Wohler AMP2-VSDA/AM User manual

TitleandContents.......................................................................
Introduction .........................................................................................
Section 1: Features, Specs, and Installation ....................
Description and Features ......................................................................
Applications and Specifications ............................................................
Installation ...........................................................................................
Section2:Operation .................................................................
Front Panel Features ............................................................................
Rear Panel Features ..............................................................................
Audio Amplifier and Speaker Configuration .........................................
Section3:TechnicalInformation .........................................
General Technical Observations ............................................................
SDI to AES Converter PCB (919096) ....................................................
AES to Analog Converter PCB (919050) ...............................................
AES Digital Gain Calibration Fine Adjustment (919050) ........................
AES Error Jumper Location (919050 PCB) ............................................
PPM Meter Specifications and Level Threshold Settings ........................
VU Meter Specifications and Level Threshold Adjustment......................
AMP2-VSDA/AVandAMP2-VSDA/AMInterconnectBlockDiagram ........
AMP2-VSDA/AM and
AMP2-VSDA/AV
2U Digital Audio Speaker Monitor
With SDI Input and Output on BNC, Two AES Inputs on
BNC and XLR, Two AES Outputs From SDI on BNC, Four
Analog Inputs on XLR, Two Selected Analog Stereo Outputs
onXLR,TwoMechanical VU(AV)orPPM(AM)LevelMeters,
SummableChannelAssignment,andPhaseIndication
Document P/N 821576 Rev-B
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CONTENTS
User Manual
ECO-2501(08/03/04)

©2004 Wohler Technologies Inc. ALLrights reserved
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AMP2-VSDA/AVandAMP2-VSDA/AM UserManual P/N 821576 Rev-B
Introduction
Introduction
ECO-2325(04/28/04)
Wohler Technologies, Inc.
713 Grandview Drive
South San Francisco, CA 94080
650 589-5676 Fax: [phone]
web: www.wohler.com
e-mail: [e-mail]
Congratulations on your selection of a Wohler Technologies AMP2-VSDA/AV or AMP2-VSDA/AM audio monitor unit. We are
confidentit representsthe best performanceand valueavailable,and weguaranteeyour satisfactionwith it.
If you have questions or comments you may contact us at:
Allrights reserved.Copyrightheld byWohler Technologies.

©2004 Wohler Technologies Inc. ALLrights reserved 3
AMP2-VSDA/AVandAMP2-VSDA/AM UserManual P/N 821576 Rev-B
Sect. 1: General Features and Specifications
General Features
and Specifications
Description
Features
Applications
Specifications
Installation
Section 1

