Behringer 921B OSCILLATOR User manual

V 1.0
Quick Start Guide
921B OSCILLATOR
Legendary Analog VCO Module
for Eurorack
Controls
(6)
(7)
(8)
(5)
(1)
(2)
(3)
(4)
(9)
(1) FREQUENCY – This knob manually adjusts the frequency
in semitones for the 921B oscillator circuit. This oscillator
can generate both audio and sub-audio frequencies for
control or audio.
(2) RANGE – This knob sets the general frequency range of
the oscillator in octaves, numbered to match pipe organ
notations, which can then be adjusted up or down by
semitones with the FREQUENCY knob.
(3) 921AB LINK FREQ – These parallel jacks accept frequency
control voltage signals from a 921A module via cables with
3.5 mm TS connectors. The parallel wiring of the jacks
also allows a control voltage signal to be sent through and
back out to drive additional 921B modules.
(4) 921AB LINK WIDTH – These parallel jacks accept 921A
control voltage signals for the rectangular wave width
parameter via cables with 3.5 mm TS connectors. The
parallel wiring of the jacks also allows a control voltage
signal to be sent through and back out to drive additional
921B modules.
NOTE: If the 921B input voltage exceeds the range of 0 to
+6 V, the excess voltage could result in the width being
0% or 100%, which means no waveform will be present
at the square wave output until the control voltage is
returned to the normal range. When using 921B with a
921A driver, the 921A’s WIDTH OF RECTANGULAR WAVE
knob can oset the control voltage output from 921A to
compensate. For example, when 921A’s WIDTH knob is set
to 50%, the 921A’s normal control voltage range into 921B
becomes -3 V to +3 V.
(5) SYNC WEAK/OFF/STRONG – Use this switch to set how
closely 921B follows the sync signal routed in via the SYNC
IN jack. If the SYNC IN input is not required, select the
center OFF switch position.
(6) SYNC IN – Use this jack to route an external sync
signal into the 921B module via cables with 3.5 mm TS
connectors. A sawtooth waveform is recommended to
produce the best sync results.
(7) AC MOD – Use this AC-coupled input jack to control
frequency modulation via a control signal.
(8) DC MOD – Use this DC-coupled input jack to control
frequency modulation via a control signal.
(9) 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.
Power Connection
The 921B 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.
1. Turn the power supply or rack case power o 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.
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.

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 xed 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.
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 nal position has been established, tighten the
screws down.
Tuning Procedure
This procedure tunes the 921B OSCILLATOR module’s
“octave scaling” to an exact 1 V/oct. calibration to facilitate
precise control.
1. Power up the 921B module and allow it to warm up for a
few minutes.
2. Prepare the following control settings on 921B:
a. Set the SYNC toggle switch to the center
OFF position.
b. Set the RANGE switch to 2’.
c. Set the FREQUENCY control knob to exactly 0
on the scale.
d. Make sure no 921AB LINK FREQ jacks are connected.
Note: All adjustment trimmers are accessible from the 921B
module’s underside. Note the positions of the FREQ ADJ, SCALE,
HI ADJ multi-turn trimmers and the OCT ADJ single-turn trimmer.
Make sure you have suitable tools to adjust the trimmers
if required.
3. Carry out an initial FREQUENCY control calibration by
adjusting the FREQ ADJ trimmer so that the 921B sawtooth
output shows exactly 640 Hz when checked with an
accurate frequency meter.
4. Fine-tune the 921B oscillator’s low-frequency scaling via
the following steps:
a. Make sure the FREQUENCY control knob remains at 0
on the scale during this procedure.
b. Apply exactly -2 V to a 921AB LINK FREQ input jack.
(A 921A module can be used to supply the -2 V or use
a similar low-impedance stable-voltage source.)
c. Trim the SCALE trimmer to set 160 Hz, then remove
the -2 V input and readjust the FREQ ADJ trimmer
to 640 Hz.
d. 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 921AB LINK FREQ input jack.
5. Fine-tune the 921B oscillator’s high-frequency scaling via
the following steps:
a. With no 921AB LINK FREQ jack connected, check the
frequency is still set for 640 Hz output, then apply
exactly +5 V to the 921AB LINK FREQ input.
b. Trim the HI ADJ trimmer to set the 921B sawtooth
output to exactly 20.48 kHz.
c. Re-check that 640 Hz is still correct when the +5 V
input is removed.
d. Repeat as required.
6. Make a nal ne-tune of the RANGE rotary switch scaling,
if required, via the following steps:
a. With no 921AB LINK FREQ jack connected, check the
frequency is still set to 640 Hz on the RANGE knob
2’ setting.
b. Set the RANGE switch to 32’ and adjust the OCT ADJ
trimmer for 40 Hz at the 921B sawtooth output.
c. Re-check to make sure that 2’ = 640 Hz and
adjust the FREQ ADJ trimmer if required.
d. Repeat as required.
Specications
LEGAL DISCLAIMER
Music Tribe accepts no liability for any loss which may be suered by any
person who relies either wholly or in part upon any description, photograph,
or statement contained herein. Technical specications, appearances and
other information are subject to change without notice. All trademarks are the
property of their respective owners. Midas, KlarkTeknik, Lab Gruppen, Lake,
Tannoy,Turbosound,TC Electronic, TC Helicon, Behringer, Bugera, Auratone
and Coolaudio are trademarks or registered trademarks of MusicTribe
Global Brands Ltd. © Music Tribe Global Brands Ltd. 2019 All rights reserved.
LIMITED WARRANTY
For the applicable warranty terms and conditions and additional information
regarding MusicTribe’s Limited Warranty, please see complete details online at
musictribe.com/warranty.
Signal Connections
Frequency control
link inputs
2 x 3.5 mm jacks, 1 V/oct.
Input Impedance 100 kΩ, unbalanced
Maximum input level -6 V to +6 V
Frequency range < 1 Hz to > 40 kHz
Rectangular width
link inputs
2 x 3.5 mm parellel jacks,
1 V/16%
Input Impedance 100 kΩ, unbalanced
Maximum input level 0 V to +6 V
Width range < 10% to > 90%
Sync input 1 x 3.5 mm jack, AC coupled
Sync input impedance 1.5 kΩ, unbalanced
Sync input lock range ± 6 semitones
Sync input response 10 Hz to 20 kHz, > -10 dBu
Maximum input level +15 dBu
AC / DC mod input 2 x 3.5 mm jacks,
AC/DC coupled
AC / DC mod
input impedance 100 kΩ, unbalanced
AC / DC mod response 10 Hz to 10 kHz, > -10 dBu
Maximum input level +4 dBu
Waveform outputs 4 x 3.5 mm jacks, mono
Waveforms Sine, triangular,
sawtooth, rectangular
Output Impedance < 800 Ω, unbalanced
Output level Typically -4 dBu
Controls
Frequency 1 x rotary knob
±12 semitone, selectable
Range 1 x rotary switch
LO / 32' / 16' / 8' / 4' / 2',
selectable
Sync selector 1 x 3-position toggle switch
Weak / o /
strong, selectable
Power
Power supply Eurorack
Current draw 45 mA (+12 V),
45 mA (-12 V)
Physical
Dimensions 58 x 40 x 129 mm
(2.3 x 1.6 x 5.1")
Rack units 8 HP
Weight 0.14 kg (0.31 lbs)
2 3Quick Start Guide921B OSCILLATOR

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