Operating Manual
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Thank you for choosing to back the Limited
Edition Chicago Mk1 project.
The name ‘Chicago’ was chosen because it’s the birthplace of House
music and the legendary analogue synthesizer bass lines.
The Chicago MK1 is a limited edition Riff and Bass synthesizer that has a
restricted amount of functionality or sound variation, but this is
compensated for by a sometimes ‘percussive’ or ‘snappy’ rich, deep
sound (Phat) that can work well ‘in the mix’, and a sound that sits in
between other classic synthesizers: It’s not quite a Moog, Roland or Korg
sounding synthesizer, so there is room for the Chicago to compliment
these legendary brands, or to find a sound that you can’t quite get with
The Chicago MK1 is not intended for those who really want to recreate a
1970’s Dr Who TV episode, or for those that want to use a pitch-bend
wheel to try and impersonate Jimmy Hendrix – it’s intention is to sound a
little more like an 80’s synthesizer playing bass lines (before the Yamaha
DX7 took over that role) and operated by the basic 80’s Atari Midi
If you did want to compare this synthesizer with any other, it sort of follows
the quirkiness of the Moog Prodigy, without the LFO modulation, but with
MIDI and a very stable oscillator. At first, the Chicago can appear to have
very little sound variations, but with a little effort, you can stumble across a
good few settings that sound truly great with that specific line that’s being
played – or even cheesy enough for a Pop track! If you have played with
the well-known Moog Prodigy Free VST plugin, you can sort of
understand the analogy.
Never the less, I really hope you enjoy what the Chicago has to offer, and
it will be so nice to hear it being used on a Soundcloud/Youtube track,
commercial track or even on TV!
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Safety First!
The Chicago is designed to be a very safe and reliable product. However
a few things need to be considered for the safe use of the product:
DO NOT power the Chicago with more than 15 VDC. Use 9 VDC
(preferred) that has a current output of at least 250 mA. Over voltages will
rupture the internal fuse.
DO NOT power the Chicago with un-isolated 9 VDC power supplies. Use
approved isolated mains power supplies: Look for any of these types of
recognisable safety symbols on the Power Supply:
DO NOT use 9 VAC power supplies – These are ‘alternating current’ and
they could stress the internal capacitors or create hum.
DO NOT power the Chicago with 110 VAC or 230 VAC.
DO NOT connect power to the Audio output, or the MIDI connectors – as
damage may occur.
DO NOT operate in the rain (IP50 when rack mounted). Keep the
Chicago dry. (You won’t get electrocuted, but galvanic corrosion may take
place if powered and the PCB is wet). Operate at between -10 oC to +40
C, <95% Relative humidity, Non-condensing (i.e. no dew or
Try not to expose to direct sunlight. Long term exposure to UV may
degrade the paint surface or lead to ‘chalking’.
1.2 )
DO NOT clean with solvent based cleaners or abrasive cleaners. Use a
lint free cloth or a damp cloth with mild detergent. Solvents may affect the
paint surface or dissolve the silk screen paint.
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Product features
Analogue signal path from the oscillator to the output.
1 x Saw or Square wave (selectable). The Saw is generated by a
discrete transistor circuit.
1 x Synced Square Sub (-1 Octave) - it also divides the Saw
frequency by 2.
4 x independent Pulse waves with automatic or manual adjustment of
the phase, and manual adjustment of the pulse width. In automatic
mode, the effect is similar to detuning the waveforms.
Tune (0 to +60 cents), Major 3rd, Perfect 4th or Perfect 5th.
MIDI In, MIDI Thru, channel selection 1 to 16.
Classic Gate mode or Gate and 'Trigger on every note' mode.
6 channel mixer.
Amplifier ADSR.
Sallen & Key 24dB/Octave Low pass filter with Attack, Peak, Decay,
Sustain and Resonance control.
Set to sine (low frequency filter) switch.
Filter decay mode switch.
482 mm (19") x 132 mm (3U) and ~40 mm from face to base.
1 Watt power dissipation.
Approx. 2 kg.
Potentiometer life expectancy 100,000 full revolutions (as per all
‘audio’ pot manufacturer’s specifications).
MTBF ~125 Years.
