Model 80 Stereo Analog
Audio Distribution Amplifier
User Guide
Issue 5, October 1999
This User Guide is applicable for serial numbers:
Model 80 M80-00360 and later
Copyright © 1999 by Studio Technologies, Inc., all rights reserved
5520 West Touhy Avenue
Skokie, Illinois 60077 U.S.A.
Telephone (847) 676-9177
Fax (847) 982-0747
www.studio-tech.com
50200-1099, Issue 5
Table of Contents
Foreword...................................................................... 5
Introduction .................................................................. 7
What This User Guide Covers ................................. 7
System Overview ..................................................... 7
System Features ...................................................... 7
Installation .................................................................... 9
Configuration ............................................................... 11
Operation ..................................................................... 12
Troubleshooting ........................................................... 12
Technical Notes ........................................................... 14
Specifications............................................................... 16
Block Diagram
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Issue 5, October 1999 Model 80 User Guide
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Foreword
I am pleased to present the Model 80 Stereo Analog Audio Distribution Amplifier. As both president and owner of Studio Technologies, I take a very personal
approach when designing products. Getting older (38 as of this writing) has
increased my appreciation of the more subtle things in lifebe they a part of
nature or the nuances contained in a well-designed piece of electronic equipment. Do the technical and operational aspects of a product work together to
feel right? A Studio Technologies design is ready to go only when I am completely satisfied.
Many fine people worked toward making the Model 80 happen. Mitch Budniak
(ace consulting engineer) designed many of the circuits. Jim Cunningham
contributed to the analog design. Carrie Loving provided engineering support.
Ben Kamen designed the automatic testing routines. Al Lux designed the
printed circuit board. Fred Roeck performed the mechanical design. Joe
Urbanczyk coordinated the safety testing and agency approvals.
Additional thanks to Timothy Powell of Metro Mobile Recording, Glenview,
Illinois, who provided his excellent ears when issues of sonic quality arose. His
extensive field and studio experience was extremely helpful in keeping me on
the audio straight and narrow.
Please contact me with your questions, comments, and suggestions. I can be
reached by voice at (847) 676-9177, fax at (847) 982-0747, or via the Internet @
www.studio-tech.com.
Sincerely,
Gordon K. Kapes
President
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Issue 5, October 1999 Model 80 User Guide
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Introduction
The Model 80 Stereo Analog Audio
Distribution Amplifier was developed by
Studio Technologies as part of its Studio
Tools group of audio support products.
standards make the Model 80 suitable
for continuous operation, even for on-air
broadcast applications.
System Features
One Stereo Input
The Model 80 is designed to work in a
large variety of applications. Specific
applications include audio production,
duplication, broadcast, and sound reinforcement. All Model 80 functions meet
or exceed the performance of the most
expensive high end audio equipment.
What This User Guide Covers
This User Guide is designed to assist you
when installing, configuring, and using the
Model 80 Stereo Analog Audio Distribution
Amplifier.
System Overview
The Model 80 from Studio Technologies,
Inc. is the first distribution amplifier that
meets the needs of the real world. The
stereo input is intended to connect to
virtually any line-level audio source. The
ExactCal input calibration section allows
for optimal audio performance over a 10
to +10dBu input level range. The eight
stereo outputs meet exacting professional
standards. Capable of driving balanced or
unbalanced loads, each output can drive
+26dBu into 600 ohms. Using front panel
switches, each output can be individually
configured for a nominal output level of
10 or +4dBu.
The front panel controls and LEDs make
installation and setup a simple job. The
AC mains internal power is factory configured for 100, 120 or 220/240V, 50/60Hz
operation. Components and construction
The differential input circuitry is compatible with balanced or unbalanced signals
having a nominal level range of 10 to
+10dBu. Using laser trimmed components, the input offers superior commonmode signal rejection. To achieve optimal
audio performance the ExactCal calibration section matches the specific input
level with the Model 80s internal gain
structure. Two controls and four LEDs
allow fast, precise calibration. Unlike other
distribution amplifiers, the Model 80
ensures that excellent audio performance
can be achieved with little or no hassle.
