Rossum TRIDENT User manual

TRIDENT
Multi-Synchronic
Oscillator Ensemble
Copyright 2019 Rossum Electro-Music LLC
www.rossum-electro.com
Operation Manual
_042419_v5

2 |
Contents
1. Introduction 3
2. Module Installation 4
3. Overview 5
4. Basic Functionality 7
5. Make Some Noise! 9
6. The Carrier Oscillator in Detail 10
7. The Modulation Oscillators in Detail 12
8. Specifications 16
9. From Dave’s Lab 18
10. Acknowledgements 21

| 3
1. Introduction
Thanks for purchasing (or otherwise
acquiring) the Rossum Electro-Music Trident
Multi-Synchronic Oscillator Ensemble. This
manual will give you the information you
need to get the most out of Trident. The
manual assumes you already have a basic
understanding of synthesis and synthesizers.
If you’re just starting out, there are a number
of good reference and tutorial resources
available to get you up to speed. One that we
highly recommend is:
Power Tools for Synthesizer Programming
(2nd Edition)
By Jim Aikin
Published by Hal Leonard
HL00131064
Support
In the unlikely event that you have a problem
with your Trident, tell us about it here:
http://www.rossum-electro.com/support/
support-request-form/
…and we’ll get you sorted out.
If you have any questions, comments, or just
want to say “Hi!,” you can always get in touch
here:
http://www.rossum-electro.com/about-2/
contact-us/
…and we’ll get back to you.
Happy music making!

4 |
2. Module Installation
As you will have no doubt noticed, the rear of
Trident is a circuit board with exposed parts
and connections. When handling Trident, it’s
best that you hold it by the edges of the front
panel or circuit board. It’s not particularly
easy to blow up, but why take chances?
More specifically, the biggest risk (to the
extent that there’s a risk), is damage by static
electricity. Particularly on dry, cold days (or if
you’ve just shued across your shag carpet
in fuzzy slippers), make a point of touching
the metal panel first, before touching any
other part of the module.
While all Rossum Electro-Music modules are
protected against reverse polarity damage,
both to your module and your system, care
should still be taken to connect the power
cable correctly. (For more detail on our
unique protection method, check out Dave’s
discussion of Circuit Protection in Chapter 9.)
Plug the included 16-pin connector into the
header on the rear of the module such that
the red stripe on the cable (the -12V side) is
on the same end of the header as the “Red
Stripe” text on the PCB.
Trident requires, at most, 290mA of +12V and
270mA of -12V.
We have included both M3 and M2.5 (for
vector rails) mounting screws. Use what fits
your system.
If rack rash is of concern to you, use the
included nylon washers when mounting
Trident in your case.

| 5
3. Overview
What is Trident?
The latest brainchild of synth pioneer Dave
Rossum, Trident is a 100% analog, triple
oscillator module that opens up a universe of
dynamic timbral textures.
At its most basic level, Trident is three
precision audio VCOs, each sporting a
unique variety of control voltage inputs.
The main or “Carrier” oscillator provides
its three waveforms simultaneously. The
two Modulation Oscillators each have a
single output and a waveform selector. The
Modulation Oscillators also have a voltage
controlled Symmetry parameter which
varies the duty cycle of the triangle wave
output from sawtooth to triangle back to
time reversed sawtooth, and also varies

