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M O D E L 1 0 1 1
D i s c r e t e Vo l t a g e C o n t r o l l e d O s c i l l a t o r
Con s t ru c t i o n
& Ope rat i o n Gu i d e
R EV B - FO R PCB V1 . 0
S L I G H T L Y N A S T Y E L E C T R O N I C S A D E L A I D E , A U S T R A L I A
S L I G H T L Y N A S T Y E L E C T R O N I C S A D E L A I D E , A U S T R A L I A
2Sp e c i f i c at i o n s
S P E C I F I C A T I O N S
PHYSICAL
FORM FACTOR: Loudest Warning / 4U
WIDTH: 3NMW / 75.5mm
HEIGHT: 1 75mm
DEPTH: ~40mm from panel front inc. components
PCB: 70 x 1 50mm, Two-Layer Double Sided
CONNECTORS: 4mm Banana
ELECTRICAL
POWER: +1 2V, 0V, -1 2V
CONSUMPTION: ~40mA +1 2V Rail , ~30mA -1 2V Rail
CONNECTOR: IDC 1 0-pin Shrouded Header, Eurorack Standard
or MTA-1 56 4-Pin Header
I/O IMPEDANCES: 1 00K input, 1 K output (nominal)
INPUT RANGES (nominal)
1V/OCT: +/- 1 0V
FM: +/- 5V
LOG: +/- 5V
SYMMETRY: +/- 5V
SYNC: +/- 5V (fal l ing-edge trigger)
OUTPUT RANGES (nominal)
OUTPUT A: +/- 5V
OUTPUT B: +/- 5V
SUBOCTAVE: +/- 5V
M O D E L 1 0 1 1 D i s c r e t e O s c i l l a t o r
IDC power connector pinout.
MTA-156 power connector pinout.
SPECIFICATIONS
Specifications / Power Requirements 2
INTRODUCTION
Introduction 4
CIRCUIT OVERVIEW
Circuit Overview 5
Exponential Converter 6
Sawtooth Core 8
Triangle / Sine Shapers 10
Pulse / Suboctave Shapers 10
Output Mixers / Amplifiers 12
CHOOSING COMPONENTS
Bil l Of Materials (BOM) 14
Choosing Components 15
Transistor Matching 16
CONSTRUCTION
Construction Overview 18
Physical Assembly 20
CONTROLS
Controls 21
CALIBRATION
Calibration Overview 22
CV Scale 23
CV Offset 24
High Frequency Compensation 24
Triangle Adjustment 25
REFERENCE
PCB Guide - Lower Board 26
PCB Guide - Upper Board 27
S L I G H T L Y N A S T Y E L E C T R O N I C S A D E L A I D E , A U S T R A L I A
3C i rc u i t Ove rv i ew
T A B L E O F C O N T E N T S
M O D E L 1 0 1 1 D i s c r e t e O s c i l l a t o r
S L I G H T L Y N A S T Y E L E C T R O N I C S A D E L A I D E , A U S T R A L I A
4I n t ro d u c t i o n
I N T R O D U C T I O N
The Slightly Nasty Model 1011 is a voltage control led osci l lator that's a l ittle bit
different. Despite featuring a host of functional ity including four mixable
waveshapes, suboctave, l inear and logarithmic FM, pulse width modulation, and
hard sync, inside it you won't find a single IC opamp or OTA. What you will find
is no less than 41 discrete transistors flying in close formation, doing their best to
output useable musical tones.
The Model 1 01 1 has been designed from the ground up to use modern "jel lybean"
components that can be cheaply and easi ly obtained from most electronics
suppl iers. Despite the unusual implementation, the architecture is actual ly a very
traditional sawtooth-core design that wil l be famil iar to most people who have
worked on VCOs before.
Three outputs provide mixable sine-triangle, saw-pulse-suboctave, and
suboctave square respectively, the pulse wave also featuring both manual and
CV-control led symmetry (pulse width). Aside from the usual 1 V/Octave input,
there are also separate inputs for both l inear and logarithmic FM, each with
input attenuators, as wel l as a hard sync input. The exponential converter is
temperature compensated for better thermal stabil ity and the sawtooth core
features high-frequency compensation for better pitch tracking.
The Model 1 01 1 uses the Loudest Warning 4U format for the front panel, and
fol lows Eurorack electrical and power standards. Al l front panel components are
PCB mounted for easy wiring-free construction. The front panel is available in
two finishes - satin anodised and gloss white powdercoat, both on 2.5mm
aluminium with robust UV-printed graphics.
M O D E L 1 0 1 1 D i s c r e t e O s c i l l a t o r
S L I G H T L Y N A S T Y E L E C T R O N I C S A D E L A I D E , A U S T R A L I A
5C i rc u i t Ove rv i ew
C I R C U I T O V E R V I E W
For full schematics, please download the separate schematics PDF. Excerpts shownin this manual may be outdated and are provided for reference only.
While the ful ly populated PCB of the Model 1 01 1 can look quite intimidating, the
circuitry can actual ly be broken down into a set of relatively simple subcircuits
that each handle a very specific aspect of the module's operation. Overal l , the
1 01 1 has a fairly standard architecture consisting of the fol lowing units:
1 . Exponential converter - this al lows the use of 1 V/Octave pitch CVs by
taking a l inear scale voltage from the CV input and converting it into an
exponential scale current to feed the sawtooth core.
2. Sawtooth core - this is the sonic heart of the module, generating the
base sawtooth signal from which al l other waveshapes are generated.
Sync is also implemented in this circuit.
3. Triangle/sine shapers - These convert the raw sawtooth signal into
triangle and sine waves by first folding the sawtooth into a triangle
shape, and then soft-cl ipping that to create a pseudo-sine.
4. Pulse/suboctave shapers - These create the pulse wave by feeding the
sawtooth signal into a comparator, using the symmetry controls to set
the threshold level. The pulse is then used to clock a pulse divider to
form the suboctave square.
5. Mixers/output amps - These al low the blending of the various
waveforms as wel l as converting the different levels and offsets of the
various raw waveform signals to match the +/-5v expected at the
outputs.
M O D E L 1 0 1 1 D i s c r e t e O s c i l l a t o r
Block diagram of the Model 1011.
Circles marked "A" are attenuators.
