Studio Technologies Limited Warranty........................................19
Schematic Diagrams ........................................Not included in PDF
Generation II User GuideIssue 3, July 1991
Studio Technologies, Inc.Page 3
Introduction
General Description
The Studio Technologies Generation II
Stereo Simulator is designed to create a
simulated stereo signal from a monaural
input. It is intended for use in applications
such as television and radio broadcasting,
film production, and audio restoration.
Specialized circuitry converts the incoming
signal into a time-domain randomized audio
field which provides an excellent stereo
“feel.”
In television applications, the Generation II
is appropriate for both on-air and production
use. The MTS television broadcaster is
faced with the reality of having a large
amount of mono audio material to broadcast. Using the Generation II Stereo Simulator can greatly improve the listener’s
appreciation of “stereo” TV. The output is
mono-compatible, ensuring that monaural
(L+R) listeners are not negatively impacted
by the use of the Generation II.
status to be set. In the fixed—music setting,
the music mode is activated, the front panel
controls are disabled, and the stereo intensity trim potentiometer is active. In the
fixed—music & voice setting, the music &
voice mode is activated, the front panel
controls are disabled, and the stereo intensity trim pot is active.
Careful circuit design provides excellent
audio performance and operational characteristics to match the special requirements
of most facilities. The line input stage is
electronically balanced, maintaining excellent common-mode rejection, low noise,
and low distortion. The audio output stages
use advanced circuitry to provide high
output level, low noise, and low distortion.
Two switches allow the input and output
levels to be set for nominal 0, +4, or +8dBu
operation. Two 3-section LED meters, along
with a meter select switch, provide monitoring of the input and output levels.
Installation
In film and video production use, the Generation II is invaluable in converting mono
audio into realistic stereo. The two modes of
operation, music and music & voice, allow
for correct processing in all audio scenarios.
In the music & voice mode, a specialized
filter is used to give greater simulation to all
frequencies
This ensures that excellent voice centering
is maintained.
In some cases, it is desirable to disable the
front panel controls. An authorized person
may want to optimize the “sound” of the
Generation II, and then restrict the changing
of those settings. A 3-position switch, located inside the unit, allows the operating
Generation II User GuideIssue 3, July 1991
Studio Technologies, Inc.Page 5
except those in the voice band.
Overview
In this section you will:
• Remove the top and, if required, the
bottom cover
• If required, install an input load resistor
• Set the input, output, and system status
switches
• Replace the cover(s)
• Mount the Generation II
• Connect the audio signals
• Connect power
• Adjust the input level
Remove the Cover(s)
The following procedures must be
performed by a qualified technician.
Operating the Generation II with
the top and/or bottom cover removed exposes the technician to points in the power
input section with hazardous voltages.
3-position switch located on the left side,
toward the back of the circuit board.
The Generation II is designed to produce
nominal audio signal levels of 0, +4, or
+8dBu. Set the desired output level using
the 3-position switch located in the center,
toward the back of the circuit board.
Ensure that the power cord is removed from
the power connector on the back panel.
Remove the top cover. Four Phillips head
screws hold the top cover to the side rails.
If an input load resistor is going to be installed, remove the bottom cover. Four
Phillips head screws hold the bottom cover
to the side rails.
Please Note: Do not touch any potentiometer on the circuit board or factory calibration may be required.
Input Load Resistor
The input impedance of the Generation II is
25k ohms. In some cases, an input termination resistor, with a value such as 150 ohms
or 600 ohms, may be desired. Provision has
been made for an input resistor to be installed in the Generation II’s circuit board.
The resistor is shown on the schematic
connected to pins 2 and 3 of the input
connector. It is labeled R2 on the circuit
board’s legend. Carefully insert the desired
resistor into the circuit board and solder the
connections. Using diagonal cutters, trim
the excess resistor lead. You may want to
label the back panel with the revised input
impedance.
Configuration Switches
The Generation II is designed to accept
nominal audio signal levels of 0, +4, or
+8dBu. Set the desired input level using the
The system status switch sets the way the
Generation II operates. This switch is located on the left side, near the front of the
circuit board.
In the front panel position, the front panel
controls are enabled.
In the fixed — music position, the front
panel controls are disabled, and the unit
operates in the music mode.
In the fixed — music & voice position, the
front panel controls are disabled, and the
unit operates in the music & voice mode.
Replace the Cover(s)
Carefully replace the top and, if removed,
bottom cover using the screws that were
previously removed.
Mounting
The Generation II Stereo Simulator is rackmountable, requiring one standard rack
space (1.75 inches) in a standard EIA 19.00
inches rack. Keeping the Generation II
relatively cool will enhance operating life.