6 |
the sawtooth output to have an upward
or downward kink in the middle, as well
as controlling pulse width when the pulse
waveform is selected.
And while each oscillator can be used
independently if desired, it’s when they’re
combined into a synchronous ensemble that
the real sonic magic happens.
That magic is what we call “Zing”
modulation. Each of the Modulation
Oscillators can modulate each of the
Carrier outputs in an amount controlled
by the Zing parameter. Zing modulation is
mathematically akin to ring modulation, but
due to the synchronization of the oscillators
(when an oscillator’s Sync button on), the
aharmonic sum and dierence sidetones of
ring modulation transform into complex but
purely harmonic overtone spectra, which
vary dynamically and dramatically with the
frequency and waveshape modulations of
the modulation oscillators. Each change
in the Modulation Oscillator parameters —
Frequency, Symmetry, Waveshape, Zing, and
(in the case of Modulation Oscillator 2) Phase
— will have a dierent eect on the timbre of
each of the three Carrier waveshape outputs.
When the modulation oscillators are set to
track the carrier oscillator, the waveshape
will remain constant as the carrier frequency
changes. In this case the overtone structure
is determined by the settings and CV
modulations of the modulation oscillators.
If instead the modulation oscillators do
not track the carrier, some of the overtone
structure will vary relative to the carrier
frequency.
What all this means is that whether you take
advantage of Trident’s unique synchronous
modulation capabilities (which you, of
course, should), or just treat it as three
superb, wide-range analog oscillators,
Trident oers a vast variety of dramatic sonic
textures.
Trident features include:
> Three precision analog oscillators with
dedicated 1V/Octave inputs and coarse
control ranges of 20Hz to 20kHz and
modulated ranges of 0.01Hz to 25 kHz.
> Main Carrier Oscillator with simultaneous
triangle, sawtooth and pulse waveforms,
with exponential and linear frequency
modulation and pulse width modulation.
> Main Carrier Oscillator hard sync input.
> Modulation Oscillator 1 with selectable
triangle, sawtooth and pulse waveforms
with exponential frequency modulation,
variable symmetry and symmetry
modulation, and variable Zing level and
Zing level modulation.
> Modulation Oscillator 2 with selectable
triangle, sawtooth and pulse waveforms
with exponential frequency modulation,
variable symmetry and symmetry
modulation, variable Zing level and Zing
level modulation, and variable phase and
phase modulation.
> Both Modulation Oscillators with
independently selectable options to sync
to the main oscillator and track the main
oscillator.
> Trident, like all Rossum Electro-Music
modules, features solid construction,
with thick aluminum panels, solid
aluminum knobs, and quality components
throughout.
For a substantially more in-depth exploration
of Trident’s technology, be sure to check out
“From Dave’s Lab” in Chapter 9.

| 7
4. Basic Functionality
Before we jump into individual functions
in detail, let’s take a quick look at Trident’s
controls.
Coarse and Fine Frequency
Controls an oscillator’s initial frequency over
a range of 20Hz to 20kHz. Modulated ranges
are from 0.01Hz to 25kHz.
1V/Oct Input
Calibrated 1 volt per octave Frequency CV
inputs (accurate over 10 octaves).
Exponential and Linear (Carrier
Oscillator only) Frequency
Modulation
CV inputs into attenuverters (exponential) or
an attenuator (linear).
Pulse Width and PW Modulation
Sets the Carrier Oscillator’s initial pulse width
from 0% to 100% and modulates it via the CV
input through an attenuverter. Note that at
audio rates, 0% or 100% pulse width results in
no audio, just a static DC level.
Symmetry and Sym Modulation
(Mod Oscillators)
Varies the duty cycle of the triangle wave
output from sawtooth to triangle back to
time reversed sawtooth, and also varies
the sawtooth output to have an upward or
downward kink in the middle. Sets the pulse
width when the pulse waveform is selected.
Symmetry can be modulated via the CV input
through an attenuverter.
Zing Level and Zing Modulation
(Mod Oscillators)
Sets the amount of a Mod Oscillator’s
Zing modulation of the Carrier Oscillator.
Modulates the Zing amount via the CV input
through an attenuverter.
Phase and Phase Modulation
(Mod 2 Oscillator only)
Varies the phase of the Mod 2 Oscillator
compared to the Carrier when Mod 2 Sync
is enabled. Modulates it via the CV input
through an attenuverter.
Sync Buttons (Mod Oscillators)
When engaged (with the LED lit), a Mod
Oscillator is hard synced to the Carrier
Oscillator’s frequency.
Track Buttons (Mod Oscillators)
When engaged (with the LED lit), causes the
Mod Oscillator to track precisely the Carrier
Oscillator’s frequency.
Carrier Oscillator Sync In
Hard syncs the Carrier Oscillator to the rising
edge of an external source or to either of the
Mod Oscillators (by patching their output to
this input).