R51251K
R519390R
R51810K
VC
C
R5201K2 1
2
3
RV5061K
CV
OF
FS
ET
AD
J.25
-tur
n tr
impo
t
R51
610
K
R51310K
R51410K
Mat
ched
pai
rT
herm
ally
cou
ple
R5212K2
1
2
3
RV50510K
R51012K
R50910K
CH
AR
GE
_CU
RR
EN
T
CV
SC
ALE
AD
J.25
-tur
n tr
impo
t
R51
1
2K2
R5152K2
R50
651
K
GN
D
R501100K
INP
UT
_1V
/OC
T
VC
C
VE
E
R5045K1
INP
UT
_LO
G
R50
851
K
R5075K1
12
3RV503100K
GN
D
1
2
3RV501100K 1
2
3RV502
10K
VC
C
C50
2
100n
F
VC
C
GN
D
R51
710
K
R50
522
K
C50
1
100n
FG
ND
INP
UT
_LIN
1
2
3RV504100K
R50
220
0K
R503200K
VC
C
VE
E
VE
E
C1
B 2
E3
Q50
1B
C55
0
C1
B 2
E3
Q50
2B
C55
0
C1
B 2
E3
Q50
3B
C55
0
C1
B 2
E3Q
504
BC
550
C1
B 2
E3Q
505
BC
550
C1
B 2
E3
Q50
8B
C56
0
C1
B 2
E3
Q50
7B
C56
0
C1
B 2
E3
Q50
9B
C56
0
C1
B 2
E3
Q50
6B
C56
0
C503
33pF
CU
RR
EN
T C
ON
TR
OL
EX
PO
NE
NT
IAT
OR
CV
SC
ALI
NG
R522
1K
3300ppmTEMPCO
D501
1n4148
R52
324
0R
C1
B 2
E3
Q51
0B
C55
0R
524
1K
R52510K
VE
E
VC
C
LIN
. FM
LE
VE
LF
ront
pan
el p
otLi
n sc
ale
LOG
. FM
LE
VE
LF
ront
pan
el p
otLi
near
sca
le
FR
EQ
. CO
AR
SE
Fro
nt p
anel
pot
Line
ar s
cale
FR
EQ
. FIN
EF
ront
pan
el p
otLi
near
sca
le
R?10K
DO
NO
T F
IT!
Jum
per
inst
ead
BO
DG
E R
ES
IST
OR
Add
to r
ear
of b
oard
S L I G H T L Y N A S T Y E L E C T R O N I C S A D E L A I D E , A U S T R A L I A
6C i rc u i t Ove rv i ew
S L I G H T L Y N A S T Y E L E C T R O N I C S A D E L A I D E , A U S T R A L I A
7C i rc u i t Ove rv i ew
Undoubtedly the finickiest part of most VCOs, the exponential converter in the
Model 1 01 1 is essential ly a discrete reimplementation of the opamp-stabil ised
transistor pair found in countless other designs. This circuit works by using the
natural ly exponential relationship of a transistor's base-emitter voltage to its
output current, using two matched transistors to mostly cancel out each others'
thermal effects and keep the conversion stable across different temperatures
and currents. A feedback-stabil ised current source on the shared emitters of the
transistors holds one transistor at a constant current, causing the exponential
current caused by changes to the input voltage to appear at the col lector of the
other one. A temperature-sensitive "tempco" resistor provides additional
correction to the aspects of the circuit's thermal response that are not cancel led
by the matched pair.
The exact operation of this sort of converter is a bit too involved to get into in
this manual, but an excel lent rundown of the basic principles can be found on
René Schmitz' website at http://schmitzbits.de/expo_tutorial/index.html
In the 1 01 1 , the exponential converter can be broken down further into three
basic sections. There are the frontend buffer/amplifiers that combine the various
CVs and panel controls into a single pitch voltage; the exponentiator itself, in the
form of the matched pair; and the feedback control led current source, which
consists of a differential pair control l ing a current source tranistor. The bulk of
the exponentiator is single rail and works between 0v and +VCC.
The input buffer/amplifiers are essential ly just crude emitter fol lowers, and
consist of transistors Q501 , Q502, and Q51 0 along with their respective passive
components. The output of Q501 and Q502 are both combined and go through
the voltage divider comprised of RV505 and the tempco resistor R522, in order
to reduce the level to the small voltage swing needed for the exponentiator.
Because the circuit is single rail , Q503 provides a buffered offset voltage so that
the resultant scaled CV is centred near the 1 /2 VCC mark. The scaled CV is
final ly buffered by Q506 before being fed into the exponentiator at Q507.
Q507 and Q509 comprise the matched-pair exponentiator, and share a common
emitter. Q507 takes the scaled pitch CV as input at its base, while Q509 has its
base held at a fixed voltage around 1 /2 VCC. The exact voltage at Q509's base
can be trimmed with RV506 in order to offset the CV response and get the
desired centre frequency for the osci l lator (usual ly middle C). D501 was original ly
intended to provide additional thermal compensation, but in the real world it
causes significant drift and must be replaced with a wire link.
Final ly, the differential pair of Q504 and Q505 along with the current source
transistor Q508 form the feedback-stabil ised current source, which would
normally consist of an opamp in a circuit of this type. Q505 is referenced to 1 /2
VCC via the voltage divider of R51 3 and R51 4, and l ike an opamp the circuit wil l
M O D E L 2 2 3 1 A s ym m e t r i c S l e w L i m i t e rM O D E L 1 0 1 1 D i s c r e t e O s c i l l a t o r
E X P O N E N T I A L C O N V E R T E R
R51251K
R519390R
R51810K
VC
C
R5201K2 1
2
3
RV5061K
CV
OF
FS
ET
AD
J.25
-tur
n tr
impo
t
R51
610
K
R51310K
R51410K
Mat
ched
pai
rT
herm
ally
cou
ple
R5212K2
1
2
3
RV50510K
R51012K
R50910K
CH
AR
GE
_CU
RR
EN
T
CV
SC
ALE
AD
J.25
-tur
n tr
impo
t
R51
1
2K2
R5152K2
R50
651
K
GN
D
R501100K
INP
UT
_1V
/OC
T
VC
C
VE
E
R5045K1
INP
UT
_LO
G
R50
851
K
R5075K1
1
2
3RV503100K
GN
D
1
2
3RV501100K 1
2
3RV502
10K
VC
C
C50
2
100n
F
VC
C
GN
D
R51
710
K
R50
522
K
C50
1
100n
FG
ND
INP
UT
_LIN
1
2
3RV504100K
R50
220
0K
R503200K
VC
C
VE
E
VE
E
C1
B 2
E3
Q50
1B
C55
0
C1
B 2
E3
Q50
2B
C55
0
C1
B 2
E3
Q50
3B
C55
0
C1
B 2
E3Q
504
BC
550
C1
B 2
E3Q
505
BC
550
C1
B 2
E3
Q50
8B
C56
0
C1
B 2
E3
Q50
7B
C56
0
C1
B 2
E3
Q50
9B
C56
0
C1
B 2
E3
Q50
6B
C56
0
C503
33pF
CU
RR
EN
T C
ON
TR
OL
EX
PO
NE
NT
IAT
OR
CV
SC
ALI
NG
R522
1K
3300ppmTEMPCO
D501
1n4148
R52
324
0R
C1
B 2
E3
Q51
0B
C55
0R
524
1K
R52510K
VE
E
VC
C
LIN
. FM
LE
VE
LF
ront
pan
el p
otLi
n sc
ale
LOG
. FM
LE
VE
LF
ront
pan
el p
otLi
near
sca
le
FR
EQ
. CO
AR
SE
Fro
nt p
anel
pot
Line
ar s
cale
FR
EQ
. FIN
EF
ront
pan
el p
otLi
near
sca
le
R?10K
DO
NO
T F
IT!
Jum
per
inst
ead
BO
DG
E R
ES
IST
OR
Add
to r
ear
of b
oard
V-
4V
+8
1
-2
+3
GND
VCC
VEE
1
23
1
23
R3
R2
VEE
R1
TE
MP
CO
GND
1V/OCT
GND
TO
_CO
RE
Traditional configuration of PNP
exponential converter with opamp
current source.
