Crown VFX-2 User manual

VFX-2
IM-1
ete
crown
INSTRUCTION MANUAL
SERIAL NO.
ISSUED TO:
VFX2
DUAL-CHANNEL
FILTER/CROSSOVER
CROWN
INTERNATIONAL,
INC.,
BOX
1000
ELKHART,
INDIANA
46514

TABLE OF CONTENTS
SECTION
Section 1
Section 2
Section 3
TITLE PAGE
INTRODUCTION
1.1 Scope of Manual
1.2. Equipment Description
1.3. Specifications ...
14 Warranty
INSTALLATION AND OPERATION
2.1
2.2
2.3
24
25
General ....
Unpacking .
Mounting
Installation
24.1 Cabling ...
2.4.2 Input Connections
24.3 Output Connections
244 Glossary of Filter Terms
Operation
occ
2.5.1 Control Functions ....
2.5.2 Setting Hi-Pass Hz Filter Frequency
2.5.3 Setting Lo-Pass Hz Filter Frequency
2.54
Setting
Controls
for
Bandpass
Filter
Operation
..
14
2.5.5
Mono
(Balanced)
Output
Application
......
CIRCUIT DESCRIPTION
3.1
3.2
33
34
General woe
Circuit Description ..
3.2.1 Filtering Circuits ..
3.2.2 Power Supply Circuits
Test Procedures
Service Policies

LIST OF ILLUSTRATIONS
FIGURENO. TITLE PAGE
1-1
VFX2
Dual-Channel
Filter/Crossover
...
wl
1-2
Typical
Frequency
Response:
IHF
Load
at
Rated
Output
3
1-3. Typical Phase Response: No Filters
1-4 Typical Phase Response: High and Low Pass Filters
1-5 % IM Distortion - All Controls Flat with IHF Load
1-6 Typical Filter Curves ...
1-7 Typical Maximum Output: IHF Load . ae
1-8 Typical Common Mode Rejection ......... aw 6
2-1 Mounting Dimensions
2-2
Typical
System
Configurations
and
Cables
.
w
@9
2-3.
Phone
Plug,
%",
3-Conductor
o...cccecceeeee
weld
2-4
Phone
Plug,
'4", 2-Conductor
......
2-5 Front Panel Controls
2-6 Rear Panel Controls and Commectors .....cccccscssssssscssessessessssssessncscsscsvessestevessesavsevancarsesans 12

SECTION 1
INTRODUCTION
REAR VIEW
FRONT VIEW
FIGURE 1-1
VFX2 DUAL-CHANNEL FILTER/CROSSOVER
1.1 SCOPE OF MANUAL
This manual is intended to provide the user
necessary technical information required to operate
the CROWN VFX2 Dual-channel Filter/ Crossover unit
properly and to maintain the unit in optimum
operating condition.
The manual is comprehensive, containing a physical
description of the VFX2, electrical and mechanical
specifications, complete installation and operating
instructions, a detailed circuit description, test
procedures and service policies. Also included are a
complete parts list and the associated VFX2
schematic to assist in identification of parts and
understanding the functional operation of the VFX2.
A thorough reading of this manual and strict
adherence to the instructions, procedures and
cautions will assure many years of professional
quality service and listening enjoyment from your
CROWN VFX2 Dual-Channel Filter/ Crossover.
1.2 EQUIPMENT DESCRIPTION
The CROWN Model VFX2 is a_ dual-channel
filter/ crossover unit specifically designed to provide
continuously variable filters to perform either high
pass/ low pass or bandpass functions in professional
or commercial sound, or home “‘hi-fi” applications.
The VFX2 is a compact, ruggedly constructed unit
designed to fit a standard 19” rack mount (W.E. hole
spacing) and occupies only 3%" of vertical rack
space. Maximum depth from the mounting surface is
5%". The chassis is all aluminum black and satinized
anodized and the entire unit weights only 6 pounds.
Front panel controls are four sets of range/vernier
knobs for the Hl and LOW PASS Hz setting of the
ilters in the two audio channels and a rotary POWER
ON-OFF switch.
Rear panel controls are a screwdriver-adjustable
LEVEL (attenuator) control and a mode switch for
selecting either CROSSOVER (low pass) or FILTER
(bandpass) outputs for each audio channel.
Rear panel connectors include a variable gain
bridging input for each channel! in addition to the
unity gain unbalanced input. Output connectors,
both high pass and low pass, are provided for
inverted and non-inverted (NORMAL) modes. An AC
ine fuse to protect the unit and the power
transformer are also located on the rear panel.

