Oberheim Two-Voice Instruction Manual

A BRIEF

INSTRUCTION MANUAL

for the

OBERHEIM TWO-VOICE SYNTHESIZER

prepared by
james michmerhuizen
director,
the boston school of electronic music

GETTING FAMILIAR WITH THE OBERHEIM TWO-VOICE SYNTHESIZER

1: The POWER SWITCH is at the top left of the cabinet.

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: The 2ND-VOICE SWITCH is at the left of the keyboard. When

the switch is off , voice module two will be gated when any
one key is pressed on the keyboard (but see also the
description of the VOLTAGE ASSIGNMENT SWTTCHES in the
mini-sequencer); when the switch is on , voice module two
will not be gated until a second key is depressed.

: The PORTAMENTO control, normally left fully counterclock-

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wise, introduces a lengthening pitch slide between different
notes on the keyboard as it is rotated to the right.

: The TRANSPOSE control switches the keyboard voltage one volt

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at a time through a range of three volts, resulting in one­octave transpositions of the two VCO's.

: The PITCH BEND control, normally centered, bends the key-

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board voltage up or down as it is rotated, producing a cor­responding pitch bend from the two oscillators.

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The MINI-SEQUENCER is described separately on a following page.
So are the VOICE MODULES; the controls of each module are iden­tical to those of the other, the only difference between them
being in the way they are controlled by the keyboard and
sequencer modules.

The OUTPUT MIXER consists of only three rotary pots and two
phone jacks. The Jack connections are shown in the diagram, and
the pots are:

: the OUTPUT LEVEL CONTROL for voice module one,

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7

: the OUTPUT LEVEL CONTROL for voice module two, and

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: the MASTER OUTPUT CONTROL for the synthesizer.

SETTING THE STAGE

Before connecting your Oberheim synthesizer to headphones or to
an amplifier, be sure that the master output control is fully

off (counterclockwise).

After making the external connection to headphones or ampli­fier, you may turn the synthesizer on. Locate the ASSIGNMENTS
switches in the minisequencer section, and be sure that they
are all down .

In each voice module, set the controls to the positions shown
on the following page by the asterisks; where there is no
asterisk use the position in the photograph itself.

You may now turn, if you want to, directly to the section
called "FIRST STEPS" and begin to explore the synthesizer. But
it would probably be better to spend just a few minutes reading
through the descriptions of the minisequencer and the voice
modules first.

On the other hand, it would be a mistake to try to memorize in
detail everything in the descriptions following; they contain
some important facts--usually in italics--and some less impor­tant but still useful information. Some of this will become
familiar to you simply from habit as you work with the synthe­sizer.

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THE MINI-

1. The CONTROL VOLTAGE PRESETS determine two different output
voltages at each of the sequencer's eight positions. Each num­bered position in this section of the panel has two independent
concentric rotary pots. The outside pot controls the SEQUENCE
OUTPUT ONE, and the inner pot determines SEQUENCE OUTPUT TWO.
An LED at each position is illuminated when that position is
active.

2. The VOLTAGE ASSIGNMENT SWITCHES determine the source and
destination of voltages from the sequencer and sample/hold. In

the module illustrated there are four switches. In the module
included with the 2-voice synthesizer there are three switches;
the description following applies to the three-switch version.

The first switch on the left selects the source of control
voltages and gates for VOICE MODULE ONE. In its lowest posi­tion, voice module one will be controlled by the keyboard only,
and will not be affected by either the sequencer output volt­ages or the sample/hold output voltages. In the center position
of this switch, voice module one will be gated by the CLOCK (#5
below) and its VCO's will be controlled by the output of the
SAMPLE/HOLD (#4 below). When the switch is in its highest posi­tion, voice module one will be gated by the CLOCK and its VCO's
will be controlled by SEQUENCE OUTPUT ONE.

SEQUENCER AND SAMPLE/HOLD.

The second switch performs the same selecting function for
VOICE MODULE TWO, except that in its uppermost position the
VCO's in voice module two will be controlled by SEQUENCE OUTPUT
TWO rather than sequence output one.

The third switch allows either KEYBOARD VOLTAGE ONE or KEYBOARD
VOLTAGE TWO to be added, respectively, to either SEQUENCE OUT­PUT ONE or SEQUENCER OUTPUT TWO. Thus one of the keyboard volt­age outputs may be used to transpose a sequence from one note
to another without affecting the pitches produced by the other
voltage in controlling the other voice module.

3. The SEQUENCE LENGTH switch is used to shorten a full eight­step sequence down to anywhere from seven steps to only one.
When this switch, for example, is set to "7", the sequencer
will count through positions 1-7 and then skip the 8th step,
starting over instead from position 1. This is useful in set­ting odd or asymmetrical rhythms.

4. The two rotary pots in this section of the panel determine
respectively the RANGE covered by the sample/hold output vol­tage, and the amount of LAG (low-frequency filtering) applied
to the sample/hold voltage. Turning the lag control to the
right produces, in other words, the same effect on pitches
being governed by the sample/hold, that the PORTAMENTO control
produces on pitches being governed by the keyboard.

5. This is the MASTER CLOCK that steps the sequencer and oper­ates the sample/hold. The rotary knob determines the frequency
of this clock--i.e. the stepping rate or tempo. The three-posi­tion switch turns the clock on and off; it can also be clicked
momentarily down to advance the sequencer one step or to cause
a new sample voltage to be taken.

A switch is incorporated into the clock tempo control, allowing
the knob to be pulled out from the panel. In this position, the
clock rate will be controlled by SEQUENCER OUTPUT TWO. This
voltage control of the clock frequency is also affected by the
third VOLTAGE ASSIGNMENT SWITCH: in its uppermost position (#2
above), the keyboard voltage is added to sequencer output two
and will therefore also determine the clock rate.

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THE VOICE MODULES

The panel controls on each module are identical. In the diagram
above they are grouped by similar functions for easy under­standing. The asterisks in sections la, 2a, 3, 4, 7, 8, and 10
are for use in the following section of the manual.

, 2a. These are the MANUAL TUNING CONTROLS for VCO 1 and

la
VCO 2 respectively. The lower flanged portion of each knob is
for coarse tuning, and the upper part of the knob is a vernier
fine tuner.

, 2b. The three-position switch selects one of three control

lb
signals, indicated on the panel, to be routed through the
rotary pot just above the switch. If this knob is rotated to
the right, the selected control voltage will affect the VCO

pulse width. If this knob is rotated to the left, the selected

control voltage will affect the VCO frequency. If the knob is
left in its vertical position (as in the photograph), the
selected control voltage will have no effect on the VCO at all.

, 2c. These are MANUAL PULSE WIDTH CONTROLS for the two

1c
oscillators. At vertical, as in the diagram, the pulse produced
in each cycle is exactly one-half as long as the cycle itself;

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