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Motomouth 12HP Eurorack Compatible, Single Coded Control-Voltage Input, 16 Vowel, Sedra+Espinoza (DABP) Analog Morphing Formant Filter
Motomouth 12HP Eurorack Compatible, Single Coded Control-Voltage Input, 16 Vowel, Sedra+Espinoza (DABP) Analog Morphing Formant Filter
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61 backers pledged £11,378 to help bring this project to life.


Motomouth 12HP Eurorack Compatible, Single Coded Control-Voltage Input, 16 Vowel, Sedra+Espinoza (DABP) Analog Morphing Formant Filter

Eurorack Coded CV Sedra+Espinoza Morphing Formant Filter




The design you currently see, is really loved by some, and not so much by others. During this campaign, I've had some really good Backer input, with various suggestions for the artwork's inclusion or deletion, and some wonderful offers of assistance.  Now this is a project that the backers are funding, and so it's only right that we should have a few plate design options to 'put to the board'.  This part is easy to do and easy to manage, because it's almost the last part to be produced, and it doesn't take long to print.  The silk screen is expensive of course, so we can really only stick with one design. So I'll post some ideas when we are all ready. ~Ren.

Some simplified examples (just examples) for the interim:

BACKGROUND (The previous synth project)

Following on from the successful Kickstarter project last year (the Chicago Mk1 limited edition synthesizer), and also the positive experience with the backers (who were all really terrific), I've decided to realise a further project, this time focussed around the exciting Eurorack Modular Synthesizer format.


CAD Drawing of the proposed finshed unit:

See also:

First, the sound it makes is what we are all MOST interested in: 

NOTE: All of the sounds are made using the Breadboard Prototype (V0) shown and described below.          

Example of very subtle and sparing use (Motomouth is intermittently used throughout):

Now for the more obvious use and the sounds:           

1.  The first ever simple morph and step examples the Motomouth Breadboard made.  The first section that plays is unaffected and it's the input sound that's used throughout - the rest is what you hear Motomouth performing on the straight and flat sound:

2.  Motomouth is set to Filter mode, and some Delay is added.  The manual pot is used to modulate the filter frequency, which can also be achieved using a LFO control signal (0V to ~1.3V).  The first riff is without Motomouth, then it's gradually mixed in goes a bit 'daft' towards the end (my fault):            

3.  PART 1 of 2: A 'raw' Dubstep bass-line stem I made up (Motomouth is not used in this part):            

4.  AND FINALLY! PART 2 of 2: MOTORING! The above stem is now processed by the Motomouth prototype, and mixed with the 'raw' stem, with a kick-drum and high-hat also added for a bit of 'direction' (reverb is added to the high hat):            

WARNING 1:  Formant filters can make a significant difference to a hook-line.  They can grab attention, add 'movement' and they can make the hook-line sound unique and interesting as well as 'slickly' produced.  However, they can often be badly sourced (the wrong sound), badly used or overused to a point of becoming annoying, so the secret is to use them the same way you would use seasoning in great food - sparingly, with good ingredients.             

WARNING 2:  Like the human 'voice box', Motomouth will not work well with nice pure Sine and Triangle Waves - Sharp Saw and double Saws work the best, where raspy FM type sounds can be really effective.  Square waves sound a bit 'electronic' or unnatural of course - our vocal cord is not a square-wave.  Oh, and also KEEP IT LOW - the deeper the better, it brings out the harmonics a lot more.

It also loves 20 Hz to 80 Hz pulse waves set at 10% or 20% duty-cycle (or 80% to 90%) - then add in some PWM!

WARNING 3:  With added 'hisses' and 'plosives' (e.g. white noise bursts and/or short low frequency tones/pulses), Motomouth can be used to 'talk' more convincingly - however, this will absorb a LOT of your time...


Motomouth is an analogue 3-Band, Sedra + Espinoza Bandpass Filter (DABP) with resonant frequencies that are tuned to the same (similar) resonant frequencies found in the human mouth and nose cavities, and these can be varied, independently, to form different 'mouth shapes', to emulate vowels such as A, E, I, O and U.  

Motomouth can emulate 16 vowels and 'morph' or 'glide' between each vowel using a single Control Voltage input (1V/Oct), and a Gate to 'snap' to each vowel when required.


With the interconnection (setup) shown below, using one or two VCA's, then the Snap-to-Gate becomes far more useful, when you need a longer (slower) Morph rate, yet be ready for the next vowel to sound when the note is pressed, without gliding to it.  This can make the effect quite 'musical' and interesting when the gate is held between some note transitions and not others (not lifting off from one key before pressing the next key or lifting off one key before pressing the next key - it sounds complicated, but it's quite a natural thing to do if you have reasonable keyboard skills, and you are familiar with a classic monophonic Synth).

Most importantly, when you start a vocal phrase, you need to snap to it and not glide to it at first, even though the passage may be morphed all the way though from that point.  So the Gate will be something that comes in real handy if you are using it in a  'musical' way.

