Paia 9720 Guide
9720 VCO 1
010321
Model 9720
Assembly and Using Manual
Dual VCO w/Modulator
(c) 2000 PAiA Electronics, Inc.
The 9720 Dual VCO w/Modulator features two independent VCOs,
each with a chromatic range of 10 octaves from 16Hz to 16kHz at a
+/- 1cent pitch error. Total range of each oscillator is from 1 cycle/
minute (0.017 Hz) to 100 kHz so either can be used as wide range
audio source or super slow multi-waveform LFO. Temperature
stability is equally extraordinary due to a novel exponential converter
that provides more accurate temp tracking than conventional designs
without the use of temperature compensating resistors.
Oscillator A has 5V p-p outputs for Ramp, Pulse (w/Width modula-
tion), Triangle and Sin waveforms. The built-in Glide Processor
provides slew rates from milliseconds to several seconds and a
convenient toggle switch transposes down from normal audio outputs
to LFO mode. The Pitch knob sets initial pitch over a 3 octave range.
The Sync input provides for “Soft Synchronization” to an external
audio source.
Oscillator B is very similar to Osc A but subtle differences optimize
the flexibility of the pair. There are outputs for Ramp, Triangle and
Pulse waveforms. A panel control for initial Pulse Width works in
conjunction with the PW CV input that is normalized to the Modulator
output. An auxiliary 1V/kHz Frequency Modulation input allows for
complex FM timbres from just a single module.
The Modulator is an Attack/Release Envelope Generator that has a
separate Trigger input for A/R envelopes and Gate input for A/R with
Sustain (ASR). Attack time is adjustable from 0.5ms to 2 seconds,
Release time from 1ms to 4 seconds. The Cycle switch allows self-
triggering for an LFO with independently adjustable rise and fall
times and a range from a cycle every few seconds to over 100Hz.
The Gate and Trigger inputs also work when in Cycle mode - a Gate
input turns the oscillator off and on and Trigger inputs syncs the
oscillator to an external source. The front panel LED brightens and
dims to indicate Modulator output.
2 9720 VCO 010321
ASSEMBLING THE 9720 DUAL VCO W/MODULATOR
Before beginning assembly, go through the manual.
Look at the drawings. Feel the parts. You’re
naturally eager to plunge right in, but take a few
deep breaths first. Check the parts supplied against
the packing list on the last page of this manual.
In some cases, notes packed with the parts will
be used to call your attention to special situations.
These notes may be in the "MISSING PARTS"
postcard. If parts are missing please notify PAiA at
Notice that each step in the manual is marked with
a checkoff box like this:
DESIGNATION VALUE COLOR CODE
( ) R27 100 ohm brown-black-brown
Checking off each step as you do it may seem
silly and ritualistic, but it greatly decreases the
chance of omitting a step and also provides
some gratification and reward as each step is
completed.
Numbered figures are printed in the Illustrations
Supplement in the center of this manual. These pages
may be removed for easy reference during assembly.
THE CIRCUIT BOARD
The 9720 VCO is built on a double-sided circuit
board. No special preparation or cleaning is necessary
before assembly. The "top" of the board is the side that
is printed with component designations and parts are
mounted from this side. The "bottom" of the board is
also called the solder side and is masked with a
conformal coating to lessen the chance of solder bridges.
Solder pads are tin-lead plated for ease of soldering and
assembly.
TOOLS
You’ll need a minimum of tools to assemble the kit
- a small pair of diagonal wire cutters and pliers,
screwdriver, sharp knife, ruler, soldering iron and solder.
9720 VCO 3
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Modern electronic components are small (in case you
hadn’t noticed) and values marked on the part are
often difficult to see. Another handy tool for
your bench will be a good magnifying glass. Also
use the magnifier to examine each solder joint as
it is made to make sure that it doesn’t have any of
the problems described in the SOLDERING section
which follows.
SOLDERING
Select a soldering iron with a small tip and a
power rating not more than 35 watts. Soldering
guns are completely unacceptable for assembling
solid state equipment because the large magnetic
field they generate can damage components.
Use only a high quality 60/40 alloy rosin core solder
(acid core solder is for plumbing, and silver solder is
for jewelry - neither is for electronics work). A proper solder
joint has just enough solder to cover the soldering
pad and about 1/16-inch of lead passing through it.
There are two improper connections to beware of:
Using too little solder will sometimes result in a
connection which appears to be soldered when
actually there is a layer of flux insulating the
component lead from the solder bead. This
situation can be cured by reheating the joint and
applying more solder.
Too much solder may produce a conducting bridge of
excess solder between adjacent pads causing a
short circuit. If WAY too much solder is used it may flow
through the hole and cause bridges between conductors
on the component side of the board or even impede the
action of mechanical components such as trimmer
potentiometers. Accidental bridges can be cleaned off by
holding the board upside down and flowing the excess
solder off onto a clean, hot soldering iron.
Use care when mounting all components. Never force
a component into place.
