Oakley Sound Modular Series User manual

Oakley Sound Systems
5U Oakley Modular Series
The SVF issue 5
Voltage Controlled State Variable Filter
Builder's Guide
V5.
Tony Allgood
Oakley Sound Systems
CARLISLE
United Kingdom

Introduction
This is the Project uilder's Guide for the issue 5 State Variable Filter 5U module from Oakley
Sound.
This document contains a basic introduction to the board, a full parts list for the components
needed to populate the board, interconnections and some basic testing methods.
For the User Manual, which contains an overview of the operation of the unit, advice on
connecting the unit and calibration procedures, please visit the main project webpage at:
http://www.oakleysound.com/svf.htm
For general information regarding where to get parts and suggested part numbers please see
our useful Parts Guide at the project webpage or http://www.oakleysound.com/parts.pdf.
For general information on how to build our modules, including circuit board population,
mounting front panel components and making up board interconnects please see our generic
Construction Guide at the project webpage or http://www.oakleysound.com/construct.pdf.
2

The SVF issue 5 PC
This is the prototype issue 5 module with natural finish Schaeffer panel. Note the use of the Sock8 board
to mount the jack sockets. Two pot brackets are used to hold the PCB firmly to the front panel.
I have provided space for the three main control pots on the PC . If you use the specified
16mm Alpha pots and matching brackets, the PC can be held firmly to the panel without any
additional mounting procedures. The pot spacing is 1.625” and is the same as the vertical
spacing on the MOTM modular synthesiser and most of our other modules.
The design requires plus and minus 15V supplies. The power supply should be adequately
regulated. The current consumption is about 30mA for each rail. Power is routed onto the
PC by a four way 0.156” MTA156 type connector or the special five way Synthesizers.com
MTA100 header. You could, of course, wire up the board by soldering on wires directly. The
four pins are +15V, ground, earth/panel ground, -15V. The earth/panel connection allows you
to connect the metal front panel to the power supply’s ground without it sharing the modules’
ground line. More about this later.
The PC has four mounting holes for M3 bolts, one near each corner. These are not required
if you are using the two 16mm pot brackets.
The issue 5 board size is 104mm (high) x 104mm (deep), while the issue 5.1 board size is
104mm (high) x 99mm (deep). Electrically both issue 5 and issue 5.1 are the same.
The board has been laid out to accept connection to our Sock8 socket board. This small board
speeds up the wiring of the eight sockets and reduces the chances of mistakes.
3

Components
For general information regarding where to get parts and suggested part numbers please see
our useful Parts Guide at the project webpage or http://www.oakleysound.com/parts.pdf.
Some special considerations for this project
The op-amps can be any decent medium (audio) speed op-amp, eg. TL072 or 4558. However,
U2 should have a low input bias current and a FET input op-amp is to be recommended. The
TL072 is perfectly good enough for this, although you could use the LF412 or AD712.
For the 470pF capacitors in positions C2 and C7, you must use good quality capacitors.
Failure to use low tolerance parts in these locations will mean your filter will be unlikely to
oscillate over the full audio range in the HIGH setting. I have suggested using 2.5% (or better)
tolerance 63V polypropylene film types. You can also use 2.5% polystyrene capacitors. These
are generally axial types, but radial types do exist. These are little silver coloured cylinders,
and offer exceptional quality, but are easy to melt with your soldering iron. Another good
quality capacitor one could use is the silvered mica type. These are quite expensive but offer
exceptional performance in a small package.
Close up showin the two transistors of the exponential pair held to ether with a cable tie. The red
capacitors you can see are 5mm polypropylene film types.
4

Parts List
For general information regarding where to get parts and suggested part numbers please see
our useful Parts Guide at the project webpage or http://www.oakleysound.com/parts.pdf.
The components are grouped into values, the order of the component names is of no particular
consequence.
A quick note on European part descriptions. R is shorthand for ohm. K is shorthand for kilo-
ohm. R is shorthand for ohm. So 22R is 22 ohm, 1K5 is 1,500 ohms or 1.5 kilohms. For
capacitors: 1uF = one microfarad = 1000nF = one thousand nanofarad.
To prevent loss of the small ‘.’ as the decimal point, a convention of inserting the unit in its
place is used. eg. 4R7 is a 4.7 ohm, 4K7 is a 4700 ohm resistor, 6n8 is a 6.8 nF capacitor.
Resistors
All resistors should be 0.25W 1% metal film (MF) types unless stated.
150R R25, R2, R24, R1
1K R27, R47, R48, R36
1K +3000ppm/k PTC R38
10K R21, R4, R16, R18, R26, R3
15K R5, R22
27K R7
33K R39
47K R42, R37, R45, R44, R28, R14, R19, R15
62K R12
82K R43, R17, R41, R46
100K R33, R20, R8, R34, R9
130K R29
150K R40
220K R35
330K R10, R11, R13*
470K R23, R6
560K R32
1M R31, R30
* R13 fitted only in 2U version
Capacitors
100nF, 63V axial ceramic C3, C4, C5, C6, C9, C10, C13, C14
4p7 C0G ceramic* C1, C8
470pF C0G ceramic 5mm** C2, C7
2.2uF, 35V electrolytic C11, C12
5