It really come into it's own if you have a Midi to CV and gate converter.

The three bands:

Two of the bands (F1 and F2) are used to form the mouth cavity, and the third band (F3) is used to from the nasal cavity, which is reasonably static.  Varying F3 makes little significant difference 'in the mix', but having it is important.

The single Control Voltage is decoded to control F1 and F2 independently, because the frequency bands for each vowel are not proportional to each other over the vowel range. So Motomouth has learned how to 'speak', so to speak, but it still needs to learn more, and that's were you come in.

The three bands:


The task is to raise funds for Motomouth's mechanical components and the PCBs in a larger quantity, at a lower cost, with the goal of eventually selling a range of 'boutique' modules through distribution.  The funds will also be used to purchase some PCB's for preliminary testing and to triple-check.  The PCB's (and mechanical assembly) for this Kickstarter project, will be lovingly hand populated and constructed, but the funds will also be useful for converting Motomouth over to surface mount technology for machine production later, or if the quantity estimate 'avalanches' (which I'm not anticipating).

KEY Features:

  • Single CV to control and set vowel shapes.
  • Automatic Morphing and morphing rates to each vowel.
  • Pure analogue single path from input to output.
  • Gate operated snap to each vowel when required.
  • Sedra+Espinoza Analogue Filter design for a high, sharp Q value and a 12 dB/octave roll-off slope.
  • Plays well from a monophonic keyboard or Midi Keyboard through a Midi to CV/Gate converter.
  • Works great with a CV Step Sequencer.
  • Filter and vowel mode selection using the same single CV input.
  • The system is managed by two ATMEGA328P Microcontrollers.

Motomouth is a Monophonic processor. Stereo can be achieved by double tracking or by using two Motomouth modules.

Selecting vowels sounds is very simple, and playable through a keyboard or a sequencer via a single Control Voltage input and an optional Gate (see hookup example below).  NOTE: The idea behind using the two VCAs is to be able to apply formant filtering where and when it's needed and not continually - although you may prefer to use the sound continually, so only one VCA is used, post-mixer (which you would normally have anyway).

The Simplified Control Voltage Code to IPA Vowel Sound table (approximate):            

The Gate is used to snap each vowel to it's 'sound' when you need to, or it may glide or morph to each vowel simply by overlapping the gate (i.e. holding down one key before the previous key is released - this is quite a simple action found on vintage synth mono-phonic keyboards and sequencers) or by selecting the glide only switch.  In short, it's easy to glide (morph) or snap to each vowel and each subsequent vowel for a more realistic vocal effect or sequence.  However, snapping to each vowel does also offer a nice effect in it's own way.            

Motomouth may also be used as a dual band, band pass filter with a unique character.

Piano-roll example of playing the phrase "Oh Yeah":  In this case, it's midi controlled for convenience, because I only have Cubase for my sequencing tasks.

THE PROJECT STATUS (where the project is 'at' right now):      

Currently, Motomouth is at the development breadboard stage.  The breadboard (V0) is show below, with labels locating the various functions within the circuit.  This works perfectly, and it's the exact same circuit used for the samples demonstrated above.  The picture below shows the total system, but Ignore the two chips top right - this is my MIDI interface for a CV output to the Motomouth CV input for convenience.

 A short video showing the prototype breadboard in action, sequentially scanning through the 'raw' vowel sounds with a 'clavinette' type input sound - (the audio quality is not so good when using a smartphone):    

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A) The PCBs and GERBER design.

The above breadboard interconnections and components have already been transferred to a CAD/CAM format in RS Designspark, ready for manufacture.  These take around 10 days to produce and deliver from the GERBER files. The BOM is also near completion and will take about 2 weeks from now to finalise and re-check.

PCB artwork (top layer shown):

PCB Cad 3D:      

 B) The Artwork:            

The Vector Graphic for the front plate is complete and ready for screen printing - this will be printed in the UK: 

 C) IGS/STP FILES:             

CAD/CAM file for laser cutting the front plate is complete.  Quotations for this are in.  It's decided to go for UK manufacture, because the company that can do this, is merely 10km or about 7 miles away!



Prefered Inputs:

Pulse wave 5% to 20% duty (or 80 to 95%) - with added PWM for effect. 

Positive (or negative) clipped Saw Wave (TB303-ish)

Saw Wave, double Saw Wave

High Pass filtered Saw Wave

Any highly distorted LF wave

FM Bass/Clavinette type sounds


Vowel Code LEDs - Blue.  Power LED - Red. Gate LED - Yellow.

Example of the Blue LEDs in first Vowel Mode, then in Filter Mode (hand adjusted).

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(The Gate LED is the same LED as the Power LED).            

Depth: 42mm from base of front plate to tip of underside power connection pins.

Width: 60.6mm (12 HP).

Height: 128.5 mm (Doepfer standard).