Most electronic equipment failures are
power-supply related. Power supplies tend
to generate heat which, when not adequately controlled, toast the power supply,
dry out electrolytic capacitors, etc. Keeping
all equipment relatively cool will reduce the
likelihood of problems occurring.
Issue 3, July 1991Generation II User Guide
Page 6Studio Technologies, Inc.
Signal Connections
All signal connections to and from the
Generation II are made via 3-pin XLR-type
connectors located on the back panel; one
female for line input, and two male for left
and right line output. For hum, noise, and
radio frequency pickup rejection, shielded
cable must be used. The shield should be
connected to pin 1 of the input and output
connectors. Pin 1 is electrically in common
with the Generation II’s power supply
ground, chassis ground, and power cord
ground leads. Following the European
convention, pin 2 is audio high and pin 3
is audio low. Maintaining consistent audio
input and output polarity is important for
correct performance. Failure to maintain
consistent left and right output polarity
will make the output audio not monocompatible.
The Generation II uses electronically balanced input and output circuitry. Best performance is achieved if the equipment
sending signal to and receiving signal from
the Generation II is operating in a balanced
mode. The input and output stages will
operate correctly in an unbalanced mode,
but selected performance characteristics
will be sacrificed. On the input side you will
lose the ability to reject common-mode
signals that balanced operation affords. On
the output side, you will lose 6dB maximum
output level. This is not a technical fault but
is inherent in electronically balanced output
stages. If unbalanced input operation is
required, strap the audio low to ground (pin
3 to pin 1). Connect input audio high to pin
2 and signal ground to the combined pins 1
and 3. If unbalanced output operation is
required, strap pin 3 to pin 1. Connect the
output audio high lead to pin 2 and signal
ground to the combined pins 1 and 3.
In broadcast settings, it is recommended
that the Generation II’s input and output
signals be connected via patch points.
Installation, testing, and servicing procedures will be greatly improved if the unit can
be easily taken off line. Make sure that the
Generation II can be “patched around”
during testing and maintenance.
The Generation II’s line outputs are low
impedance, electronically balanced, line
level. They are capable of driving virtually
all line inputs (low or high impedance,
transformer or transformerless).
In most cases, transformer coupling between audio equipment is neither required,
nor desirable. If the equipment sending
signal to, or receiving signal from the
Generation II requires the isolation given
by a transformer, but does not contain
internal transformers, external transformers
can be added. Refer to the Technical Notes
section of this manual for recommended
transformers.
Connecting to Power
The Generation II may be operated from
either nominal 115Vac or 230Vac, 50/60Hz.
Units shipped to North America and Japan
are factory selected for 115V operation and
are supplied with a 0.50A 3AG fuse. Units
shipped outside North America or Japan are
selected for 230V operation and are supplied with a 0.25A 5x20mm fuse. Before
connecting the unit to power, determine the
actual line voltage and check to see that the
voltage selector switch located on the back
panel is set to the appropriate voltage. If the
voltage selector switch is set for 230V, a
0.25A fuse is required; 115V requires
0.50A.
Generation II User GuideIssue 3, July 1991
Studio Technologies, Inc.Page 7
Caution: An incorrect voltage setting and/or
incorrect fuse could seriously damage the
unit.
The Generation II uses an IEC standard
connector to mate with the line cord. The
line cord supplied has a North American
standard plug at one end and an IEC connector at the other. In non-North American
applications, the plug must be cut off and an
appropriate plug attached. The wire colors
in the line cord conform to the internationally recognized CEE color code and should
be wired accordingly:
use a sine wave input signal when attempting to perform this, or any other Generation
II adjustment. A single frequency input
signal produces output signals that have
level characteristics very different from
those produced by normal audio input
signals. When testing, it is best to use
normal program audio or pink noise.
Operation
Using the Controls
ConnectionWire Color
Neutral (N)Light Blue
Live (L)Brown
Protective Earth (E)Green/Yellow
The Generation II does not contain a power
switch. The unit will start to operate as soon
as power has been connected.
Input Trim Adjust
Once the unit has been installed and is
operating, the input trim potentiometer may
be adjusted. This control is accessible from
the back panel, directly next to the input
connector. The trim pot allows the input
level to be adjusted over a small range,
approximately ±0.75dB. Use this control
only if you need to precisely match the
signal levels in your audio chain. In most
installations, the pot can be set at 50 percent rotation, and then forgotten about. The
Generation II’s electronically balanced
output stages have slight output level
changes as a function of load impedance. It
is normal to find a 0.35dB drop in output
level when driving a 600 ohm load, versus
driving a 20k ohm load. The input trim pot
can be set to “make up” this loss. Do not
There are two switches and one potentiometer on the front panel of the Generation II.