8 |
Outputs
The Carrier Oscillator provides simultaneous
triangle, sawtooth, and pulse outputs. The
Mod Oscillators each have a single output
with selectable waveforms.

| 9
5. Make Some Noise!
If you’ve already followed along with the
Make Some Noise! section of the printed
Trident Quick Start Guide included with your
module, you can skip this chapter and go
directly to the next. However, if you haven’t,
spending a few minutes here will give you a
quick introduction to the function and eects
of the basic controls.
Given Trident’s plethora of knobs and mod
inputs, experimentation is the order of the
day. To get you started:
> Monitor the triangle output of the Carrier
Oscillator.
> Turn up the Zing level of Mod 1 and turn
down the Zing level of Mod 2. Ensure that
Mod 1’s Sync and Track are enabled.
> Vary Mod 1’s Frequency, Symmetry, Zing
settings, and waveform and listen to their
eect. Try modulating the parameters with
external signals (or with the output of Mod
2).
> For dual Zing Modulation, turn up the Zing
on Mod 2 and vary its parameters and
waveform.
> Try disengaging Sync and/or Tracking on
each Mod Oscillator and listen to their
eects.
> Zing!

10 |
6. The Carrier Oscillator in Detail
Trident’s Carrier Oscillator is a precision
voltage controlled oscillator in the tradition
of the legendary oscillators Dave designed
for the original E-mu Modular System. It
can, of course, stand alone as a superb
VCO, but it truly comes alive as the target of
Zing Modulation by one or both of Trident’s
Modulation Oscillators.
Here’s what it oers:
COARSE and FINE FREQUENCY
Using the COARSE FREQUENCY and FINE
FREQUENCY controls, the Carrier Oscillator’s
initial frequency can be set between 20Hz
and 20kHz.
With the addition of the frequency
modulation CVs described below, the
available range is between 0.01Hz and 25kHz.
1V/OCT Input
The 1V/OCT CV Input is a
calibrated full level control voltage
input that is summed with the
values of the Coarse and Fine
Frequency controls and the Expo
FM input.
Trident’s 1V/Octave tracking is accurate over a
10 octave range.
EXPO FM
The EXPO FM Input is a
control voltage input that is
modified by its associated
attenuverter and then
summed with the value
of the Coarse and Fine
Frequency controls and the
1V/OCT input.
When the attenuverter knob
is set to its “0” position, no
control voltage is passed
to Trident. As the knob is turned clockwise
from 0, the amplitude of the control voltage
increases until, at maximum clockwise
rotation, the full amplitude of the signal at the
EXPO FM Input is passed through and results
in a nominal 1V/Oct response.
As the knob is turned counterclockwise from
0, the signal at the EXPO FM input is inverted
(e.g., a CV of +2.5V becomes -2.5V). The
farther counterclockwise the knob is turned,
the less the attenuation of the inverted signal,
until, at maximum counterclockwise rotation,
the full amplitude of the inverse of the signal
at the EXPO FM input is passed through, also
at a nominal 1V/Oct response.
A TIP: You can use the Carrier Oscillator
(or, in fact, any of the three oscillators) as
precision LFOs by setting the Coarse and
Fine Frequency controls to their minimum
(fully CCW) positions and patching 5V (or
more) into the Exponential FM input. Adjust the
input’s attenuverter in the negative range to set
the LFO’s frequency.