1.3 SPECIFICATIONS
Frequency Response
Phase Response
Output
Inputs
Gain
Hum and Noise
Distortion
Filters
Semiconductor
Complement
Power Requirements
Fusing
Controls
Connectors
Chassis Finish
Dimensions
Weight
VFX-2
Dual Channel Variable Electronic Filter-Crossover
+0.1dB 20Hz to 20KHz with IHF load
Typically +0.2dB 2Hz to 58KHz with IHF load,
+0.5dB 18Hz to 38KHz with 600 2 load
All tests with filters flat and at rated output. (See graph)
See graph.
10V Maximum before overload, 2.5V rated
50
2
output
impedance
accepts
600
2
load
(typically
6.4V
maximum
into
600
@
)
All outputs available in normal (non-inverted) and inverted modes.
Two types per channel:
Transformerless bridging input with 4" phone jack or attenuator, 20K ohm bal-
anced, 10K ohm unbalanced
OR
Unity gain input 4” phone jack, 1M ohm unbalanced. For balanced input common
mode rejection see graph.
0-15.5dB from balanced/ unbalanced input
More than 100dB below rated output with OdB gain, 20Hz to 20KHz.
All tests with filters flat.
IM distortion less than 0.01% at rated output.
IHF or 6002 with filters flat or set at 20Hz and 20KHz (See graph).
Separate 18dB Butterworth Highpass and Lowpass Filters with adjustable corner
frequencies. Can be internally cascaded to form band pass and band reject
filters. (See graph)
10 integrated circuits (20 operational amplifiers equivalent to 400 transistors and
40 diodes) for a total of 402 transistors, 2 zeners and 56 diodes.
2 Watts 120 VAC or 240 VAC 50-400Hz
For 120 VAC use 3 AG 1/8 Amp 250 VAC fuse
(For 240 VAC use AGC 1/16 Amp 250 VAC fuse)
Range and vernier controls for corner frequencies and power switch are on
front panei.
Screwdriver-adjustable input attenuator on rear panel.
Inputs — 3 conductor 4" phone jack balanced/ unbalanced
2 conductor 4" phone jack unbalanced unity gain
Outputs — 2 conductor ’” phone jack
AC line — Three wire (grounded) male connector on 5 ft. minimum cable
All aluminum black and satinized anodized
19” standard rack mount (W.E. hole spacing), 3%" height, 5%” maximum depth
(from mounting surface)
6 Ibs.

1.4 WARRANTY
cluded
with
this
manual.
The
WARRANTY
is
subject
to
the
conditions
contained
therein.
Upon
receipt
of
the
registration
form,
CROWN
will
issue
a
WAR-
RANTY
TITLE.
This
title
applies
to
the
original
end-
purchaser
as
well as
subsequent
purchasers.
CROWN
guarantees
this
equipment
to
perform
as
specified.
CROWN
also
warrants
the
components
and
workmanship
of
this
equipment
to
be
free
from
defects
for
a
period
of
3
years
from
date
of
purchase.
This
warranty
does
not
extend
to
fuses,
and/or
com-
You,
the
purchaser(s),
are
responsible
for
accurate,
ponent
or
equipment
damage
due
to
negligence,
complete
records
(sales
slips,
invoices,
etc.)
for
FULL coverage!
misuse,
shipping
damage
or
accident;
or
if
the
serial
, altered or removed.
A
copy
of
the
FULL
THREE-YEAR
WARRANTY
is
in-
number has been defaced
1db
Odb
-2db
1Hz
10Hz
100Hz
1KHz
10KHz
100KHz
1Hz
FIGURE 1-2
TYPICAL
FREQUENCY
RESPONSE:
IHF
LOAD
AT
RATED
OUTPUT
DEGREES
in
=
-15°
-30°
1Hz
10Hz
100Hz
1KHz
10KHz
100KHz
THz
FIGURE 1-3
TYPICAL PHASE RESPONSE: NO FILTERS

DEGREES
360°
in
a
tt
a
a
]
180°
90°
0°
I
fee
oS
po
a
90°
-7180°
-270°
-360°
LHz
10Hz
100Hz
1KHz
10KHz
100KHz
MHz
FIGURE 1-4
TYPICAL
PHASE
RESPONSE.
HIGH
AND
LOW
PASS
FILTERS
% iM
-0010
100V
10V
1v
1V
-01V
FIGURE 1-5
— ALL CONTROLS FLAT WITH IHF LOAD
IM DISTORTION
%

2 3
-20db
1Hz 10Hz 100Hz 1KHz 10KHz 100KHz
-1Hz
10db
-
Sa
aaa
|
setates,
Odb
-10db
-20db
1Hz 10Hz 100Hz 1KHz 10KHz 100KHz
-1Hz
FIGURE 1-6
TYPICAL FILTER CURVES
So =
1Hz 10Hz 100Hz 1KHz 10KHz 100KHz
Hz
7
TYPICAL MAXIMUM OUTPUT; IHF LOAD
FIGURE 1

Yn
‘i
{
|
|
-
des
SLaoemiape
aera
nota
(abet
ate
ae
ts
Seis
Pal
a
sr
ten
anes
s
Soe
ae
ee
(occa
Sees
iceman
:
:
;
i
60db
70db
80db
90db
100db
110db
120db
1Hz 10Hz 100Hz 1KHz 10KHz 100KHz
Hz
FIGURE 1-8
TYPICAL COMMON MODE REJECTION