In addition, there is a trim potentiometer
accessible via an opening in the front panel.
There is no power switch; the Generation II
is designed for continuous operation. Not
having a power switch means that the unit
cannot be accidently turned off.
Mode Switch
The mode switch controls the overall sound
of the Generation II. The mode switch is
active only when the internal system status
switch is set to the front panel position. In
the music position, the full audio bandwidth
of the input signal is simulated. This mode
is appropriate for audio material with little or
no voice only content. In the music & voice
position, the input signal is sent through a
band-reject filter prior to getting sent to the
simulator circuits. This creates stereo simulation over the low and high frequency
range, while limiting simulation in the voice
band. This mode is appropriate for audio
material that contains voice only content,
such as a film track or television show.
Issue 3, July 1991Generation II User Guide
Page 8Studio Technologies, Inc.
Meter Switch
The meter switch selects which signals are
monitored by the two LED meters. In the
input position, the left meter displays the
line input signal and the right meter is not
active. In the output position, the left meter
displays the left line output and the right
meter displays the right line output.
Stereo Intensity Control
The stereo intensity control determines the
amount of stereo simulation that is produced. The stereo intensity control is active
only when the internal system status switch
is set to the front panel position. In the fully
counterclockwise position, no simulated
stereo is produced. The mono input signal
is sent equally to the left and right outputs.
As the control is turned clockwise, the
amount of stereo simulation increases. The
size of the stereo image that is produced is
directly related to the setting of the stereo
intensity control.
Stereo Intensity Trim Control
To the lower left of the stereo intensity
control is a small opening in the front panel.
This opening allows access to a trim potentiometer. This trim pot controls the stereo
intensity when the internal system status
switch is set to the fixed — music or fixed —
music & voice positions. This trim pot allows
the sound of the Generation II to be adjusted, but “hides” the control from unauthorized personnel.
Panel Controls Disabled LED
On the left side of the front panel is a yellow
panel controls disabled LED. This LED is lit
when the internal system status switch is
set to the fixed — music or fixed — music &
voice positions. It alerts the user that the
front panel mode switch and stereo intensity
potentiometer functions are not active. This
also indicates that the stereo intensity trim
potentiometer is active.
Mode LEDs
The operating mode of the Generation II is
displayed by two red LEDs labeled music
and music & voice. If the panel controls
disabled LED is lit, the fixed operating mode
will be displayed via one of the two LEDs. If
the front panel controls are active, the LEDs
will follow the operation of the mode switch.
Audio Signal Level LEDs
Two sections of the LED meter display the
audio input and output levels. These meters
are not intended to be calibrated, VU- or
peak-type, but strictly to provide a relative
level indication. The green LEDs show the
presence of low level signal in the Generation II. The yellow LEDs show the presence
of moderate signal levels. The red LEDs
light when the signal level approaches,
within about 10dB, the internal clipping
level.
Normal Operation
You should now feel confident that the
Generation II Stereo Simulator has been
carefully installed and is ready to go to
work. With normal audio input signals, the
green and yellow LEDs should light most of
the time. On peaks, the red LEDs may light.
However, if they light steadily, you should
reduce the level of the input signal. If you
have any questions concerning the unit,
now is a good time to give us at Studio
Technologies a call. Otherwise, set the
controls for your desired simulated stereo
sound and that’s it.
Generation II User GuideIssue 3, July 1991
Studio Technologies, Inc.Page 9
Technical Notes
former. This should give very good results
on both the input and output sides.
Definition of Level
Studio Technologies has opted to use the
dBu designation as it seems to be quite
rational. Using dBm was fine when all audio
line outputs were terminated with 600 ohm
loads. In this way, it was easy to say that
0dBm is 1 milliwatt dissipated in the known
load (i.e., 0dBm across 600 ohms will measure 0.7746V). In contemporary situations,
an audio output line is rarely terminated in
600 ohms; generally it’s 20k ohms or
higher. The dBu designation is a better
reference because it refers to dB referenced to 0.7746V, with no reference to load
impedance. This takes into account today’s
audio scene with load impedances varying
greatly. When the Generation II’s specifications refer to the maximum output level in
dBu, this would translate to dBm only when
the output is terminated with 600 ohms.