* C1 and C8 have a lead spacing of 5mm for the issue 5 SVF and a lead spacing of 2.5mm for
issue 5.1.
** The PC board locations for C2 and C7 were originally designed for 5mm 1%
polypropylene capacitors and you can still use these if you wish. However, it is easier to get
good quality C0G capacitors which work equally as well.
Discrete Semiconductors
1N4148 signal diode D1, D2, D3, D4
3V6 500mW zener diode D6
6V2 500mW zener diode D5
C550 NPN transistor Q2
C560 PNP transistor Q1
Integrated Circuits
LM13700 dual OTA U1
TL072 dual op-amp U2, U3, U4, U5, U6
Trimmers
100K 6mm trimmer OFF1, OFF2
100K multiturn trimmer TUNE
20K multiturn trimmer V/OCT
Potentiometers
47K linear Alpha 16mm CV1-DEPTH, FREQUENCY
10K linear Alpha 16mm RESONANCE
Two Alpha pot brackets are also required. The FREQUENCY pot has no bracket.
Switch
SPST or SPDT toggle switch RESONANCE MODE
The lower two contacts on the switch connect to the PC pads marked SAT.
Miscellaneous
Leaded Ferrite beads L1, L2
Knobs to fit 6mm shafts Three off
6

Cable tie for holding Q1 and Q2 together
Molex or MTA 4 way header PSU – Oakley/MOTM power supply
MTA100 6-way header PWR – Synthesizers.com power supply
Molex/MTA 0.1” header 6-way UPPER – for connecting to sockets
Molex/MTA 0.1” header 8-way LOWER – for connecting to sockets
Molex/MTA 0.1” housing 6-way UPPER – for connecting to sockets
Molex/MTA 0.1” housing 8-way LOWER – for connecting to sockets
1/4” sockets Eight off mounted either on the Sock8 board or on panel
Hook up wire (26awg).
Additional components required if using optional Sock8 board
Molex/MTA 0.1” header 6-way UPR
Molex/MTA 0.1” header 8-way LWR
Molex/MTA 0.1” housing 6-way UPR
Molex/MTA 0.1” housing 8-way LWR
112APC Switchcraft 1/4” socket SK1, SK2, SK3, SK4, SK5, SK6, SK7, SK8
If using Molex KK you'll also need at least 28 crimp terminals.
Suitable lengths of wire to make up the two interconnects and three cable ties.
You need to fit a wire link in L1 on Sock8 issue 2 boards.
Additional parts required for the 2U version
You won't be needing the Sock8 board since all the sockets will need to be wired up
individually.
Make sure that R13 is fitted and is 330K.
Miscellaneous
1/4” sockets IN3, 1V/OCT
Offboard Pots (2U format only)
47K Log IN1, IN2, IN3
47K Linear CV2
7

Mounting the Resonance Mode switch
The switch is connected so that the when the toggle is in the up position the two connections
of SAT are shorted together. You will need to connect your switch so that the lower two lugs
of the switch are connected to the SAT pads on the board. This can be done with either
insulated multistrand wire or solid core wire.
This is an APEM to le switch wired to the PCB with solid core wire. Note also that R13 is not fitted as
this is a 1U wide filter core module.
8

Connections
Power connections – MOTM and Oakley
The PSU power socket is 0.156” Molex/MTA 4-way header. Friction lock types are
recommended. This system is compatible with MOTM systems.
Power Pin number
+15V 1
Module GND 2
Earth/PAN 3
-15V 4
Pin 1 on the LWR header has been provided to allow the ground tags of the jack sockets to be
connected to the power supply ground without using the module’s 0V supply. Earth loops
cannot occur through patch leads this way, although screening is maintained. Of course, this
can only work if all your modules follow this principle.
Power connections – Synthesizers.com
The PWR power socket is to be fitted if you are using the module with a Synthesizers.com
system. In this case you should not fit the PSU header. The PWR header is a six way 0.1”
MTA, but with the pin that is in location 2 removed. In this way location 3 is actually pin 2 on
my schematic, location 4 is actually pin 5 and so on.
Power Location number Schematic Pin number
+15V 1 1
Missing Pin 2
+5V 3 2
Module GND 4 3
-15V 5 4
Not connected 6 5
+5V is not used on this module, so location 3 (pin 2) is not actually connected to anything on
the PC .
If fitting the PWR header, you will also need to link out pins 2 and 3 of the PSU header. This
connects the panel ground with the module ground. Simply solder a solid wire hoop to join the
two middle pads of PSU together.
9

