Bastl Instruments KASTLE v1.5 User manual

v1.5
KASTLE
BASTL
INSTRUMENTS

KASTLE v1.5
Features
●complex oscillator
●3 synthesis modes on the main output: phase
modulation, noise mode, track & hold modulation
●3 more modes on the secondary OSC output: phase
distortion, tonal noise mode, formant synthesis
●PITCH control with oset and CV input with attenuator
●TIMBRE control with oset and CV input with attenuator
●WAVESHAPE control with oset and CV input
●voltage controllable LFO with triangle and square
outputs and reset input
●stepped voltage generator with random, 8 step and 16
step loop mode
●2 I/O CV ports that can be routed to any patch point
●the main output can drive headphones
●3x AA battery operation or USB power selectable by a
switch
●open source
●possibility of exchanging dierent LFO and OSC chips
●durable black & silver PCB enclosure
What’s in the box
●kastle synth
●10 patch cables
●sticker
●for environmental reasons we are excluding the batteries
from the package

INTRODUCTION
Kastle v1.5 is a mini modular synthesizer with a headphone
output, 2 in/out ports for interfacing other gear and it runs
on just 3 AA batteries or USB power.
It is DIY friendly and ideal for beginners in modular
synthesis, but it will add some quite unique functionality to
any modular synthesizer system. It delivers the fun of
modular synthesis at a low cost and fits into your pocket so
you can play it everywhere!
Kastle has a unique digital lo-fi sound and it can be melodic
as well as very noisy and drony, soft or harsh. It is designed
to be fun on its own but it is most powerful when combined
with other modular gear.
Kastle is an open source DIY project which runs on two
ATtiny 85 chips that can be reprogrammed with an Arduino
(google: “programming ATtiny 85 with Arduino”). One chip
is dedicated to sound generation while the other one
handles modulation. Several firmwares for the Attiny chips
are available thru gitHub.
The v1.5 version combines a complex oscillator and LFO
with a stepped waveform generator.
The oscillator section has 3 sound parameters: PITCH,
TIMBRE and WAVESHAPE – all under voltage control and
with 6 dierent synthesis modes. It has a main output and a
secondary waveform output. Both can be used
independently or in combination.
The 3 synthesis modes available thru the main output are:
phase modulation, noise mode and track & hold
modulation.

There are 3 more modes on the secondary OSC output:
phase distortion, tonal noise mode and formant synthesis.
Each mode utilizes one or two oscillators.
The PITCH parameter controls the main oscillator, the
TIMBRE sets the PITCH of the modulating oscillator and
the WAVESHAPE depends on the synthesis mode.
The voltage controllable LFO has a triangle and square
output and a reset input.
The stepped waveform generator is inspired by the Rungler
circuit by Rob Hordijk. It can produce 8 dierent voltages
either in random order or in 8 or 16 step looping patterns
depending on how the BIT IN is patched.

INSTRUCTIONS
Kastle is a mini modular synth and as in every modular
synth the sounds are programmed by connecting outputs to
inputs.
Outputs are labeled by a silver outline around the patch
points. Inputs don‘t have the silver outline.
Feel free to also connect inputs with inputs and outputs with
outputs. Nothing bad will happen. And sometimes
something interesting can happen with strange
connections!
0 POWER UP
Find a microUSB cable or go to your nearest store and buy
3 AA batteries. You can catch Pokemons on the way,
though you don‘t have to, but the important thing is that on
average you will burn 50 calories. Also, not shipping the
batteries to you from us is environmentally friendly.
Connect the USB cable to a powered 5V USB socket or
insert the batteries to the battery compartment the right way
- as indicated on the battery holder.
Flip the power switch to the USB or BATT position based on
which power source you are using. There is a LED close to
the LFO RATE knob which should light up. If it doesn‘t it
means the USB socket is not powered or you connected
the batteries in a wrong way or they are completely
depleted.
1 OUT
Use the OUT jack to connect your headphones or an audio
cable from your speaker system. The main output of the
complex oscillator is routed to the OUT jack.

2 PITCH
Turn the OSC PITCH knob to adjust the PITCH of the main
oscillator. A modulation signal can be connected to the
PITCH MOD socket and the PITCH MOD knob controls the
amount of the modulation.
3 MODULATION
Turn the OSC TIMBRE knob to adjust the PITCH of the
modulating oscillator.
A modulation signal can be connected to the TIMBRE MOD
socket and the TIMBRE MOD knob sets the amount of the
modulation.
4 WAVESHAPE
Turn the WAVESHAPE knob to adjust the 3rd parameter of
the sound. A modulation signal can be connected to the
WAVESHAPE socket to modulate this parameter. The
WAVESHAPE also sets the pulse width of the OSC PULSE
output.
5 OSC OUT
This patch point on the device can be either used as
another signal for your patch or when any other output is
connected to this output it will be passively mixed with the
oscillator output and will go to the OUT jack. This is most
useful for adding more power by connecting the
SECONDARY OSC OUT.
6 SECONDARY OSC OUT
The SECONDARY OSC OUT provides an alternative
waveform based on the secondary modulating oscillator
and the waveform can be adjusted by the WAVESHAPE
parameter. It can be either used to modulate parameters
within the Kastle synth or patched to the OSC OUT socket