Transformer Coupling
As discussed in the Installation section of
this manual, there may be cases where
transformer isolation of the Generation II’s
line input and/or output signals may be
required. As the unit has excellent electronically balanced input and output circuitry,
interfacing with most other equipment
should not require transformer isolation
except in the strangest of cases. If you do
find a case where you need them, we suggest using transformers from Jensen Transformers Incorporated, 10735 Burbank Blvd.,
North Hollywood, CA 91601, telephone
(213) 876-0059. They make excellent parts
and we recommend their JE-11-DMCF, a
600 ohm to 600 ohm output type trans-
Resistor Loading
Some audio and broadcast operations
maintain as standard practice termination
resistors on all audio lines. This is usually
done at the input stage of all pieces of audio
equipment. This is not necessary with the
design of most contemporary audio equipment. Current practice calls for low source
impedances and high input impedances.
The Generation II follows this practice. A
problem can occur if you choose to load the
line input and output signals connected to
the Generation II. Double loading can occur
if you have wired the Generation II via a
patch bay and you patch around the unit.
The output of the device driving the Generation II will now be driving the two line
inputs of the device connected to the outputs of the Generation II. This double loading may reduce the audio level being sent to
the next piece of audio equipment. The best
solution is to load neither one. In fact, loading the Generation II’s line outputs does
nothing to improve performance. It basically
just wastes output current. Be aware of this
situation if you decide to use load resistors.
Non-standard Input and Output Levels
Studio Technologies designed the Generation II to match the audio operating levels of
most facilities. If you are the creative type
who likes to experiment, or the unlucky one
who inherited a facility and has an operating
level different from 0, +4, or +8dBu (ref.
0.7746V), don’t despair. The 0, +4, or +8
settings are used to optimize the Generation II’s performance, and using a slightly
different operating level will make only
minor differences in performance. If you are
Issue 3, July 1991Generation II User Guide
Page 10Studio Technologies, Inc.
within 2dB of one of the Generation II’s
preset levels, set the input and output
switches to the closest value. If you are
exactly in between two of the choices, go
for the lower one. An example would be a
facility running +6dBu. Set the input and
output levels for +4. If you are running an
operating level below 2dB or above +10dB,
contact Studio Technologies for details on
simple operating level modifications.
Circuit Description
In this section, we will review the Generation II’s circuitry. This information will assist
you in understanding the operation of the
unit, as well as providing a guide to troubleshooting any problems that may arise.
Operational amplifier sections of an integrated circuit will be referred to as an “op
amp section,” or as an “op amp.”
Proof of Perf ormance T esting
Proof of performance tests on a broadcast
facility commonly use sine waves of different frequencies and levels to check such
things as frequency response, noise, and
distortion. Very unusual results can occur if
Generation II performance tests are made
using sine wave or constant frequency
signals. These results are due to the way
the unit creates simulated stereo, taking a
mono input and delaying, randomizing, and
gyrating the signal into a good stereo image. Simulating stereo from a fixed frequency input will result in different left and
right output levels that will appear to change
randomly as the input frequency is varied
slightly. This is completely normal and
expected. Remember that the usual input
signal is complex music, voice or other
natural sound.
To get rational proof of performance data,
either take the unit out of the signal path, or
reduce the stereo depth control to the
minimum, fully counterclockwise position. If
you wish to check The Generation II with
stereo simulation taking place, you need to
use pink noise. The randomness of pink
noise will allow left versus right frequency
response observation.
Po wer Suppl y
A step down transformer converts the
incoming line voltage to nominal 40Vac.
The primary of the transformer is tapped for
either 115Vac or 230Vac input. A switch on
the back panel selects which tap is connected. A fuse in series with the primary
protects the unit in case of a component
malfunction. The Generation II contains no
power switch. The power line is connected
directly, via the fuse, to the transformer.
This prevents the unit from being accidently
turned off. The secondary of the transformer has a center tap, which acts as the
circuit common, as well as being strapped
to the metal chassis and line cord ground
wire. The secondary of the transformer
connects to a full wave bridge rectifier. The
full wave bridge produces nominal ±30Vdc.
From the unregulated ±30Vdc two fixed
voltage 3-terminal regulators produce
±15Vdc. A resistor and zener diode combination produces 22Vdc. The audio circuitry
uses ±15Vdc, and the delay line oscillator
FET switch uses 22Vdc. An LED indicator,
in series with a resistor, is connected to
+15Vdc to provide an indication that the unit
has incoming power.
Generation II User GuideIssue 3, July 1991
Studio Technologies, Inc.Page 11
Meter Circuit
Line Input
Two, three-stage LED level meter circuits
provide the user with an indication of several Generation II internal operating levels.