Special thanks to the
beta crew -
Scott Lee
Mike Murphy
Johnny Klonaris
David Hillel Wilson
and me - John Simonton
4 9720 VCO 010321
Resistors
Solder each resistor in place following the parts placement
designators printed on the circuit board and the
assembly drawing fig 1. Note that resistors are nonpolarized
and may be mounted with either lead in either of the holes
in the board. Before mounting each resistor, bend its leads
so that they are at a right angle to the body of the part. Put
the leads through the holes and then push the resistor firmly
into place. Cinch the resistor in place by bending the leads
on the solder side of the board out to an angle of about
45 degrees. Solder both ends of each resistor in place
as you install it. Clip each lead flush with the solder joint
and save a few of the clippings for use in later steps.
The 9720 VCO uses 1% film resistors in precision circuitry
and 5% carbon film resistors in non-critical locations. Not
all resistors are mounted on the circuit board, some will be
"left over" when the board is finished and will be installed
later in the assembly procedure.
First we’ll install the 5% resistors. These resistors are
identified by their 4 color bands. A tip: If you can't find the
location for a resistor, go on to the next one and come back.
DO NOT CHECK OFF A PART UNTIL IT IS INSTALLED
AND SOLDERED.
DESIGNATION VALUE COLOR CODE A-B-C
( ) R21 1.5m brown-green-green
( ) R43 1.5m brown-green-green
( ) R97 1.5m brown-green-green
listed below: 100k brown-black-yellow
( ) R3 ( ) R6 ( ) R10 ( ) R12
( ) R35 ( ) R38 ( ) R89 ( ) R90
( ) R94 ( ) R95 ( ) R96
listed below: 10k brown-black-orange
( ) R34 ( ) R47 ( ) R56 ( ) R68
( ) R78
( ) R63 10meg brown-black-blue
( ) R73 10meg brown-black-blue
listed below: 120k brown-red-yellow
( ) R7 ( ) R18 ( ) R45 ( ) R77
( ) R79
5% Resistors have
4 color bands
9720 VCO 5
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DESIGNATION VALUE COLOR CODE A-B-C
( ) R19 12k brown-red-orange
( ) R54 12k brown-red-orange
( ) R61 12k brown-red-orange
( ) R66 1500 brown-green-red
( ) R75 1500 brown-green-red
( ) R91 150k brown-green-yellow
( ) R76 15k brown-green-orange
( ) R60 180k brown-grey-yellow
listed below: 18k brown-grey-orange
( ) R4 ( ) R11 ( ) R81 ( ) R86
( ) R31 1k brown-black-red
( ) R57 1k brown-black-red
( ) R1 22 red-red-black
listed below: 220 red-red-brown
( ) R24 ( ) R46 ( ) R50 ( ) R88
listed below: 2200 red-red-red
( ) R13 ( ) R15 ( ) R22 ( ) R32
( ) R65 ( ) R74 ( ) R83 ( ) R84
( ) R100 220k red-red-yellow
( ) R102 220k red-red-yellow
( ) R106 220k red-red-yellow
( ) R25 2400 red-yellow-red
( ) R52 2400 red-yellow-red
listed below: 27k red-violet-orange
( ) R51 ( ) R62 ( ) R67 ( ) R72
listed below: 3300 orange-orange-red
( ) R26 ( ) R33 ( ) R49 ( ) R53
( ) R70 ( ) R99 ( ) R104
( ) R9 33k orange-orange-orange
( ) R85 33k orange-orange-orange
( ) R17 390k orange-white-yellow
( ) R41 390k orange-white-yellow
( ) R28 39k orange-white-orange
( ) R55 39k orange-white-orange
( ) R30 470k yellow-violet-yellow
listed below: 47k yellow-violet-orange
( ) R39 ( ) R69 ( ) R92 ( ) R105
( ) R2 56 green-blue-black
6 9720 VCO 010321
DESIGNATION VALUE COLOR CODE A-B-C
listed below: 5600 green-blue-red
( ) R36 ( ) R37 ( ) R64 ( ) R82
listed below: 56k green-blue-orange
( ) R20 ( ) R23 ( ) R44 ( ) R48
( ) R71 ( ) R93
( ) R29 750 violet-green-brown
( ) R98 82k grey-red-orange
( ) R101 82k grey-red-orange
listed below 91k white-brown-orange
( )R8 ( ) R59 ( ) R80 ( ) R103
1% FILM RESISTORS
The 1% metal film resistors are identified by their 5 color bands.
DESIGNATION VALUE COLOR CODE A-B-C-D
listed below: 100k 1% brown-black-black-orange
( ) R14 ( ) R16 ( ) R40 ( ) R42
Disk and Polystyrene Capacitors
Many of the capacitors used in the 9720 are nonpolarized
Ceramic Disk and Polystyrene types. For each of these,
either lead can go in either of the holes in the circuit board.
The leads of the Ceramic Disk capacitors are already parallel
to each other but still may need to be bent slightly to match
the spacing of the circuit board holes. The leads of the
Polystyrene capacitors will need to bend down prior to installation
and may be further apart than the spacing of the circuit board holes.