| 11
LINEAR FM
The LINEAR FM Input is an
AC coupled control voltage
input that is modified by its
associated attenuator to allow
Linear Frequency Modulation
of Trident’s output frequency.
When the input’s associated
attenuator knob is set to its
maximum counterclockwise
position, no control voltage is
passed to Trident. As the knob
is turned clockwise, the amplitude of the
control voltage increases until, at maximum
clockwise rotation, the full amplitude of the
signal at the LIN FM Input is passed through.
NOTE: It’s beyond the scope of this
manual to provide an in-depth discussion
of Linear versus Exponential FM, but
for those interested, Chris Meyer (as part
of his Learning Modular series) oers clear
explanations, along with audio examples, here:
https://learningmodular.com/
understanding-the-dierences-between-
exponential-linear-and-through-zero-fm/
For those not-so-interested, the tl;dr version
is that unlike exponential FM, linear FM does
not typically result in shifting the pitch of the
target oscillator with changes in modulation
depth (as long as the modulation depth does
not result in driving the pitch of the target
oscillator below 0Hz).
PULSE WIDTH and PW MOD
The PULSE
WIDTH control
lets you set
the initial
pulse width
of the Carrier
Oscillator’s pulse
wave output
from 0% to
100%.
IMPORTANT NOTE: At audio rates, when
the pulse width is set to 0% or 100%, there
will be no audio output, just a static DC
level. At 0%, the output will be a continuous
-5V and at 100%, it will be a continuous +5V.
A TIP: If you aren’t using the Carrier
Oscillator Pulse output for audio, you
can turn the Pulse Width to 0% and use
it as a source of -5V to bias one of the Mod
Oscillators to the LFO range.
The PW MOD input is a control voltage input
that is modified by its associated attenuverter
to allow CV control of the pulse wave’s
pulse width. The attenuverter functions as
described in the EXPO FM section above.
SYNC IN
Hard syncs the Carrier Oscillator to
the rising edge of a signal patched
into this input when the signal
exceeds a threshold of 3.5V. The
signal can be from an external
source or from either of the Mod Oscillators
(by patching their output to this input).
AUDIO OUTPUTS
The Carrier Oscillator provides
simultaneous triangle,
sawtooth and pulse outputs.

12 |
7. The Modulation Oscillators in Detail
Like the Carrier Oscillator, Trident’s two
modulation oscillators can serve as full-
function, stand-alone oscillators with
independent frequency control and unique
CV-controlled waveform symmetry. But it’s
their roles as Zing Modulation sources that
open up a virtually unlimited variety of unique
timbral textures.
MODULATION OSCILLATOR 1
COARSE and FINE FREQUENCY
Using the
COARSE
FREQ and
FINE FREQ
controls,
the Mod 1
Oscillator’s
initial
frequency can be set between 20Hz and
20kHz.
With the addition of the frequency
modulation CVs described below, the
available range is between 0.01Hz and 25kHz.
NOTE: When using Mod 1 as a stand-alone
oscillator, the frequency controls (and the
frequency CVs described below) function
as you’d expect to change the frequency of
the oscillator. However, when using Mod 1 as
a modulation source for Zing Modulation with
the Sync function activated, the frequency
controls and CVs serve to define and modulate
the timbre of the Carrier Oscillator. For that
reason, using the EXPO FM input described
below to modulate frequency is one of the
keys to dynamic Zing Modulation textures.
With that being said, if you monitor the
output of Mod 1 while it is serving as a Zing
Modulation source, you will still hear the
expected frequency modifications that result
from adjustments of its frequency controls
and CVs.
1V/OCT CV
The 1V/OCT CV Input is a calibrated full level
control voltage input that is summed with
the values of the COARSE and FINE FREQ
controls and the EXPO FM input.
NOTE: In terms of the Track function’s
eect on Zing Modulation:
With TRACK on, the Carrier Oscillator’s
waveshape will remain constant as the
Carrier’s frequency changes.
With TRACK o, the Carrier Oscillator’s
waveshape will vary with changes in the
Carrier frequency.
EXPO FM
The EXPO FM Input is a control
voltage input that is modified
by its associated attenuverter
and then summed with the
value of the Coarse and Fine
Frequency controls and the 1V/
OCT input. As above, when
the Track function is active, it is
also summed with the Carrier
Oscillator’s COARSE and FINE
FREQUENCY controls, 1V/ OCT
input, and EXPO FM input.
The Attenuverter functions
exactly as described in the
Carrier Oscillator’s EXPO FM section in the
previous chapter.