The meters are not intended to give a
precise reading, but simply to provide general level indications. The right meter displays the level of the right channel signal
just prior to the right channel line driver
stage. The input to the right meter comes,
via the meter select switch, from the output
of the op amp that serves as a right channel
difference/gain section. The left meter is
switch-selectable to display the level of the
input signal or the level of the left channel
signal just prior to the left channel line driver
stage. The input to left meter comes from
either the output of the line input section, or
the op amp that serves as the left channel
summing/gain section.
Op amps configured as half wave rectifiers
convert the incoming meter audio into DC.
This DC voltage is fed to three sections of
op amp which are configured as voltage
comparators. Voltage dividers provide
reference voltages for the comparators. The
comparator outputs act as current sinks to
light the LEDs. The LED current is resistor
limited to 10mA for the green and red LEDs,
and 15mA for the yellow LEDs. The different currents compensate for the different
LED efficiencies.
The green LEDs have a low lighting threshold, making them act as “signal present”
indicators. The yellow LEDs are set to light
with moderate signal levels. The red LEDs
are set to light when internal signal levels
approach clipping.
The purpose of the line input stage is to
take a balanced audio input signal, reduce
its level by a fixed amount, and convert it to
unbalanced. For best operating performance, the internal operating level of the
Generation II is 6dBu. This level combines
a good signal to noise figure with ample
peak signal headroom for circuits operating
with ±15Vdc power sources. Since different
facilities run different average operating
levels, the line input stage is switch-selectable for 0, +4, or +8dBu operation. This
translates to attenuating the input signal by
6, 10, or 14dB.
Signal enters the Generation II via a female
XLR-type connector. A resistor position has
been left vacant on the circuit board if an
input load resistor is desired. The input
signal is direct coupled to a differential line
receiver integrated circuit. This IC is truly
optimized for audio applications, providing
many fine features, including excellent
common-mode rejection, low distortion, and
low noise. The now unbalanced signal
enters a passive attenuator section consisting of a 3-position switch, fixed resistors,
and a trim pot. This attenuator reduces the
signal level to the nominal 6dBu internal
operating level from the nominal input levels
of 0, +4, and +8dBu. The trim pot allows the
input level to be adjusted over a ±0.75dB
range. One section of op amp buffers the
attenuated signal to correctly drive the
band-reject filter, the summing/gain and
difference/gain sections, and the system
status switch.
Issue 3, July 1991Generation II User Guide
Page 12Studio Technologies, Inc.
Band-Reject Filter
The band-reject filter is made up of four
sections of op amp. The 3dB points of the
filter are 400Hz and 2.2kHz, with an 11dB
dip at 1.1kHz. This filter is set to attenuate
signals in the voice band, while leaving low
and high frequency audio signals unaffected. This filter is the reason why the
Generation II in the music & voice mode
adds simulation primarily in the non-voice
region of the audio spectrum. The signal
leaves the band-reject filter and proceeds
to the system status and front panel mode
switches.
Status Switch
Spread out over several of the schematic
pages is the system status switch. It is a
4-pole, 3-position slide switch. What it does
is really quite simple. In the fixed—music &
voice position: the output of the band-reject
filter is sent to the input of the compressor,
the bucket brigade delay’s clock oscillator is
set to the high frequency position, and the
wiper of the stereo intensity trim pot is sent
to the summing/gain and difference/gain op
amps. In the fixed—music position: the
output of the line input stage is sent to the
input of the compressor, the oscillator is set
to the low frequency position, and the wiper
of the stereo intensity trim pot is sent to the
summing/gain and difference/gain op amps.
In the front panel position: the mode switch
and stereo intensity potentiometer on the
front panel are active.
filter is in or out of the signal sent to the
compressor, and controls the BBD’s clock
oscillator frequency. This allows the users
to select if the Generation II operates in the
music or the music & voice mode.
Audio Delay
A large part of the Generation II’s circuitry
involves time delaying the audio input
signal. The “heart” of the time delay is an
integrated circuit that implements a bucket
brigade delay (BBD) line. A BBD is an
analog technique that samples a signal and
stores an analog representation of its level.
This analog signal is then passed, “bucket
to bucket” to achieve a delay. The more
buckets, and the more time the signal is
stored in each bucket, the longer the time
delay. The length of time the signal sits in a
bucket is inversely related to the frequency
of its clock signal. The higher the clock
frequency, the shorter the time delay. An
anti-aliasing filter is required to prevent the
BBD from receiving input signals greater
than one half the lowest clock frequency. A
low-pass filter on the output of the BBD
prevents clock signal from being present in
the audio output. A compandor scheme is
used to improve the BBD’s signal to noise
ratio. The input signal is compressed prior
to being sent to the BBD, and then expanded afterwards. Charge pumps help the
compressor and expander circuits respond
to signal transients.
