Aphex 9901 User manual
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EQUALIZER MODEL 9901
OPERATING GUIDE
1.0
INTRODUCTION
The
APHEX
EQUALIZER
MODEL
9901
is
a
three
band
fully
parametric
equalizer with superb
flexibility
and
performance.
It
was designed with
the
knowledge
that
each
user
of
a parametric
equalizer has a different opinion as
to
what
sounds "good". Extensive listening tests did, however,
reveal a
number
of
operating
and circuit features which
made
important
contributions
to
functionality
and
sound.
The
most
important
operational
features
were
included given
the
amount
of
space
available
on
the
front
panel
of
the
MODEL
9901.
The
"sound"
of
any equalizer
is
the
result
of
the
equalizer topology
and
how
well
that
topology
is
realized by
an
electronic circuit.
Change
in
sound
quality, beyond
the
amplitude
change
caused by
the
equalizer,
is
generally caused by
phase
shift in
one
or
more
parts
of
the
spectrum
and
audio
degradation
introduced
by
the
circuit.
The
MODEL
9901 uses a
unique
topology
to
achieve minimum
phase
shift
and
a pristine audio
path
to maintain audio quality.
TABLE OF CONTENTS
1.0 INTRODUCTION
............
.
2.0 PRINCIPLES OF GAIN REDUCTION .
3.0 EQUALIZER INSTALLATION
....
.
4.0 FRONT PANEL
.............
.
5.0 SETTING
THE
EQUALIZER CONTROLS
6.0 SPECIFICATIONS
7.0 BLOCK DIAGRAM
.............
.
8.0 SCHEMATICS
................
.
1
2
3
6
8
9
10
11
Your
EQUALIZER
wa
s carefully packed at the factory, and the containerwas designed to protect the unit from rough handling.
Nevertheless,we recommend careful examination of the shipping carton and its contents for any sign
of
physical damage which could have
occurred
in
transit. If damage
is
evident, do not destroy the container
or
packing material. Immediately notify the carrier
of
a possible claim
for damage. Shipping claims must be made
by
the consigne
e.
1.1
Limited Warranty
Aphex Systems, Ltd.warrants to the original owner that the E
QUALIZ
ER
will
be free from defects
in
parts and labor for a period
of
one (1)
year from the date of purchase.
THE
ABOVEWARRAN1Y IS IN LIEU
OF
ANY OTHERWARRAN1Y, WHETHER
EXPRESSED,
IMPLIED
OR
STATUTORY,
INCLUDING, BUT NOT LIMITED
TO
, ANY WARRAN1Y OF MERCHANT
ABILl1Y
, FITNESS
FOR
ANY PARTICULAR PURPOSE,
OR
ANY WARRAN1Y ARISING
OUT
OF ANY PROPOSAL, SPECIFICATION,
OR
SAMPLE. APHEX SYSTEMS SHALL NOT
BE
LIABLE FOR INCIDENTAL
OR
CONSEQUENTIAL DAMAGES. APHEX SYSTEMS NEITHER ASSUMES
NOR
AUTHORIZES ANY
PERSON
TO
ASSUME
FOR
IT ANY OTHER LIABILl1Y
1.2 Service Information
If
it
becomes necessary to return a unit for repair,
contact
Aphex
for
a
return
authorization
number,
repack it
in
the original carton and
packing material, and insure the shipment.
If
a warranty repair, enclose a copy
of
proof
of
purchase and send package to:
APHEX
SYS
TE
MS
, LTD.
11068 Randall Street
Sun Valley, CA 91352
PH
: (818) 767-2929 FAX: (818) 767-2641
WARNING:
TO
REDUCE
1HE
RISKS
OF
FIRE
OR
ELECIRIC
SHOCK,
DO
NOf
~Enns
APPLIANCE
TO
RAIN
ORMOISlURE.
Copyright@ 1991 by Aphex Systems, LTD. All
rights
reserved. All Aphex
product
names
are
trademarks
or
registered
trademarks
or
Aphex Sytems, LTD.
Other
brand
and
product
names
are
trademarks
or
registered
trademarks
or
their
respective
holders.
dbx® ls a registered
trademark
or
Carillon
Electronics
Corp.
9210htw
APHEX
SYSTEMS
Equalizer Model
9901
-
Page
1
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2.0 PRINCIPLES OF EQUALIZATION
Equalization
is
a change in the amplitude
of
a
part
of
the
spectrum
of
a signal.