| 13
A TIP: As also described in the previous
chapter, You can use the Mod Oscillators
as precision LFOs by setting the Coarse
and Fine Frequency controls to their minimum
(fully counterclockwise) positions and patching
5V (or more) into the Exponential FM input.
Adjust the input’s attenuverter in the negative
range to set the LFO’s frequency.
SYMMETRY and SYM MOD
The SYMMETRY
control lets you
smoothly and
continuously vary
the shapes of the
Mod Oscillator’s
waveforms. The
eect on the various
waveforms are as
follows:
Triangle: Varies the
waveform from a
sawtooth (at the fully
counterclockwise position) to a pure triangle
(at the 12:00 o’clock position) to a time
reversed sawtooth (at the fully CW position).
Sawtooth: Varies the waveform from a
sawtooth with a downward kink in the middle
(at the fully counterclockwise position) to a
pure sawtooth (at the 12:00 o’clock position)
to a sawtooth with an upward kink in the
middle (at the fully CW position).
Pulse: Varies the pulse width from 0% to
100%. Like the Carrier Oscillator’s Pulse Width
control, when the pulse width is set to 0% or
100%, there will be no audio output. At 0%,
the output will be a continuous 0V and at
100%, it will be a continuous 5V.
The SYM MOD input is a control voltage input
that is modified by its associated attenuverter
to allow CV control of the Mod Oscillator’s
waveform shapes.
A TIP: Symmetry, like the Mod Oscillator’s
other continuous controls, can have a
dramatic eect on the Carrier Oscillator’s
sound, particularly when modulated by a CV.
ZING LEVEL and ZING MOD
The ZING control is
the key that opens
the door to Trident’s
universe of sounds.
The ZING control
lets you set the
initial amount of
the Mod Oscillator’s
modulation
of the Carrier
Oscillator. At its fully
counterclockwise
position, Mod 1
Oscillator’s Zing
modulation is disabled. As it is rotated
clockwise, the amount of Zing Modulation
increases.
The ZING MOD input is a control voltage
input that is modified by its associated
attenuverter to allow CV control of the Mod
Oscillator’s Zing Modulation amount. By this
point, you’re probably pretty clear on how
the attenuverter works.
A TIP: Like the Frequency and Symmetry
controls described above (and the Phase
control described below), Trident really
comes alive with dynamic timbres. The
Modulation Oscillators’ CV inputs are the
primary tools for building dramatic, evolving
sounds.
SYNC
Pressing the SYNC button will
toggle the Sync function on
and o, as indicated by the
associated LED. When turned on,
the Mod Oscillator will be hard
synced to the output of the Carrier Oscillator.
The Sync function is the key to Zing
Modulation’s unique ability to create rich,
dynamic timbres with complex but purely
harmonic overtone spectra. You can check
out Chapter 3 for a brief discussion of how
this works, or Chapter 9 for Dave’s more
in-depth explanation. But honestly, it’s not

14 |
necessary to understand it to create amazing
sounds with it.
NOTE: You can, of course, turn SYNC o
and use the Mod Oscillators’ controls to
create dense, clangorous timbres bristling
with aharmonic spectra.
A TIP: While Zing modulation works best
when Sync is engaged, if you engage
Track, but not Sync, don’t use any FM,
and tune the Mod Oscillator carefully, you can
get Zing-like eects with some extra timbral
motion in the sound.
ANOTHER NOTE: Since Trident is
100% analog, your Sync setting is not
remembered when the module is turned
o. Sync is always set to “on” when the module
is powered on.
TRACK
Pressing the TRACK button will
toggle the Track function on and
o, as indicated by the associated
LED.
When the Track function is engaged, the
Carrier Oscillator’s COARSE and FINE
FREQUENCY controls, 1V/OCT input, and
EXPO FM input are all summed with the Mod
Oscillator’s frequency controls and CV inputs.
As a result, the Mod Oscillator will track the
frequency of the Carrier Oscillator (with the
addition of any of the Mod Oscillator’s own
frequency controls and CV inputs).
NOTE: In terms of the Track function’s
eect on Zing Modulation:
With Track on, the Carrier Oscillator’s
waveshape will remain constant as the
Carrier’s frequency changes.
With Track o, the Carrier Oscillator’s
waveshape will vary with changes in the
Carrier frequency.
ANOTHER NOTE: As mentioned above
for Sync, your Track setting is not
remembered when the module is turned
o. Track is always set to “on” when the
module is powered on.
A TIP: While the main intent of the Track
Function is its use with Zing Modulation,
it also makes it easy to create stacked
oscillator sounds by patching your frequency
control CV(s) into the Carrier Oscillator, turning
on Track for the two Mod Oscillators, and
tuning (or detuning) the three oscillators as
desired.
AUDIO OUTPUT
Each Modulation Oscillator lets
you select a triangle, sawtooth or
pulse output. Press the waveform
selection button to sequentially
cycle between the three options.
The waveform’s associated LED
will light to indicate the current
choice.
A TIP: When using a Mod Oscillator for
Zing Modulation, the selected waveform
can have a dramatic eect on the
resulting sound. Once you have a patch set
up, be sure to audition the eects of the three
choices.