S L I G H T L Y N A S T Y E L E C T R O N I C S A D E L A I D E , A U S T R A L I A
D i s c r e t e O s c i l l a t o r
8
M O D E L 1 0 1 1
C i rc u i t Ove rv i ew
try to get the opposite input (the base of Q504) to match this level . That base is
connected to R51 8, on the col lector of Q507, and so the circuit wil l try to hold
the voltage across R51 8 at 1 /2 VCC - and consequently maintain a constant
current through both it and Q507. It does this by control l ing the current that
feeds the exponentiator pair through Q508. C503 performs a similar role to
bypass found caps in opamp feedback paths - preventing osci l lations that can
develop due to various phase effects. The buffered l inear FM input is AC-coupled
through C501 and feeds directly into the base of Q504 along with the feedback
signal.
R526 is not present on the board and must be added (see Construction Guide).
The sawtooth core in the Model 1 01 1 basical ly consists of a timing capacitor with
a discharge FET across it, and a reset comparator. The core of the reset
comparator is formed by Q204, Q205, and Q206 - with the first two once again
forming a differential pair and the latter serving as the gain stage / output. One
input of the comparator (the base of Q205) is connected to the timing capacitor,
and the other (the base of Q204) is fed the reset threshold voltage set by the
voltage divider formed by R206 and R205 (these are chosen to get a ~6v P-P
amplitude on the sawtooth).
Q202 and Q203 are used to pul l down the threshold to a lower voltage when
activated, in order to implement the hysteresis needed in a relaxation osci l lator.
When the capacitor passes the threshold voltage, the comparator's output goes
high and simultaneously switches on the discharge FET Q207 and the threshold
pul ldown transistor Q203. This means that the capacitor now needs to discharge
down to the new, lower threshold voltage before the comparator output goes
back to low and completes the cycle.
The second threshold pul ldown transistor Q202 (and its inverting input buffer
Q201 ) is dedicated to the sync input, and triggers a reset cycle whenever a
sufficiently powerful fal l ing edge triggers it. The necessity of a second dedicated
pul ldown transistor for this is due to the possibi l ity of the comparator being
knocked into an undesirable region of operation where instead of acting as a
comparator, the feedback path formed through Q203 causes the circuit to turn
instead into a voltage fol lower, tracking the threshold voltage and locking up the
osci l lator. To prevent this, the feedback path has to be kept from reaching the
metastable point near the threshold voltage, and so the sync input is given its
own transistor outside the feedback loop.
RV202 and D201 form the high-frequency compensation circuit (a.k.a Franco
compensation). This works by using the voltage developed across RV202 by the
charge current to trigger the reset sl ightly earl ier as the current increases (and
S A W T O O T H C O R E
Voltage across timing capacitor (top)
vs. voltage on the base of disharge
FET Q207. Blue shows charging
period and red discharging. Note
that the discharge time is
exaggerated for clarity, and in most
cases can be considered virtually
instantaneous.
S L I G H T L Y N A S T Y E L E C T R O N I C S A D E L A I D E , A U S T R A L I A
9C i rc u i t Ove rv i ew
R21
010
K
VC
C
RE
SE
T C
OM
PA
RA
TO
R
R2069K1
C20
6
10nF
1
2
3
Q20
7
2n70
00
R2132K2
SA
WT
OO
TH
CO
RE
R2082K2
R20922K
SA
WT
OO
TH
INP
UT
_SY
NC
R2072K2
1
2
3
Q20
8
2n70
00
VE
ER20510K
C20
2
100n
F
SY
NC
INP
UT
C201
1nF
R20410K
R20
210
0K
CH
AR
GE
_CU
RR
EN
T
R21
210
0K
1
2
3
RV2021K
HF
CO
MP
EN
SA
TIO
N25
-tur
n tr
impo
t
VC
C
VE
E
GN
D
C20
3
100n
F
D201
1N4148
R20310K
R201100K
R21110K
C1B 2
E3
Q20
1B
C55
0
C1
B 2
E3
Q20
2
BC
550
C1
B 2
E3
Q20
3
BC
550
C1
B 2
E3
Q20
4B
C55
0
C1
B 2
E3 Q
205
BC
550
C1
B 2
E3
Q20
6B
C56
0
R21410K
R21510K
S L I G H T L Y N A S T Y E L E C T R O N I C S A D E L A I D E , A U S T R A L I A
D i s c r e t e O s c i l l a t o r
1 0
M O D E L 1 0 1 1
C i rc u i t Ove rv i ew
with it the pitch). This means that higher frequency cycles are shortened sl ightly,
and thus increased in pitch to counteract the droop caused by other effects in
the circuit, such as capacitor discharge time and so on. D201 l imits the maximum
compensation effect of the circuit, to prevent excessive drops in sawtooth
amplitude at very high frequencies where pitch is less discernable.
Q208 and R21 3 are the high-impedance output buffer for the sawtooth core, and
prevent the downstream circuits draining charge from the timing capacitor and
affecting the frequency.
The triangle shaper in the Model 1 01 1 takes advantage of the normally
undesirable behaviour of an inverting transistor amplifier when the input and
output signals "cross over". Because the transistor's base voltage can't be higher
than its col lector (in the case of an NPN transistor), once the output at the
col lector drops too low it "col l ides" with the base voltage and can't go any lower
- causing the output to fol low the base voltage instead. We can use this to "fold"
the sawtooth over on itself to create a triangle wave just by offsetting the input
sawtooth by the right amount.
Q301 is our inverting unity-gain amplifier, which is AC coupled to the sawtooth
signal so that the input can be offset by the resistors R301 and R302. C301 helps
to shape the inescapable gl itch in the triangle at the sawtooth's reset point so
that it can be smoothed out more effectively by the lowpass fi lter R305/C302.
The pair of inverting amplifiers at Q302 and Q303 amplify the triangle signal to
the desired amplitude.
The triangle signal is attenuated through the R31 2/R31 3 voltage divider before
being soft-cl ipped by the pair of diodes. This distorts the triangle into something
approximating a sinewave, which is then amplified back up to useable levels by
Q304 and Q305.
The pulse waveform of the Model 1 01 1 is generated in the same way as most
VCOs - by feeding the sawtooth signal into a comparator and varying the
threshold voltage to implement pulse width control . The basic circuit is the same
three-transistor comparator used elsewhere in the module, taking the sawtooth
signal as one input and the summed "symmetry" CV and front panel voltages as
T R I A N G L E / S I N E S H A P E R S
P U L S E / S U B O C T A V E S H A P E R S
Principle of triangle formation by
folding sawtooth wave. Intermediate
stage is shown for clarity, in reality
this is a single-stage process.
Pulse formation with comparator,
showing PWM via varying threshold.