Compressor
Front Panel Mode Switch
If the status switch is set to the front panel
position, the front panel mode switch is
active. The switch selects if the band-reject
Generation II User GuideIssue 3, July 1991
Studio Technologies, Inc.Page 13
Audio enters the delay circuitry via an
inverting buffer op amp associated with the
compressor portion of an integrated circuit
compandor. A simple resistor/capacitor preemphasis network precedes the inverting
buffer. The compressor attack time is
speeded by a charge pump, which reduces
transient distortion that is often associated
with compandors.
Input Low-pass Filter
The compressed signal connects to an antialiasing low-pass filter. Three sections of op
amp form a 6-pole, 20kHz Butterworth lowpass filter. This reduces the possibility of
audio frequencies aliasing with the BBD’s
clock signal.
BBD Clock
An oscillator integrated circuit provides
three signals for the BBD: clock 1, clock 2,
and a voltage reference. Clock 1 and clock
2 are identical square wave signals 180
degrees apart in phase. The frequency of
clock 1 and clock 2 is set by a resistorcapacitor (RC) combination, in association
with an FET-controlled frequency select
circuit. In the music mode, the FET is biased to the non-conducting state. In the
music & voice mode, a shorter delay is
required and the FET is turned on, reducing
the time constant of the RC circuit and
raising the clock frequency. The clock is set
for 64±1kHz in the music mode and
switches to approximately 119kHz in the
music & voice mode.
Output Low-pass Filter
The time delayed audio enters a 5-pole,
20kHz Butterworth low-pass filter created
using three sections of operational amplifier.
This filter removes clock signal from the
BBD’s output signal.
Expander
The signal was compressed prior to being
delayed. The expander portion of the
compandor integrated circuit is used to
recreate the original dynamic range. Again
a charge pump is used, this time in the
compandor rectifier. The audio signal has
now been delayed and is ready to go to
work!
Randomizing Network
The delayed signal enters a proprietary
randomizing circuit which is in the form of a
sealed module. Frankly, the great sound of
the Generation II’s simulated stereo is
created by this network. The randomizing
circuit modifies the delayed signal to ensure
that the peaks and dips in the soon to be
created comb filter do not fall on objectionable harmonics, preserving the natural
sound of the audio. The output of the network connects to both the front panel and
trim stereo intensity potentiometers.
Summing/Gain and Difference/Gain
The simulated left and right signals are
created by two sections of op amp. The left
channel is created by summing the output
of the front panel or trim potentiometer
stereo intensity control with the direct input
signal. This creates a comb filter which
breaks the audio signal into hundreds, or
thousands, of little pass-bands. The right
channel is created by producing the difference between the output of the front panel
or trim potentiometer stereo intensity control
and the direct input signal. Again, combs
are created, but with every comb 180 degrees out of phase with those created in the
left channel. These combs are what give the
Issue 3, July 1991Generation II User Guide
Page 14Studio Technologies, Inc.
listener the illusion of space, i.e., stereo!
Both op amp sections add gain according to
the position of the 3-position output level
switch.
The mono-compatibility of the Generation
II’s simulated stereo can be easily understood by a careful study of how the stereo is
actually made. The output of network module is really the “stereo information.” The left
channel is created by adding some of the
stereo information to the incoming mono
signal; the right channel is created by subtracting the same amount. The amount
added and subtracted is directly related to
the setting of the front panel or trim stereo
intensity controls. When listening to the
simulated left and right output signals in
stereo, a feel of “space” is perceived. When
listening in mono, the left and right signals
are summed (added together), dropping out
the stereo information and giving the original signal. The Generation II’s stereo information exactly cancels out! What is added
to the left channel is subtracted from the
right.
This process holds true in the music and
music & voice modes. In the music mode,
full bandwidth delayed input audio is added
and subtracted. In the music & voice mode,
band-passed delayed input audio is added
and subtracted. In either case, perfect
mono compatibility is maintained.
Line Output Sections
The output stages use sophisticated, balanced line driver integrated circuits. These
ICs are optimized for audio applications
such as the Generation II. Unbalanced
signal enters the ICs via the summing/gain
section for the left channel, and difference/
gain section for the right channel. The
nominal level fed to the ICs is 6, 2, or
+2dBu, depending on where the output
level switch is set. The line driver IC adds
6dB of gain, giving final nominal output
levels of 0, +4, or +8dBu. The line driver ICs
are capable of driving high signal levels into
600 ohm or greater loads, remaining stable
even when driving unbalanced loads. This
means that if one side of a line output is
grounded, the IC is not harmed and the
other side of the line output still functions
correctly. The output signals are direct
coupled to the XLR-type line output
connectors.