In addition to separate left and right input
connectors, two input loop-through connectors are also provided. This simple
feature can make installation with related
equipment much easier. The loop-through
connectors allow the Model 80s input
source to be connected to another Model
80 or to yet another device.
Eight Stereo Outputs
The Model 80 contains eight independent
stereo output sections. For compatibility
with a range of facilities, each output
section can be separately configured for
10 or +4dBu nominal output level. Each
output features an electronically balanced
circuit capable of driving balanced or
unbalanced loads. Operating an output
in an unbalanced configuration does not
cause its nominal output level to change.
Short circuit resistant, the rugged output
circuits can drive full signal levels into 600
ohm or greater loads.
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Studio Technologies, Inc. Page 7
The Model 80s architecture precludes the
need for individual output-level trim potentiometers. With the input signal calibrated
using the ExactCal section, the eight
stereo outputs use 1%-tolerance components to provide precise 10 or +4dBu
outputs.
Audio Performance
The Model 80 is the result of exacting
circuit design combined with the latest
state-of-the-art components. Like all
Studio Technologies products, the Model
80 has survived tough listening evaluations by industry professionals. These
veterans had the ears to guide us in
achieving the right performance. The
outcome is a product that achieves
sonic excellence.
Design Philosophy
After careful study Studio Technologies
concluded that these adjustments confused, and often interfered with the process of getting maximum audio performance. After checking with personnel in the
field, it became clear that what is desired
in virtually every distribution-amplifier
applications are multiple audio outputs all
operating at a standard reference level.
By implementing the ExactCal system, the
Model 80s internal operating level can be
easily calibrated to match the input signal.
Once this input level matching is accomplished the eight stereo outputs can be
individually configured for a 10 or +4dBu
nominal operating level. In conclusion,
output trim pots are not included on the
Model 80 for the simple reason that better
audio performance can be achieved
without them!
Most audio distribution amplifiers contain
a level trim adjustment on each output.
Model 80 Front Panel
Power
present LED
Input
level control
Input level
calibration LEDs
Model 80 Back Panel
Right input
trim control
10 or +4 output level
configuration switches
AC mains
connection
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Page 8 Studio Technologies, Inc.
Stereo line-level
outputs
Loop through
output
Stereo line-level
input
Installation
In this section you will be installing the
Model 80 in an equipment rack. Audio
input and output connections will be made
using the Model 80s multitude of phone
jacks. AC mains power will be connected
to the Model 80.
System Components
The shipping carton contains a Model 80,
User Guide, and warranty card. Units
destined for North America are shipped
with an AC mains cord. Your dealer or
distributor will provide an AC mains cord
for non-North American destinations.
Balanced Connection
(Input & Output)
Ring ()
Tip ( + )
Sleeve
(Shield)
(Switchcraft No. 297, Neutrik NP3C, or equivalent)
Unbalanced Connection
(Input & Output)
Tip ( + )
Mounting the Model 80
The Model 80 requires one space in a
standard 19-inch (48.3cm) equipment
rack. It is desirable to locate the Model 80
to allow easy access to both the front and
the back panels. The back panel contains
the input and output connectors. The front
panel is used to access the calibration
controls and output-level switches. The
front panel also contains several LED
indicators. The Model 80 is secured to
the equipment rack using two mounting
screws per side.
Audio Inputs and Outputs
The Model 80s audio input and output
connections are made using ¼-inch
3-conductor phone jacks. The choice of
phone jacks was simply a matter of real
estate20 XLR connectors dont quite
fit on the back of a one rack-space unit!
Dont be concerned about damage to
your audio quality, the jacks used in the
Model 80 are manufactured by Neutrik
of Switzerland and feature gold-plated
contacts for excellent performance.
Sleeve
(Shield)
(Switchcraft No. 280, Neutrik NP2C, or equivalent)
Caution: For reliable audio interconnection, the plugs you use must comply with
industry standard RS-453. Switchcraft No.
297, Neutrik NP3C, or equivalent will work
correctly. Refer to the Technical Notes
section for details.