Like the resistors, insert the leads of these parts through the holes
in the board and push the part against the circuit board as far as
it wants to go. Don't force it, it's OK if it sits a little off the board.
Capacitors are often marked with obscure codes that
indicate their values. The 3 digit number that specifies
value may be preceded or followed by letters indicating
such things as tolerance. If you get confused about
which capacitors are which, it may help to group them
by same type and check them against quantities on the
packing list at the end of this manual.
1% Resistors have
5 color bands
9720 VCO 7
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Ceramic Disk Capacitors
DESIGNATION VALUE MARKING
( ) C13 0.001uF 102
( ) C17 0.001uF 102
listed below: 0.01uF 103
( ) C3 ( ) C5 ( ) C9 ( ) C15
( ) C20 ( ) C23
listed below: 15pF 15
( ) C7 ( ) C8 ( ) C10 ( ) C14
( ) C18 ( ) C19 ( ) C21
Polystyrene Capacitors
DESIGNATION VALUE MARKING
( ) C11 4700pF 4700J
( ) C16 4700pF 4700J
Electrolytic Capacitors
The remaining capacitors are electrolytic types.
Unlike the previous components, electrolytic
capacitors are polarized and the leads are not
interchangeable. Leads are marked "+" and/or "-"
and the "+" lead must go through the "+" hole in the
circuit board. Frequently the positive lead of the
capacitor is significantly longer than the negative lead.
Usually the Negative lead of the capacitor is marked rather
than the positive. It naturally goes through the unmarked hole.
Capacitors supplied with specific kits may have a higher
Voltage (V) rating than the minimum specified below.
DESIGNATION VALUE
( ) C12 1uF / 15V.
( ) C22 1uF / 15V.
( ) C1 470uF / 25V.
( ) C2 470uF / 25V.
( ) C4 4.7uF / 15V
( ) C6 4.7uF / 15V
Capacitors
Disk Polystyrene
8 9720 VCO 010321
Diodes
Like the Electrolytic Capacitors, diodes are polarized
and must be installed so that the lead on the banded
end of the part corresponds to the banded end of the
designator on the circuit board. Bend the leads so they
are at right angles to the body of the part and insert
them through the holes provided in the circuit board.
Diodes are also somewhat heat sensitive so the
soldering operation should be done as quickly as possible.
DESIGNATION TYPE
listed below: 1N4148 Silicon Diode
( ) D1 ( ) D2 ( ) D3 ( ) D4
( ) D5 ( ) D6 ( ) D7 ( ) D8
( ) D9 ( ) D10 ( ) D11 ( ) D12
( ) D13 ( ) D14 ( ) D15 ( ) D16
( ) D17 ( ) D18
Transistors
Install the transistors by inserting their three leads
through the holes provided for them in the circuit board.
Note that the transistors are polarized by the flat side
of the case. When the transistors are properly
installed this flat will align with the corresponding mark
on the circuit board legending.
Four of the transistors are supplied as pairs that have been
specially selected to have matching characteristics and will
be packed together. Keeping these pairs together is important
for optimum circuit performance.
Notice that two different types of transistors (2N3904 and 2N3906)
are used. The type will be written on the body of the part.
DESIGNATION TYPE
listed below: 2N3906 PNP Silicon Transistor
( ) Q2/Q3 ( ) Q8/Q9 matched pairs
( ) Q1 not matched
( ) Q4 not matched
listed below: 2N3904 NPN Si Transistors not matched
( ) Q5 ( ) Q6 ( ) Q7 ( ) Q10
The straight line of the pc
graphic symbol corresponds
to the flat face of the
transistor case.
Note flat
Note diode
polarity band
9720 VCO 9
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Trimmer Potentiometers
Mount the four trimmer potentiometers by inserting their
three pins into the holes provided. Press them down
until the "shoulders" of the solder pins are resting
on the surface of the circuit board. Solder all three pins on
each part.
DESIGNATION VALUE MARKING
( ) R5 10k Trimmer
( ) R87 10k Trimmer
( ) R27 1k Trimmer
( ) R58 1k Trimmer
Integrated Circuits
Of all the parts, the ICs are the most easily damaged
and should be treated with some respect. In particular,
they may be destroyed by discharges of static electricity.
Modern ICs are not nearly as sensitive to this kind
of damage as were earlier versions, but it is still good
practice to handle these parts as little as possible.
Also good practice: don't wear nylon during assembly.
Don't shuffle around on the carpet immediately before
assembly (or if you do, touch a lamp or something to
make sure you're discharged). Don't be intimidated.
It's rare for parts to be damaged this way.
ICs are polarized in one or both of two ways; A dot
formed into the case of the IC corresponding to pin 1
or a semicircular notch that indicates the end of the
package with pin 1. Take care that this polarizing
indicator corresponds to the similar indicator on the
circuit board graphics.
The pins of the ICs may be splayed somewhat and not
match the holes in the circuit board exactly. Carefully
re-form the leads if necessary so that they are at right
angles to the part.