Troubleshooting
The following procedures must be
performed by a qualified technician.
Operating the Generation II with
the top and/or bottom cover removed exposes the technician to points in the power
input section with hazardous voltages.
Equipment Required
• Low Distortion Audio (Sine Wave)
Generator, must have tone burst
capability
• Qty 2, AC Voltmeter, high input
impedance type
• Frequency Counter (200kHz minimum
measuring ability)
• Audio Distortion Analyzer, Sound
Technology 1710A or equal
• DC Voltmeter, high input impedance type
• Oscilloscope, Tek 465 or equal
• Test Probes for above
• Audio Cables as required
Generation II User GuideIssue 3, July 1991
Studio Technologies, Inc.Page 15
P ower Supplies
The first step in troubleshooting the
Generation II is to remove the top cover
(two Phillips head screws on each side
panel). It is common for failures associated
with contemporary audio equipment to be
power-supply related. The components
most likely to fail in the power supply are
the 3-terminal regulators (one each for +15
and 15) and the large filter capacitors.
Power Supply Voltages
Caution: DO NOT attempt to adjust any of
the trim pots inside the unit before you
understand the entire alignment procedure
and are equipped to go through the entire
process.
All signal measurements are made in reference to test point COM. This test point is
common to the +15, 15V, and 22Vdc
power supplies, pin 1 of the three connectors, chassis ground, and earth ground via
the power cord.
With the DC voltmeter common lead connected to COM test point: check +15 test
point for +15±1Vdc, 15 test point for
15±1Vdc.
Analog Problems
If the power supplies are not at fault, use
standard troubleshooting procedures to
locate the problem. A simple technique is to
connect an audio signal to the line input and
trace the signal (again, using the schematic)
until the source of the problem is found.
Alignment
Alignment is required after any repair involving the compandor, BBD, or associated
circuitry. Alignment is not required after
repairs are made to the line input, bandreject filter, summing/gain, difference/gain,
meter, or line driver circuits. The following
paragraphs will aid in aligning the circuits,
which will restore proper operation. It is
important to perform the alignment procedures whenever you have replaced any
components in the aforementioned circuits.
Alignment can be tricky and, if possible,
factory repair and realignment is recommended.
Procedure
1)Apply power to the Generation II. Be
Very Careful: High voltage is present
in the power entry area.
2)On the Generation II’s front panel: set
the mode switch to the music mode,
and the stereo intensity control to the
fully counterclockwise (min) position.
3)On the Generation II’s circuit board: set
the system status switch to the front
panel mode, input level switch to 0,
output level switch to 0, and input trim
pot R1 (accessible via the back panel)
to 50 percent the (middle) position.
4)Connect the signal generator output to
the line input, located on the back
panel.
5)Set the signal generator frequency to
1kHz, with output level to OFF so that
no signal is getting sent to the line input.
The signal generator signal must be a
sine wave.
Initial Compandor Adjustments
1)Again, ensure that no audio is coming
into the unit.
Issue 3, July 1991Generation II User Guide
Page 16Studio Technologies, Inc.
2)With the DC voltmeter common lead
connected to test point COM: check test
point COMP for 1.35±0.5Vdc. If not
within this range, set R85 to give
1.35Vdc at test point COMP.
3)With DC voltmeter common lead connected to test point COM: check test
point EXP for 1.35±0.5Vdc. If not within
this range, set R88 to give 1.35Vdc at
test point EXP.
BBD Clock Frequency
1)Connect common lead of frequency
counter to test point COM. Check test
point CLK for 64±2kHz. Remember, you
must have the unit in the music mode. If
not within this range, set R63 to give
64±2kHz.
Incoming Audio T est Signal
5)Reduce the generator level 20dB.
Observe level at AUDIO 2. It should
drop 15±0.3dB. If not, again adjust R85
to get this condition.
BBD Distortion
1)Set the audio generator’s frequency to
5kHz; adjust its level to give 10dBu
when measured at test point AUDIO 1.
2)Set the front panel stereo intensity
control to give 10dBu when measured
at test point AUDIO 3.
3)Connect distortion analyzer to measure
at test point AUDIO 3.
4)Adjust R13 to give minimum distortion
(THD + Noise). The acceptable minimum distortion is 0.35 percent or lower.
The usual minimum is 0.10 to 0.25
percent.
1)Connect the AC voltmeter common
lead to test point COM.