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3) Block diagram
Oscillator timing
Manual width
Auto phase control*
Pulse 1
Pulse 2
Square Oscillator
Pulse 3
Pulse 4
ADSR Control
Manual phase control
* Each LFO triangle wave
has a different frequency
Sallen + Key
LP Filter
Resonance control
APDS Control
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The micro’s & analogues
This is a section for the more technically inquisitive.
MIDI processing MCU
(ATTiny48 @ 8MHz)
Oscillator Tune and amplitude leveller
MCU (ATMEGA328P @ 16 MHz)
ADSR generator and
amplifier MCU
(ATTiny48 @ 8MHz)
The ‘bare’ PCB
Analog mixer section
Discrete Transistor
Saw-tooth oscillator
LFO and trigger/event
timing manager MCU
(ATTiny48 @ 8MHz)
The constant current
based Pulse generation
Analogue Sallen & Key 4pole filter with feedback
APDS generator and filter MCU
(ATMEGA328P @ 20MHz)
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Connecting up
5-Pin DIN
2.1 mm Power
5-Pin DIN
Connections are underside, on
the left hand side of the unit.
6mm Mono
Jack output
5-Pin DIN
To the mixer
line input
1st Chicago
To the mixer
line input
2nd Chicago
DAW or MIDI Keyboard
Sometimes Keyboards have a USB MIDI
setting or a Classic 5-pin MIDI setting – so
choose the classic 5-Pin DIN MIDI setting.
To get from USB to 5-PIN MIDI, a converter
like the Roland™ UM-ONE works well.
The first Chicago, if only using one Chicago, will be
panned centrally on the mixer channel (or panned
however you need). When using two Chicago’s in
unison, then panning one left or half way left, and
panning the other right or half way right, and
detuning one slightly, the true stereo effect is quite
Roland UM-ONE
5-Pin DIN
Use the ‘connect to MIDI in’ plug.
The ‘connect to MIDI out’ plug will connect to your keyboard.
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Power supply
9 VDC and more
than 250 mA.
Power Pug
Any polarity
will work.
Power Socket
Power supply specification
9 VDC Output, and is capable of delivering at least
250 mA can be used. The power plug must be a 2.1 mm type, with an outer
barrel diameter of 5.5 mm. You don’t have to worry about whether the Pole is
Any power supply that has a
Positive or Negative, because the Chicago Power input can work with any
A 12 VDC power supply may be used if you can’t get a 9 Volt version. The
Chicago just runs a bit warmer and loses a little more energy.
Here is an example of a power supply for reference, which you can get from
Farnell or Digikey:
Manufacturer: XP POWER
Manufacturer Part No VER05US090-JA
The power supply has not been included, because you may already have one, or
you may prefer desk-top types rather than ‘wall-warts’, and you may need a
specific cable length. Also, you may not like the idea of universal plug connectors
or you may prefer a certain safety approval. However, these are inexpensive
items that are really easy to get hold of. Any music shop will also stock them (for
guitar pedals mainly).
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! Infrasonic
Keyboard range:
Fundamental range
ALL Notes and Intervals above
C4, remain at C4!
SUB (-1 Oct)
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Setting the MIDI Channel
MIDI Channel Switches
Gate LED
Selecting the MIDI channel number uses a classic method, similar to the DIP
switches used on the Boutique Synthesizers of the 80’s. It’s in Binary. If you can
count in binary, then it is straight forwards, but here is some help if you need:
When the matching MIDI channel is set on the DAW or on the MIDI keyboard,
any note press or sequencer note will activate the Gate LED, so you know it is
Illegal MIDI commands (history behind the dreaded dropped and stuck notes).
There are some DAWs that send out successive Same-Note, MIDI Note On
commands as a priority, so that timing can be tighter. This is actually ‘illegal’ in
terms of the MIDI specification and true Piano characteristics. You may have
encountered stuck notes and notes dropping out of sequences, wherever the
same-notes are butted against each other, and this is often the cause. The
Chicago can deal with this, but if it does occur, then a solution is to apply a little
gap between the end of one note and the beginning of the next. Overlaps are
fine when they are different notes.
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The Pulse Waves and
Nuance control
Pulse 1
Pulse 2
Pulse 3
Pulse 4
Pulse phase
Pulse width
The pulse waves are adjustable manually or automatically for the phase position,
from 0 to ~300 Degrees, to the fundamental saw or square wave (or sub wave).