©2004 Wohler Technologies Inc. ALLrights reserved
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AMP2-VSDA/AVandAMP2-VSDA/AM UserManual P/N 821576 Rev-B
Features
AMP2-VSDA/AV and
AMP2-VSDA/AM
Powered Audio Monitors
Description
Section1:Features,Specs,andInstallation
AMP2-VSDA/AMSeries FrontPanel
The AMP2-VSDA/AV and AMP2-VSDA/AM are exceptionally high quality stereo audio monitoring systems in compact, two
rackspace cabinets. All AMP2 Series units contain three audiophile-quality drivers and three power amplifiers; two amplifiers
(and two speakers) that reproduce midrange and high frequency information in stereo, and a third amp/driver combination (and
speaker) that handles summed Low Frequency (LF) information below the 500 Hz crossover point. The AMP2 Series unique
audio design has two important advantages. First, it provides optimally focused sound in an Ultra Near Field tm (1 to 3 feet)
environment. This allows higher SPL for the operator while reducing overall ambient sound and adjacent bay crosstalk. Second,
electronic rather than acoustic cancellation of bass frequencies provides positive audible detection of reversed polarity (“out of
phase”) audio feeds. A unique LED display also visually shows “phase” (polarity) relationships of the signals selected for
monitoring.
The AMP2-VSDA/AV model features mechanical meters with VU ballistics characteristics and the AMP2-VSDA/AM model
features these meters with PPM ballistic characteristics. A toggle switch on the front panel allows selection between SDI or AES
input sources. Two banks of four buttons on the front panel are used to independently assign from one to to four (summed)
channels to each of the two (left and right) speaker channels. AES signal status is indicated by two bi-color (RED/GREEN) LEDs,
while SDI signal status is indicated by one bi-color (RED/GREEN) LED.
The rear panel features an SDI input and loop-through on BNC connectors, two AES inputs on unbalanced BNC connectors, two
alternate AES inputs on balanced XLR connectors, two AES outputs (converted from the SDI input) on BNC connectors, four
Analog outputs (of the selected digital source) on balanced Phoenix connectors, a stereo analog output of the two channels
assigned to the left and right speakers on two balanced XLR connectors, and four analog inputs on XLR connectors with a switch
on the front panel for selecting between the selected digital (AES or SDI) and the Analog inputs.
Wohler Technologies proprietary three-LED stereo phase indication feature allows visual monitoring of phase relationships of the
sources selected for monitoring through the speakers.
•Fouranalogoutputs(fromselecteddigitalsource)onbalanced
Phoenixconnectors
•Stereoanalogoutputofthechannelsmonitoredbytheleftand
right speakers on two balanced XLR connectors
• Independantly assign and sum together two, three, or four
channels of the selected source to left and right speakers via
two banks of four button switches on the front panel
•SelectAESorSDIinputsourceviaafrontpaneltoggleswitch
•Selectanalogorselecteddigitalinput sourceviaafrontpanel
toggleswitch
• One SDI signal status/error indication LED
• Two AES signal status/error indication LEDs
• Headphone output
• Power indication LED
• 104 dB SPL at two feet
• Only two rack spaces high
•Excellenthighfrequency response forpositivedetectionof
backgroundwhineandnoise
•Audibleandvisualindicationofphase/polarityproblems
•Thoroughmagneticshieldingforplacementnexttovideo
monitors
• Choice of either VU or PPM high quality mechanical level meters
• SDI input and loop-through on unbalanced BNC connectors
• Two AES/EBU inputs on unbalanced BNC connectors
• Two alternate AES/EBU inputs on balanced XLR connectors
• Four analog inputs on balanced XLR connectors
•TwoAESoutputs(convertedfromSDIinput)onunbalancedBNCconnectors

©2004 Wohler Technologies Inc. ALLrights reserved 5
AMP2-VSDA/AVandAMP2-VSDA/AM UserManual P/N 821576 Rev-B Section1:Features,Specs,andInstallation
Applications
The AMP2-VSDA/AV and AMP2-VSDA/AM are ideally suited for use in VTR bays, mobile production vehicles, teleconferencing
installations, multimedia systems, satellite links and cable TV facilities, and on-air radio studios. Designed and manufactured in the U.S.,
both models are backed by a strong warranty and a satisfaction guaranteed return policy.
Units are designed to meet, at time of manufacture, all currently applicable product safety and EMC requirements, such as those of
CE. 0 dbV ref. 0.775V RMS. Features and specifications subject to improvement without notice.
General Specifications
InputConnectors:
AnalogInput Impedance:
DigitalInput Impedance:
PeakAcousticOut(@2ft.):
PowerOutput,
RMSEachSide(4ΩΩ
ΩΩ
Ω):
RMSBass(4ΩΩ
ΩΩ
Ω):
FrequencyResponse,
SixthOctave:
InputLevelforMaximum
Output(VolumeFullOn):
HumandNoise(analog):
Distortion,Electrical:
Distortion,Acoustic:
InputOverload:
ConvertedAnalogOutS/N:
ConvertedAnalogOutTHD:
MagneticShielding:
PowerConsumption
(AverageMaximum):
ACMainsInput:
SDI:BNC,AES:BNC/XLR,Analog:XLR
XLR: 70K Ω, bal.
BNC: 75 Ω, unbal., XLR: 110 Ω, bal.
104 dBSPL
14Wtransient/10Wcontinuous
35Wtransient/25Wcontinuous
80Hz- 16kHz ±5 dB)
(-10dB@40Hz,20kHZ)
0dBvbalanced/-10dBunbalanced
Betterthan-68dBbelowfulloutput
Lessthan0.15%atanylevelbelow
input threshold
6%orlessatworstcasefrequencies
above120Hz,includingcabinet
resonance;typicallylessthan1.5%
+26dBvbalanced
>90dB
<0.008%
<0.8Gaussanyadjacentsurface
45 W
100-240VAC,50-60Hz Universal
Physical Specifications
Audio Response Curve
Typical 1/6 Octave Audio Response Curve
B
d
0
+10
-20
-30
-10
Hz 10k
5k
2k1k50020010050 20k20
18lbs.(8.2 kg)
3.5 x 19 x 12 inches
(89 x 483 x 305 mm)
Weight:
Dimensions(HxWxD):
NOTE: See page 19 for SDIspecifications and page 20 for AES specifications.