Building the 1U Filter Core module using the Sock8 board
This is the simplest way of connecting all the sockets to the main board. The Sock8 board
should be populated in the way described in our construction guide found on the project
webpage. There are only two headers, UPR (for upper) which is six way, and LWR (for
lower) which is eight way. oth headers are fitted to the bottom side of the board.
If you have an issue 2 Sock8 board. Don't forget to fit a wire link in position L1.
You need to make up two interconnects. The six way one should be made so that it is 80mm
long. The eight way should be made to be 130mm.
The prototype unit showin the detail of the board to board interconnects. Here I have used the Molex KK
0.1” system to connect the Sock8 to the main PCB.
10

Building the 1U Filter Core module by wiring the sockets manually
If you have bought Switchcraft 112A sockets you will see that they have three connections.
One is the earth or ground tag. One is the signal tag which will be connected to the tip of the
jack plug when it is inserted. The third tag is the normalised tag, or NC (normally closed) tag.
The NC tag is internally connected to the signal tag when a jack is not connected. This
connection is automatically broken when you insert a jack.
Once fitted to the front panel the ground tags of each socket can be all connected together
with solid wire. I use 0.91mm diameter tinned copper wire for this job. It is nice and stiff, so
retains its shape. A single piece of insulated wire can then be used to connect those connected
earth tags to pin 1 of LWR. Pin 1 is the square solder pad.
All the other connections are connected to the signal lugs of the sockets. The tables below
show the connections you need to make:
UPPER
Pin Pad name Socket Connection Lu Type
Pin 1 ANDPASS Connect to P Signal lug
Pin 2 Not connected
Pin 3 Not connected
Pin 4 NOTCH Connect to NOTCH Signal lug
Pin 5 module ground Connect to IN1 & IN2 NC lugs
Pin 6 IN1 Connect to IN1 Signal lug
LOWER
Pin Pad name Socket Connection Lu Type
Pin 1 Panel ground Connects to all sockets Ground lugs via wire frame
Pin 2 LOWPASS Connect to LP Signal lug
Pin 3 KEY-CV Connect to 1V/OCT Signal lug
Pin 4 HIGHPASS Connect to HP Signal lug
Pin 5 module ground Connect to 1V/OCT NC lug
Pin 6 IN2 Connect to IN2 Signal lug
Pin 7 module ground Connect to CV1 NC lug
Pin 8 CV1 Connect to CV1 Signal lug
11

2U SVF full format
I am not going into great detail with this format as the PC has been primarily designed with
the 1U filter core module in mind. However, I will mention a few things that may be useful to
you if you do decide to build the larger format design.
The 2U format contains ten sockets and four additional pots. You can use any pots you like,
but I am rather partial to the 16mm Alpha pots sold by anzai which have the solder lugs and
not the usual PC mounted ones you have used on the board. You may be tempted to use the
larger 24mm Alpha pots, indeed, these are great pots, but the width of them may mean that
the top pot will clash with your choice of mounting rail.
Your first job will be to ground the earth lugs on each socket. Do this by joining the earth lugs
of each vertical row of sockets together first with stiff single core wire. Then use another
piece of solid core wire, going across horizontally, to connect all four vertical wires together.
Take a single insulated piece of wire back to on the PC and connect it to pin 1 of the header
LOWER. This now connects all the sockets' ground lugs to earth/pan connection on the PC .
This in turn goes, via pin 3 of the PSU header, back to the power supply.
It is also advisable to ground the NC lugs of the six input sockets too. Do this in the same way
you have commoned the earth lugs. Simply connect all three sockets' NC lugs in each of the
right hand columns together with two pieces of stiff wire. Then, with two more short lengths
of insulated multistrand wire, connect the stiff wire pieces to pins 5 and 7 of UPPER
respectively.
The connections of the signal lugs of the CV and audio output sockets that go directly to the
PC are summarised below:
UPPER
Pin Pad name Socket Connection Lu Type
Pin 1 ANDPASS Connect to P Signal lug
Pin 2 Not connected
Pin 3 Not connected
Pin 4 NOTCH Connect to NOTCH Signal lug
Pin 5 Module ground
Pin 6 Not connected
12