The pulse width is adjustable from approx. 5% to 55%. The pulse width is
maintained for any phase potion, unless the phase exceeds the width:
Fundamental Saw Wave
Pulse Wave with 0 phase shift
Manual control
180 Deg.
Pulse Wave with 180 phase shift
Manual control
Auto control
Pulse width
The pulse width can be adjusted between
about 5% (narrow) to about 55% (wide) duty
cycle. The wider the pulse, the ‘phatter’ the
The 4 internal independent LFO’s
automatically moves the phase shift
depending on the phase control amount. This
can be between 0 and 300 Degrees. The effect
is similar to detuning the oscillators. Each LFO
has a different frequency, which is fixed.
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When in Automatic mode, and sometimes in Manual mode, and the low pass filter
decay is short, changes to the pulse controls have little noticeable effect,
particularly the phase control. Increasing the width does add a thicker sound, but
the difference between pulses is not highly discernible.
With shorter pulses widths in manual mode, and the filter sustain set high, subtle
nuances can be obtain with the sound, which changes the character of the sound,
further enhanced by the pulse 2 and pulse 4 mixer controls. This is quite good for
’Clav’ type sounds.
It takes a bit of adjustment, but occasionally, you can achieve very nice subtle
It’s often best to start with a basic saw wave, by turning the Pulses low (or off) on
the Mixer, then gradually add each pulse in turn. The tendency is to set
everything on full, to instantly achieve that ‘Phat’ sound, and if truth be known,
this is often what you do with the top end synthesizers anyway when playing bass
The Mixer
Pulse 2 and Pulse 4 volume
controls are a little different.
The top centre is ‘0’ volume.
As you pan left, the volume
increases, and the wave is
inverted. As you pan right, the
volume increases and the
wave is not inverted. Inverted
waves can give a different
sound, or balance the wave a
little to reduce signal clipping.
Pulse 1 volume (0 to +)
Pulse 3 volume (0 to +)
Sub volume (0 to +)
This is -1 Octave to the
fundamental saw.
Adding this to the saw,
and at 100% volume,
makes the saw decrease
by one octave.
Saw/Square volume (0 to +)
Saw/Square selector switch.
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10) The Modifiers
The modifiers are tailored more for bass and riff characteristics, without over
complicating the sound or modifying the sound too much (to sound ‘silly’). It must
be remembered that the envelope controls are interactive, and slightly different to
capacitor based envelope generators. The Filter sustain is semi-linear, so it
quickly gets up to the highs, at the later part of the Pot turn. This is sort of useful
in that the lower end is more subtle, and gives a better, less rapid, ‘wow’ effect
when used on a sustained note or a sequence. There is a little interaction
between the automatic filter control and the manual set point of the filter sustain.
Sometimes it can jump to the automatic filter control if the change between the
two is rapid enough (but it doesn’t always happen) – this can be avoided by
making slower manual changes or using longer notes. Over time, you will get
used to the characteristics of the filter controls and their quirkiness (either
limitation or advantages).
Amplifier ADSR
Amplifier Attack
Amplifier Decay
Amplifier Sustain
The Amplifier controls are
subtle, but the one that would
be used the most is the
Amplifier decay, to adjust from
a very tight cut-off on note
release, to a reasonably long
decay. It can sometimes add a
little ‘click’ with a very tight
decay (set to 0), because it can
actually ‘chop’ the wave. This
is solved by adding just a tiny
bit of decay if you do come
across a ‘click’ on deeper bass
Filter Attack
This switch changes the
Decay characteristic of
the filter.
With no notes pressed,
this switch sets the filter
to a low sine type wave,
and disables any filter
peak for deep ‘lounge’
type basses.
Filter Peak
This limits the attack to a given
filter peak value, reducing or
increasing the ‘brightness’ of the
note at the attack phase.
Amplifier Release
Filter Sustain
Filter Decay
Filter Resonance
Filter APDS
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11) Signal gain
If either, or both, of the Red clipping LED’s are illuminating or glowing, then turn
down the gain control and/ or you can reduce the volume controls on the mixer.