Solder each IC in place as it is installed by initially
soldering two pins in diagonal corners of the
pattern. Make sure that the part is seated firmly
against the circuit board by pressing it down while re-
melting the solder joint at first one corner, then
the other. Finally, solder the remaining
connections.
CAUTION: Too much solder
here may flow through and
cause problems
Note
p
in 1
10 9720 VCO 010321
DESIGNATION PART NO. DESCRIPTION
( ) IC4 LM13700 Dual Operational Transconductance Amp
( ) IC5 LM13700 Dual OTA
( ) IC3 TL084 Quad J-FET OpAmp
( ) IC7 TL084 Quad J-FET OpAmp
( ) IC8 LM324 Quad OpAmp
( ) IC6 LM339 Quad Comparator
Voltage Regulators
The voltage regulators are polarized and
must be mounted so that their tabs correspond to
the tab markings on the circuit board graphics.
Solder all three leads and clip any excess off
flush with the solder joint.
( ) IC1 7912 -12V Voltage Regulator
( ) IC2 7812 +12V Voltage Regulator
LEDs
LEDs are polarized by the flat in the collar at the base
of part. When properly installed, this flat will align with
the corresponding flat in the LED symbol printed on
the circuit board.
When the 9730 is installed behind its front panel, the
LED will engage the holes in the front panel
and be supported by its leads.
Cut a 1/2" length of the small diameter sleeving supplied
over the lead opposite the polarizing flat. Push the
two leads through the holes in the circuit board; if the sleeving
is too long to allow soldering trim it slightly. When satisfied
with the spacer length, confirm the orientation of the LED
and solder both leads. Trim the longer lead off flush with
the solder joint - the shorter lead may need no trimming.
DESIGNATION TYPE
( ) LED1 Red LED
LM13700
16 pins
LM339
TL084
LM324
14 pins
Use 1/2" length of the
small diameter sleeving
as a spacer and
insulator on the LED.
Note Tab
1/2"
sleeving
Flat
9720 VCO 11
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"Flying" Wires
(i.e. those which go from circuit board to panel mounted parts.)
In the following steps, wires will be soldered to the 9720 board
which in later steps will be connected to the front panel controls
and switches. At each step, cut a piece of wire to the specified
length and strip 1/4" of insulation from each end. Twist the
exposed wire strands together and "tin" them by melting a small
amount of solder into the strands. This will make soldering easier
when the wires are installed and prevents fraying
of the wire strands when they are pushed through
the holes. Solder each connection as it is made
and clip any excess wire from the solder side
of the board.
PC POINT WIRE LENGTH PC POINT WIRE LENGTH
( ) "A" 7-1/4" ( ) "B" 7-3/4"
( ) "C" 7-1/2" ( ) "D" 7-1/2"
( ) "E" 7" ( ) "F" 7"
( ) "H" 6-1/4" ( ) "I" 6"
( ) "J" 6" ( ) "K" 7-3/4"
( ) "L" 7-1/4 ( ) "M" 7-1/4"
( ) "N" 7-1/4" ( ) "O" 8"
( ) "P" 8" ( ) "R" 7"
( ) "S" 8" ( ) "T" 6-1/2"
( ) "U" 6-1/4" ( ) "V" 6-1/4"
( ) "W" 7" ( ) "X" 6"
( ) "Y" 5-3/4" ( ) "Z" 5-3/4"
( ) "AA" 6" ( ) "AB" 6-3/4"
( ) "AC" 5" ( ) "AD" 7-3/4"
( ) "AE" 7-1/2" ( ) "AF" 8"
This completes assembly of the 9720 circuit board. Admire your work for a few minutes
then take a break. When you come back, admire your work again but this time be critical. It
would be a good time to double check the orientation of polarized parts and that the right
resistors and capacitors are in the right places. Examine the solder joints. On the component
side make sure excess solder has not flowed though the hole. On the solder side, are they all
nice and shiny? If they have the "lumpy" granular look that indicates a cold joint, reheat them.
Solder bridges are less likely with a solder masked circuit board but they can still happen. If
you're not sure about a bridge refer to the foil patterns in fig 1.
Front Panel Controls
Now we will put the circuit board aside temporarily and mount the
controls, switches and jacks on the front panel. If you have the optional
panel available from PAiA, you will be installing these parts at the
locations shown in fig 2.
Note:Note:
Note:Note:
Note: If you also have the
9720frm FracRak
Accessory kit do not use
the wire from that kit in
these steps. 9720frm
wires are already cut to
length for use with the
power connector.
Be very careful not to nick wire
strands while stripping
insulation. An inexpensive wire
stripper is a good tool to have
here. When soldering the wire
to the board do not allow the
insulation to slip through the
hole - make sure you are
soldering to wire.
12 9720 VCO 010321
( ) Using the nuts supplied with them, mount the eighteen
1/8" Closed Circuit Phone Jacks as shown in fig 2.
Note that while both Mono and Closed Circuit Jacks are
shown in the schematic (Fig 7), CC jacks are used for
both types. Orient the jacks as shown in fig 3 before fully
tightening the nuts to secure them.