©2004 Wohler Technologies Inc. ALLrights reserved
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AMP2-VSDA/AVandAMP2-VSDA/AM UserManual P/N 821576 Rev-B
(Thispageintensionallyleftblank)
Installation
Mounting
The unit should be mounted where convenient for operating persons, ideally at approximately ear/eye level for best high frequency
response and visual observation of the level meters. Its superior magnetic shielding eliminates concerns about locating it adjacent
to most types of CRT monitors, including even high-resolution color monitors.
Heat Dissipation
Heat dissipated by the speaker amps is conducted directly to the left side of the chassis; no special considerations for cooling are
necessary as long as the ambient temperature inside the rack area does not exceed approximately 60°C (140°F).
Sympathetic Vibration
Sympathetic vibration from other equipment (cables, etc.,) in the rack may be serious enough to interfere with the unit’s sound
quality out in the listening area. The use of thin card stock and/or felt or foam weather-stripping type materials between adjacent
vibrating surfaces, or tying up loose cables, etc., may be required to stop vibrations external to the unit.
Mechanical Bracing
Even though the unit is fairly heavy, the chassis is securely attached to the front panel at eight points along its surface, not just at
the four corners of the chassis ears. This feature will reduce or eliminate rear bracing requirements in many mobile/portable
applications. The weight of internal components is distributed fairly evenly around the unit.
Audio Connections
Connection of the audio feeds is straightforward. Please refer to the system interconnect block diagram on page 24 for clarification of the
general signal paths into and out of the unit.
AES/EBU inputs are via female BNC or 3-pin female XLR connectors. Digital BNC inputs are configured for 75 Ωunbalanced
connections; digital XLR inputs are configured for 110 Ωbalanced connections. Analog inputs are via four 3-pin female XLR
connectors. Analog inputs are configured for 70K Ωbalanced connections. Care should be exercised to avoid mismatched cable types
and other similar causes of undesired reflections in RF signal systems. If severe enough, such reflections can result in corruption of the
digital datastream.
AC Power
The unit's AC mains connection is via a standard IEC inlet, with safety ground connected directly to the unit's chassis. The
universal AC input (100-240VAC, 50/60Hz) switching power supply is a self-resetting sealed type, with automatic over-voltage
and over-current shutdown. There is no user-replaceable fuse in either the primary or secondary circuit.
Section1:Features,Specs,andInstallation

©2004 Wohler Technologies Inc. ALLrights reserved 7
AMP2-VSDA/AVandAMP2-VSDA/AM UserManual P/N 821576 Rev-B
Operation
Front Panel Features
Rear Panel Features
Audio Amplifier and Speaker Configuration
Section 2