Panel: 2mm thick, Aluminium finish. 

Silk Screen: Black.

Power connection:  10-pin universal (not keyed) Header with Doepfer Standard +12, -12 and 0 Volt connections (Doepfer standard: 10-pin cable, with Red flash on -12V side).

Consumption: +12V, 60mA max (0.72W).

CV Input range (Vowel Mode): 0 Volts to 1.25 Volts at 1V/octave scaling for Vowel 1 to Vowel 16. 

CV Input Rage (Filter Mode): 0 Volts to 1.25 Volts ~200 Hz (1.25V) to ~2 kHz (0V) respectively. TBD.

IMPORTANT: If you are running a LFO to sweep the filter, then it should be shifted (bias/offset) and attenuated (level) to give 0 V trough to 1.25 V peak (or lower, with any bias in between). Ideally, a sine wave works best - but sample and hold will also sound great.

GATE:  0V = Off, Typically 5V = On (2.5V* to 12V = On). [*EDIT]

Input sensitivity: 0.1* Vp-p to 10 Vp-p. [*EDIT]

Output: 10V p-p max (depending on resonance).

Filters:  3 x classic Sedra & Espinoza Dual Amplifier Bandpass Filters with Q's set to between 5 and 25 and F set to between 200 Hz to 3,000 Hz.

Resonance wave resolution: Analogue.

Input/output:  Monophonic, 3.5mm Jack.

CV and Gate Jacks: 3.5mm

Control:  One ATMega Microcontroller for decoding and general I/O work, and one ATMega Microcontroller, clocked at 20 MHz, for indirect filter control.

System operational Voltage: 5 VDC, Linear Regulated.  +/- 12VDC for the output amplifier.

Front Plate Dimensional Drawing:

Power Cable:  

The power cable is included:

10 Pin Header connector for Motomouth, and 16 Pin Doepfer Standard non-keyed Header connector for your rack (Motomouth is reverse polarity protected).  Let me know what cable lengths you would like, and I will go with the consensus and include the minimum length (there seems to be different lengths for different racks and skiffs, so I need to cover as much as I can with one cable - I can't supply one of each length of course). 

Power connection:


There is no Tax or Duty to pay if you are in the EU ...until 'Brexit' happens :-(

Very kindly, most non-EU Governments do not charge Duty for important stuff like synthesizers and some musical instruments.  The Duty and/or Tax is not included in the price because at this point it's not known where they will be shipped, but you will, more than likely, not have to pay any Duty or Tax.  If you do, it will be a small amount.

If you need to check - the Commodity code is 9207 10 50 00.  Synthesizers are under # 10 50 00 and the intrastat # is 92071050.

I known that the USA and perhaps Canada do not require Duty to be paid on Synths, nor, I think, Japan and Hong Kong.

The Certificate of Origin is: United Kingdom.

Quality and Safety

All components are Lead-free and Cadmium-free.

All components are sourced from Farnell, RS, Mouser, TME and Digikey for quality and traceability.

The power supply is Linear, so there are no power-side EMC/RFI switching frequencies to consider.  All MCU's are decoupled with 10uF and 100nF capacitors.

The voltages used are in the ELV (extra-low-voltage) domain, and providing the Power Supply (not in the scope of this product supply) is isolated in accordance with the relevant standards, Motomouth will fall under the SELV category (safety-extra-low-voltage).

Any fault will not lead smoke or fire.        

Risks and challenges

The same obstacles seen with Chicago Mk1 will no doubt appear at some point if allowed, but this time, the project is simpler and more manageable, where previous obstacles will be anticipated and avoided well in advance. The parts are all standard and well stocked, I know how to design and source the boxes for them, with added protection for shipping (I have an account with DHL, who delivered and tracked all my Chicago's globally without a hitch). So this project should be risk and challenge free.


The pots can be on a 12 Week lead time. This is factored into the delivery target already. The stock is good at the moment, and I do have some stock of one pot type. So if the backer numbers are realistic, then I could be shipping in advance of July. However, if the backing numbers are 'silly' (200+, which I'm really not antincipating), then plan B can be executed: This will involve translating the PCB's into SMD format (a simple task) and pre-ordering components at a larger quantity - which the manufacturers like. The delivery target will still be met.

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  1. Select this reward

    Pledge £157 or more About US$ 197

    Motomouth Module

    One complete fully tested Motomouth 12HP Eurorack Module. Strong dual-box packing and Airfreight is extra. See P&P cost for your specific country if listed - or use ROW or EU cost if not.

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    55 backers
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  2. Select this reward

    Pledge £314 or more About US$ 395

    2 Motomouth Modules + shipping discount

    Two complete fully tested Motomouth 12HP Eurorack Modules. Free Delivery for Europe, and £13 for 'Rest of World'

    Estimated delivery
    Ships to Anywhere in the world
    4 backers
    Kickstarter is not a store.

    It's a way to bring creative projects to life.

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Funding period

- (30 days)