2.1 GENERAL
This
section
contains
information
for
unpacking
the
unit,
reporting
procedures
for
damaged
shipments,
mounting
instructions,
cabling
diagrams
for
various
operational
modes
and
a
description
of
control
functions
and
settings.
2.2 UNPACKING
Immediately
upon
receipt
of
the
VFX2
shipment,
inspect
the
unit
for
any
damage
incurred
in
transit.
The
unit
was
carefully
inspected
and
tested
and
left
the
factory
unmarred.
Notify
the
transportation
company
immediately
if
any
damage
is
found.
Only
the
consignee
may
initiate
a
claim
with
the
carrier
for
damage
during
shipment.
However,
CROWN
will
cooperate
fully
in
such
an
event.
Be
sure
to
save
the
carton
as
evidence
of
damage
for
the
shipper’s
inspection.
CROWN
recommends
that
you
save
the
packing
materials,
even
if
the
unit
arrives
in
perfect
condition.
They
will
prove
valuable
in
preventing
SECTION 2
INSTALLATION
AND
OPERATION
damage
should
there
be
occasion
to
transport
or
ship
the
unit.
Both
the
carton
and
internal
pack
are
specifically
designed
for
protection
during
transit.
Do
not
ship
the
unit
without
this
factory
pack!
2.3 MOUNTING
The
VFX2
is
specifically
designed
for
standard
19”
rack
mounting,
but
may
be
custom
mounted
if
suf-
ficient
support
is
provided.
Refer
to
Figure
2-1
for
mounting
dimensions.
Supplied
with
the
VFX2
is
a
decorative
smoked
acrylic
overlay.
The
overlay
functions
as
a
protective
shield
preventing
the
front
panel
control
settings
from
being
accidentally
bumped.
The
VFX2
can
be
mounted
to
the
rack
or
cabinet
by
using
the
10-8
adapter
stud
supplied.
The
overlay
then
fits
over
the
stud
and
is
secured
by
black
dress
nuts.
cy
D-----+
in
alalaialaate
3172"
3
&
|
Bowe
enters
foc
|.
Ja
3/8"
is"
8
3a"
(STANDARD
RACK
MOUNT
} (
MAX.
DEPTH
FROM
MOUNTING
SURFACE)
FIGURE
2-1
MOUNTING
DIMENSIONS

VFX 2 INPUT — OUTPUT
USE REAR PANEL CONNECTIONS
BASS AMP CH.1 TREBLE AMP CH. |
CROSSOVER
peers
|
2
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°
Om:
2 CHANNEL
(0) SYSTEM © © jv Je - C) (eo) a
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BASS AMP. CH. 2
CH. 1 AMP.
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®
BAND PASS FILTER
® 2 CHANNEL
SYSTEM
a “AMP. CH. 2
FILTER
a ©@®@
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INPUTS —
FIXED OR
VAR.
®®©
°
@
FILTER
CH. 2 AMP.
BASS AMP CROSSOVER
oO
® ®
ey
‘TRIAMPLIFICATION FIXED OR
@®
1
CHANNEL
@©
°
boa
SYSTEM ©
CROSSOVER
MIDRANGE AMP. TREBLE AMP
BASS AM
eee FILTER
BIAMPLIFICATION ®
AND BAND PASS
® FILTER ©
I CHANNEL sysTEM| ©)
TREBLE ANP,
CHANNEL 1 BASS AMP.
CHANNEL | TREBLE AMP,
CHIN CHIN
CH. 2 IN CH. 21N
en
a
@
@°
@aa
OUTPUT TO PRO- XED OR
VIDE
MONO
OUT-
®
‘i
a
@®
(9)
se
PUT FROM sTeREO| ©)
AMP,
{CAN BE EM-
PLOYED IN ANY OF
THE ABOVE USES CH. 2 IN CH.2IN
SHOWN FOR BI-AMP cH. 1 IN cH. IN
2 CHANNEL
SYSTEM } CHANNEL 2 BASS AMP. CHANNEL 2 TREBLE AMP
~~ FOUR STEREO AMPLIFIERS REQUIRED
—— OUTPUT CONNECTED BETWEEN CH.1 AND CH. 2
HOT OUTPUT LEAOS ON EACH AMP
CONNECTIONS AND CONTROL SETTINGS
FRONT PANEL SETTINGS
—— CHANNEL- 2 ————
CHANNEL-!
OVO) OO: SO OrOO
Lin passe! Loomssied Linmss te Lro piss te!
ALL FILTERS SET AT CROSSOVER FREQUENCY
CHANNEL~I CHANNEL- 2
Lat pass He LLomssts Lin pass ne Luo masse
LO ROLLOFF HI ROLLOFF Lo ROLLOFF Hi ROLLOFF
FREQ. FREQ. FREQ. FREQ.
CHANNEL-1| CHANNEL- 2
Lon pass Hz LiomssHe+ Lu pass Het Lio passe! POWER
LO CROSSOVER LO CROSSOVER HI CROSSOVER HI CROSSOVER
FREQ. FREQ. FREQ. FREQ.
CHANNEL-| ———— CHANNEL- 2
Lvipasst: + ULo pass He) Leas Hz J Lio pass He J POWER
Lo ROLLOFF LO CROSSOVER HI CROSSOVER HI ROLLOFF
FREQ. FREQ. FREQ. FREQ.
CHANNEL- 2
CHANNEL-1
Chesomomeoncnens
Lo pisstie S Lio passH: J Cn mssHzt Lito pass He
ALL FILTERS SET AT CROSSOVER FREQUENCY
FIGURE 2-2
TYPICAL SYSTEM CONFIGURATION & CABLES
OUTPUT SPECTRUM
|
|
l
BO
CROSSOVER
FREQ.
20KHz
|
I
|
H
\
|
| |
|
1
!
!
5
t
t
He
LO
ROLLOFF
HiROLLore
=
20KHE
FREQ FREQ
|
|
|
|
|
|
|
i)
1
|
| |
!
!
+-
+
se!
LO
CROSSOVER
Hi
CROSSOVER
aokHe
|
i
|
1 ]
I 1 '
i
I
I
|
|
|
!
t
20Hz
20KHz
LO
ROLLOFF
CROSSOVER
FREQ.
HI
ROLLOFF
1
|
I
|
I
|
1
20H:
t
20KHe
CROSSOVER FREQ.