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AMP2-VSDA/AVandAMP2-VSDA/AM UserManual P/N 821576 Rev-B
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Please refer to Figure-2a on the facing page to familiarize yourself with the front panel features of the AMP2-VSDA/AV and
AMP2-VSDA/AM units. The following sections describe these features and are referenced, by number, to Figure-2a.
Front Panel Features Section2: Operation
(Continued)
Speakers
The monitor features two mid-range speakers (left and right) and one woofer speaker. Two amplifier/driver combinations
handle midrange and high frequency information in the left and right (stereo) speaker channels, while the third channel
reproduces and sums the left and right channel information below the 500 Hz crossover point in the woofer (bass) speaker(s).
Note that the woofer channel is NOT a dedicated LFE (subwoofer) or Center channel. See page 16 for more information
concerning the AMP2 Series audio amplifier/speaker configuration.
Audio Level Meters - Mechanical
Audio levels for the left and right sources selected for monitoring are respectively displayed in the left and right mechanical
level meters. The AMP2-VSDA/AV model uses meters exhibiting VU ballistic characteristics. The AMP2-VSDA/AM
model uses meters exhibiting PPM ballistic characteristics. See page 23 for Threshold Level adjustment and settings for
the VU and PPM type of meter.
Speaker Assign Channel Buttons (Left and Right)
Use the left bank of four buttons to assign one to four of the four available channels for monitoring from the left speaker
channel. Use the right bank of four buttons to assign one to four of the four available channels for monitoring from the
right speaker channel. Channel buttons toggle On/Off and will light up BLUE to indicate they are selected.
Operation for channel selection for each bank of four buttons is as follows:
Single Channel Select: Press and release a single channel button to select that channel (and deselect any previous
selection). Pressing and releasing the selected channel button again will deselect it.
Multi-Channel Select (Summing): Press and hold down a desired channel button, then press other channel buttons to
add (sum) additional channels (or press any again to deselect). Release all buttons to accept the selection set. When
multiple channels are selected, pressing and holding an already selected channel button will allow further modification to
the selection set. Releasing all buttons accepts the new selection set. Pressing and immediately releasing an already
selected channel button will select only it and deselect all other channel selections. Note that if channels assigned to
either the left or right level meters are multi-channel (summed), then the respective level meter will indicate summed audio
levels.
If the user presses a previously selected (lighted) channel button, but then decides not to make any changes to the selection
set, the user should keep the button depressed for at least 1.5 seconds before releasing it.This will preserve the current
selection set as though the button was never pushed.
Power LED
This LED glows GREEN to indicate the unit is connected to mains power and an operation voltage is present.
AES Status LEDs (AES 1 and AES 2)
These two bi-color GREEN/RED LEDs (AES1 and AES2) indicate the input presence and status of the two AES input
signals. Either LED glows GREEN as long as a valid AES/EBU digital datastream for the associated input channel is
being received. Either LED glows RED to indicate errors in signal reception or data errors (if the data has been tagged
as inappropriate for conversion to analog by having the validity bit set). These LEDs function whether or not the AES
digital signals are selected for monitoring through the unit.
Note: If you wish to disable data error indication (and leave only indication of signal reception errors) you can place
jumpers on H14 and H18 of the 919050 AES-to-Analog conversion PCB. See page 22 for component locations.
Headphone Jack
Select the headphone audio sources as you would for the internal speakers. When you plug in headphones, the speakers will
mute. This jack accepts a standard 1/4” phone type stereo plug.
Volume Control
This controls the loudness of the audio reproduced by the internal speakers or connected headphone. Clock-wise rotation
of this control increases the loudness of the monitored audio.
Analog/Digital Source Select Switch
This two position toggle switch allows the operator to choose between two primary input sources; ANALOG or DIGITAL.
When this toggle switch is set to ANALOG, the unit will monitor the signals as input on the rear panel ANALOG IN
XLR connectors (Item K, page 14). When this toggle switch is set to DIGITAL, the unit will monitor the digital
source (AES or SDI) as selected by the AES/SDI Digital Source Select Switch (Item 10, page 10).
1)
2)

©2004 Wohler Technologies Inc. ALLrights reserved 9
AMP2-VSDA/AVandAMP2-VSDA/AM UserManual P/N 821576 Rev-B Section2: Operation
Figure-2a: Front Panel Features

©2004 Wohler Technologies Inc. ALLrights reserved
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Section2: Operation
(Continued)
Front Panel Features
Phase Indication LEDs
These three LEDs indicate the instantaneous and average phase (polarity) conditions between the two signals in the channel
pair (or downmix) assigned to the left and right speaker channels. The two smaller LEDs labeled FAST show instantaneous
phase relationships in the signal. The larger LED labeled AVG will indicate the average phase condition. Indication is as
follows:
• The left FAST LED glows (or blinks) GREEN for in-phase signals.
• The right FAST LED glows (or blinks)AMBER for out-of-phase signals.
• The large AVG LED indicates the average phase condition by glowing GREEN for in-phase signals, or RED for
out-of-phase signals.
In general, observing the AVG LED alone is sufficient for proper phase monitoring. While it is normal for stereo signals to
contain some intermittant instantaneous out-of-phase and in-phase conditions (FAST LEDs), a steady RED glow of the
AVG LED indicates an out-of-phase alarm condition.
AES/SDI Digital Source Select Switch
This two position toggle switch allows the operator to choose between the two digital input sources; SDI or AES. When
this toggle switch is set to AES, the unit will monitor the AES signals as input on the AES IN BNC connectors (IN 1 and IN
2) on the rear panel (Item C, page 12). When this toggle switch is set to SDI, the unit will monitor the SDI signals as input
on the SDI IN BNC connector on the rear panel (Item G, page 12).
Balance Control
This control changes the volume balance between the left and right speaker channels. Note that this control attenuates the
signal from the source, so that the left and right bass frequencies (summed together and reproduced in the woofer channel)
will respond to balance adjustments in tandem with the left and right speaker channels. See page 16 for more information
concerning the balance control characteristics.
SDI Status LED
This bi-color (GREEN/RED) LED, labeled SDI, glows GREEN as long as a valid SDI digital datastream is being received.
It glows RED if TSR errors are present in the signal. If there is no SDI signal present the LED will be unlit. This LED
functions whether or not the SDI digital signal is selected for monitoring through the unit.

