m o d e l 1 0 1 1 - slightly nasty · 2017. 6. 29. · q505 bc550 c 1 b 2 e 3 q508 bc560 c 1 b 2 e...

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


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


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



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.




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.


Block diagram of the Model 1011.

Circles marked "A" are attenuators.

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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

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Traditional configuration of PNP

exponential converter with opamp

current source.

http://schmitzbits.de/expo_tutorial/index.html


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.



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1 0

M O D E L 1 0 1 1


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.


1 1C i rc u i t Ove rv i ew

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1 2

M O D E L 1 0 1 1


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.


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


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


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.


C H O O S I N G C O M P O N E N T S

http://www.thonk.co.uk

http://store.synthrotek.com


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!


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.

http://www.dragonflyalley.com/synth/images/TransistorMatching/ianFritz-transmat0011_144.pdf


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.


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



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.


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.


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 .


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.


C O N T R O L S


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


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.


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).



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.


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.




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



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).


T R I A N G L E A L I G N M E N T

Triangle alignment. Centre image is

correctly aligned.


26Re fe re n c e

P C B G U I D E - L O W E R


LOWER BOARD - TOP LOWER BOARD - BOTTOM

Additional 10K resistor (R526)

between +ve rail and base ofQ508


27Re fe re n c e

P C B G U I D E - U P P E 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

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m o d e l 1 0 1 1 - slightly nasty · 2017. 6. 29. · q505 bc550 c 1 b 2 e 3 q508 bc560 c 1 b 2 e...

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