It will be easier to do the ground wiring of J11-J18 before the rest
of the panel controls are mounted.
( ) Cut a 4-1/4" length of the bare wire supplied and pass it through
the holes in the "S" lugs of J11 and J17 (lift these two lugs away
from the panel and twist them so the wire can pass through).
Lift the "S" lug of J18 and connect the end of the wire extending
beyond J17 to J-18 lug S.
At this point there should be a stub of wire about 3/4" long extending
beyond the "S" lug of J11 which will be connected in later steps.
( ) Solder the connections between the wire and J11 and J17
before connecting the "S" lugs of J12-J16 to the wire by bending
them up until they touch the wire then soldering the two
together. DO NOT SOLDER the connection at J18.
( ) Using the flat washers and nuts supplied, mount
the seven potentiometers to the panel as shown
in fig 2. Note that four different values are used so be
careful that the correct value is placed in the correct
location. Value is stamped or printed on the body
of the part. Orient the pots with the solder lugs as
shown in fig 3 and fully tighten the nuts to secure them.
A tip: marking the part number (e.g. R200) on the back
of the pots with an indelible pen will make later wiring
easier and less prone to error.
( ) Using the nuts supplied with them, mount the two
miniature toggle switches as shown in fig 2.
Orient the switches as shown in fig 3 and fully
tighten the nut to secure it. The switch is
symmetrical so whichever soldering lug
is on the left or up is #1.
Bend or remove this tab s
o
against the front panel.
that the pot will seat flush
SPDT switches may
be supplied even
though only SPST
are required.
S
X
T
T
S
X
Closed Circuit Jacks
have 3 lugs
2
2
3
1
13
9720 VCO 13
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Now we’ll continue wiring of the front panel parts as shown in fig 3. First,
notice that individual solder lugs are identified by part number and lug number.
For example, R200-1 means the lug labeled “1” of the Potentiometer R200.
Also, this convention will be followed in these steps: Do not solder a connec-
tion to a lug until told to do so with an instruction such as (s2), which means
that at that point there will be two wires on the lug in question. If there are not
the number of wires specified at the lug when you get ready to solder, recheck
to see what has gone wrong. Connections which should not be soldered yet
will be marked (ns) for NO SOLDER. On these unsoldered connections simply
push the end of the wire through the lug and crimp it back to mechanically
secure it.
( ) Connect the free end of the solid wire extending beyond J11-S to
R203-1 (ns).
( ) Cut a 3-3/4" length of bare wire and pass it through the holes
in the "S" lugs of J1 and J9. DO NOT SOLDER these two
connections. Bend the "S" lugs of J2-J8 up to meet the wire
and solder these seven connections.
In the following steps cut a piece of bare wire to the length indicated and
use it to connect the component lugs specified. Route the wires as shown
in Fig 3 and push them down close to the front panel so they will not short
against the lugs of switches and jacks and future wiring. The "clipping"
length means that a resistor or capacitor lead clipped earlier should be used.
LENGTH FROM TO
( ) clipping R201-2 (s1) R201-3 (ns)
( ) clipping R200-2 (s1) R200-3 (ns)
( ) clipping R205-2 (s1) R205-3 (ns)
( ) 3-1/4" S2-1 (s1) R204-1 (ns)
( ) 2" R204-1 (ns) R202-1 (ns)
( ) 3/4" R206-1 (ns) J10-S (ns)
( ) 3/4" J7-X (ns) S1-2 (ns)
Many point-to-point panel connections are made using the
14 9720 VCO 010321
insulated stranded wire. For each of these cut piece of wire
to the length specified, strip 1/4" of insulation from each end
and twist and tin the exposed strands. Proceed by columns.
LENGTH FROM TO LENGTH FROM TO
( ) 4" R203-1 (ns) J1-S (ns) ( ) 3-3/4" R203-3 (s1) R204-3 (s2)
( ) 2" R204-3 (ns) R206-3 (ns) ( ) 1-3/4" R204-1 (s3) R206-1 (s2)
( ) 1-1/2" J18-T (s1) R202-2 (ns) ( ) 4" R202-2 (s2) J10-X (s1)
( ) 1-1/2" J9-S (s2) S1-2 (s2) ( ) 1-3/4" J18-S (s2) R202-1 (s2)
( ) 2-1/2" J7-X (s2) J4-X (s1)
The resistors and capacitor not used during circuit board assembly
will now mount directly on the lugs of panel parts (see fig 3).
( ) Cut the leads of the remaining 100k ohm 1% resistor
(brown-blk-blk-orange) to a length of 1/2". Connect one lead
to J1-S (s3) and the other to J1-T (ns). This is R209.
( ) Cut the leads of the .001uF ceramic disk capacitor (marked 102)
to a length of 3/8". Connect one lead to J8-T (s1) and the other
to J9-T (ns). This is C24.
( ) Locate the 750 ohm 5% resistor (violet-green-brown).
