Behringer 921 Quick Start Guide
Quick Start Guide
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921 VOLTAGE
CONTROLLED OSCILLATOR
Legendary Analog VCO Module
for Eurorack
Controls
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(6 ) CNTRL IN – T hese summed jack s allow control volt age and
modulati on signals for the re ctangular wavef orm to be
routed in v ia cables with 3.5 mm T S connectors.
(7 ) CLA MPING POINT – Use this knob t o set the point at whic h
the oscillator waveform resets.
(8 ) TRIG (V/S) – Thes e jacks allow cont rol signals for the
clamping p oint to be routed in vi a cables with
3.5 mm TS conne ctors. The clam ping point can be tr iggered
with a V-Trig (voltage t rigger) signal via th e
V jack, or a S -Trig (switch tr igger) signal via the S j ack.
(9 ) AUX OUT WAVEFOR M – Use this knob to sele ct a waveform
for the auxiliary output signal, including sine, triangular,
sawtooth, inverted sawtooth, square and inverted
square waveforms.
(10) AUX OUT LEVEL – Use t his knob to adjust th e output level
for the AUXILIARY OUTPUT jacks.
(11) AUXILIARY OUTPUTS – Use th ese jacks to rout e an auxiliary
wavefor m signal out of the modu le via cables with 3. 5 mm
TS connectors.
(12 ) FREQUENCY CONTROL INPUTS – Use these s ummed jacks
to route con trol voltage and mo dulation signals in to the
oscillat or via cables with 3. 5 mm connectors .
(13 ) WAVEFORM OUTPUTS – Use these jack s to route oscillato r
signals ou t of the module via cab les with
3.5 mm jack s. Four waveforms a re available: sine, tri angular,
sawtooth and rectangular.
Power Connection
(1) FREQUENCY – Use this k nob to set the osci llator frequenc y.
The freq uency setti ngs for this knob are c ontrolled by the
COARSE RNG and SC ALE toggle switc hes, as well as the
RANGE rot ary switch.
(2 ) RAN GE – This knob sets th e general frequ ency range of the
oscillat or in one-oct ave steps, which can t hen be adjusted
up or down wi th the FREQUENCY kn ob.
(3 ) SC ALE – This switch cont rols whether the f requency knob
scale is ±6 o ctaves or ±12 semitones, whic h gives ner
frequency control.
(4 ) COARSE RN G – This switch contr ols whether the os cillator
freque ncy functio ns in the audio range o r in a lower
freque ncy range that ex tends below the au dio threshold.
(5 ) RECTANGULAR WIDTH – U se this knob to set a de fault
width fo r the rectangul ar waveform. The wid th can then be
furt her controlled and v aried by control vo ltages routed in
via the CNTR L IN jacks.
The 921 VOLTAGE CONTROLLED OSCILL ATOR module comes with t he
require d power cable for con necting to a sta ndard Eurorack pow er
supply sy stem. Follow thes e steps to connec t power to the module.
It is easier to m ake these connec tions before th e module has been
mounted in to a rack case.
1. Turn the power supp ly or rack case power o and disconnec t
the power c able.
2. Ins ert the 16-pin conn ector on the power c able into the
socket on t he power supply or rac k case. The connec tor has
a tab that wi ll align with the gap in t he socket, so it can not
be inser ted incorrec tly. If the power supply d oes not have a
keyed socke t, be sure to orient pi n 1 (-12 V) with the
red str ipe on the cable.
2 3Quick Start Guide921 VOLTAGE CON TROLLED OSCILL ATOR
3. Ins ert the 10-pin co nnector into the s ocket on the back of
the modul e. The connector ha s a tab that will align wi th the
socket for correct orientation.
4. Af ter both ends of the po wer cable have been se curely
attac hed, you may mount the mo dule in a case and tur n on
the power supply.
Installation
The neces sary screws ar e included with th e module for mount ing
in a Eurorac k case. Connect t he power cable bef ore mounting.
Dependi ng on the rack case, th ere may be a series of xed holes
spaced 2 HP ap art along the leng th of the case, or a tr ack that
allows indi vidual threaded p lates to slide along th e length of the
case. The f ree-moving th readed plates allow p recise positi oning
of the modu le, but each plate shoul d be positioned in t he
approxim ate relation to the mo unting holes in your m odule before
attaching the screws.
Hold the mo dule against the Eur orack rails so that e ach of the
mounting h oles are aligned wi th a threaded rail o r threaded
plate. Att ach the screws par t way to start, w hich will allow small
adjustments to the positioning while you get them all aligned.