S L I G H T L Y N A S T Y E L E C T R O N I C S A D E L A I D E , A U S T R A L I A
1 1C i rc u i t Ove rv i ew
R301200K
R304100K
R303100K
C30
1
33pF
1
2
3
RV301100K
R30
533
K
C30
2
220p
F
TR
IAN
GLE
ALI
GN
25 tu
rn tr
impo
t
SA
WT
OO
TH
TO
TR
IAN
GLE
VC
C
R31
410
0K
D301
1n4007
D302
1n4007SIN
E S
HA
PE
R
SA
WT
OO
TH
TR
IAN
GLE
R31310K
R312100K
R3072K2
C304
0.68F
R3061K2
C30
3
0.68
F
VE
E
R309270K
R308560K
R3102K2
R3111K
R3021M
R3181K
R31910K
R31
710
K
R316120K
VE
E
R3212K2
R3201K
C305
100nF
SIN
E
C1
B 2
E3
Q30
1B
C55
0
C1
B 2
E3
Q30
3B
C55
0
C1
B 2
E3
Q30
4B
C55
0
C1
B 2
E3
Q30
2B
C56
0
C1
B 2
E3
Q30
5B
C56
0
R3221M
GN
DC306
10uF
R60751K
VE
E
GN
D
VC
C
SA
WT
OO
TH
R61010K
SQ
UA
RE
R61
510
KR
616
10K
R6172K2
R6142K2
C601
10nF
R61
110
K
SU
BO
CT
AV
E
R61210K
C60
4
1nF
C60
7
1nF
D601
1n4148
D602
1n4148
R613100K
R618100K
SU
BO
CT
AV
E D
IVID
ER
R60
415
0K
R601150K
R60
530
0K
R60662K
R6033K3
R60210K
VC
C
GN
D
INP
UT
_PW
M
C60
2
100n
F
VC
C
GN
D
R60810K
1
2
3RV601100K
VC
C
VE
E
C1
B 2
E3
Q60
1B
C55
0C1
B 2E3
Q60
3B
C56
0
C1
B 2
E3
Q60
5
BC
550
C1
B 2
E3
Q60
6
BC
550
C1
B 2
E3
Q60
4B
C55
0
1
2
3RV602100K
GN
D
C610
10uF
C1
B 2
E3
Q60
2B
C55
0
VC
C
PW
INP
UT
PU
LSE
CO
MP
AR
AT
OR
PW
M L
EV
EL
Fro
nt p
anel
pot
Lin
scal
e
PU
LSE
WID
TH
Fro
nt p
anel
pot
Lin
scal
e
S L I G H T L Y N A S T Y E L E C T R O N I C S A D E L A I D E , A U S T R A L I A
D i s c r e t e O s c i l l a t o r
1 2
M O D E L 1 0 1 1
C i rc u i t Ove rv i ew
the other.
The suboctave is sl ightly different to the other waveshapes, in that it isn't formed
by just shaping the sawtooth in some way. Instead a classic two-transistor
multivibrator circuit is clocked from the positive-going edges of the pulse
waveform, creating a square output at half the frequency. C601 and Q604
convert the pulse signal into buffered positive-edge pulses, feeding it into the
multivibrator circuit via C604 and C607.
Both the pulse and suboctave circuits output unipolar 0v to VCC waveforms, in
the case of the pulse this isn't an issue as it is eventual ly mixed directly with the
l ikewise unipolar sawtooth wave, however the suboctave is AC-coupled through
the large 1 0uF capacitor C61 0 in order to centre it around 0v.
At this point, al l of the various waveforms in the Model 1 01 1 are at various
amplitudes and offsets, and the role of the mixers and output amplifiers is to
combine these disparate elements and ensure that the final outputs are in the
+/-5v range expected in most modular systems.
The two amplifiers are built around what are essential ly discrete op-amps,
comprising a differential pair for input, a single transistor gain stage, and a two-
transistor push-pul l output. The suboctave signal goes through a much simpler
push-pul l output buffer that doesn't need to worry about l inearity or crossover
distortion on account of it being a purely squarewave signal.
Amplifier A takes the triangle and sine signals which are already at matching
levels and combines them via the mix pot RV403 before feeding them into the
amp's positive input. The amp output is fed back into the negative input via
R41 8, and so the circuit operates as a standard voltage fol lower opamp circuit.
Amplifier B is only sl ightly more complex, it has an additional network of voltage
dividers before the mix pot to match the levels of the sawtooth and pulse signals,
and the suboctave signal is fed into the negative input via an attenuator.
Because the negative input is no longer just connected directly to the output
feedback, the gain of the amplifier actual ly changes as the suboctave attenuator
is adjusted, in order to keep the output level within +/-5V regardless of how
much suboctave is added.
Final ly, al l outputs go through a 1 K output resistor to protect the amps and
buffers from short-circuits and provide the expected 1 K output impedance.
O U T P U T M I X E R S / A M P L I F I E R S
Suboctave formation, showing the
positive edge pulses generated by
C601 / Q604 causing the multi-
vibrator to flip state.
S L I G H T L Y N A S T Y E L E C T R O N I C S A D E L A I D E , A U S T R A L I A
1 3C i rc u i t Ove rv i ew
R412100K
R413100K
D402
1n4148
R415100K
R4161M
R41
71K
1
2
3RV401100K
GN
D
R40
310
0KS
UB
OC
TA
VE
1
2
3RV402100K
R40
13K
3S
AW
TO
OT
H
R40
212
KS
QU
AR
E
R40412K
GN
DR4059K1
C401
100nF
R4081M
GN
D
OU
TP
UT
_B
VE
E
VC
C
GN
D
D401
1n4148
R41010K
R40
610
0K
R411100K
R414100K
D404
1n4148
R4191M
R42
01K
OU
TP
UT
_A
VE
E
VC
C
GN
D
D403
1n4148
R40910K
1
2
3RV403100K
TR
IAN
GLE
SIN
E
C1
B 2
E3
Q40
2B
C55
0
C1
B 2
E3
Q40
4B
C55
0
C1
B 2
E3
Q40
7B
C55
0
C1
B 2
E3
Q40
8B
C56
0
C1
B 2
E3
Q40
5B
C56
0
C1
B 2
E3
Q41
0B
C56
0
C1
B 2
E3
Q40
9B
C55
0
C1
B 2
E3
Q40
6B
C56
0
C1
B 2
E3
Q40
3B
C55
0
C1
B 2
E3
Q40
1B
C55
0
R40
710
0K
R418100K
C40
3
10pF
C40
2
10pF
C1
B 2
E3
Q41
1B
C55
0
C1
B 2
E3
Q41
2B
C56
0
R4231M
R42
41K
OU
TP
UT
_SU
B
GN
D
R42
120
0K
VE
E
VC
C
C40
4
100n
F
C40
5
100n
FG
ND
VC
C
VE
E
AM
PLI
FIE
R A
AM
PLI
FIE
R B
SU
BO
CT
AV
E B
UF
FE
R
MIX
B
MIX
A
SU
B. L
EV
EL
RESISTORS2 R101, R102
240R 1 R523390R 1 R5191K 7 R311, R318, R320, R417, R420, R424, R524
1 R5221K2 2 R306, R5202K2 11 R207, R208, R213, R307, R310, R321, R511, R515, R521, R614, R6173K3 2 R401, R6035K1 2 R504, R5079K1 2 R206, R40510K 27
12K 3 R402, R404, R51022K 2 R209, R50533K 1 R30551K 4 R506, R508, R512, R60762K 1 R606100K 19
120K 1 R316150K 2 R601, R604200K 4 R301, R421, R502, R503270K 1 R309300K 1 R605560K 1 R3081M 6 R302, R322, R408, R416, R419, R423
CAPACITORS10pF 2 C402, C40333pF 2 C301, C503220pF 1 C3021nF 3 C201, C604, C60710nF 1 C601
1100nF 9 C202, C203, C305, C401, C404, C405, C501, C502, C6020.68μF 2 C303, C304
2 C306, C6102 C101, C102
SEMICONDUCTORS1n4148 71n4007 2 D301, D302BC550C 26
BC560C 11 Q206, Q302, Q305, Q405, Q406, Q408, Q410, Q412, Q506, Q508, Q6032 Q507, Q509
2n7000 2 Q207, Q208
POTENTIOMETERS2 RV202, RV5061 RV505
10K 1 RV502100K 8 RV401, RV402, RV403, RV501, RV504, RV503, RV601, RV602
1 RV301
CONNECTORSBanana Socket 8 P102, P103, P104, P105, P106, P107, P108, P109IDC 10-pin Header 1MTA-156 4-pin Heade 1