Cut two 5/8" lengths of the small sleeving supplied and
slip one over each resistor lead. Trim the leads so that
1/4" extends beyond the sleeving. Use this part as R207
to make the connection from R200-1 (s1) to R201-1 (ns).
( ) Similarly insulate the leads of the 39k ohm 5% resistor
(orange-white-orange). Use this part as R208
to make the connection from J3-X (s1) to J10-S (s2).
This completes the wiring between parts on the front panel.
Before going further, make sure that the bare wire is dressed
down against the panel and not in danger of shorting to unintended
solder lugs. Dress the insulated wires down also - they need not be
close to the panel but should not loop out away from the assembly.
A few connections will be made between the circuit board and
front panel before the two are fastened together. These connections
will be close to components on the circuit board when it is attached
to the panel so sections of clear tubing are used for insulating
sleeves. Cut a 3/8" long piece of large tubing from the length supplied
and slip it over the wire before making the connection. When the solder
joint has cooled, slide the tubing down over the lug (see fig 4).
FROM TO FROM TO
T
T
Slide tubing
over wire
Then over
connection
9720 VCO 15
010321
( ) "W" J11-T (s1) ( ) "F" J15-T (s1)
( ) "V" J12-T (s1) ( ) "S" J16-T (s1)
( ) "AB" J13-T (s1) ( ) "D" J17-T (s1)
( ) "L" J14-T (s1)
Now it's time to use the #4 hardware and "L" brackets to attach the
front panel to the circuit board. Before beginning, take a good look
at the "L" Brackets and note that one of the holes is threaded and
the other is not.
( ) Attach the "L" brackets to the circuit board using two
4-40 X 1/4" Machine Screws through the board from the
solder side and then through the unthreaded holes in
the "L" brackets. Secure each with a #4 nut. Some
adjustment will be required when the panel is attached,
so do not fully tighten the screws.
( ) Bend the LED over so that it engages the hole provided
for it in the front panel as shown in fig 2. Attach the circuit
board to the front panel by passing 4-40 X 1/4" Machine
Screws through the panel from the front and into the
threaded hole in the "L" brackets. When satisfied with
the alignment of panel, LED and circuit board, fully
tighten the hardware.
Finish panel assembly by connecting the remaining wires from
the circuit board to the jacks and controls on the front panel.
Solder as indicated. (See Fig 4)
FROM TO FROM TO
( ) "B" J7-T (s1) ( ) "C" R203-1 (s3)
( ) "I" R203-2 (s1) ( ) "K" R201-3 (s2)
( ) "M" R200-3 (s2) ( ) "N" S1-1 (s1)
( ) "AA" R206-2 (s1) ( ) "AD" R202-3 (s1)
See Fig 5 for an illustration of the rest of the wiring:
( ) "R" R204-2 (s1) ( ) "H" J2-T (s1)
( ) "A" R206-3 (s2) ( ) "U" J3-T (s1)
( ) "AC" S2-2 (s1) ( ) "E" J4-T (s1)
( ) "AE" R201-1 (s2) ( ) "P" J5-T (s1)
( ) "J" R205-1 (s1) ( ) "O" J6-T (s1)
( ) "Y" R205-3 (s2) ( ) "AF" J9-T (s2)
( ) "T" J10-T (s1) ( ) "X" J5-X (s1)
( ) "Z" J1-T (s2)
POWER CABLE AND CONNECTOR
16 9720 VCO 010321
If you have the 9720frm accessory kit, locate the power connector
housing and pins. You will be connecting wires to the pins and
will need to be able to hold the pin steady while soldering. Using an
old-fashioned wooden clothes pin as a vise is a good choice, but try to
find one these days. A pair of needle-nose pliers with a rubber band
around the handle to hold the jaws closed works but too heavy a rubber
band can apply too much pressure and crush the pin.
Proceed with assembly of the power connector as follows:
( ) Prepare the four 16" lengths of stranded insulated wire
supplied with the 9720frm kit by stripping 1/4" of insulation
from one end of each wire only. Twist and tin the exposed
wire strands then clip off the tinned end so that a 1/8" stub
remains.
( ) Solder one of the power connector pins to the end of each
wire. Steady the pin as discussed above and lay the tinned
end of the wire in the "trough" of the pin as shown in the
illustration. Solder the connection by holding the soldering
iron against the wire and pin until the solder remelts. You
should not need to add more solder. Allow the joint to cool
and test it by wiggling the wire to make sure the joint is firm.
Do not wrap the "wings" of the pin around the wire.
( ) Slide the power pins into the connector body. Note the
orientation of the pin as shown in the illustration. Slide
the pin in until the catch on the back of the pin engages
the slot in the connector body and you feel the "snap" as
it locks in place. Give the wire another good tug to test
the solder joint and that the pin is latched in place.
If the wire comes loose, don't panic. The pins can be released from
the connector by using a knife blade or small tool to reach through
the slots in the connector body to press down the catch.