Audio Input
The Model 80 provides one stereo linelevel input. It is electronically balanced,
and is compatible with balanced or unbalanced signals that have a nominal level
range of 10 to +10dBu. The ExactCal
section allows precise level calibration
with the connected input signal. It is
anticipated that in most cases a stereo
signal will be connected to the input. The
Model 80 can also be used as a 1-input/
16-output monaural distribution amplifier,
or as a dual 1-input/8-output monaural
distribution amplifier.
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Studio Technologies, Inc. Page 9
Prepare the input plugs so that tip is
positive (+ or hot), ring is negative ( or
cold), and sleeve is shield. The input
jacks will also accept unbalanced ¼-inch
2-conductor phone plugs. With unbalanced phone plugs, tip is positive (+ or
hot) and sleeve is shield. If 3-conductor
phone plugs are used to connect unbalanced signals, connect positive (+ or hot)
to tip and connect shield to ring and
sleeve.
Loop-Through
The two loop-through jacks are electrically
wired in parallel with the two input jacks.
With this arrangement several applications
are possible, such as allowing the input
signals to be routed to another stereo
input without the use of Y-adapters. The
source signals would be connected to the
input jacks. The loop-through jacks would
be used to connect the source signals to
the next piece of equipment using ¼-inch
3-conductor patch cords.
Another application would be where more
than one Model 80 is used to distribute the
same input signal. Two ¼-inch 3-conductor patch cords would link the loopthrough jacks on the first Model 80 to the
input jacks on the second Model 80.
Yet another application would be where
the Model 80 is used as a 1-input/16output monaural distribution amplifier. The
monaural input would be connected to the
left input jack, and a ¼-inch 3-conductor
patch cord would connect the left loopthrough jack to the right input jack.
Audio Outputs
The Model 80 contains eight independent
stereo line-level outputs which are intended for connection to a variety of analog audio devices. The outputs are
electronically balanced and capable of
driving balanced or unbalanced loads of
600 ohm or greater. The outputs can be
individually configured for a nominal
output level of 10 or +4dBu, so you
can connect to all line-level inputs with
no hassle.
Prepare the output plugs so that tip is
positive (+ or hot), ring is negative ( or
cold), and sleeve is shield. The output
jacks will also accept unbalanced ¼-inch
2-conductor phone plugs. With unbalanced phone plugs, tip is positive (+ or
hot) and sleeve is shield. If a 3-conductor
phone plug is used in an unbalanced
application, connect positive (+ or hot) to
tip and connect shield to ring and sleeve.
AC Mains Power
The Model 80 is internally configured to
operate from either 100, 120, or 220/240V,
50/60Hz. In most cases, units shipped to
North America are factory selected for
120V operation. Units bound for Japan are
selected for 100V, while our friends down
under and in Europe receive units set for
220/240V. Before connecting the Model 80
to AC mains power, check that it is configured to match the local mains voltage.
Look on the back panel, adjacent to the
power entry connector, for the configured
voltage(s). Note that an incorrect configuration could seriously damage the unit.
Should it be necessary to change the
units operating voltage it must be
performed only at the factory or by
an authorized service technician.
The Model 80 uses an IEC standard connector to mate with the AC mains cord.
The wire colors in the AC mains cord
should conform to the internationally
recognized CEE color code and must
be wired accordingly:
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Connection Wire Color
Neutral (N) Light Blue
Line (L) Brown
Protective Earth (E) Green/Yellow
Safety Warning: The Model 80 does
not contain an AC mains disconnect
switch. As such the mains cord plug
serves as the disconnection device.
Safety consideration requires that
the plug and associated outlet be
easily accessible to allow rapid disconnection of mains power should it prove
necessary.
As soon as mains power is connected, the
Model 80s power present LED will light.
The unit is now ready for years of trusty
service!
Configuration
Input Level Calibration
With the ExactCal calibration section its
simple to match the nominal level of the
input signal with the Model 80s internal
circuitry. Two controls, level and right trim,
along with four LEDs are the ExactCal
operator controls. The level control is a
stereo device, adjusting the input sensitivity for both the left and right inputs. The
right trim control allows the input sensitivity for the right channel to be adjusted
over a 3dB range. This allows compensation to be made for small differences in
the left and right input levels. Two LEDs,
labeled Lo and Hi, are associated with
each input. They are provided as an aid
to calibration, as well as serving as signal
present indicators.