©2004 Wohler Technologies Inc. ALLrights reserved 11
AMP2-VSDA/AVandAMP2-VSDA/AM UserManual P/N 821576 Rev-B Section2: Operation
Figure-2a: Front Panel Features

©2004 Wohler Technologies Inc. ALLrights reserved
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AMP2-VSDA/AVandAMP2-VSDA/AM UserManual P/N 821576 Rev-B
G
E
D
Please refer to Figure-2b on the facing page to familiarize yourself with the rear panel features of the AMP2-VSDA/AV and AMP2-
VSDA/AMunit. The following sections describe these features and are referenced, by letter, to Figure-2b.
Rear Panel Features Section2: Operation
(Continued)
A
B
C
Power Connector
Attach a standard IEC-320 power cord between this connector and mains power (100 - 250VAC, 50/60 Hz). The front panel
Power LED (Item 4, page 8) will glow GREEN to indicate operating voltages are present.
AES Balanced XLR Input Connectors (AES IN 1 and AES IN 2)
These two 3-pin female XLR input connectors (AES IN 1 and AES IN 2) are meant to receive standard AES signals and
are configured for balanced, 110 Ωconnections. Note that the unit will monitor these inputs only when the Analog/Digital
Source Select Switch (Item 8, page 8) is set to DIGITAL,and the AES/SDI Digital Source Select Switch (Item 10,
page 10) is set to AES.For XLR pinout information see the diagram under SelectedAnalog Output Connectors (Item J,
page 14).
Note: Do not input signals simultaneously to the XLR and BNC (Item C) AES input connectors of the same channel (i.e.
XLR connector AES IN 1 and BNC connector AES IN 1).
AES Unbalanced BNC Input Connectors (AES IN 1 and AES IN 2)
These two female BNC input connectors (AES IN 1 and AES IN 2) are meant to receive standard AES signals and are
configured for unbalanced, 75 Ωconnections. Note that the unit will monitor these inputs only when the Analog/Digital
Source Select Switch (Item 8, page 8) is set to DIGITAL and the AES/SDI Digital Source Select Switch (Item 10,
page 10) is set to AES.
Note: Do not input signals simultaneously to the BNC and XLR (Item B) AES input connectors of the same channel (i.e.
BNC connector AES IN 1 and XLR connector AES IN 1).
AES Output (From SDI Input) Connectors (1 and 2)
These two "AES OUT-FROM SDI" BNC connectors output an AES digital signal as converted from the SDI IN input
connector (Item F) and function regardless of any monitor selection settings. The left AES OUT-FROM-SDI connector
(next to AES IN 1) outputs a signal converted from SDI sub-group 1 (channels 1/2) and the right AES OUT-FROM-SDI
connector (next to AES IN 2) outputs a signal converted from SDI sub-group 2 (channels 3/4).
AES Input Termination DIP Switch
This 4-position DIP switch module is used to set the termination characteristics for the AES inputs. In the event that either
of the two AES input channels is fed to downstream equipment, the associated DIP switch section (section 1 = AES IN 1
and section 3 = AES IN 2)must be placed in the UP (Unterminated) position. If there is no downstream equipment
connected, then the associated DIP switch section must be placed in the DOWN (Terminated) position. See below for a
diagram of termination settings. Note: Sections 2and 4of the DIP module are not used.
SDI Output Connector
The SDI OUT loop-through connector outputs a reclocked (regenerated) copy of the signal entering the SDI IN input
connector (Item G). This female BNC connector is configured for an unbalanced, 75 Ωconnection.
SDI Input Connector
The SDI IN input connector is meant to receive a standard SDI signal. This female BNC connector is configured for an
unbalanced, 75 Ωconnection. The unit monitors sub-group 1 (channels 1/2) and sub-group 2 (channels 3/4) of SDI Group
ID #1. Note that the unit will monitor the SDI input only when the Analog/Digital Source Select Switch (Item 8, page 8)
is set to DIGITAL, and the AES/SDI Digital Source Select Switch (Item 10, page 10) is set to SDI.
IN 1
Unterminated
Note: Positions S2 and S4 of DIP switch are not used.
AES Input 1Termination (919050)
Term. 2
12344 132
IN 1
Terminated
41 3
21 2 34
AES Input 2Termination (919050)
Term. 1 Term. 2Term. 1 Term. 2Term. 1 Term. 2Term. 1
IN 2
Unterminated IN 2
Terminated
F