( ) Prepare the free ends of the wires by stripping 1/4" of
insulation from the end and twisting the exposed wire
strands tightly. Do not tin these wires. Push each wire
though the "+", "G", "SG" and "-" holes in the board as
shown in the illustration (note the polarizing tabs on the
connector body) and check to make sure there are no
stray wire strands that did not make it through the hole
before soldering in place. Clip off any excess on the solder
side of the board.
Use the 3 nylon wire ties to group the four wires together by placing
16"
9730 VCF
polarizing tabs
press catch here
to remove pin
heat to remelt
solder
97xx Module
9720 VCO 17
010321
one in the middle and the other two halfway to either end. Cinch
the ties tight and clip off the excess.
( ) Locate the power connector header and install it in the
appropriate location on the FracRak format power
supply you will be using. Note the orientation of the
locking tab shown in the illustration. Push the 4 pins
through the board but solder one pin only. Examine the
header to see that it is seated flush on the board and if not,
remelt the single joint and push the connector fully into place.
When satisfied, solder the remaining three pins.
( ) Turn the control shafts of all the potentiometers fully counter
clockwise and mount each knob in turn by placing it on the
shaft and aligning the pointer with CCW end of the panel
graphic. Tighten the set screw slightly and rotate the control
back and forth to see that its range of rotation is centered
with respect to the panel graphic. Loosen the screw and
realign the knob as needed and fully tighten when done.
The moment of truth is at hand, the next step will be to power up the module and start testing.
This is an excellent time to take another break, stretch and think about something else for a
while. When you come back take the time to do a final check. The flying wires to the panel
aren't bundled with wire ties yet, and we'll leave them that way for now, so move them around a
little to check the connections. Inspect the wiring on the panel and make sure none of the bare
wire used as the panel ground is in danger of shorting against other connections. One more
pass of inspecting the board for component polarity and quality of solder joints is a good idea
too.
TESTING
Set Scale A and B trimmers (R27,R58) to the midpoint
of their rotation, corresponding to a 1V/oct scale. Also
set Sym A and B (R87,R5) trimmers midscale. Make
sure the power supply is turned off and mate the
power connectors.
1) Set the 9720 knobs and switch as shown and turn on
power. First observe the POWER light on the power
supply and if it doesn't come on stop and find out why.
It may be just a dead outlet or some more serious
problem such as a solder bridge on the 9720 board.
If the power supply light comes on when the 9720 is
disconnected, it's a sure sign of a problem on the 9720
board. The most likely area for this problem is in the
area around the power connector, R1, R2, C1, C2 and
the voltage regulators IC1 and IC2.
2) Check the modulator light on the 9720 front panel. It
locking tab
FracRak format
power supply
(9770, midi2cv8, etc.)
18 9720 VCO 010321
should be lit, but not very brightly. If the LED is dark or
seems fairly bright, quickly feel around on the circuit
board to see if any parts are hot or very warm. If you
find any, disconnect the power and carefully
examine the circuitry around the hot part looking for
solder bridges, backward capacitors or other polarized
parts. If nothing seemed warm but the LED is dark and
the panel switch is set to "Cycle" it may be a problem in
the Modulator circuit. Carefully check the modulator
parts (Q4-Q6, IC8, panel controls R200-R202 and
associated components). Check the LED, it may be
in backwards or may be bad. It's human to suspect bad
ICs but most problems relate to the mechanics of
assembly - the wrong part in the wrong place or facing
the wrong way or not soldered well.
3) Rotate the Modulation Attack control to the midpoint of its rotation. The LED should now
increase in intensity over a 2 second period then suddenly go dark and repeat the cycle. Turn
the Modulation Release control to about the midpoint of its rotation and observe that the LED
slowly brightens and slowly dims with about a 5 second period. If that goes well, crank both
Attack and Release controls full ClockWise and observe that the period is about 15 seconds. If
there are problems here, check the modulator components outlined in step 2, paying particular
attention to correct values. If cycle times are significantly different (half or twice more, for
instance) it may indicate an incorrect component value or power supply lines that are out of
spec - check for hot parts among the power supply components mentioned in step 1, and if a
Volt Meter is available check the regulated supply lines - IC3 pins 4 (+12V) and 11
(-12V) are handy places.
4) Listen to the Ramp outputs ( ) of OscA and OscB in turn. Each should be about 120 Hz
and of equal amplitude. If you have a Volt meter handy, use it to measure the voltages on
these outputs. Both outputs should be about the same and when the meter is set to read DC
you should measure 200mVolt (0.2V) or less. With the meter set to AC you should read 1.25V.
If no meter is available do not be concerned with these measurements unless there are
problems in future steps.
While listening to OscA's ramp output, rotate the Pitch control fully CounterClockWise and
observe that the pitch falls by about 3 octaves to 15 Hz. or so. Do the same with OscB. Be
sure to return both Pitch controls to max (fully ClockWise) for future tests.
Problems here can come from a lot of different sources. If there is no audible output from OscA
check IC7:A & :B and IC6:D, Q10 and associated components. Corresponding parts in OscB
are IC3:A &:B IC6:A and Q7. If there is output but it's very high or low frequency or doesn't
change as described above it may be CV summing/current sources. For OscA these comprise
IC4, Q2, Q3 and associated components. If OscB is not functioning properly IC5, Q8, Q9 and
components associated with them should be examined. These ramp outputs must be working
before any of the others will work properly.
