Weston TZ0 User manual

© 2023 Weston Precision Audio
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TZ0
Thru Zero Oscillator
Eurorack Module
User Manual
Weston Precision Audio
Designed In Portland, Oregon
Revision 01 - September 25, 2023

DESCRIPTION
TZ0 is an analog voltage-controlled
triangle-core oscillator with the ability to
modulate through zero-frequency (See
figure 1). This allows for deeper,
cleaner, more natural sounding
frequency modulation and allows for
additional sonic expression not
available with standard linear FM. TZ0
is a 12 HP Eurorack module which is
available as a pre-built module or as a
DIY project. This VCO has been
engineered for extremely good 1 V/oct
response over a large tuning range and
great thermal stability.
Figure 1: A typical triangle wave modulating
through a zero-frequency crossing
SPECS
Module Size: 12HP
VCO Output (All outputs ~1kOhm
Impedance): Sine, Triangle*, Sawtooth,
Square*, Pulse
(* = Directly from VCO core)
Inputs (All inputs >=100kOhm
Impedance): 1 Volts/Octave, Linear
Frequency Modulation, FM Modulation
Envelope, Sync, Pulse Width Modulation
All wave outputs: 10 Volts peak-to-peak
nominal
VCO range: 0Hz - 28kHz
Power input: +12V & -12V via standard
10 pin Eurorack connector.
Power consumption (+12V / -12V):
Typ: 75mA / 60mA
Max: 85mA / 70mA
Tuning error: < +/- 5 cents over 7 octave
typical
MAXIMUM LIMITS
Supply Voltage: +13.5V / -13.5V
FM, PWM, and Sync Inputs: 20Vpp
(nominal 10Vpp)
Envelope Input: +10V (nominal 0-5V)
1 Volt/Oct Input: +12V
© 2023 Weston Precision Audio
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© 2023 Weston Precision Audio
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TZ0 Overview Tuning
Potentiometers
Large = coarse
adjustment, small = fine
adjustment
Linear Frequency
Modulation Section
See Page 3 for detail
PWM Section
See Page 4 for
detail
Primary Wave Outputs
Sine, Triangle, Sawtooth, Square, Pulse
Frequency CV
Input
Changes oscillator
pitch on a 1 volt
per octave scale.
Sync Input
See Page 4 for
detail

MODULATION SECTION (Thru-Zero
FM)
One of the features of TZ0 that many
analog VCOs do not have is through-
zero linear FM. A VCO with standard
linear FM, when presented with a
modulating signal that will take it all the
way down to 0Hz frequency, will simply
stop making any sound. This produces
an effective DC offset of the modulating
signal that increases with more
modulation, thus bending the primary
pitch of the oscillator upward as
modulation increases. On the other
hand, a TZFM oscillator core will simply
modulate towards 0Hz, then “start
spinning backwards” and continue to
modulate. The result is natural sounding
modulation, such as that of a bell or a
pipe being struck, without the bending
of the fundamental pitch like regular
linear FM.
The FM section of TZ0 is shown in the
above block diagram. The “0Hz” point
discussed above is simply adjusted with
the “TZ Offset” knob. This has the side-
effect of modulating the primary pitch of
the oscillator, so adjustments in “TZ
Offset” need to be accompanied with
re-tuning via the tuning pots.
One interesting usage of the “TZ Offset”
pot, is to set it completely counter-
clockwise (to zero). This means that the
oscillator core itself will not make any
sound on it’s own, but it can be
modulated with a signal from the “Lin
FM” input. This has the effect of
reversing the role of the tuning pots and
the “Lin FM” input: The “Lin FM” signal
effects the overall pitch heard, and the
tuning knobs (and V/oct input) change
the timbre of the sound.
Finally, a simple VCA has been included
right after the “Lin FM” input. This
allows the amount of TZFM modulation
to be shaped by an envelope or other
signal.
The “Lin FM” input on TZ0 is AC-
coupled.
© 2023 Weston Precision Audio
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PWM Section
The rightmost output on TZ0 is a PWM
or pulse-width-modulated output. A pulse
signal with PMW is a square-shaped
signal that can vary its duty-cycle (the
amount of time the wave is high vs low).
The PWM signal is derived by simply
feeding the triangle from the VCO core
to a comparator, with the other voltage
of the comparator being some voltage.
The TZ0 PWM section is shown in the
diagram above. The overall initial pulse-
width is simply set by using the “PW”
knob. When the knob is centered, the
pulse output will be 50% duty cycle (a
square). Turning the knob CCW makes
for narrower pulses, and CW makes for
wider ones.
Finally, any signal such as a LFO or
VCO or envelope can be inserted into
the “PWM” jack and used to modulate
the width of the pulse output. It is simply
summed with the DC value which is
adjusted by the “PW” knob.
Sync
The oscillator core of TZ0 can be sync’d
from another oscillator with the “Sync”
input. It is a “reset” or “hard” sync type
which resets the triangle’s integrating
capacitor on the rising edge of the
inputted sync signal. Try keeping the
sync signal fixed and adjusting the
tuning put constant for classic sync
sounds.
The diagram below shows the action of
the “Sync” input:
© 2023 Weston Precision Audio
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MAINTANENCE
TZ0, like most modular synth equipment
will not need any particular
maintenance. However, some people
may want to adjust the trimmer pots on
the module, such as perfecting the V/oct
response for your particular case, MIDI
converter, etc.. The following trimmer
pots are located on the rear PCB of TZ0
and are labeled on the top side of the
board with their function:
-V/oct trimmer *
-High Frequency compensation trim *
-Sine roundness trim
* If you wish to fine tune the V/oct and
HF compensation trimmer, remember to
set the “TZ Offset” pot to center (high
noon) while doing so.
CONCLUSIONS
As with any piece of modular synth
equipment, it is best to just play with it
by itself and with other modules. Find
what you like and most importunely,
have fun making music!!
© 2023 Weston Precision Audio
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-12V Node
R21
4.7k

REVISION HISTORY
01: Initial release.
© 2023 Weston Precision Audio
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