2)Adjust the audio generator output level
to give a 10dBu reading at test point
AUDIO 1.
Compressor
1)Move the AC voltmeter lead to test
point AUDIO 2. Note the reading that
you observe. It should be 10±2dBu.
2)Reduce the generator level by 20dB.
3)Observe the level at AUDIO 2. It should
have dropped 15±0.3dB. If not, adjust
R85 to get this condition.
4)Raise the generator level 20dB. Observe level at AUDIO 2.
Expander
1)Set generator frequency to 1kHz; adjust
its level to give 10dBu at test point
AUDIO 1.
2)Measure level at AUDIO 3. You should
have left the front panel stereo intensity
control where it was set a few steps
previously.
3)Reduce the generator level 20dB. Level
at AUDIO 3 should drop 20±0.3dB. If
not, adjust R88 to get this condition.
4)Raise generator level 20dB. Observe
level at AUDIO 3.
5)Drop generator level 20dB. Observe
level at AUDIO 3. It should drop
20±0.3dB. If not, again adjust R88 to
get this condition.
Generation II User GuideIssue 3, July 1991
Studio Technologies, Inc.Page 17
Expander Transient Response
1)Adjust the generator level to give 0dBu
when measured at test point AUDIO 1.
Set the generator to the tone burst
mode: two cycles on, 64 cycles off. In
this way, two cycles of audio pass to the
Generation II, then 64 cycles of no
audio, etc.
2)Observe AUDIO 3 on the oscilloscope.
Adjust R34 to give the flattest base
band signal. The signal should not over
or under shoot.
Gain Variation T rim Potentiometer
1)Set the audio generator frequency to
1kHz; adjust its output level to give
10dBu when measured at test point
AUDIO 1.
Specifications
Mounting
One space in a standard 19-inch (48.3cm) rack
AC Mains Requirements
115Vac or 230Vac, 10%, switch selectable,
50/60Hz, 10 watts
Fuse
0.5A for 115V, 0.25A for 230V; units shipped to
North America and Japan contain 0.5A 3AG type;
all others shipped with 0.25A 5x20mm type
Connectors
Input: 3-pin XLR-type female, pin 2 high
Outputs: 3-pin XLR-type male, pin 2 high
Input
Electronically balanced, direct coupled, load termination resistor optional
Input Level
0, +4, or +8dBu, switch selectable
2)Adjust R98, Gain Variation Adjust, to
give 10dBu when measured at the
output (pin B) of the Network Module.
It is easier to measure this signal at
the clockwise connection of the stereo
intensity controls.
Input Level Adjust
Approximately ±0.75dB
Input Impedance
25k ohms, nominal
Input Common Mode Rejection
100dB @ DC and 60Hz, 70dB @ 20kHz, 62dB @
40kHz (typical)
Output
Electronically balanced, direct coupled
Output Level
0, +4, or +8dBu, switch selectable
Output Level at Clipping (0dBu = 0.7746V)
+25dBu into 600 ohms, balanced
Frequency Response
Better than ±0.1dB, 20Hz to 20kHz (no simulation
added)
Signal to Noise Ratio (Simulator In Circuit)
76dB
Distortion (THD + Noise, 20Hz to 20kHz)
Simulator In Circuit: less than 0.40%
Issue 3, July 1991Generation II User Guide
Page 18Studio Technologies, Inc.
Dimensions (Overall)
19.00 inches wide (48.3cm)
1.75 inches high (4.5cm)
7.00 inches deep (17.8cm)
Studio T echnologies
Limited W arranty
Weight
4.2 pounds (1.9kg)
Specifications and information contained in
this instruction manual are subject to
change without notice.
The Studio Technologies, Inc. product
which you have purchased is guaranteed
against defects in material and workmanship under normal use and service for a
period of three (3) years from date of manufacture.
During this warranty period, any components of the product that prove to be defective will be repaired (or, at the discretion of
Studio Technologies, Inc., replaced) at no
charge provided that the product is returned, shipping prepaid, to the manufacturer.
Information on obtaining service is available
by contacting the dealer from whom the
product was purchased, or by contacting
Studio Technologies, Inc.
This warranty does not apply if, in the opinion of Studio Technologies, Inc., the product
has been damaged due to abuse, misuse,
misapplication, accident or as a result of
service or modification by other than an
authorized dealer service center.
No other warranties are expressed or
implied, including, but not limited to, any
implied warranties of merchantability
and fitness for a particular purpose.
Studio Technologies, Inc. shall not be
held responsible for any consequential
damages or losses arising from the use
of this product.
Generation II User GuideIssue 3, July 1991
Studio Technologies, Inc.Page 19
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