The following is a step-by-step procedure
for using the ExactCal section to match an
input signal with the Model 80:
Set the level control fully counterclock-
wise (all the way to the left end of the
travel).
Supply a 1kHz sine wave to both the
left and right line inputs. Set the level
of the source to be precisely the nominal operating level. If, for example, the
output of a console is connected to the
input of the Model 80, the console
output should be adjusted so that the
meters read 0dB or 100%. If the output
of the console is a +4-type, then
setting the consoles left and right
output levels to nominal should find
the console output levels to be exactly
+4dBu.
Slowly turn the level control clockwise.
As you increase the level, watch the
LEDs associated with the left channel.
The LED labeled Lo will light first, then
both LEDs will light, then only the LED
labeled Hi will light. The correct setting
is where both LEDs light. Careful
adjustment is required as the window
where both LEDs light is somewhat
less than 1dB.
Observe the LEDs associated with the
right channel. If they are both lit no
adjustment of the right trim control is
required. If only one is lit adjust the
right trim control, using a small flat
blade screwdriver, so that both LEDs
light. (We like the Xcelite R3324 screwdriverit has the clear green handle
and is commonly used to calibrate
audio equipment.)
Model 80 User Guide Issue 5, October 1999
Studio Technologies, Inc. Page 11
For practice, mess up the settings of
the level and right trim controls. Again
follow the calibration procedure and
again get things set up correctly.
For future reference it may be helpful
to mark the correct input level and right
trim adjustment points. Use a grease
pencil or a piece of adhesive tape so
as not to damage the front panel.
Disconnect the 1kHz signal and con-
nect the normal audio source.
Output Level Selection
Each of the eight stereo line-level outputs
is individually configurable for a 10 or
+4dBu nominal output level. Eight DIPtype switches, located on the right side of
the front panel, are used to set the output
levels. The legend on the switches correspond to the output channel numbers. A
switch that is set to the up position sets its
associated output channel for 10dBu. A
switch set to the down position sets the
output for +4dBu. A small screw driver
may be of assistance when setting the
switches.
any time the input signal is greater than
0.5dB below the nominal operating level.
This sounds a bit confusing but isnt really
so hard to understand. As an example, if
you have a nominal +4 signal connected to the Model 80s line input and
the ExactCal section has been used to
calibrate the input, the Lo LED will light
when the signal is between 14 and
+4.5dBu, the Hi LED will light when the
signal exceeds 3.5dBu.
In most cases the input level control
shouldnt be changed, as it will change
the input calibration. In special applications you may want to use it as a fader,
simultaneously adjusting the level on all
eight stereo outputs. In the fully counterclockwise position the eight outputs are
completely off. Before you use the level
control as a fader ensure that you mark
the position of the knob where the input
is calibrated.
If you change the input source you can
use the ExactCal section to recalibrate the
input. Refer to the configuration section of
this guide for details.
Each of the eight outputs are fully independent. You can patch, reconnect, or
Operation
Now that youve installed and configured
the system, youre ready to go. You
should find operation very easy, as there
is almost nothing to do on a day-to-day
basis. For peace of mind, the ExactCal
LEDs will give you a visual indication
whenever audio signals are present on
the Model 80s input.
The LED labeled Lo will light whenever
the input signal is within the range of 18dB
below and 0.5dB above the nominal operating level. The LED labeled Hi will light
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Page 12 Studio Technologies, Inc.
even short out an interconnecting cable
without effecting the other outputs. Using
the front-panel DIP switches you can
change the output level of any or all of
the outputs whenever you wish.
Troubleshooting
If youre having problems getting the
Model 80 up and running, this section can
help. If you havent read the other sections
of this guide, you should do so before
proceeding.
If the Model 80 Doesnt Work At All
A source of AC mains power must be
connected to the Model 80. Depending on
the version you have purchased, 100, 120,
or 220-240Vac, 50/60Hz is required. Confirm what mains voltage is required by
observing the selection boxes to the left
of the AC mains connector on the back
panel. Whenever mains power is connected the front panel power present LED
should light. If the LED is not lit confirm
that the main power source is active
(hot) and that the connector on the
cord is securely mated with the plug on
the back panel.