| 15
MODULATION OSCILLATOR 2
Modulation Oscillator
2 is identical to
Modulation Oscillator
1, with the exception
that it provides
an additional CV
controlled parameter:
Modulation Phase.
PHASE and
PHASE MOD
The PHASE control
lets you vary the
phase of the Mod 2 Oscillator relative to
the Carrier Oscillator when Mod 2 Sync is
enabled.
NOTE: This control has no audio eect
when simply listening to MOD 2. It is
solely for aecting the timbre of the Zing
modulation of the Carrier Oscillator.
The PHASE MOD input is a control voltage
input that is modified by its associated
attenuverter to allow CV control of the
phase of MOD 2’s Zing Modulation. The
attenuverter, not surprisingly, is just like all the
other attenuverters.
A TIP: While Phase adjustments can result
in interesting static timbres, the really
cool stu happens when you use a CV to
dynamically vary the phase.

16 |
8. Specifications
CARRIER OSCILLATOR
CONTROLS
Coarse Frequency
Fine Frequency
Pulse Width
SYNC IN
1x 3.5mm mono socket
100kΩInput Impedance
3.5V Rising Edge Threshold
1 V/OCT CV
1x 3.5mm mono socket
100kΩInput Impedance
ATTENUVERTED EXPONENTIAL FM CV
1x 3.5mm mono socket
100kΩInput Impedance
ATTENUATED LINEAR FM CV
1x 3.5mm mono socket
Min 80kΩInput Impedance
ATTENUVERTED PULSE WIDTH MODULATION CV
1x 3.5mm mono socket
100kΩInput Impedance
AUDIO OUTPUTS
3x 3.5mm mono socket
1kΩImpedance
MODULATION OSCILLATOR 1
CONTROLS
Coarse Frequency
Fine Frequency
Symmetry
Zing Level
Sync On/O
Track On/O
Output Waveform
1 V/OCT CV
1x 3.5mm mono socket
100kΩInput Impedance
ATTENUVERTED EXPONENTIAL FM CV
1x 3.5mm mono socket
100kΩInput Impedance
ATTENUVERTED SYMMETRY MODULATION CV
1x 3.5mm mono socket
100kΩInput Impedance
ATTENUVERTED ZING LEVEL CV
1x 3.5mm mono socket
100kΩInput Impedance
AUDIO OUTPUT
1x 3.5mm mono socket
1kΩImpedance
MODULATION OSCILLATOR 2
CONTROLS
Coarse Frequency
Fine Frequency
Symmetry
Zing Level
Phase
Sync On/O
Track On/O
Output Waveform
1 V/OCT CV
1x 3.5mm mono socket
100kΩInput Impedance
ATTENUVERTED EXPONENTIAL FM CV
1x 3.5mm mono socket
100kΩInput Impedance
ATTENUVERTED SYMMETRY MODULATION CV
1x 3.5mm mono socket
100kΩInput Impedance
ATTENUVERTED ZING LEVEL CV
1x 3.5mm mono socket
100kΩInput Impedance
ATTENUVERTED PHASE MODULATION CV
1x 3.5mm mono socket
100kΩInput Impedance
AUDIO OUTPUT
1x 3.5mm mono socket
1kΩImpedance

| 17
POWER REQUIREMENTS
+/-12V (+/- 2.5%) via 16-pin, Doepfer-style
connector
CURRENT DRAW
290mA +12V, 270mA -12V (maximum)
DIMENSIONS
30HP (W); Panel to power connector (with
connector plugged in) 25mm (D)
SUPPLIED ACCESSORIES
1x 16-pin, Doepfer-style cable
4x M3 screws
4x M2.5 screws
4x Nylon washers
1x Quickstart Guide