3 Use standard breakaway pin strip.
3
HARDWAREM3 x 20mm Screw 4M3 Washer 16
4
M3 Nut 4
10R 1/2W
1K 3300PPM/C
R203, R204, R205, R210, R211, R214, R215, R313, R317, R319, R409, R410, R509, R513, R514, R516, R517, R518, R525, R526*, R602, R608, R610, R611, R612, R615, R616 * Additional bodge resistor – see Construction Guide for details
R201, R202, R212, R303, R304, R312, R314, R403, R406, R407, R411, R412, R413, R414, R415, R418, R501, R613, R618
10nF (C0G/NP0) C206 (Optionally use standard 10nF film capacitor)
10uF Electrolytic100uF Electrolytic
D201, D401, D402, D403, D404, D501*, D601, D602 *Replace with wire link
Q201, Q202, Q203, Q204, Q205, Q301, Q303, Q304, Q401, Q402, Q403, Q404, Q407, Q409, Q411, Q501, Q502, Q503, Q504, Q505, Q510, Q601, Q602, Q604, Q605, Q606
MATCHED BC560C
1K 25-turn10K 25-turn
100K 25-turn
P101 (Option 1)P101 (Option 2)
10-pin 2.54mm pin header
10 pin-2.54mm female pin header
M3 x 10mm Threaded Metal Hex Spacer
S L I G H T L Y N A S T Y E L E C T R O N I C S A D E L A I D E , A U S T R A L I A
1 4B i l l O f M ate r i a l s
B I L L O F M A T E R I A L S
RESISTORS2 R101, R102
240R 1 R523390R 1 R5191K 7 R311, R318, R320, R417, R420, R424, R524
1 R5221K2 2 R306, R5202K2 11 R207, R208, R213, R307, R310, R321, R511, R515, R521, R614, R6173K3 2 R401, R6035K1 2 R504, R5079K1 2 R206, R40510K 27
12K 3 R402, R404, R51022K 2 R209, R50533K 1 R30551K 4 R506, R508, R512, R60762K 1 R606100K 19
120K 1 R316150K 2 R601, R604200K 4 R301, R421, R502, R503270K 1 R309300K 1 R605560K 1 R3081M 6 R302, R322, R408, R416, R419, R423
CAPACITORS10pF 2 C402, C40333pF 2 C301, C503220pF 1 C3021nF 3 C201, C604, C60710nF 1 C601
1100nF 9 C202, C203, C305, C401, C404, C405, C501, C502, C6020.68μF 2 C303, C304
2 C306, C6102 C101, C102
SEMICONDUCTORS1n4148 71n4007 2 D301, D302BC550C 26
BC560C 11 Q206, Q302, Q305, Q405, Q406, Q408, Q410, Q412, Q506, Q508, Q6032 Q507, Q509
2n7000 2 Q207, Q208
POTENTIOMETERS2 RV202, RV5061 RV505
10K 1 RV502100K 8 RV401, RV402, RV403, RV501, RV504, RV503, RV601, RV602
1 RV301
CONNECTORSBanana Socket 8 P102, P103, P104, P105, P106, P107, P108, P109IDC 10-pin Header 1MTA-156 4-pin Heade 1
3 Use standard breakaway pin strip.
3
HARDWAREM3 x 20mm Screw 4M3 Washer 16
4
M3 Nut 4
10R 1/2W
1K 3300PPM/C
R203, R204, R205, R210, R211, R214, R215, R313, R317, R319, R409, R410, R509, R513, R514, R516, R517, R518, R525, R526*, R602, R608, R610, R611, R612, R615, R616 * Additional bodge resistor – see Construction Guide for details
R201, R202, R212, R303, R304, R312, R314, R403, R406, R407, R411, R412, R413, R414, R415, R418, R501, R613, R618
10nF (C0G/NP0) C206 (Optionally use standard 10nF film capacitor)
10uF Electrolytic100uF Electrolytic
D201, D401, D402, D403, D404, D501*, D601, D602 *Replace with wire link
Q201, Q202, Q203, Q204, Q205, Q301, Q303, Q304, Q401, Q402, Q403, Q404, Q407, Q409, Q411, Q501, Q502, Q503, Q504, Q505, Q510, Q601, Q602, Q604, Q605, Q606
MATCHED BC560C
1K 25-turn10K 25-turn
100K 25-turn
P101 (Option 1)P101 (Option 2)
10-pin 2.54mm pin header
10 pin-2.54mm female pin header
M3 x 10mm Threaded Metal Hex Spacer
S L I G H T L Y N A S T Y E L E C T R O N I C S A D E L A I D E , A U S T R A L I A
1 5Ch oo s i n g Compon en t s
Selecting the right components for the 1 01 1 is fairly straightforward, with only a
couple of parts needing any special attention. Al l resistors should be 1 % tolerance
metal fi lm types, most capacitors are standard rectangular fi lm caps and
electrolytics. Three types of transistor are used, the bulk being BC550C and
BC560C, with a pair of 2N7000 FETs used in the sawtooth core. Diodes are
mostly the ubiquitous 1 n41 48.
In the exponential converter there is a 1 K 3300ppm/C tempco resistor that wil l
need to be bought from a suppl ier that special ises in synthesiser components,
such as Thonk (www.thonk.co.uk) or Synthrotek (store.synthrotek.com ),
among others. The exponential converter also requires a matched pair of the
BC560C transistors (see the section on transistor matching over the page), which
can be selected from your inventory of transistors using a simple matching
circuit.
In the sawtooth core, the main timing capacitor responsible for generating the
sawtooth wave can be either a normal fi lm capacitor, or a more thermally stable
part if greater stabil ity is desired. Traditional ly, polystyrene caps were used for
this role in VCOs, but as these are now becoming rare and expensive a much
better option is one of the new generation of C0G/NP0 ceramic capacitors.
The sine shaper uses a pair of 1 N4007 diodes instead of the usual 1 N41 48s to get
a sl ightly better sine shape, though 1 N41 48s wil l work also.
The module is designed to use either side or top-adjustment 25-turn trimpots
for cal ibration adjustment - side adjustment is usual ly the better option as it
means the unit can be more easi ly cal ibrated when connected to the rack's
power bus.