For safety in the event of a major internal
failure or the connection of incorrect AC
mains voltage, the Model 80 contains a
fuse inside the cabinet. The fuse will open
(blow) if the failure of an internal component causes excessive current to be drawn
from the internal power supply. The fuse
will also open should 220-240Vac be
connected to a Model 80 that is configured for 100 or 120Vac operation. The
fuse is intended to be replaced only by a
qualified service technician. This person
will have the training to safely access the
guts of the Model 80 and identify where
a problem is located.
Incorrect Output Levels
You must correctly set the input level
and right trim controls for the eight stereo
outputs to receive a precise 10 or +4dBu
nominal output level. These controls
match the level of the audio input signal
with the Model 80s internal circuitry. Refer
to the Configuration section of this guide
for detailed instructions.
Intermittent Audio Connections
Should you experience audio connections
that seem to be flaky or intermittent,
refer to the Technical Notes section of
this guide. The ¼-inch 3-conductor phone
jacks used on the Model 80 are of very
high quality, conforming to the industry
standard EIA RS-453. Some plugs do not
meet this standard, specifically in the
shape of the tip conductor. In rare cases
you may have to replace plugs on interconnecting cables to remedy an interconnection problem. Switchcraft No. 297 or
Neutrik NP3C phone plugs will function
correctly.
Headphones as a Troubleshooting Tool
One of the simplest means of checking
for the overall presence of a line-level
audio signal is to listen to the signal
using a pair of stereo headphones. The
signal level and source impedance of
contemporary audio output circuitry can
easily drive headphones to quite a high
sound pressure level. Carefully used,
headphones are a great means of rapidly
determining if signal is present on an
audio line. Note that in a few cases the
plugs used by headphone manufacturers
do not comply with the EIA-453 specifications for ¼-inch plugs. You may want to
designate a pair of headphones for linelevel testing and attach a plug of known
quality. We have found that even some
very high quality headphones have nonstandard plugs; be warned!
Warning: Safety First! Do not plug a
pair of headphones into a jack on the
Model 80 while the headphone ear
pieces are against your ears. High
sound pressure levels may be present.
Only after a signal is connected should
you slowly put the headphone transducers near your ears!
Model 80 User Guide Issue 5, October 1999
Studio Technologies, Inc. Page 13
To confirm that a signal is present on the
input of the Model 80 you can plug the
headphones into the loop-through connectors associated with the left and right
channels. After ensuring that the level will
not hurt your ears, you can listen for the
presence of audio and get an idea of the
general quality of the source. With a balanced input signal you should hear the
input in both the left and right earpieces
of the headphones. With an unbalanced
source you would, in most cases, hear
signal in only the left channel of the
phones.
To confirm that signals are present on
the eight stereo outputs you can plug the
headphones into the left and right output
jacks. Outputs configured for +4dBu
operation will be significantly louder in
the headphones. Since all Model 80 outputs are balanced, you should observe
signal in both the left and right earpieces.
Rapidly walking through the 16 output
jacks will confirm the proper operation of
the Model 80.
Technical Notes
¼-Inch Plugs versus EIA RS-453
An incompatibility problem lurks between
some ¼-inch phone plugs and the jacks
found on professional audio equipment.
While all the plugs seem to look the
same, some do not comply with the industry standard, called EIA RS-453. This
standard defines the physical dimensions,
including the shape of the plugs tip. It
seems that some plug manufacturers
dont bother to make the tip comply with
the standard. Why is this relevant to you?
Because the phone jacks used on the
Model 80 do comply with the standard.
They expect to be mated with plugs that
also meet the specification. When interfacing with the Model 80 be careful with the
plugs you utilize. Should a connection
appear flaky, sound noisy, or make an
intermittent contact, the most likely problem is a nonstandard phone plug. Replace
the plug if this is the case. You should find
that all plugs from Switchcraft or Neutrik
will work correctly, specifically Switchcraft
No. 297 or Neutrik NP3C.