2.4 INSTALLATION
These
paragraphs
describe
the
most
common
system
configurations
for
the
VFX2
Dual-Channel
Crossover/Filter,
provide
cabling
diagrams
and
control
settings
for
these
system
configurations
and
detail
the
various
types
of
inputs
and
outputs
available
for
use
with
the
VFX2.
2.4.1 Cabling
Refer to Figure 2-2,
2.4.2 Input Connections
Three
types
of
inputs,
balanced,
unbalanced
and
a
unity
gain
unbalanced
input,
may
be
used
with
the
VFX2.
Details
are
shown
below.
a. Balanced Input
Refer
to
Figure
2-3.
To
form
a
balanced
input
for
the
VFX2,
connect
one
side
of
a
balanced
line
to
the
tip
of
a
3-conductor,
%"
phone
plug,
connect
the
second
side
of
the
balanced
line
to
the
ring
of
the
phone
plug
and
the
ground
or
center
tap
to
the
barrel
of
the
phone
plug.
For
standardization,
assume
tip
is
in
phase
(+)
with
output
signal;
ring
is
out
of
phase
(-)
with
output
signal.
Insert
the
phone
plug
into
the
(BALANCED)
input
jack
on
the
rear
panel
of
the
VFX2
(Refer
to
Figure
2-6).
The
gain
of
the
channel
is
ad-
justable
using
the
LEVEL
(Attenuator)
control.
RING
FIGURE 2-3
PHONE PLUG, %", 3-CONDUCTOR
b. Unbalanced Input
Refer
to
Figure
2-3.
To
form
an
unbalanced
input
for
the
VFX2
(with
attenuation
available),
connectthe
“signal”
line
to
the
tip
of
a
3-conductor,
4"
phone
plug,
and
connect
the
“ground”
line
to
the
barrel
of
the
phone
plug.
Insert
the
phone
plug
into
the
(BALANCED)
input
jack
on
the
rear
panel
ofthe
VFX2
(Refer
to
Figure
2-6).
The
gain
of
the
channel
is
adjustable
using
the
LEVEL
control.
CAUTION:
Be
certain
that
the
ring
of
the
phone
plug
is
left
open.
(Do
not
connect
anything
to
it.)
Failureto
observe
this
precaution
can
cause
latch-up
of
the
VFX2
output,
with
high
impedance
unbalanced
inputs.
c. Unity Gain Unbalanced Input
Refer
to
Figure
2-4.
To
form
a
unity
gain
unbalanced
input
for
the
VFX2,
wire
a
2-conductor,
‘4"
phone
plug
as
described
in
paragraphb.
above.
Insert
the
phone
plug
into
the
UNITY
GAIN
input
jack
on
the
rear
panel
of
the
VFX2.
The
LEVEL
(attenuator)
control,
adjacent
to
the
UNITY
GAIN
jack,
is
inoperative
in
this
application.
BARREL uP
FIGURE 2-4
PHONE
PLUG,
'4",
2-CONDUCTOR

TO SELECT TO SELECT TO SELECT TO SELECT
HIGHPASS LOWPASS HIGHPASS LOWPASS
CORNER CORNER CORNER CORNER POWER
FREQUENCY FREQUENCY FREQUENCY FREQUENCY SWITCH
——" — ——— —"
pea ncaromcanecmrscinatenanenatstnnaato she 2 IRA NS NRHN Ra RH MB |
: crown & VFx-2
VERNIER RANGE RANGE 'VERNIER VERNIER. RANGE RANGE’ VERNIER
FIGURE 2-5
FRONT PANEL CONTROLS
SWITCHED NORMAL HIGH PASS BALANCED or UNBALANCED
OUTPUTS NORMAL OUTPUT INPUTS
Controlled by mode Waveform is same Determined by wiring
switches for low pass potarity as input. of input phone plug.
or bandpass output. Has adjustable gain.
SWITCHED INVERTED Waveform is same wianibase
UTPUTS i
Controlled by mode poverty genes INVERTED OUTPUT ATTENUATOR
switches for low pass Waveform is opposite Adjusts input gain
or bandpass output. polarity from input. of balanced inputs
Waveform is opposite
polarity from input. MODE SWITCH inpuTe
Selects
low
pass
Unbalanced
fixed
or
bandpass
for
gain
gives
output
POWER
FUSE
switched
outputs.
same
level
as
input
a sa sw
EBEECGERLS
@
a
a
w
*-
had
i,
i
POWER LOW PASS HIGH PASS
AC LINE CORD TRANSFORMER FILTERS FILTERS
FIGURE 2-6
REAR PANEL CONTROLS AND CONNECTORS
12

