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6
921 VOLTAGE CONTROLLED OSCILLATOR
921 VOLTAGE CONTROLLED OSCILLATOR Controls
Controls
(EN)
1
3
2
4
5
6
9
7
8
10
12
11
13
1.
FREQUENCY – Use this knob to set the oscillator frequency. The frequency
settings for this knob are controlled by the COARSE RNG and SCALE toggle
switches, as well as the RANGE rotary switch.
2.
RANGE – This knob sets the general frequency range of the oscillator
in one-octave steps, which can then be adjusted up or down with the
FREQUENCY knob.
3.
SCALE – This switch controls whether the frequency knob scale is
±6 octaves or ±12 semitones, which gives finer frequency control.
Power Connection
P1
Red Stripe
2
1
10
9
200 mm ± 10
Connect end P1 to the module socket
Connect end P2 to the power supply
The 921 VOLTAGE CONTROLLED OSCILLATOR module comes with the required
power cable for connecting to a standard Eurorack power supply system.
Follow these steps to connect power to the module. It is easier to make these
connections before the module has been mounted into a rack case.
4.
COARSE RNG – This switch controls whether the oscillator frequency
functions in the audio range or in a lower frequency range that extends
below the audio threshold.
RECTANGULAR WIDTH – Use this knob to set a default width for the
5.
rectangular waveform. The width can then be further controlled and varied
by control voltages routed in via the CNTRL IN jacks.
CNTRL IN – These summed jacks allow control voltage and modulation
6.
signals for the rectangular waveform to be routed in via cables with 3.5 mm
TS connectors.
7.
CLAMPING POINT – Use this knob to set the point at which the oscillator
waveform resets.
8.
TRIG (V/S) – These jacks allow control signals for the clamping point to be
routed in via cables with 3.5 mm TS connectors. The clamping point can
be triggered with a V-Trig (voltage trigger) signal via the V jack, or a S-Trig
(switch trigger) signal via the S jack.
9.
AUX OUT WAVEFORM – Use this knob to select a waveform for the
auxiliary output signal, including sine, triangular, sawtooth, inverted
sawtooth, square and inverted square waveforms.
10. AUX OUT LEVEL – Use this knob to adjust the output level for the
AUXILIARY OUTPUT jacks.
11. AUXILIARY OUTPUTS – Use these jacks to route an auxiliary waveform
signal out of the module via cables with 3.5 mm TS connectors.
12. FREQUENCY CONTROL INPUTS – Use these summed jacks to route
control voltage and modulation signals into the oscillator via cables with
3.5 mm connectors.
13. WAVEFORM OUTPUTS – Use these jacks to route oscillator signals out of
the module via cables with 3.5 mm jacks. Four waveforms are available:
sine, triangular, sawtooth and rectangular.
P2
1
2
HOT USED
15
16
+ 12V
+ 12V
GROUND
GROUND
- 12V
- 12V
1.
Turn the power supply or rack case power off and disconnect the
power cable.
2.
Insert the 16-pin connector on the power cable into the socket on the
power supply or rack case. The connector has a tab that will align with the
gap in the socket, so it cannot be inserted incorrectly. If the power supply
does not have a keyed socket, be sure to orient pin 1 (-12 V) with the red
stripe on the cable.
Installation
The necessary screws are included with the module for mounting in a Eurorack
case. Connect the power cable before mounting.
Depending on the rack case, there may be a series of fixed holes spaced 2 HP
apart along the length of the case, or a track that allows individual threaded
plates to slide along the length of the case. The free-moving threaded plates
allow precise positioning of the module, but each plate should be positioned in
the approximate relation to the mounting holes in your module before attaching
the screws.
Tuning Procedure
This procedure tunes the 921 VOLTAGE CONTROLLED OSCILLATOR module's
"octave scaling" to an exact 1 V/oct. calibration to facilitate precise control.
1.
Power up the 921 module and allow it to warm up for a few minutes.
2.
Prepare the following control settings on the 921 module:
a. Set the SCALE toggle switch to the ±12 SEMI position.
b. Set the RANGE toggle switch to the AUDIO position.
c. Set the RANGE rotary switch to 2'.
d. Set the FREQUENCY control knob so that the sawtooth output is
exactly 640 Hz as measured with an accurate frequency meter.
e. Make sure none of the FREQUENCY CONTROL INPUTS jacks
are connected.
Note: All adjustment trimmers are accessible from the 921 module's underside.
Note the positions of the SCALE and HI ADJ multi-turn trimmers, and make sure
you have suitable tools to adjust the trimmers if required.
Quick Start Guide
3.
Insert the 10-pin connector into the socket on the back of the module. The
connector has a tab that will align with the socket for correct orientation.
4.
After both ends of the power cable have been securely attached, you may
mount the module in a case and turn on the power supply.
Hold the module against the Eurorack rails so that each of the mounting holes
are aligned with a threaded rail or threaded plate. Attach the screws part way
to start, which will allow small adjustments to the positioning while you get
them all aligned. After the final position has been established, tighten the
screws down.
3.
Fine-tune the 921 oscillator's low-frequency scaling via the following steps:
a. Apply exactly -2 V to a FREQUENCY CONTROL INPUTS input jack.
(A 921A module can be used to supply the -2 V or use a similar low-
impedance stable-voltage source.)
b. Trim the SCALE trimmer to set 160 Hz, then remove the -2 V input and
readjust the FREQUENCY knob to 640 Hz.
c. Repeat this cycle until both 160 Hz and 640 Hz are accurate to ±1 Hz
when the -2 V is plugged in and out of the FREQUENCY CONTROL
INPUTS jack.
4.
Fine-tune the 921 oscillator's high-frequency scaling via the
following steps:
a. With no FREQUENCY CONTROL INPUTS jack connected, check the
frequency is still set for 640 Hz output, then apply exactly +2 V to the
FREQUENCY CONTROL INPUTS input.
b. Trim the HI ADJ trimmer to set the 921 sawtooth output to exactly
2.560 kHz.
c. Re-check that 640 Hz is still correct when the +2 V input is removed.
d. Repeat as required.
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