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.

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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
p405.340.6300, f340.6378, or [email protected] .
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.

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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

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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

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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