After th e nal position has b een establishe d, tighten the
screws d own.
Tuning Procedure
This proce dure tunes the 921 VOLTAGE CONTROLLED OS CILLATOR
module’s “oct ave scaling” to an ex act 1 V/oct. calibrat ion to
facilitate precise control.
1. Power up the 921 module an d allow it to warm up for a
few minutes.
2. Prepare the following control settings on the 921 module:
a. Set the S CALE toggle swi tch to the ±12 SEMI posit ion.
b. Set the R ANGE toggle switch t o the AUDIO position.
c. Set the R ANGE rotary sw itch to 2’.
d. Se t the FREQUENCY cont rol knob so that the
sawtoo th output is exac tly 640 Hz as meas ured with
an accurat e frequency me ter.
e. Make s ure none of the FREQUENC Y CONTROL INPUTS
jacks are connected.
Note: All adj ustment trimme rs are accessible f rom the 921
module’s und erside. Note the pos itions of the SCALE a nd HI ADJ
multi-tu rn trimmers, an d make sure you have suitab le tools to
adjust the trimmers if required.
3. Fine-tune the 921 oscillator’s low-frequency scaling via the
following steps:
a. Ap ply exactly -2 V to a FREQUEN CY CONTROL INPUTS
input jac k. (A 921A module can b e used to supply the
-2 V or use a similar low -impedance sta ble-voltage
sou rce.)
b. Trim the S CALE trimmer to se t 160 Hz, then remove
the -2 V input and re adjust the FREQUENC Y knob
to 640 Hz .
c. Re peat this cycle un til both 160 Hz and 640 H z are
accurate t o ±1 H z when the -2 V is plugged in and
out of the FRE QUENCY CONTROL INPUT S jack.
4. Fine-tune the 921 oscillator’s high-frequency scaling via
the following steps:
a. Wi th no FREQUENCY CONTRO L INPUTS jack
connec ted, check the fr equency is stil l set for 640 Hz
output , then apply exac tly +2 V to the FREQUEN CY
CONTROL INPUTS input.
b. Trim the H I ADJ trimmer to set the 921 saw tooth
output to e xactly 2.560 kH z.
c. Re -check that 6 40 Hz is still corr ect when the +2 V
input is rem oved.
d. Repeat as r equired.
Specications
Signal Connections
Frequency control inputs 3 x 3.5 mm jacks, summed,
Rectangular width
control inputs
Input Impedance 100 kΩ, unbalanced
Maximum input level -6 to +6 V
Clamping point
trigger inputs
V-trig input impedance 10 kΩ, unbalanced
S-trig input impedance 30 kΩ, unbalanced
Maximum input level +12 V
Auxiliary outputs 1 x 3.5 mm jack, mono,
Output Impedance 50 Ω, unbalanced
Maximum output level +10 dBu
Waveform outputs 4 x 3.5 mm jacks, mono
Waveforms Sine, triangular, sawtooth,
Output Impedance < 800 Ω, unbalanced
Output level Typically -4 dBu
Controls
Scale 1 x toggle switch
Coarse range 1 x toggle switch
1 V/oct.
2 x 3.5 mm jacks, summed,
1 V/15%
2 x 3.5 mm jacks
(1 x V-trig, 1 x S-trig)
+/- polarity
rectangular
±6 octaves / ±12 semitone,
selectable
Sub-audio range, typically
0.01 Hz to 800 Hz
Audio range, typically
1 Hz to 80 kHz
Frequency 1 x rotary knob
±6 octaves
Range 1 x rotary switch
32' / 16' / 8' / 4' / 2' / 1',
selectable
Rectangular width 1 x rotary knob
10% to 90%, selectable
Clamping point 1 x rotary knob
10% to 90%, selectable
Aux out waveform 1 x rotary switch
Sine / triangular / inverted
sawtooth / sawtooth /
rectangular / inverted
rectangular, selectable
Aux out level 1 x rotary knob
O to +10 dBu, selectable
Power
Power supply Eurorack
Current draw 50 mA (+12 V),
50 mA (-12 V)
Physical
Dimensions 45 x 71 x 129 mm
(1.8 x 2.8 x 5.1")
Rack units 14 HP
Weight 0.18 kg (0.40 lbs)
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Zhongshan Eurotec Electronics Limited
No. 10 Wanmei Road, South China Modern Chinese Medicine Park,
Nanlang Town, 528451, Zhongshan City, Guangdong Province, China
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