The
highest amount
of
change
is
the
BOOST
when
there
is
an increase in amplitude and CUTwhen there
is
a decrease.
The three main types
of
equalization characteristics are
PEAKING,
SHELVING
and
HIGH
and
LOW
CUT
FILTERING.
2.1
PEAKING
A peaking circuit has a bell shape characteristic. A shelving circuit changes amplitude up to a certain
frequency, and from that frequency to
one
or
the
other
end
of
the spectrum
the
response
is
flat.
In
a peaking circuit,
the
frequency with
the
highest amount
of
boost
or
cut
is
the
CENTER
FREQUENCY,
sometimes called
the
resonant frequency.
The"Q"
is
the bandwidth
of
a peaking circuit.
It
is
defined
as
the
result
of
the
center
frequency divided
by
the difference between
the
frequencies
where
the
amplitude
is
.707 times (-3dB)
the
voltage
of
the
center frequency.
The
higher
the
"Q",
the
narrower
the
bandwidth.
The
lower
the
"Q",
the wider
the
bandwidth.
2.2 LOW CUT and HIGH
CUT
Filters
LOW
CUT
and
HIGH
CUT
filters (also known
as
high pass and low pass filters) reduce the frequency
response
of
the signal at a certain rate expressed in
"dB
per
octave".
The
frequency at which the signal
is
attenuated 3dB
is
called the
CORNER
FREQUENCY.
A shelving equalizer's
CORNER
FREQUENCY
is
also defined
by
the
3dB down point.
There are circuits which boost higher frequencies according to a specific curve. This
is
called
pre-emphasis and
is
not
usually generated
by
an equalizer but rather by a dedicated, calibrated filter
circuit.
Various frequency response curves and characteristics are generated when the same
or
different
equalization circuits are used in combination
either
in parallel
or
serially.
2.3 Types of Equalizers
A
PARAMETRIC
EQUALIZER
is
an equalizer in which some
of
the parameters
of
BOOST
/CUT,
PEAKING/SHELVING,
"Q",
AND
CENTER
FREQUENCY
are adjustable.
It
typically has
three
or
more bands.
A
GRAPHIC
EQUALIZER
is
an equalizer in which only the amount
of
BOOST
or
CUT
is
adjustable.
The number
of
bands it has
is
expressed
as
a fraction
of
an octave (e.g. one-third octave) indicating
that there are
three
bands
of
equalization
per
octave.
Graphic equalizers typically employ higher "Q"s so that changing the amplitude
in
a band will have
little
or
no effect in adjacent bands.
Generally speaking, the higher the
"Q"
and amount
of
amplitude change, the greater the amount
of
phase shift. Since the amount
of
shift affects the sound, a parametric equalizer
is
used for "musical"
applications and graphic equalizers
are
used to correct for room resonances or to reduce noise in a
narrow band.
Page
2 -Equalizer Model
9901
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3.0 EQUALIZER INSTALLATION
3.1. Physical Considerations
The 9901
EQUALIZER
is
designed to
fit
into one slot
of
an Aphex 9000 frame and dbx® 900 series
frames.
The
thumbscrews (#6-32) secure the module to the frame.
3.2 Electrical Considerations
3.2.1 Power
The
9901
is
powered
by
+/-15V. The power
is
bussed to the unit on the backplane
of
both
the
Aphex
and the dbx® racks.
The
+/-24Vwhich appears on the dbx® rack
will
not affect
the
9901 in any
way.
NOTE:
The
9901 consumes 107mA worst case. Compute the total power consumption
of
all
modules
in
the rack to determine ifsufficient power
is
available from the power supply.
On the Aphex rack model 9000R the audio ground and chassis ground come
out
the the power screw
terminal connector separately (see figure 1).
The
terminal
,&,-
marked may
be
jumpered to the
terminal
rh
marked to electrically connect the audio and chassis grounds together.
3.2.2 Edge Connector Pin-out (see schematics)
P.in.
..
#..
