breath control has a special feature that makes the VCA open faster at higher settings. This gives a fuller sound when you sweep the filter with breath pressure. It however has a side effect in that the sound from the triangle output will reach full level at lower breath pressures with higher settings of the VCF breath control. This can be used for a sort of crossfading between the variable triangle and the VCF output. In ADR mode, the breath knob instead controls the amount of sweep from EG 2.

Since this filter has voltage controlled resonance, there is a possibility to modulate it. You have two switches with high and low settings for breath pressure and EG. With the high setting the filter will easily oscillate at the EG peak or when you blow hard.


The MiniStorm has no less than four bandpass filters. These are biquad filters. This means that the bandwidth remains constant when you adjust the frequency. You have 100, 200 and 400 Hz bandwidth to choose from. The passband gain can me set to 6 dB, 9 dB or off. For the 400 Hz wide setting, the gain are instead 3 dB and 6 dB. I found this more useful. There is a signal strength indicator that lights yellow at good signal and red at dangerously close to clipping.
The center frequency of the filters can be adjusted between circa 270 and 6000 Hz with the knobs. The reason the controls go “backwards” is that they use logarithmic pots and there are no reverse logarithmic stereo pots for vertical mounting, as far as I know.


This is a Minimoog clone VCA, which consists of two sections. The first is controlled by the signal from the knobs. You have fixed gain plus modulation from LFO, break and EG. The second is controlled by breath pressure in wind mode and determines the level of the final output from the synth. To be able to use the synth for bass and other sounds, I added an ADR-mode, which is activated by the switch. Then the output is controlled by a second envelope generator, instead of breath pressure. This EG has settings for attack, decay and release but no knobs on the front panel. There are connections for pots at the edge of the circuit board. I use thumbwheel switches to set these parameters but you could use trimmers or externally mounted pots instead. The latter will of course make the synth larger.
There is a signal strength indicator that lights yellow at good signal and red at dangerously close to clipping.

The EG

The envelope generator is my very special design. It's designed primarily to create attack transients. Therefore it has settings only for attack and decay. With the switch in the up position, the EG is routed inverted to VCO frequency. So the VCO will bend down with this function activated. You can adjust the amount of bend with a trimmer at the left panel edge or connect an external pot to make it easily adjustable.

The EG can also be used as an LFO with variable up and down rates, by switching it to repeat. In this mode you get a waveform that can continuously be varied from up saw through triangle to down saw. It will repeat as long as the gate is high.

Additionally, the EG has a threshold function. It will only trigger if you blow harder than the set level. At moderate to high settings it will only trigger when you tongue the notes. So if you start the note soft and then crescendo, it will not trigger.

Finally, there is a built-in VCA that lets breath pressure determine the EG amplitude more or less, depending on the tracking setting.

Since the EG is voltage controlled, you can modulate the attack and decay times. There are trimmers for note and breath tracking of attack and decay. These can be replaced by external panel-mount potentiometers if you wish.

Thumbwheels for adjusting autobend and breath and note tracking of attack and decay. Note the small holes in the panel frame. That's where you insert a screwdriver to trim VCO modulation by LFO and noise high and low levels.

The Break

This is a unique module of my own design. It is intended to simulate register breaks I wind instruments. As a matter of fact, it is necessary to prevent the variable triangle from dividing down when you play up the scale and want the pulse width to be constant. You set the break to the note where you want the break to occur. There is a yellow LED to indicate this. You set the break to note mode and adjust the break knob on pulse width up, to get the desired sound above the break. The break module's output jumps from 0 to 10 volts when the input exceeds the set level. It does this with a slew, so the jump will not create a pop in the sound.

The break module can also be used for breath pressure (switch in middle position). Then it will ho high above at set breath level. A third mode (switch down) is the same as note mode except that the pulse width knobs are fed with breath pressure voltage. Use this mode if you want to sweep the pulse width with breath pressure.

Since a break value of 0 or 10 isn't of any use, these settings are used to activate a sample and hold, instead of the break. At the 0 setting, the sample and hold triggers every note-on. This is useful if you want some parameter vary every note. At the 10 setting the S & H is triggered by the LFO. The usefulness of this can be debated but this module was carried over from the Transister project.

The Level scaler

This module adjusts the loudness depending on the note played. You can set a breakpoint (note) and how much the loudness will increase or decrease above or below the breakpoint. This is for taming sounds that gets too loud or soft at one end of the note range. This module controls an extra VCA that is located between the BPF and the main VCA.


On the front panel circuit board there is a simple ADR envelope generator. This is not used in wind mode. In ADR mode it controls the final VCA, like on a Minimoog and most other monosynths. In this mode, there is an extra VCA switched in between the Level scaler and the final VCA. This is controlled from a jack at the back. It is recommended to connect a velocity CV there. If the jack is left open, it is normaled to 10 volts, to make the MiniStorm work like a non-keyboard sensitive synth.

Thumbwheels for adjusting attack, decay and release.


On the back panel, there are connections for line out, external in and CV in. There is also send and return for an external effects unit. This enables you to hear the sound with effects in the earphones. Further, it has a 9 volt output for powering the midi to CV converter and a toggle switch for selecting CV from the front or back input.

The front has jacks for the wind controller and earphones (two types). There is a switch that adds the breath CV to the pitch CV (two strengths) for doing bends with breath. Further, a gate button for triggering the EGs manually and a power switch.

I use a Kenton Pro Solo midi to CV converter for playing the MiniStorm from my DAW.

If you want more possibilities than the MiniStorm offers, you can connect an expander to this jack. It offers power and CV out plus an audio connection that goes to the VCF input. All you need for adding extra VCOs, for instance. There also is an audio output, if you want to add a module with further sound processing.

What's in the box

The MiniStorm contains the following modules:

1 VCO with sawtooth, variable triangle, pulse and double pulse
1 suboctave generator
1 noise generator
1 VCF ladder type, 24 dB/octave lowpass
4 variable bandpass filters
4 fixed 24 db/oct lowpass filters
1 VCAD envelope generator
1 ADR envelope generator
1 Break generator
1 Sample and hold
1 Level scaler

It has switches for all signal routing, replacing patch cords.
Building a Eurorack system with the above features would require much more space and would be much slower to create patches on.

Sound clips

A bass sound, using the ADR mode