©2004 Wohler Technologies Inc. ALLrights reserved 13
AMP2-VSDA/AVandAMP2-VSDA/AM UserManual P/N 821576 Rev-B Section2: Operation
Figure-2b: Rear Panel Features

©2004 Wohler Technologies Inc. ALLrights reserved
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AMP2-VSDA/AVandAMP2-VSDA/AM UserManual P/N 821576 Rev-B
Rear Panel Features Section2: Operation
High (+)
Low (-)
Gnd
(Shield)
Pin-1 Pin-2
Pin-3
Pin-1
Gnd
(Shield)
Pin-2
High (+)
Pin-3
Low (-)
Female XLR Pinout Male XLR Pinout
(Continued)
H
I
J
K
AES Input Level Gain Calibration DIP Switch
Input Level Gain Calibration, the analog level which corresponds to a given digital input value, is settable via this DIP
switch. The factory setting is +4 dB (analog) = -20 dBFS (digital). See the silk-screened chart on the rear panel or the
diagram below for Level Gain Calibration settings.
Converted Analog Out Connectors (1-4)
These four Phoenix connectors output analog signals converted from the selected digital inputs (but not the Analog
inputs). These ouputs are not affected by the position of the Analog/Digital Source Select Switch (Item 8, page 8).
These 3-pin male Phoenix connectors are configured for a balanced low impedance connection. Phoenix connector pin-out
information is silk-screened just above these connectors on the rear panel (see Figure-2b).
Selected Analog Output Connectors
These two 3-pin male XLR connectors are analog outputs of the selected source(s) as assigned to the left and right
speakers. The left connector outputs the left channel (ChannelA) and the right outputs the right channel (Channel B).
Both connectors are configured for low impedance connections and the output signals are not affected by the volume/
balance controls or headphone mute. For XLR pinout information see the diagram below.
Analog Input Connectors (CH. 1 - CH. 4)
These four 3-pin female XLR connectors accept standard analog audio signals and are configured for balanced 70K Ω
connections. For XLR connector pin-out information, see the diagram under Item J. Note that the Analog inputs are
monitored only when the Analog/Digital Source Select Switch (Item 8, page 8) is set to ANALOG.

©2004 Wohler Technologies Inc. ALLrights reserved 15
AMP2-VSDA/AVandAMP2-VSDA/AM UserManual P/N 821576 Rev-BSection 2: Operation
Figure-2b: Rear Panel Features