2.4.3 Output Connections
Six outputs (high pass, low pass and bandpass —
both balanced and unbalanced) are available from
the VFX2. Details are described below.
a. Unbalanced High Pass Output
To pick up an unbalanced high pass output from
the VFX2, insert a 2-conductor, 4%” phone plug wired
as shown in Figure 2-4, into the HIGH PASS NORMAL
output jack on the rear panel of the VFX2.
b. Balanced High Pass Output
To pick up a balanced high pass output from the
VFX2, insert a 2-conductor, 4” phone plug wired as
shown in Figure 2-4, into both the HIGH PASS
NORMAL and the HIGH PASS INVERTED phone
jacks. Thetips of the two 4" phone plugs become the
two sides of the balanced line. The barrels become
the ground or center tap.
c. Unbalanced Low Pass Output
To pick up an unbalanced low pass output from
the VFX2, insert a 2-conductor, 4" phone piug wired
as shown in Figure 2-4, into the LOW PASS NORMAL
output jack on the rear panel of the VFX2 and set the
MODE switch to CROSSOVER (LOW PASS).
d. Balanced Low Pass Output
To pick up a balanced low pass output from the
VFX2, insert a 2-conductor, 4" phone plug wired as
shown in Figure 2-4, into both the LOW PASS
NORMAL and the LOW PASS INVERTED phone jacks
on the rear panel of the VFX2. The tips of the two 4%”
phone plugs become the two sides of the balanced
line. The barrels become the ground or center tap.
Set the MODE switch to CROSSOVER (LOW PASS).
e. Unbalanced Bandpass Output
To pick up an unbalanced bandpass output from
the VFX2, insert a 2-conductor, 4" phone plug wired
as shown in Figure 2-4, into the LOW PASS NORMAL
phone jack on the rear panel of the VFX2. Set the
MODE switch to FILTER (BANDPASS).
f. Balanced Bandpass Output
To pick up a balanced bandpass output from the
VFX2, insert a 2-conductor, 4” phone plug wired as
shown in Figure 2-4, into both the LOW PASS
NORMAL and the LOW PASS INVERTED phone jacks
on the rear panel of the VFX2. The tips of the two 4”
phone plugs become the two sides of the balanced
line. The barrels become the ground or center tap.
Set the MODE switch to FILTER (BANDPASS).
13
2.4.4 Glossary of Filter Terms
a. Crossover Network
A selective network used to divide the audio
frequency output of an amplifier into two or more
bands of frequencies. The band below the crossover
frequency is fed to the woofer loudspeaker, while the
high-frequency band is fed to the tweeter. Also called
dividing network and loudspeaker dividing network.
b. Crossover Frequency
The frequency at which a dividing network
delivers equal power to the upper and lower
frequency channels when both are terminated in
specified loads.
c. Bandpass Filter
A filter that transmits alternating signals whose
frequencies are between given upper and lower
cutoff values, while substantially attenuating all
frequencies outside this band.
d. Corner Frequency
A frequency at which the filter goes from a
condition of passing the signal unattenuated to
“rolling off” or attenuating the signal according to its
frequency. It is also sometimes referred to as the
“cutoff” frequency or the “break” frequency. It is also
defined as 3dB below the maximum output.
2.5 OPERATION
Most modes of operation depend upon the selection
of various input and output combinations which are
required by a specific system configuration. The
following notes apply to input selection.
a) A balanced input must be inserted into the
(BALANCED) INPUTS on the VFX2 rear panel. See
paragraph 2.4.2 a for wiring a balanced input phone
plug. A balanced line input has an adjustable
attenuation (LEVEL) potentiometer adjacent to the
input jack.
b) An unbalanced input may be inserted into the
(BALANCED) INPUTS or theUNITY GAIN INPUTS on
the VFX2 rear panel. See paragraph 2.4.2 b for wiring
an unbalanced input phone plug. An unbalanced
input, connected to the (BALANCED) INPUT jacks,
has a variable attenuation (LEVEL) potentiometer.
When the unbalanced input is connected to the
UNITY GAIN INPUT jacks, the variable attenuator
(LEVEL) adjustment is removed from the circuit and
the line has a fixed unity gain.