to mix with the main waveform or it can be output separately
via the I/O jack.
7 MODE
The MODE socket lets you select the synthesis mode. The
synthesis mode aects both the OSC OUT and the
SECONDARY OSC OUT.
When nothing is connected the synthesis mode at OSC
OUT is phase modulation and at SECONDARY OSC OUT
is phase distortion.
When a modulation signal plugged into this jack is high (or
just patched to the “+” socket), the synthesis mode
becomes track & hold modulation on the OSC OUT and
formant synthesis on the SECONDARY OSC OUT.
When the signal connected here is low (or just patched to
“–” socket) you are in dual noise mode with more tonal
character at the SECONDARY OSC OUT.
See the Synthesis Types section for more information.
8 +/– SOCKETS
To set the MODE socket statically to specific synth mode
use the low = ”–” or high = ”+” patch sockets. These patch
points can be also useful to set the BIT IN pin. “+” can be
used to oset any modulation signal and “–” connects
directly to ground so it can be used to connect grounds
between several instruments.
9 LFO RATE
The LFO RATE sets the speed of the modulation. The
modulation is displayed by an LED close to the LFO RATE
knob. A modulation signal can be connected to the RATE
MOD socket and the RATE MOD knob sets the amount of
the modulation. This is especially useful when creating

more complex modulation curves. See Tips & Tricks
section for more info.
10 LFO TRIANGLE
The LFO TRIANGLE socket outputs a simple triangle
waveform, but it can be altered by modulating the LFO
RATE or triggering the LFO RST to get some complex
modulation shapes.
11 LFO PULSE
The LFO PULSE socket outputs the PULSE wave in sync
with the TRIANGLE wave.
When the TRIANGLE wave is rising the PULSE output is
high and when it is falling the output is low. This signal can
be used for synchronizing external equipment.
12 LFO RST
The LFO RST resets the phase of the LFO to the highest
point of the triangle and then the triangle begins to fall. This
is very useful for creating complex modulation curves or for
synchronizing with external clock.
13 STEPPED
The STEPPED generator is inspired by the Rungler circuit
by Rob Hordijk. It can produce 8 dierent voltages. It
generates new voltage twice per period of the LFO (every
time the direction changes from rising to falling). The
voltage is based on the current state of 3 bits of internal
binary 8 bit shift register. The shift register is shifted with
every new voltage generated. When this happens - based
on the signal at the BIT IN socket - the new bit arriving at the
shift register remains the same (BIT IN is low), is inverted
(BIT IN is not connected) or is generated randomly (BIT IN
is high). It means that when BIT IN is not connected the
STEPPED output generates a 16 step pattern.

When it is low it generates an 8 step pattern. When it is high
it keeps generating a random pattern and when it is altering
it generates a semi-random pattern. The STEPPED output
is very useful for modulating every parameter in the Kastle
synth or any external device with the I/O port.
14 I/O CV port
The I/O CV port enables you to connect up to 2
modulation/audio/clock signals from Kastle to external gear
or to connect any external signal to modulate the Kastle
synth. The signals are output with a stereo jack and the
patch points L and R connect either to the left or right
channel. To use both channels with a modular synth you
can use stereo to mono splitter adapter or you can just use
one channel (L) with a mono cable connected to the I/O
jack. When connecting external modulation to Kastle,
please note that the signal will be rectified and Kastle will
respond only to signals 0-5V.
TIPS & TRICKS
Percussive sounds
Connect the LFO PULSE to the LFO RST socket. This
results in SAW waveform at the LFO TRIANGLE output
(because as soon as the TRIANGLE starts rising it receives
the PULSE and therefore goes to the highest point and
starts falling and therefore skips the rising stage). Use the
SAW waveform to modulate any of the oscillator
parameters (or several at once). On top of that, connect the
STEPPED output to the LFO RATE socket. Adjusting the
LFO RATE and the RATE MOD knobs will result in dierent
lengths of SAW modulation signals and therefore dierent
rhythms.