Descri~tion
1 No connection
2 No connection
3 Ground (Chassis)
4 Ground (Audio)
5 +15V
6 -15V
7 no connection
8 no connection
9 no connection
10
no connection
11
Ground
12
Input+
13
Input -
14
Output+
15
Output -
Equalizer
Model
9901 -
Page
3
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3.2.3 Rear Panel Connections (screw terminals on rear
of
racks)
0
-24
0
At
Input
high
0
A+
0
+24
0
A-
Input
low
0
A-
0
GNO
0
,/,
Ground
0
,/,
0
+I5
0
B+
Output
high
0
B+
0
-I5
0
B-
Output
low
0 8-
0
"'
0
c+
No
connection
0
c+
0
A,
0
c-
No
connection
0
c-
0
,/,
Ground
0
¢
0
o+
No
connection
0
0+
0
0-
No
connection
0 0-
Fig:
1
Rear
Panel Connections
3.2.4 Audio Input and Output Connections
The
9901 may
be
driven balanced
or
unbalanced.
If
balanced, "high" should
be
connected to
A+,
"low"
connected to A- and shield connected to Ground.
If
unbalanced, connect
"high"
to
A+,
"low"
to A-
and connect a jumper from A- to Ground.
The
output can drive either balanced
or
unbalanced loads. Connect
B+
for output "high" and B- for
output
"low".
Do
not connect shield.
If
driving a known unbalanced load, connect a jumper between B-
and Ground.
3.2.5 Impedances
The
EQUALIZER
features a high input impedance (22kQ balanced), allowing it to be easily driven by
any
other
piece
of
audio equipment, including consumer gear. However, a piece
of
equipment
designed to work into a 600Q load may show unusually low output meter readings, even though
the
unit
is
driving
the
EQUALIZER
properly.
Or
the
unit
may
considerably overdrive the
EQUALIZER's
input, while still indicating
OVU.
In either case, installing a 600Q resistor across each
EQUALIZER
input to lower
the
input
impedance to 600Q.
Page 4 -EqualizerModel 9901
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4.0 FRONT PANEL
4.1
CLIP L.E.D.
Lights when any stage- input, the
three
bands
or
the
output-
is
less than
ldB
under clipping.
4.2 HIGH FREQUENCY BOOST/CUT POTENTIOMETER
Adjusts
the
amplitude
of
the high frequency band +/-15dB.
Center
detent
is
OdB,
full CW
is
+ 15dB, full CCW
is
-15dB.
4.3 HIGH FREQUENCY PEAK/SHELF SWITCH
Switches the response
of
the high frequency band from a peaking response in
the
OUT
position to a high frequency shelving response
in
the
IN
position.
4.4 HIGH FREQUENCY
nan
POTENTIOMETER
Adjusts
the
"Q"
of
the
high frequency band when
in
peaking response from 1
(broad) at full CCW to 10 (narrow) at
full
CW. This has no effect when
the
high
frequency band
is
in
shelving response.
4.5
HIGH
FREQUENCY
CENTER
FREQUENCY
POTENTIOMETER
Adjusts the center frequency
of
the high band in the peaking mode from 500Hz
at full CCW to 20kHz at full CW. When the high band
is
switched
to
shelving
response and
the
gain
is
at either full boost
or
cut,
the
setting indicates
the
approximate corner frequency.
4.6 MIDDLE FREQUENCY BOOST/CUT POTENTIOMETER
APHEX
9901
EQ
Adjusts
the
amplitude
of
the middle frequency band +/-15dB.
Center
detent
is
OdB,
full
CW
is
+ 15dB,
full CCW
is
-15dB.
4.7 MIDDLE FREQUENCY PEAK/SHELF SWITCH
Switches the response
of
the
middle frequency band from a peaking response in
the
OUT
position to a
high frequency shelving response in
the
IN
position.
4.8 MIDDLE FREQUENCY
nan
POTENTIOMETER
Adjusts
the
"Q"
of
the
middle frequency band when in peaking response from 1 (broad) at full CCW to
10 (narrow) at full CW. This has no effect when
the
middle frequency band
is
in shelving response.
4.9 MIDDLE FREQUENCY CENTER FREQUENCY POTENTIOMETER
Adjusts the center frequency
of
the
middle band in
the
peaking mode from
lOOHz
at full CCW to
4kHz at full CW. When the middle band
is
switched to shelving response and
the
gain
is
at either full
boost
or
cut
the
setting indicates the approximate corner frequency.
4.10 LOW FREQUENCY BOOST/CUT POTENTIOMETER
Adjusts the amplitude
of
the low frequency band +/-15dB.
Center
detent
is
OdB,
full
CW
is
+ 15dB,
full CCW
is
-15dB.
Equalizer Model
9901
-
Page
5
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