©2004 Wohler Technologies Inc. ALLrights reserved
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AMP2-VSDA/AVandAMP2-VSDA/AM UserManual P/N 821576 Rev-B Section2: Operation
Audio Amplifier and Speaker Configuration
General Description
All models in the AMP Series contain high performance transducers (speakers) driven by three power amplifiers; two amplifier/
driver combinations handle midrange and high frequency information in the left and right (stereo) speaker channels, while the third
amplifier channel sums the left and right channel information below the 500 Hz crossover point in the woofer (bass) speaker(s). Note
that the woofer channel is NOT a dedicated LFE (subwoofer) or Center channel.
Speaker Configuration
All AMP2 (2U) products are configured with two speaker channels (left and right) to reproduce midrange and high-range audio
frequencies (in stereo) and one woofer speaker channel to reproduce the summed (combined) low-range audio frequencies from
the left and right speaker input channels.
See below for a simplified diagram of the AMP2 audio amplifier/speaker configuration.
Balance Control Characteristics
The balance control attenuates the signal from the source, so that the left and right bass frequencies (summed together and
reproduced in the woofer channel) will also respond to the balance control.
Example:
If an audio signal of a voice speaking English is fed to the left (A) input and a voice speaking Spanish is fed to the right
(B) input, then the left speaker channel will reproduce the midrange and high-range frequencies of the English speaking
voice, the right speaker channel will reproduce the midrange and high-range frequencies of the Spanish speaking voice,
and the woofer speaker channel will reproduce the summed (combined) low-range frequencies of both voices.
If the balance control is rotated to the left (English), then the Spanish speaking voice in the right speaker channel will
diminish in volume and the Spanish speaking voice in the woofer speaker channel will also diminish.
The converse is true if the balance control is panned to the right.
Note that if the balance control is rotated completely to the left, the volume in both the left speaker channel and woofer speaker
channel will increase slightly to maintain overall output level. See the simplified diagram below for placement of the balance control
in the audio amplifier circuit.

©2004 Wohler Technologies Inc. ALLrights reserved 17
AMP2-VSDA/AVandAMP2-VSDA/AM UserManual P/N 821576 Rev-B
Technical Information
General Technical Observations
SDI to AES Converter Module PCB (919096)
AES to Analog Converter Module PCB (919050)
AES Digital Gain Fine Adjustment (919050)
AES Error Jumper Locations (919050)
PPM Level Meter Specifications and Level Threshold Settings
VU Level Meter Specifications and Level Threshold Adjustment
AMP2-VSDA/AM Series Interconnect Block Diagram
Section 3

©2004 Wohler Technologies Inc. ALLrights reserved
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AMP2-VSDA/AVandAMP2-VSDA/AM UserManual P/N 821576 Rev-B Section3: TechnicalInformation
General Mechanical Observations
Elimination of cabinet and component sympathetic vibrations (resonances) requires considerable attention to mechanical details.
Because of this, and the physical constraints of the speaker’s acoustic enclosures, even minor changes to any of the mechanical
details of the unit can seriously impair its acoustic performance. This especially applies to the speaker baffles. If mechanical
work on the unit is necessary, be sure to make adequate notes to permit accurate reassembly.
Unfortunately, the unusual and wholly proprietary method of magnetic shielding is usually degraded slightly by any disassembly of
the unit, except removal of the rear panel. Almost any maintenance or repair will require removal of the cover. If an immediately
adjacent video monitor shows magnetic interference after reassembly of the unit, it must be returned to the factory to restore the
shielding completely.
General Audio Circuitry Observations
Since a single-sided power supply is used, all amplifier sections are “biased” with a 1/2 supply reference, so all opamp signal
terminals on the main board should have a DC level of +12V, +/-0.7V. Signal inputs to the main audio board from any of the input
select circuits are via the balanced input stage, in lieu of the XLR analog inputs on the basic unit. Signal feed points for level
meters and the phase indicator are immediately after the input stage, and before the volume control section.
The signal pick-off for the headphones is after the volume and balance controls. Speaker muting is controlled by circuitry that
senses connection of headphones to the jack.
The power amps are attached to an aluminum heatsink plate (which is also connected to the circuit common for these devices).
The heatsink plate forms an operational module separate from the chassis, which allows access to the solder side of the circuit
board while power is applied to the circuitry. To avoid thermal shutdown of the power amp(s), they should NOT be operated
without their tabs being fastened to the heatsink plate.
Variations in the frequency response of different production runs of drivers has sometimes required minor adjustments in the
equalization/crossover components in individual runs of units. Some of these components may have values slightly different than
those indicated in the schematic, which are the nominal ones. If any of the drivers (speakers) are replaced, it may be helpful to
change some of these components to achieve maximum flatness of response.
The operating threshold of the woofer limiter is critical to both satisfactory reproduction of musical transients and preventing
damage to, or destruction of, the speaker itself. The side speaker output limiter circuits are similarly important, though not as
critically adjusted.
The woofer power amps are arranged in a bridge configuration; care must be taken to avoid letting EITHER speaker terminal
contact the chassis (common) OR THE GROUNDED LEAD OF ANY TEST EQUIPMENT so as not to short out the power amps.
The side speaker outputs are single-ended, so these precautions are not necessary for them.
General Technical Observations