The use of the VFX2 controls in the different modes of
operation available is described in the following
paragraphs.
2.5.1 Control Functions
Although the uses and possible applications of the
VFX2 are almost unlimited, the operation of the
controls is quite simple. In addition to the POWER
switch, there are only four types of controls:
Attenuator (LEVEL), Mode, Range and Vernier. One
attenuator (screwdriver-adjusted pot) and one mode
switch are provided on the rear panel for each
channel. One range and one vernier switch for each
of the four filters are provided on the front panel. A
simplified, functional block diagram is located on the
rear panel of the VFX2 to aid in understanding the
operation of the unit. This block diagram is also
shown in Figure 2-6.
a. INPUT LEVEL (Attenuator)
The attenuators are screwdriver adjustments
located on the rear panel. Each attenuator controls
the gain of the adjacent (BALANCED) input. With the
input attenuator fully CW, a maximum gain of 15.5
dB is obtained. Minimum gain is unity at full
attenuation, fully CCW. The input impedance of the
(BALANCED) input is independent of the attenuator
(gain) setting.
b. MODE Switch
Two mode switches, one for each channel, are
located in the center of the rear panel. These two-
position, slide switches are labeled LOW PASS —
BANDPASS. This switch determines the source of
the input signal for the low pass filter stage. Set to
LOW PASS, the input signal is selected directly from
the input. Set to BANDPASS, the input signal is
selected directly after the high pass filter stage. The
mode switch affects only the LOW PASS outputs,
adjacent to the power transformer on the rear panel.
c. RANGE and VERNIER Controls
Four pairs of controls for the four filter sections are
located on the front panel. These include one
VERNIER potentiometer, and one RANGE switch for
each High Pass and Low Pass filter. The controls are
used to set the (3 dB) corner frequency for the filters.
The VERNIER potentiometer selects the first
significant digit (2 to 20) of the selected frequency;
the four-position RANGE switch (OFF-X10-X100-
X1K) selects the appropriate multiplier.
14
EXAMPLE:
Selected
frequency
=
30 Hz
1.
Set
VERNIER
potentiometer
to
3.
2.
Set
RANGE
switch
to
X10.
The
corner
frequency
for
the
filter
is
now
set
to
30
Hz.
Setting
the
RANGE
switch
to
the
OFF
position
removes
the
related
filter
section
from
the
circuit
and
allows
the
signal
to
pass
unfiltered.
d. POWER Switch
A
pushbutton
switch,
located
on
the
right
side
of
the
front
panel,
controls
power
applied
to
the
VFX2.
Depress
the
POWER
switch
to
apply
power;
it
should
tock
in
the
depressed
position
and
a
green
indicator
should
show
that
power
is
applied.
To
remove
power,
depress
the
POWER
switch;
it
should
return
to
the
original
extended
position
and
the
green
indicator
should disappear.
'
2.5.2
Setting
Hi-Pass
Hz
Filter
Frequency
First,
choose
the
desired
(3dB)
corner
frequency.
The
high-pass
filter
will
attenuate
all
signals
below
this
frequency.
Example:
30
Hz
corner
frequency
1.
Set
the
VERNIER
potentiometer
to
3.
2.
Set
the
RANGE
switch
to
X10.
When
the
RANGE
switch
is
set
to
OFF,
the
signal
will
pass
through
the
VFX2
unfiltered.
Use
the
HIGH
PASS
OUTPUTS
as
described
in
paragraph
2.4.3.
2.5.3
Setting
Low-Pass
Hz
Filter
Frequency
First,
choose
the
desired
(db)
corner
frequency.
The
low-pass
filter
will
attenuate
all
signals
above
this
frequency.
Example:
6KHz
corner
frequency
1.
Set
the
VERNIER
potentiometer
to
6.
2.
Set
the
RANGE
switch
to
X1K.
When
the
RANGE
switch
is
set
to
OFF,
the
signal
will
pass
through
the
VFX2
unfiltered.
Use
the
LOW
PASS
OUTPUTS
as
described
in
paragraph
2.4.3.
2.5.4
Setting
Controls
For
Bandpass
Filter
Operation
First,
choose
the
desired
upper
and
lower
(3dB)
corner
frequencies.
Set
the
lower
of
the
two
corner
frequencies
on
the
HI-PASS
Hz
filter
controls
as
shown
in
paragraph
2.5.2.
Set
the
higher
of
the
two
corner
frequencies
on
the
LO-PASS
Hz
filter
controls
as
shown
in
paragraph
2.5.3.
Set
the
MODE
switches
on
the
rear
panel
to
FILTER
(BANDPASS).
Use
either

the
balanced
or
unbalanced
bandpass
outputs
as
described
in
paragraph
2.4.3
e
and
f.
2.5.5
Mono
(Balanced)
Output
Application
Any
CROWN
amplifier
can
be
used
with
the
VFX2
for
a
mono
(balanced
output)
configuration
with
no
physical
modification
to
the
amplifier.
1.
Select
the
type
of
output
to
be
used
(high
pass,
low
pass
or
bandpass).
2.
Connect
the
NORMAL
output
from
the
VFX2
to
one
amplifier
INPUT.
15
3.
Connect
the
INVERTED
output
from
the
VFX2
to
the
other
amplifier
INPUT.
The
mono
(balanced
output)
amplifier
signal
is
now
available
on
the
two
red
binding
posts
(amplifier
outputs).
Refer
to
individual
amplifier
manuals
for
mono
(balanced)
output
connections.
NOTE:
For
maximum
output,
both
amplifier
level
controls
should
be
set
at
full
gain
in
this
configuration.