The front panel PCB fits Alpha brand 9mm vertical-mount round shaft
potentiometers, these are widely available from stores such as Thonk, Tayda,
Smallbear, Mouser etc. The module should fit a number of different banana jack
sockets, but the "correct" parts are the Cinch Connectivity range of jacks.
The intended knobs are Davies Molding parts - the 1 91 3BW, 1 91 0CS, and 1 900H -
though given the outrageous pricing of the actual Davies 1 900H I'd strongly
recommend using a good qual ity clone. Avoid the cheaper clones without an
internal brass bushing - Thonk sel ls an excel lent brass-bushed 1 900H clone for a
very reasonable price that I use in al l of my own builds.
Alternatively, feel free to use any knobs that have similar diameters and wil l fit
the Alpha round shaft pots. The Davies parts are 29mm, 1 9mm, and 1 3mm
respectively, and many other manufacturers make knobs of similar sizes. The
classic si lver top Moog-style knobs actual ly work quite wel l also for the larger
diameters.
M O D E L 2 2 3 1 A s ym m e t r i c S l e w L i m i t e rM O D E L 1 0 1 1 D i s c r e t e O s c i l l a t o r
C H O O S I N G C O M P O N E N T S
S L I G H T L Y N A S T Y E L E C T R O N I C S A D E L A I D E , A U S T R A L I A
1 6Tran s i s to r M atc h i n g
T R A N S I S T O R M A T C H I N G
The 1 01 1 uses a pair of matched BC560 PNP transistors in the exponential
converter to ensure a stable and rel iable conversion across different
temperatures and pitch ranges. These transistors need to be matched to ensure
that they have the same VBE (base-emitter voltage drop) at a given temperature,
which requires testing a number of transistors to find ones that have the closest
Vbe values.
A common mistake made by inexperienced builders is to match the transistors
using a multimeter transistor tester, using the transistors that show the best
matching values. This wil l not work. The transistor tester built into many
cheaper multimeters measure the hFE (current gain) of the transistor, and not
the base-emitter voltage that we are interested in. Testing for VBE requires
setting up or building a small test circuit to al low measurement of the differencein VBE between transistor pairs.
Recently a number of smal l , cheap component testers have appeared on the
market that do measure VBE, however while these are handy to roughly check
component values and find faulty parts they do not have the resolution or
accuracy required for matching exponential converter pairs.
There are a number of circuit designs available for matching transistors, but I
personal ly recommend the Ian Fritz method for its simplicity and rel iabi l ity.
There are a few variations on this method, but the circuit I use is shown here.
Essential ly it consists of setting the transistors up as diodes with precisely
matched resistance on the emitters of each (using a 25-turn trimpot to zero out
the tolerance errors of the 1 00k resistors), then measuring in mil l ivolts the
difference between the emitter voltages of the two transistors. The switch shown
here swaps the resistors between the two transistors to al low the trimpot to be
accurately set. I 'd strongly recommend building a socketed version of this circuit
on stripboard, to keep on the workbench for future projects that need matched
transistors.
When testing transistors I recommend setting up a fan blowing across the test
circuit, to ensure that both transistors are kept at an identical temperature. It's
also worth leaving each pair for a couple of minutes to al low the transistors'
internal temperatures to stabil ise. If the temperature in the room is relatively
stable, you can speed up the process by leaving one transistor in the circuit
permanently, and swapping out the other position one by one, taking note of the
voltage difference of each tested part. Once you've found a few transistors that
seem to show very close or identical differences to the fixed "reference"
transistor, you can take the reference transistor out and test the rough-matched
pairs against each other as normal to find the ones that have the closest match.
Even if you don't test al l the rough-matched transistors, keep them together for
future projects, because searching through label led pairs that are already fairly
close is a lot faster than finding matches between random parts!
M O D E L 1 0 1 1 D i s c r e t e O s c i l l a t o r
C 1
B2
E 3
C 1
B2
E 3
100K
100K
100K
+12V
0V/GND
MULTIMETER
MULTIMETER
12
312
3
TO SET TRIMPOT:With a pair of transistors fitted, measure thevoltage difference while switching between thetwo switch positions. Adjust the trimpot untilthe voltage is the same in both positions.
Set multimeter to mV range when measuring.Polarity is not important as long as it's kept thesame when testing multiple transistors.
DPDT SWITCH
TRANSISTORS UNDER TEST
PNP VERSION
NPN VERSION
1
23
1
23
12
3 12
3
MULTIMETER
MULTIMETER
0V/GND
+12V
100K
100K
100K
This is essentially the exact same circuitbut with the power reversed and thetransistors installed accordingly.
S L I G H T L Y N A S T Y E L E C T R O N I C S A D E L A I D E , A U S T R A L I A
1 7Tran s i s to r M atc h i n g
C 1
B2
E 3
C 1
B2
E 3
100K
100K
100K
+12V
0V/GND
MULTIMETER
MULTIMETER
12
312
3
TO SET TRIMPOT:With a pair of transistors fitted, measure thevoltage difference while switching between thetwo switch positions. Adjust the trimpot untilthe voltage is the same in both positions.
Set multimeter to mV range when measuring.Polarity is not important as long as it's kept thesame when testing multiple transistors.
DPDT SWITCH
TRANSISTORS UNDER TEST
PNP VERSION
NPN VERSION
1
23
1
23
12
3 12
3
MULTIMETER
MULTIMETER
0V/GND
+12V
100K
100K
100K
This is essentially the exact same circuitbut with the power reversed and thetransistors installed accordingly.
S L I G H T L Y N A S T Y E L E C T R O N I C S A D E L A I D E , A U S T R A L I A
1 8Con s t ru c t i o n
C O N S T R U C T I O N
NOTE: the V1.0 PCB needs an additional 10K resistor added between the positiverail and the base of Q508. See the PCB guides at the end of this document forplacement details.
For the most part the 1 01 1 can be constructed l ike any other PCB project, but
there are a couple of special components that need consideration. The
exponential converter uses a matched transistor pair and a 3300PPM/C tempco
resistor to achieve a good degree of thermal stabil ity, and these need to be
mounted together in a specific way in order to ensure that they are al l in close
contact and share the same temperature during operation. See the section
label led Transistor Matching for details on how to find a pair of matched
transistors, the 1 K 3300PPM/C tempco can be bought at synth part suppl iers
such as Thonk (www.thonk.co.uk) and Synthrotek (store.synthrotek.com) among
others.
The majority of construction can be performed like any PCB build, starting with
the lowest-profi le components (resistors and diodes) and working through to the
tal ler ones (Capacitors, transistors, etc.). The simplest way to populate the board
is simply to work through the BOM, doing each component type and value in
one chunk before moving on to the next. Avoid fitting the special components
for now (Q507, Q509, and R522)
Given the unusual number of discrete transistors in the build, it's worth
commenting on how to best populate them without risking damage or ending up
with a motley forest of strangely angled TO-92 packages. My preferred technique
is to put a batch of the transistors in place and bend the outer legs as usual,
taking care to get the height roughly the same between each, and then soldering
only the centre leg of each. Once these are al l done, fl ip the board over and
use a pair of tweezers to straighten each transistor unti l they al l look correct.