Definition of LeveldBu
Whenever possible, 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 0.7747V).
In contemporary situations an output is
rarely terminated with 600 ohms; generally
10k ohms or higher. The dBu designation
is better because it refers to dB referenced
to 0.7747V, with no reference to load
impedance. This takes into account
todays audio scene where signals have a
low source impedance, and a high input
impedance. The dBu designation is becoming the standard for the professional
audio industry.
10 Output Level Reference
To those of you who are technical
nitpickers we feel than an explanation
is in order. Operational simplicity, rather
than historical convention, led Studio
Technologies to make the 10 outputs
referenced to dBu rather than to dBV. We
are well aware that in the past a 10
output was often referenced to 1 volt, not
to 0.7747. When the Model 80 was first
designed it was assumed that the +4
Issue 5, October 1999 Model 80 User Guide
Page 14 Studio Technologies, Inc.
output would be in dBu and the 10
output would be in dBV. We soon realized that this would cause cranium
problems for many users. A user monitoring one of the Model 80s outputs would
expect to see a 14dB drop on their VU
meter when going from the +4 to the 10
DIP switch position on the Model 80s front
panel. They actually would be switching
from a +4dBu output to a 10dBV output,
a difference of 11.78dB; confusion would
immediately reign! To avoid this situation
we took the liberty of keeping the 10
referenced to dBu. This should in no way
effect the ability of the Model 80 to interface with other equipment, while making
life easier for everyone.
Model 80 User Guide Issue 5, October 1999
Studio Technologies, Inc. Page 15
Specifications
Audio Input: 1, stereo (separate left and right
input connectors)
Loop Through: hardwired in parallel with input
(separate left and right loop-through connectors)
Type: electronically balanced, direct coupled
Input Compatibility: can be connected to
balanced or unbalanced signals
Impedance: 24k ohms
Nominal Input Level: 10 to +10dBu
Input Level Control: allows calibration over 10
to +10dBu input range
Right Trim Control: allows adjustment of right
input level over a 3dB range, nominal
Maximum Input Level: +27dBu balanced,
+21dBu unbalanced
Common Mode Rejection: 90dB @ DC and
60Hz, 85dB @ 20kHz, 60dB @ 400kHz (typical)
Audio Outputs: 8, stereo (separate left and right
output connectors)
Type: electronically balanced, direct coupled,
intended to drive loads of 600 ohms or greater,
can be connected balanced or unbalanced
Nominal Output Level: 10dBu (245mV) or
+4dBu (1.228V), each output individually switch
configurable
Maximum Output LevelBalanced: +27dBu
into 10k ohms, +26dBu into 600 ohms
Maximum Output LevelUnalanced: +21dBu
into 10k ohms, +20dBu into 600 ohms
Output Impedance: 50 ohms
Frequency Response: 10Hz-70kHz +0/0.5dB
(down 1dB @ 110kHz)
Distortion (THD+N): 0.004% (measured at
+4dBu input, +4dBu output, 20Hz-20kHz)
S/N Ratio: 91dB (20Hz-20kHz, ref. +4dBu)
Crosstalk: 75dB (1kHz, ref. +4dBu)
LED Indicators: 5, 1 power present, 4 input level
calibration
Fusing: 1
Type: 5 x 20mm time lag (Littelfuse 218-series or
equivalent)
Rating: 0.400A for 100 and 120V mains power,
0.200A for 220/240V mains power
Connectors:
Audio: dual, ¼-inch, 3-conductor phone jacks,
gold-plated contacts. (Manufactured by Neutrik)
Mates with all plugs specified by EIA RS-453.
AC Mains: standard 3-blade plug, meets IEC 320
specifications
AC Mains Requirement:
100, 120, or 220/240V, ±10%, factory configured,
50/60Hz, 100-120V 0.4A maximum, 220/240V
0.2A maximum
Dimensions (Overall):
19.00 inches wide (48.3cm)
1.72 inches high (4.4cm)
6.65 inches deep (16.9cm)
(1 standard rack space)
Weight:
7.0 pounds (3.2kg)
Specifications and information contained in this
User Guide subject to change without notice.
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