The Resonance control also boosts the lower end, and this can lead to clipping
HOWEVER – clipping is distortion, and in certain settings or sounds, with
everything turned up, it can be quite nice sounding. In essence, the gain control
is an effect – but use it carefully (it can sound bad in some cases).
Gain control
Red Peak/Trough
clipping LED’s
12) Keyboard Mode
The Keyboard (or sequencer) can be played in two modes:
The first is Gate Mode. In gate mode, overlapped notes do not trigger the filter
The second mode is Gate + Trigger Mode. In Gate + trig. Mode, every note
press, even with overlapped notes, will trigger the filter envelope.
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13) Volume and tune
Master Volume
This can be used to detune the oscillator from 0 to +
60 Cents, which is useful when double tracking or if
using two Chicago’s’ together. It is also possible to
tune to a Major 3 interval, Perfect 4 interval or
Perfect 5 interval when using two Chicago’s.
NOTE: The tune cannot be applied to a held or
sustained note, the note has to be pressed first
to activate any new tuning.
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14) MIDI control from a DAW
(Digital Audio Workstation)
For those who are thinking about using a MIDI sequencer, my preference would
be Cubase, but other DAWs like Logic, Pro Tools, Cakewalk, Ableton, Reaper
etc. are equally capable. I prefer Cubase because it’s quite easy to set up and
navigate around, and the Piano-Roll editor/composer and quantising is quite
intuitive, giving the hardware sequencer users an alternative (but similar) way of
composing. The Mix between Audio and MIDI is also great in Cubase, where they
are treated the same right down to the Mixer and the Effects.
When using a DAW, the Chicago can be played using the integrated MIDI
sequencer, or from your keyboard if you have one connected.
In this example, Cubase 8™ is used, and the Midi Interface is the Roland UMONE (this can be any Midi interface device you choose). Make sure it’s plugged
in before launching Cubase (or other DAWs).
To set up the UM-ONE and a Cubase Midi channel, first add a Midi Instrument
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Select Midi IN and OUT, in the Inspector column, using the UM-ONE: Midi IN is
from the Keyboard, Midi OUT goes to the Chicago.
Select the Midi Chanel to correspond to the one set on the Chicago (this is
exampled as Chanel 1) – see section 7. Make sure your Keyboard is also
outputting Midi Chanel 1 and it is using the Classic Midi output (if also USB
To play the Chicago, you must select the Instrument Track (in this case it’s titled
MIDI 01).
NOTE: The Chicago has been tested with: Roland UM-ONE, SEQ24, Cubase 5
and 8. Yamaha Workstation (5-Pin Midi), ESI Keycontrol 25XT (5-Pin Midi), and
Moog Sub 37 (5-Pin Midi). DAW Platform PC i7 64 bit with USB Midi.
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EU regulation conformance
Health and the Environment
All component and metal casings are Lead-Free and Cadmium-Free.
The Low Voltage Directive
The device is operated under the Extra-Low-Voltage limits, so the Low-Voltage
Directive will not apply. The Power supply will come under the Low Voltage
Directive, but this item will not be supplied with this product. However, advice on
selecting a suitable and conformant power supply is given.
There are no switching components or switch-mode circuits used, and the
Microcontrollers are each decoupled with a 10uF electrolytic capacitor and a
100nF ceramic capacitor, where this is further blocked by the incoming Linear
Regulator, which is Tantalum-capacitor decoupled. All trace designs and
decoupling for each component is followed in accordance with the manufacturer’s
recommendations. The PCB comprises a digital and analogue ground-plain
connected in a ‘star’ topology. Therefore radiated and conducted EMC is
The Chicago Synths is not affected by an iPhone4 ‘updating’ at a distance of 100
mm, whereas all other associated branded audio equipment, with CE marking, is
affected at a distance of 300 mm. All other Radio signals will not affect the
Chicago because the impedance path is very low and kept very short, assisted by
PCB ground-planes.
Power Factor
The Chicago operates from a DC source, so there is no power phase shift. The
PF is effectively 1. Where the total power dissipated is 1W.
The Chicago is classified as a ‘Musical Instrument’, and normally sub-grouped
with ‘Synthesizers’. It is intended to be used for recreation and entertainment,
where its functionality is demonstrated through the various examples on the web
It is designed to be a high quality and reliable product when used in accordance
to this instruction/operating manual.
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