18 |
9. From Dave’s Lab
Circuit Protection
Eurorack suers from the problem of power
connector reversal. When 10 pin connectors
are used, mis-insertion results in a swap
of +12V and -12 V, and protection is easily
accomplished using various techniques such
as series diodes.
But more systems are providing the +5V
supply and thus use the full 16 pin connector.
When this is reversed, a diode-protected
module is still safe, but the six connected
ground pins in the module will short
together the system’s +5V and +12V supplies,
potentially damaging the power supply and
any modules that use +5V.
To prevent this, Rossum Electro-Music
modules deviate from the standard Eurorack
power connector by leaving power
connector pins 9 and 10 open, rather than
connecting them to ground. When plugged
in backwards, this leaves the system +12V
supply disconnected. Since ground is still
supplied by four pins as well the chassis and
any patch cords connected to the module,
the dropping of these two pins has no
measurable eect on circuit performance,
but it means that if a Rossum Electro module
is accidentally plugged in backwards,
no stress is placed on the +5V supply or
modules that use it.
Trident Technology in Depth
Since we launched Rossum Electro and
produced our first module (Evolution), folks
have been bugging me to build an analog
VCO. In their day, the E-mu Modular VCOs
were the most stable and had widest range
of any of that era. But I waited for inspiration
to strike, and it did, twice!
So what is “Zing Modulation” anyway? In
thinking about what makes an interesting
timbre, I have always felt ring modulation
(actually, “four quadrant multiplication”) held
a prime spot, but it’s limited in usefulness
because it produces frequencies that are not
harmonically related to its inputs. This is due
to the trigonometric identity
2 x sin(A) x cos(B) = sin(A + B) + sin(A - B)
where A and B are frequency components of
the ring modulator inputs.
But I realized that if the two inputs could
be forced to be periodic with the same
frequency, this limitation would disappear.
To understand why, just realize that there is
no “memory” in a ring modulator — if you
start over from the same spot and give it the
same waveforms, it will produce the same
output every time. So the output of two
inputs that have the same period must itself
be periodic at that same frequency, which
means all its frequency components must
be harmonics of that frequency. And it’s fairly
easy to arrange two oscillators to be precisely
periodic — it’s called hard sync1. Bingo!
1I’m pretty sure I was the person who first coined the
term “hard sync.” I didn’t invent hard sync; I think that
honor goes to Serge Tcherepnin. When I heard about it
and how great it sounded, I immediately implemented
it. But E-mu modular VCOs already had one form of
sync, so we needed another name to distinguish the
two. Hence “hard sync” and “soft sync”.

| 19
But because of that crazy trigonometric
identity, there are going to be zillions of
harmonic components, all adding together
in weird combinations of phases, and these
will vary in interesting ways depending on the
exact details of the incoming waveshapes.
Here are some examples of the bizarre
waveshapes coming out of Trident. The
yellow waveshape is the carrier oscillator with
Zing modulation; the green is the original
carrier waveshape. The blue and red traces
are the modulation oscillators. The second inspiration was to build a VCO
that would provide interesting yet precise
control of the waveshapes. The circuitry
underlying Trident’s symmetry control
was remarkably challenging. Varying the
symmetry of a triangle wave from sawtooth,
through triangle, to inverted sawtooth has
been done many times before, but doing
so in a fully analog, voltage controlled
manner that has absolutely no eect on
the underlying frequency is extremely
challenging. Add to that challenge the
requirement for the waveforms to be visually
perfect up to 20kHz — now that would be fun
(i.e. really hard)! I had to throw away an entire
prototyped design because it wasn’t quite
accurate enough at the highest frequencies.
The final circuit is the only time I’ve ever had
to specify a capacitor as small as 0.5pF to get
the precise results I wanted. Here are some
of the pure waveshape ‘scope photos. The
first picture below shows the shapes at about
250 Hz, the picture after it shows the shapes
at about 20kHz!

20 |
Finally, I realized that I’ve never seen anybody
play with the phase relationship between
hard synced oscillators. Combining that with
Zing modulation gives even more voltage
controlled timbral variation. These waveforms
dier only by the phase of the MOD 2
oscillator!