Fl ip the board back over and then solder one of the remaining legs of each of
the transistors, then final ly go through and solder the final legs once al l those are
done. This way each transistor gets the chance to cool down between each joint
being soldered, which reduces the risk of damage.
When soldering transistors it's important to hold the iron long enough to get a
sol id joint that extends down into the plated hole, but not so long that you risk
thermal damage to the transistor junction. With a properly heated iron, a few
seconds on each should be al l that's required.
When soldering rectangular capacitors, I l ike to solder one leg on each, then hold
the board in one hand while applying a very l ight pressure on top of the
capacitor with a free finger, using the other hand to reheat the solder joint unti l
the capacitor sl ides down tight against the PCB's surface. Continue this process
for al l the instal led capacitors then go back and solder the remaining legs. This
approach also works wel l to mount other components that need to mount
M O D E L 1 0 1 1 D i s c r e t e O s c i l l a t o r
S L I G H T L Y N A S T Y E L E C T R O N I C S A D E L A I D E , A U S T R A L I A
1 9Con s t ru c t i o n
securely onto the board, such as trimpots, IC sockets and pin headers.
Care must also be taken to ensure that the PCB-mounted potentiometers are
mounted as vertical ly as possible on the board - one option is to cl ick the
potentiometers into place, then mount them to the front panel before soldering
them. Also note that most potentiometers have a small anti-rotation tab on
them that wil l need to be removed before soldering them into position, these can
be cut off with a sharp pair of sidecutters, and I personal ly l ike to clean up any
remaining protrusions with a few passes of a needle fi le as wel l .
The pin headers that interconnect the two boards are another component that
needs a bit of additional care when assembling to ensure correct al igment. The
best course of action is to solder one side of al l the interconnects (either the pins
or socket) into place, being careful to get them straight and flush with the board.
Then connect the other halves onto them, lay the other PCB in place over the
top (I would even recommend mounting the boards together with screws and
spacers as they wil l be when final ly assembled), and solder al l the pins of the
other side. Once they are al l soldered, careful ly separate the two boards, taking
care to not bend the headers in the process.
When fitting the matched transistors and tempco resistors, these need to be
thermally connected to ensure the best stabil ity. The two BC560Cs should be
joined face-to-face with a band of heatshrink tubing (I also l ike to smear a very
thin layer of thermal compound between the two, making sure none gets near
the conductive legs). Careful ly bend the legs with a pair of tweezers so that they
match the hole spacing on the PCB, and solder them into place. Once the
transistors are instal led, the tempco resistor can be mounted on top, using
something l ike an epoxy or l iquid electrical tape to keep it thermally coupled to
the transistors and insulated from ambient temperature changes.
M O D E L 1 0 1 1 D i s c r e t e O s c i l l a t o r
A NOTE ON POWER FILTERING
It's common practice among some builders to replace the 1 0 ohm power
fi lter resistors with ferrite beads, in the bel ief that this wil l prevent power
rail fluctuations under varying current loads while sti l l providing the
fi ltering action desired. This is not recommended . Ferrite beads do not
even begin to show reactivity unti l somewhere up around the 1 MHz mark,
an order of magnitude beyond the audio range. Within the audio band
(and for a long way beyond it) they are electrical ly identical to a wire
jumper.
Assembly of the matched pair using
heatshrink tubing. After fitting the
tempco resistor, a covering of non-
conductive material should be added
to thermally insulate the assembly.
S L I G H T L Y N A S T Y E L E C T R O N I C S A D E L A I D E , A U S T R A L I A
20Con s t ru c t i o n
P H Y S I C A L A S S E M B L Y
Assembling the finished PCBs and front panel is very simple. Begin by fitting the
M3 hardware to the panel-side PCB. screwing the hex spacer tight to hold it al l
together. Once al l four screws are in place, start fitting the banana sockets into
their respective holes on the front panel - making sure to al ign the flat terminals
vertical ly (if using the Cinch-style sockets). The banana sockets need to be
tightened sol idly to prevent them coming loose in use, something l ike a dab of
hot glue between the nut and thread can also help prevent loosening.
Make sure that the nuts and washers have al l been removed from the PCB-
mount potentiometers on the front panel PCB, as wel l as the anti-rotation tabs
on the pots themselves (if present). Now you can join the front panel and panel
PCB by pushing the pot shafts through their respective holes, fitting their
washers and nuts, and tightening everything into place.
Now you'l l need to connect the banana sockets to the front PCB using either
some offcut component leads, or tinned copper wire. The simplest way is to
solder the straight pieces of wire vertical ly into the pad on the PCB, then bend
them over to meet the banana socket and solder that end to the flat side of the
terminal. This way they can be easi ly disconnected for servicing by simply
heating the terminal with the iron and pushing the wire away once the solder
reflows.
Once the sockets are al l connected, put M3 washers on al l four mounting screws
and careful ly fit the second PCB into place - taking care to get the interconnects
correctly seated. Unti l cal ibration is completed I would not fit the final washers
and nuts to al low easy separation of the PCBs when troubleshooting, just making
sure to take extra care plugging and unplugging the power connector when the
PCB is unsupported.
When the module is confirmed to be working properly you can fit the final M3
washers and nuts and tighten up the whole assembly. Double check that the hex
spacers haven't loosened in the meantime as wel l .
M O D E L 1 0 1 1 D i s c r e t e O s c i l l a t o r
Connection of the two PCBs using
standard M3 hardware. Washers are
necessary on the inside to correctly
space the boards for the
interconnects. Screw head should go
on panel side.
Connecting the banana sockets
using an offcut component lead or
similar.
FREQUENCY CONTROLS
Fine and coarse adjustment of
inital osci l lator pitch.
MIX KNOBS
Crossfades the respective output
between two waveshapes
A & B OUTPUTS
Outputs mixed sine-triangle (A) and
mixed saw-square-suboctave (B)
SUBOCTAVE OUTPUT
Outputs the raw suboctave signal.
SUBOCTAVE LEVEL
Controls the amount of suboctave
that is mixed into output B
INPUT JACKS
AC coupled inputs for Linear FM
and Sync signals, and DC coupled
inputs for 1 V/Octave pitch CV,
Logarithmic FM, and Symmetry CV.
INPUT ATTENUATORS
Allow 0-1 00% attenuation of the
FM signal, Symmetry CV and Log
CV.
SYMMETRY
Sets the inital symmetry (or pulse
width) of the pulse waveform.
Centred is 50:50 squarewave.
M O D E L 2 2 3 1 A s ym m e t r i c S l e w L i m i t e rM O D E L 1 0 1 1 D i s c r e t e O s c i l l a t o r
C O N T R O L S
S L I G H T L Y N A S T Y E L E C T R O N I C S A D E L A I D E , A U S T R A L I A
21Con t ro l s
SLIGHTLY NASTY JACK COLOURS
RED Bipolar signal output
BLUE Bipolar signal input
YELLOW AC-coupled input
BLACK Logic output
WHITE Logic Input
S L I G H T L Y N A S T Y E L E C T R O N I C S A D E L A I D E , A U S T R A L I A
22Ca l i b rat i o n
C A L I B R A T I O N
Calibration of the 1 01 1 consists of adjusting the four cal ibration trimpots on the
back of the module to set the fol lowing values (in order):
1 . CV scale - sets the scal ing of the pitch CV to ensure that a 1 v change in
CV produces a one octave change in pitch.