©2004 Wohler Technologies Inc. ALLrights reserved 19
AMP2-VSDA/AVandAMP2-VSDA/AM UserManual P/N 821576 Rev-B
The 919096 (Serial Digital to AES Converter) module allows selected Wohler Technologies audio monitoring systems to be
connected directly to a serial digital video signal containing embedded audio. Two levels of component signals (eg., D1, D5, and
Digi Betacam type) are currently supported; synchronous audio at 48 KHz with either 20-bit data packets or audio and extended data
packets. The 919096 module demultiplexes (extracts) the audio data from the video data, reformatting it to the AES standard. A
companion digital-to-analog converter module (919050) is used to convert the AES signal to Analog audio.
In the AMPDigital Series units, channels 1 and 2 (first subgroup) and channels 3 and 4 (second subgroup) from SDI Group ID
#1 are demuxed before being input to the AES to analog conversion module (919050). Access to SDI Group ID #2, #3, and #4
is optional and should be specified at time of order.
SDI to AES Converter Module PCB (919096)
919096 Specifications
Inputcharacteristics:
Receiver type:
Sensitivityperformance:
SDI input level:
Inputformats:
Audiosamplingrate:
SDIoutputtype:
SDIoutput:
SDI output level:
AESfromSDIoutput:
AESdatabits:
ErrorIndication:
75Ohm(BNC),ACcoupled,15dBminimumreturnloss,10-270MHz
Autoequalizingwithclockregeneration
Tolerates cable loss of at least 30 dB @ 135 MHz
400- 1000mV
Component,either 525or 625linesw/ 48KHz audio
48KHz
FullyregeneratedcopyofSDIinputsignal(equalizedandregenerated,
scrambledNRZI)
15 dB minimum return loss, risetime 0.75-1.5 ns (20-80%)
800mV+/-10%
75 ΩBNC
20
Bi-colorLED(red/green)
Off = no signal
Green= signalpresent
Red = Error
Section3: TechnicalInformation

©2004 Wohler Technologies Inc. ALLrights reserved
20
AMP2-VSDA/AVandAMP2-VSDA/AM UserManual P/N 821576 Rev-B Section3: TechnicalInformation
Description
The 919050 Digi-2 (Dual Input AES to Analog Converter) module allows selected Wohler Technologies products to receive
input signals in the AES or SPDIF digital audio data formats. Sampling rate and format selection are sensed and set automatically.
Two front panel mounted bi-color (RED/GREEN) LEDs provide visual indication of input signal status. The LEDs light GREEN
when receiving a valid, error-free data stream, but turn RED when errors are detected. See Item 5, page 8for more information
about error detection and indication.
There are two AES inputs, which are configured with unbalanced 75 ΩBNC connectors and balanced 110 ΩXLR connectors. This
module also features a four-channel balanced analog line-level output, which can be configured with unbalanced 75 ΩBNC
connectors or balanced 110 ΩPhoenix or XLR connectors.
919050 Specifications
Inputformats:
Digital-to-AnalogConversion:
Samplingrate:
Termination:
Analogout(ofdigitalsource),
S/N:
THD (full output):
Max output of analog out:
Nominal output level for "Full
Code" digital source:
D toA gain calibration,
(dB = dBFS):
Standard input connectors:
Optional input connectors:
Standard output connectors:
Optional output connectors:
Error Indication:
AES/EBUorSPDIF
24-bitlowjitter
31kHzto 48kHz
Removable(DIPswitchselectable)
Greaterthan96dB
Lessthan0.008%
+24dBv(0 dBv= 0.775vRMS)
+24dBv
+8 = -20, +4 = -20, +6 = -9, 0 = -18 (DIP switch selectable)
BNC:75 Ω,unbalanced
Phoenixor XLR:110 Ω,balanced
BNC: 75 Ω, unbalanced
Phoenixor XLR:110 Ω,balanced
TwoBi-Color LEDs(on frontpanel):
Green = OK
Red = Error, no lock to signal, or no signal.
AES to Analog Converter Module PCB (919050)