Dierent rise and fall times
Connect the LFO PULSE to the RATE MOD socket. Now
the RATE MOD and LFO RATE knobs set dierent
proportions between the rise and fall time of the triangle.
This will also create a swing eect on the STEPPED
waveform. You can also use the STEPPED output to
connect to the RATE MOD socket to change the slope time
with every new voltage generated at the STEPPED output.
Thick sound
Connect the SECONDARY OSC OUT to the OSC OUT
socket to mix both oscillator waveforms
together. This can result in a really thick sound which is
great for further filtering.
Sync
The LFO and STEPPED generator on Kastle can be synced
with other gear. You can use the LFO PULSE out when you
want Kastle to be the master clock or connect clock from
another device to the LFO RST when you want it to be the
slave. Simply connect the I/O jack to your device and patch
the L socket to the LFO RST or LFO PULSE.
Connect everything to everything !
There are several connections that might surprise you while
exploring the sounds. Here are a few of the ones you should
try out for sure:
●Connect SECONDARY OSC OUT to the BIT IN to
create varying random patterns.
●Connect SECONDARY OSC OUT to any of the OSC
inputs to see what happens.
●Connect any LFO signal to the MODE pin to change the
synthesis mode on the go.

●Connect SECONDARY OSC OUT to the LFO RST pin to
create chaotic modulation waveforms.
Kastle takes some common synthesis methods and
implements them with a very lo-fi twist which gives it a very
distinct character full of aliasing artifacts.
SYNTHESIS TYPES
Phase modulation
(OSC OUT, MODE disconnected)
Very similar to linear FM (frequency modulation), phase
modulation is a method pioneered by John Chowning and
later used by Yamaha in their famous DX synths.
Kastle implements only two operator sinewave PM with a
modulation amount. PITCH sets the main oscillator
(carrier), TIMBRE sets the modulating oscillator
(modulator) and WAVESHAPE sets the amount of
modulation.
Phase distortion
(SECONDARY OSC OUT, MODE disconnected)
It was historically first used in 1984 in Casio synths of the
CZ range. It is based on two synced ramp oscillators.
The synced (higher tuned) oscillator is scanning the sine
wave wavetable and is multiplied by the inverse of the lower
tuned oscillator. In practical terms this was supposed to
emulate sweeps of a resonant filter on a sawtooth
waveform.
The implementation in Kastle is an adaptation of this
method with wider ranges on the oscillators and more
formant-vocally character. There is also the third
WAVESHAPE parameter which crossfades from secondary

sine wave thru soft synced sinewave all the way to the
phase distortion.
Track & Hold Modulation
(OSC OUT, MODE connected to “+”)
This is a not so common synthesis method. The main sine
wave oscillator is going thru a comparator which turns it into
a variable pulse width waveform which is gating a track &
hold circuit.
The second oscillator is being fed thru the track & hold
which means that when the pulse of the main oscillator is
high the signal passes and when it becomes low it holds
static voltage.
The threshold (WAVESHAPE) on the comparator sets the
pulse width and therefore the amount of the modulation
while the PITCH and TIMBRE set the frequencies of the
oscillators.
Formant synthesis
(SECONDARY OSC OUT, MODE connected to “+”)
This mode is inspired by the Helmholz Synthesizer (made
in 1905) which was an acoustic synthesizer based on
several pitchforks tuned as several harmonic multiples of a
fundamental frequency that have been amplified by
adjusting a mechanical shutter of an acoustic resonator of
corresponding frequency.
Such a device could emulate vowel sounds made up by
sine waves of dierent harmonic frequencies mixed
together.
On Kastle the WAVESHAPE knob selects dierent
combinations of harmonic frequencies and their
proportions built up on the secondary oscillator.

Because the combinations of formants are stepped,
modulating the WAVESHAPE results in musical arpeggios.
Noise Mode
(OSC OUT, MODE connected to “-”)
The Noise mode on Kastle is implemented by a granular
playback of the flash memory (where the program is stored)
of the sound processing chip. In other words it is a data
player of a piece of computer code (that runs the sound
core of the Kastle synth) that has very distinct sonic
qualities on its own - often referred to as “glitch” in aesthetic
terms.
However this mode is so purposeful that instead of talking
about a mistake we should be talking about being true to
what the true nature of Kastle truly is in very modernistic
terms (it is a digital synthesizer).
The PITCH controls the speed of the playback, the
WAVESHAPE controls the loop length of the playback and
the TIMBRE controls the secondary oscillator that
modulates the amplitude of the final signal.
Tonal Noise Mode
(SECONDARY OSC OUT, MODE connected to “-”)
A byproduct of the Noise mode while enhancing the PITCH
of the secondary oscillator which is tuned a few octaves
higher than in the normal noise mode.
In this mode the oscillator is implemented as a thru zero
oscillator meaning that from a certain position (11 o‘clock)
the PITCH rises in both directions but in a dierent phase.

BASTL
more info
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www.bastl-instruments.com