2. CV offset - sets the centred "zero point" for the front panel frequency
knobs.
3. High frequency compensation - this al lows you to "boost" the CV
response at higher frequencies to compensate for the tendency of VCOs
to "droop" at higher pitches.
4. Triangle wave alignment - This sets the folding point of the saw-to-
triangle shaper to make sure that the reset point of the wave l ines up
correctly and forms a nice uninterrupted triangle wave.
M O D E L 1 0 1 1 D i s c r e t e O s c i l l a t o r
BEFORE YOU BEGIN
Before powering up the module for the first time, use a multimeter
to check the resistances between the three power rails. Make sure
that they show a resistance higher than 1 KOhm, any lower and it's
possible there is a short circuit or incorrectly oriented semiconductor
somewhere on the PCB.
Before cal ibrating the CV response, al low the osci l lator to warm up for a
few minutes - the frequency wil l drift in this period as al l the components
settle into their operating temperatures.
While I 've given a specific order to these operations, you can expect to
have to go back and forth on some of them, particularly the CV Scale
and CV Offset cal ibration. Also if you notice the osci l lator pitch seems
way too high or low when you get to the CV Scale step, feel free to adjust
the CV offset control to get it in the right place.
Also, you'l l want to disable the High Frequency Compensation before you
start the CV calibration steps, which means measuring the resistance
across the two outer pads of the "HF.COMP" trimmer and adjusting it
unti l it reads 0 ohms (or as low as it wil l go).
S L I G H T L Y N A S T Y E L E C T R O N I C S A D E L A I D E , A U S T R A L I A
23Ca l i b rat i o n
The goal with this step is to get the osci l lator to respond with an accurate
1 V/Octave response to the frequency CV - so that a change of +/- 1 V on the
input results in a +/- 1 octave change in the output pitch (ie. doubl ing or halving
of its frequency). We're not real ly worried about absolute pitch here, only that
the amount of change relative to the CV is correct.
Getting the CV scale right is always one of the more tedious jobs when
cal ibrating osci l lators, and different people have developed various systems over
the years to get the job done. However you choose to do it, I would strongly
recommend using whatever 1 V/Oct source you wil l be using when the module is
completed, such as a your midi-CV converter or a keyboard with 1 V/Oct output.
A first basic step is to either hook up a frequency counter or instrument tuner
that shows frequency (if you have one) and your l istening system, and play notes
on the keyboard that are one octave apart, somewhere around middle C. Adjust
the CV Scale trimmer unti l the resulting pitches from the osci l lator are as close
as you can get to being one octave apart (the higher note should be double the
frequency of the lower one). Because the actual frequencies of both the notes
wil l be changed each time you adjust the trimmer, just be sure to play them
each a couple of times between each adjustment to determine what the
relationship between them currently is.
Once you're more or less happy with the response over one octave, try playing
notes that are further apart, such as the next octave down from your low note,
and the next octave up from the higher one. Once again adjust the trimmer
unti l you get the correct relationship between the notes - in this case the high
note should be 8x the frequency of the lower one. Make sure to occasional ly go
back and check the notes that are closer together again, to make sure that
they're also staying in cal ibration (they should if the exponential converter is
providing an accurate conversion).
Get the response as accurate as you can, but don't obsess over it yet, because
you'l l want to fine tune this a l ittle further once the CV offset has been trimmed.
M O D E L 1 0 1 1 D i s c r e t e O s c i l l a t o r
C V S C A L E
While this adjustment is quite critical in a keyboard synth where the osci l lators
are expected to have a very specific voltage-pitch response, in a modular where
we've got big frequency knobs on the front panel to adjust the pitch, it's real ly
just a convenience. Essential ly al l you want to do here is set the osci l lator to play
middle C (using your CV converter/source), set the coarse and fine frequency
knobs to their centre positions, and then adjust the CV Offset trimmer unti l the
osci l lator is outputting middle C (261 .6Hz). Don't worry about getting this exact,
because tiny movements of the coarse tune knob wil l throw this off substantial ly,
and tuning osci l lators is a completely normal task when patching modulars to
play melodical ly. This setting just makes sure that similar knob positions on
individual osci l lators give consistent frequency ranges.
Once the osci l lator is responding fairly accurately in the low-mid pitch range, it's
time to set up the high-frequency compensation. This is necessary because
various electrical effects in the circuit usual ly cause the 1 V/Oct response to
"droop" at higher frequencies, meaning that notes wil l get progressively flatter
and flatter (too low in pitch) as you continue up the musical scale. The high
frequency compensation circuit adds a boost to the osci l lator frequency as the
frequency increases, to counteract this drooping and restore the expected
1 V/Oct response.
Setting this up general ly just consists of playing notes higher up on the scale to
see how flat they are, and slowly turning up the HF compensation trimmer unti l
their pitch is adequately corrected. It's worth also playing notes at lower pitches
while you're adjusting to make sure that the adjustments aren't upsetting their
cal ibration.
S L I G H T L Y N A S T Y E L E C T R O N I C S A D E L A I D E , A U S T R A L I A
24Ca l i b rat i o n
M O D E L 1 0 1 1 D i s c r e t e O s c i l l a t o r
H I G H F R E Q U E N C Y C O M P .
C V O F F S E T
S L I G H T L Y N A S T Y E L E C T R O N I C S A D E L A I D E , A U S T R A L I A
25Ca l i b rat i o n
The 1 01 1 generates the triangle wave by folding the sawtooth onto itself, and to
form a smooth and uninterrupted triangle the fold point must be set accurately.
Turn the front panel sine-triangle mix knob al l the way to the right and scope
the output - you should see the triangle wave with a sl ight gl itch on the topmost
corners. Use the frequency knobs to set the osci l lator's frequency to something
comfortable l ike 200Hz or so, then adjust the trimmer unti l the gl itch looks to be
as central in the wave as you can get it.
Once you're happy with how it looks, hook up the output to your l istening
system and fine tune the trimmer by ear unti l you find the position where the
triangle has the least upper harmonics (this is wherever the triangle sounds the
smoothest and has the least "buzz" to it).
M O D E L 1 0 1 1 D i s c r e t e O s c i l l a t o r
T R I A N G L E A L I G N M E N T
Triangle alignment. Centre image is
correctly aligned.
S L I G H T L Y N A S T Y E L E C T R O N I C S A D E L A I D E , A U S T R A L I A
26Re fe re n c e
P C B G U I D E - L O W E R
M O D E L 1 0 1 1 D i s c r e t e O s c i l l a t o r
LOWER BOARD - TOP LOWER BOARD - BOTTOM
Additional 10K resistor (R526)
between +ve rail and base ofQ508
S L I G H T L Y N A S T Y E L E C T R O N I C S A D E L A I D E , A U S T R A L I A
27Re fe re n c e
P C B G U I D E - U P P E R
M O D E L 1 0 1 1 D i s c r e t e O s c i l l a t o r
LOWER BOARD - TOP LOWER BOARD - BOTTOM
w w w . s l i g h t l y n a s t y . c o m
T R I A N G L E A L I G N M E N T