LOWER
Pin Pad name Socket Connection Lu Type
Pin 1 Panel ground Connects to all sockets Ground lugs via wire frame
Pin 2 LOWPASS Connect to LP Signal lug
Pin 3 KEY-CV Connect to 1V/OCT Signal lug
Pin 4 HIGHPASS Connect to HP Signal lug
Pin 5 module ground See text NC lugs
Pin 6 Not connected
Pin 7 module ground See text NC lugs
Pin 8 CV1 Connect to CV1 Signal lug
All your other connections will be made via the four two way 0.1" headers that are situated on
the board near the pots. These are labelled appropriately to help you connect up your module
correctly. They are IN-1, IN-2, IN-3 and CV2.
Pots have three pins. Two of these pins will be connected to PC , whilst the remaining one
will be connected to the appropriate socket's signal lug.
The middle pin of the pot, the wiper, will carry the signal to the appropriate header on the
PC . The pots' wires will attach to the underside of the board at each header, and thus be
soldered from the topside of the board. For each header, pin 1 is connected to the wiper of the
pot. Pin 1 is the square pin so its easily spotted even from the underside of the board.
The pot has two other pins, one will be connected to ground, the other to the signal lug on the
socket it controls.
With pins facing down and looking at the back of the pot, the right hand pin should go to the
ground connection of the header, that is pad 2 on each of the headers. Take a wire from the
right hand pin to the round pad on the PC next to the one that the associating wiper
connects.
Now each pot will have one unsoldered pin left. Connect these to the appropriate socket. The
wire should go to the signal lug of the socket. IN 1 goes to the signal lug on the socket
labelled IN 1, and so on.
There are a quite lot of wires here, but it should be quite neat once it is all done.
13

Testing, testing, 1, 2, 3...
Apply power to the unit making sure you are applying the power correctly. Check that no
device is running hot. Any sign of smoke or strange smells turn off the power immediately and
recheck the polarity of the power supply, and the direction of the ICs in their sockets.
Assuming everything is OK so far, it is time to apply an audio input. Use a bright signal like a
sawtooth output from a VCO. Middle A, 440Hz is a good note to use.
Moving the FREQUENCY control should produce the usual and distinctive filter effect from
the low pass output. From the high pass output, you should hear the sawtooth get brighter and
less smooth as the cut-off frequency is increased. The band pass output should produce a sort
of wah-wah sound as the Frequency pot is moved back and forth. The notch output will be
more subtle, and will appear to sound like a mild phasing effect. Turning the Resonance up
will accentuate the ‘electronic’ nature of the sound on all four outputs.
Remove the audio input and ensure the RESONANCE mode switch is set to HIGH. Check
that at maximum resonance the filter output will oscillate across the whole audio band. You'll
probably need to turn up the cut-off frequency pot to above the mid-point first to actually get
the SVF to start to oscillate – it does not tend to oscillate naturally at frequencies below 1kHz
or so. eware, it is quite possible to get this filter to oscillate above the range of hearing. So
be careful so as not to damage your studio monitor’s tweeters.
Now click the MODE switch to NORM and you should find that the loudness of the
oscillation drops somewhat. It will also probably cease to oscillate at all at frequencies below
800Hz or so.
Listening to the band pass output with the sawtooth input still connected, patch a LFO or EG
output to the CV inputs. The 1V/octave input should produce large sweeps of cut-off. Check
also that with the LFO or EG connected to the CV1 input, the CV1 pot allows you to control
the depth of the sweep. Fully clockwise the CV1 input should produce very deep sweeps.
Notice that the minimum sweep depth should occur with the CV1 pot at its mid point. Use a
sawtooth waveform on your LFO, and see if the CV1 depth pot allows you to invert the
modulation input. You should get a ‘dow-dow-dow...’ from one side and a ‘yit-yit-yit...’ from
the other.
Check that both the audio inputs behave identically.
If all this happens, the chances are that you have a working module. Now before you start to
use it in your modular you will need to calibrate it. The full calibration procedure can be found
in the User Manual.
14

Final Comments
If you have any problems with the module, an excellent source of support is the Oakley Sound
Forum at Muffwiggler.com. Paul Darlow and I are on this group, as well as many other users
and builders of Oakley modules.
If you can't get your project to work and you are in the EU, then Oakley Sound Systems are
able to offer a 'get you working' service. If you wish to take up this service please e-mail me,
Tony Allgood, at my contact e-mail address found on the website. I can service either fully
populated PC s or whole modules. You will be charged for all postage costs, any parts used
and my time at 25G P per hour. Most faults can be found and fixed within one hour, and I
normally return modules within a week. The minimum charge is 25G P plus return postage
costs.
If you have a comment about this builder's guide, or have a found a mistake in it, then please
do let me know. ut please do not contact me directly with questions about sourcing
components or general fault finding. Honestly, I would love to help but I do not have the time
to help everyone individually by e-mail.
Last but not least, can I say a big thank you to all of you who helped and inspired me. Thanks
especially to all those nice people on the Synth-diy and Analogue Heaven mailing lists and
those at Muffwiggler.com.
Tony Allgood at Oakley Sound
Cumbria, UK
© June 2010 – updated September 2018
No part of this document may be copied by whatever means without my permission.
15