3.1 GENERAL
This
section
contains
a
detailed
description
of
Circuitry
operation,
test
procedures
and
service
information
required
for
a
qualified
service
technician
to
properly
adjust
and
maintain
the
VFX2
in
optimum
operating
condition,
3.2 CIRCUIT DESCRIPTION
The
VFX2
Dual-Channel
Electronic
Filter/
Crossover
consists
primarily
of
two
identical
channels
of
active
IC
operational
amplifier
tunable
filters.
Components
for
each
channel
are
found
ona
printed
circuit
board
located
behind
the
associated
channel
front
panel
controls.
The
following
circuit
description
applies
equally
to
both
channels.
Refer
to
schematic.
The
VFX2
also
contains
two
separate
internal
power
supplies
which
generate
regulated
+15
VDC
and-15
VDC
for
distribution
to
all
ten
dua!
operational
amplifier
IC’s.
The
VFX2
requires
about
2
Watts
for
normal
operation.
The
power
supply
can
be
wired
for
120
VAC
or
240
VAC
line
voltage
and
operates
on
any
frequency
from
50
Hz
to
400
Hz.
3.2.1 Filtering Circuits
The
balanced
input,
a3-conductor,
4”
phone
jack,
is
applied
to
ICLA.
The
IC1A
lownoise,
dual
operational
amplifier
allows
use
of
a
transformerless
balanced
input
and
provides
isolation
from
filter
loading.
R8,
a
25K
ohm
attenuator
(LEVEL)
potentiometer,
enables
control
of
the
gain
of
IC1A
from
unity
gain
at
maximum
attenuation
to
15.5
dB
gain
at
minimum
attenuation,
The
input
impedance
of
the
balanced
input
is
completely
independent
of
the
gain
setting
of
that
input.
SECTION 3
CIRCUIT DESCRIPTION
Inserting
an
unbalanced
input,
a
2-conductor,
4"
phone
plug,
into
the
(BALANCED)
INPUT
jack
un-
balances
the
line
by
grounding
the
negative
input
line.
R4, a 500-ohm trim potentiometer in the positive
IC1A
input
line,
is
factory
adjusted
for
maximum
common
mode
rejection
and
in
normal
applications
should not be readjusted.
An
unbalanced
input
may
be
inserted
into
theUNITY
GAIN
INPUT
jack.
This
input
is
applied
directly
to
operational
amplifier
1C1B.
The
variable
attenuator
(LEVEL)
potentiometer,
R8,
has
no
effect
on
this
input.
The
unity
gain
output
of
|C1B
is
applied
to
the
input
circuit
of
IC2A
(HI
PASS
FILTER)
only,
or
to
that
circuit
plus
the
input
circuit
of
IC4A
(LO
PASS
FILTER)
depending
on
the
position
of
the
CROSSOVER/
FILTER
mode
switch.
The
IC1B
output
may
also
go
directly
to
the
LOW
PASS
OUTPUT
jack
or
the
HIGH
PASS
OUTPUT
jack
depending
on
the
position
of
the
RANGE
switches.
Circuit
operation
for
all
switch
combinations
is
described
below:
a. RANGE Switches, OFF — CROSSOVER/FILTER,
Either Position
With the RANGE switches in OFF, the unity gain
output of IC1B bypasses all filtering circuits and
appears as a flat output at the Hl and LO PASS
OUTPUT jacks. Operational amplifier IC3B creates
an inverted output at the HI PASS INVERTED
OUTPUT jack and IC5B creates an inverted output at
the LO PASS INVERTED OUTPUT jack.
b. RANGE Switches (X10, X100, X1K), Mode Sw in
CROSSOVER
The RANGE switch determines the appropriate
group of 5% matched capacitors to be used in the
filter. See Table 3-1.
TABLE 3-1
RANGE
SWITCH
CAPACITOR
GROUPS
RANGE SW
POSITION
HI
RANGE
LO
RANGE
X10
C3,C6,C9
47
mid
C16,
C19,C22
.47
mfd
X100
C4,C7,C10
.047
mfd
C15, C18,
C21
.047
mfd
X1K
C5, C8,
C11
.0047
mfd
C14,
C17,
C20
.0047
mfd
17

The HI VERNIER potentiometer (R14, R16, R18) and
LO VERNIER potentiometer (R23, R25, R27) consist
of matched sets of three 15K-ohm resistive elements
used to determine the location of the desired corner
frequency of the filter. Refer to paragraph 2.5.1 for
the proper method of using the VERNIER/ RANGE
controls to select the corner frequency for the filters.
The signal from IC1B is applied through selected RC
filter components to dual operational amplifier IC2A,
which, along with IC2B and IC3A, forms a 3-pole,
high-pass, 18 dB/octave Butterworth filter. This
produces the non-inverted HI PASS OUTPUT.
Operational amplifier IC3B creates the HI PASS
INVERTED OUTPUT.
The HI PASS OUTPUT signal from IC3A is also
applied through the mode switch to the selected RC
filter components to dual operational amplifier |C4A,
which, with IC4B and IC5A, forms a3-pole, low-pass,
18 dB/octave Butterworth filter. This filter produces
the non-inverted LO PASS OUTPUT. Operational
amplifier IC5B creates the LO PASS INVERTED
OUTPUT.
c. CROSSOVER (Low Pass), FILTER (Bandpass)
Switches
The rear panel mode switches select either a LOW
PASS or BANDPASS output at the LOW PASS
QUTPUT jacks. With the mode switch inCROSSOVER
(LOW PASS), the input, from IC1B, is tied directly to
the LOW PASS filter sectian; in FILTER (BANDPASS),
the output of the H! PASS filter signal, from iC3A, is
tied directly to the LOW PASS filter section.
3.2.2 Power Supply Circuits
AC power is applied to the power transformer, which
may be wired for either 120 VAC or 240 VAC
operation. The AC input line is fused with a 3AG 1/8
A fuse for 120 VAC or an AGC 1/16 A fuse for 240
VAC. The bridge rectifier, D1-D4, together with C1,
R1, Q1 and Zener D5 provides a regulated + 15VDC;
the bridge rectifier and C2, R2, Q2 and Zener D6
provide a regulated -15 VDC. The+15 VDC is applied
to pin 8 and the -15 VDC is applied to pin 4 of all dual
operational amplifier IC’s.
18
3.3 TEST PROCEDURES
This paragraph lists precautions essential to obtain
accurate test measurements when dealing with high-
purity filtering equipment such as the VFX2.
1. Use the proper line voltage (120 VAC or 240 VAC)
for which the power supply has been wired for normal
operation. The line voltage should be measured with
a peak reading AC voltmeter and adjusted to the rms
equivalent voltage.
2. The input LEVEL controls (attenuators) should be
set to maximum for all distortion tests to assure
repeatability of all test measurements. Filter settings
may greatly change distortion measurements
(usually reducing these measurements and many
times making them invalid). Most distortion
measurements should be made with the RANGE
switches set to OFF, for the same reason.
3. When measuring hum and noise, all inputs should
be disconnected from the VFX2 and the LEVEL
(attenuator) controls set to minimum (or to
maximum for certain tests).
4. Always monitor the test oscillator when
measuring frequency response. Use a wideband AC
voltmeter or use the same meter for both input and
output level measurements, if the meter’s frequency
response is known not to be dependent on attenuator
settings.
5. Residual distortion and noise levels should be
fully Known for all test equipment in order to
accurately evaluate the performance of the VFX2.
6. Never measure hum and noise when in the
presence of strong magnetic fields. The VFX2 should
be at least 4 inches from any large metallic objects or
shield plates for a reading to be*meaningful.
7. Noise measurement should be taken with the
output bandpass filtered for 20Hz - 20KHz. For audio
purposes the measurement of noise above 20KHz is
meaningless.