9720 VCO 19
010321
5) Listen to the Pulse output ( ) of each
oscillator. They should be the same pitch as
the Ramp outputs and approximately as loud.
The two Pulse outputs will probably be set to
different pulse widths so timbres may not be
identical. OscA Pulse problems point to
IC6:C and the resistors associated with it.
The OscB Pulse output is shaped by IC6:B
and it's associated parts.
While listening to the OscB Pulse output rotate
the Pulse Width control from fully CCW to fully
CW and observe the characteristic "flanging"
timbre of varying duty factors. Check the wiring
of R206 if there is no change or if the output
goes quiet at either end of the control rotation.
Set the Pulse Width control to the CCW limit and adjust the Modulator's Attack and Decay
control so the output LED shows a cycle time of a second or so. While listening to OscB pulse
output increase Modulator output level and observe PWM effect. Observe that rotation of the
Modulator Output control CW beyond the 3 o'clock cause the output to be silent for a part of
each Modulator cycle.
Use a Patch cord to connect the Modulator out to OscA PW input and listen to observe PWM
effect. Notice that the output is silent for a part of each cycle when the Output control is CW
beyond the 12 o'clock position. Problems with these tests of the Pulse outputs will likely trace
to resistor value or soldering problems in the components associated with the Pulse Width
shapers.
Switch OscA to LFO and observe 50 Hz at Pitch max decreasing to less than a cycle/minute at
min. Problems here focus on wiring of S2.
6) Listen to Triangle outputs ( ). Adjust sym A (R87) and sym B (R5) for most mellow tone
which should happen about mid range. If there is no "most mellow" point between the ex-
tremes of the trimmer's rotations check A- IC8:B B-IC3:C
7) Listen to the Sine output of OscA ( ) for a mellow sine sound. If not check IC8:A and
polarity of diodes D11-D13,D17,D18.
We're now ready to calibrate the oscillators so that a 1V change in Control Voltage produces a
1 octave change in pitch. The calibration procedure is written as if no equipment such as
Oscilloscope, Frequency Counter or digital voltmeter is available. If you have this kind of
equipment it may be used and there are some tips and pointers at http://paia.com/
9720test.htm. But the results produced using this equipment will be no more accurate the
equipment-free procedure that follows.
20 9720 VCO 010321
During calibration one
oscillator will be used as a
fixed reference while the
other oscillator is adjusted.
Use the Triangle outputs
( ) of OscA and OscB
and arrange for both
to be heard at the same
time at approximately equal
amplitudes. If a PAiA 9710
Triple VCA is available it's
L and R inputs can be used
to mix the two to a single
output. Lacking a mixer, the
L and R inputs of a Stereo Amp switched to Mono can be used as shown in the illustration.
8) Begin calibration with OscA. Apply a 1V/octave controller, such as a midi2cv8, to the P2
input of OscA and cause the controller to output 4V (typically by pressing the 5th C on a
keyboard). Adjust OscA Pitch control until the pitch of OscA is 2 octaves above that of OscB.
Cause the controller to output 0V (typically by pressing lowest C) and adjust Scale A trimmer
(R27) until the pitch of OscA is 2 octaves below the reference.
Once again cause the controller to output 4V and again adjust OscA Pitch for 2 octaves above
reference, then 0V again while adjusting Scale A for 2 octaves below the reference.
Iterate the above procedure until satisfied with both the high and low end.
OscB is calibrated in the same manner. Disconnect the controller from OscA P2 and reconnect
to OscB P2 as shown in grey in the illustration. With 4V. output from the controller adjust OscB
pitch for 2 octaves above OscA then with 0V output adjust Scale B trimmer (R52) for a pitch 2
octaves below OscA. Iterate this procedure until satisfied with the tuning at high and low end.
Disconnect the controller from OscB P2 input and reconnect to OscA P1 so that both Oscilla-
tors track the controller and observe tracking as pitch CV varies. Some further tweaking of the
calibration of one or both VCOs may be necessary for best tracking. It's unlikely that the VCOs
will pass previous tests and then not calibrate properly. If it happens, most likely cause will be
a resistor with an incorrect value. Double check values of resistors associated with the CV
summing/current sources as outlined in step 4.
9) Test OscA Sync input by reconnecting the controller to OscA P2 input and using a patch
cord to connect OscB Pulse output to OscA Sync as shown on the facing page. Set both Pitch
and Pulse Width controls of OscB fully CW. While listening to the Sine output of OscA only,
press the 3rd C on the controller for a 2V. CV output. As you rotate the OscA Pitch control you
should hear the output switch between a number of timbres that are considerably more
complex than a simple sine wave. As pitch is varied by playing up and down scale notes on the
controller the timbre should stay the same. If there are problems here check the wiring of J4
and C17 and R9 on the circuit board.
(10) Switch the Modulator from Cycle to
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