3.4
SERVICE
POLICIES
Due
to
the
sophisticated
circuitry,
only
a
fully-trained
competent
service
technician
should
be
allowed
to
service
the
VFX2
Dual-Channel
Crossover/Filter.
User
servicing
should
be
confined
to
routine
replacement
of
the
fuse
on
the
rear
panel.
For
other
service,
it
is
recommended
that
the
unit
be
returned
to
the
factory
or
to
an
authorized
CROWN
warranty
center
in
the
original
packing
or
replacement
packing
obtained
from
the
CROWN
factory.
The
CROWN
warranty
is
described
in
paragraph
1.4.
For
warranty
service
the
unit
must
be
returned
to
the
factory
or
approved
warranty
stations.
Many
parts
are
standard
items
stocked
by
local
electronics
supply
houses.
However,
some
parts
which
appear
to
be
standard
parts
are
actually
selected
by
CROWN
from
standard
parts.
Best
results
will
be
obtained
with
CROWN
factory
replacement
parts,
although
standard
parts
may
be
19
used
in
an
emergency.
A
number
of
the
parts
are
special
and
are
available
only
from
CROWN.
When
ordering
parts,
be
sure
to
give
the
VFX2
model
and
serial
number
as
well
as
the
part
number
and
description
of
the
parts
ordered.
If
possible,
inctude
schematic
“reference
designation”
of
parts
ordered.
Before
returning
a
VFX2
unit
to
the
factory
for
service,
authorization
should
be
obtained
from
the
service
manager.
All
shipments
must
be
sent
by
UPS,
or
truck
freight,
and
should
be
insured
at
total
value.
Shipments
should
be
made
at
CROWN’s
expense.
The
factory
will
return
your
serviced
unit
by
UPS
or
truck
freight,
Prepaid,
and
will
add
C.O.D.
charges
only
in
the
event
that
the
cost
is
not
covered
by
registered
warranty.
Rated
firms
will
be
billed,
otherwise
shipments
will
be
C.0.D.

Schematic
Designation
R3
R4
R5, R21, R22,
R31, R32
R6, R7,
R10, Ril
RO
R12
R13, R15, R17,
R24, R26, R28
R14-16-18
R23-25-27
R19, R20
R29, R30
R33, R34
R35
C3, C6, C9
C16, C19, C22
C4, C7, C10,
C15, C18, C21
C5, C8, C11,
C14, C17, C20
C12, C13,
C23, C24
IC-1,2,3,4,5
D7,8,9,10,11,12
PARTS LIST, VFX-2 Page 1
Description
MAIN FILTER MODULE
Resistors
10.2K % watt 1% film
500 ohm trim pot
10K % watt 1% film
4.12K % watt 1% film
620 ohm % watt 10%
1M ohm % watt 5%
1.6K ohm % watt 10%
15K ohm linear pot
100 ohm % watt 10%
47 ohm % watt 5%
1K ohm 44 watt 10%
Capacitors
.47 MF 100V poly
.047 MF 200V Filmatic mylar
,0047 MF 200V poly
25 MF 15V NP Vertical
Semiconductors
RC 4558 Dual op amp
Miscellaneous
8 pin DIL IC socket
3P 4 position Rotary switch
Blank PC board
Diodes
1N4148
Crown
Part # Other Information
41670 Two used per unit
2344
3668
2343
3119
3872
3198
3873
3870 3 sections
2872
1011
2627
4119 Sel. 5%
3978 Sel. 5%
3996 Sel. 5%
3186
3919
3451 Used to mount all IC’s
3871 High and Lo range switch
9626 All holes drilled
3181