Wohler AMP2-SDA/AVU 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 (919117) Description .............................
PPM Meter Specifications and Level Threshold Settings ........................
VU Meter Specifications and Level Threshold Adjustment .....................
AMP2-SDA/AVUandAMP2-SDA/APPInterconnectBlockDiagram........
AMP2-SDA/AVU and
AMP2-SDA/APP
2U Digital Audio Speaker Monitor
With SDI Input and Output on BNC, AES Input on BNC,
AES Out (from SDI) on BNC, Two Analog Inputs on XLR,
Two Selected Analog Stereo Outputs on XLR,
TwoMechanicalVU(AVU)orPPM(APP)
LevelMeters,andPhaseIndication
Document P/N 821587 Rev-A
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CONTENTS
User Manual
ECO-2600(08/25/04)

©2004 WohlerTechnologies Inc. ALL rights reserved
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AMP2-SDA/AVUandAMP2-SDA/APPUserManual P/N 821576 Rev-A
Introduction
Introduction
Wohler Technologies, Inc.
713 Grandview Drive
South San Francisco, CA 94080
650 589-5676 Fax: [phone]
web: www.wohler.com
e-mail: [e-mail]
CongratulationsonyourselectionofaWohlerTechnologiesAMP2-SDA/AVUor AMP2-SDA/APPaudio monitor unit. We areconfident
itrepresentsthebestperformanceandvalueavailable,andweguaranteeyoursatisfactionwithit.
If you have questions or comments you may contact us at:
Allrightsreserved.CopyrightheldbyWohlerTechnologies.

©2004 WohlerTechnologies Inc. ALL rights reserved 3
AMP2-SDA/AVUandAMP2-SDA/APPUserManual P/N 821576 Rev-A
Sect. 1: General Features and Specifications
General Features
and Specifications
Description
Features
Applications
Specifications
Installation
Section 1

©2004 WohlerTechnologies Inc. ALL rights reserved
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AMP2-SDA/AVUandAMP2-SDA/APPUserManual P/N 821576 Rev-A
Features
AMP2-SDA/AVU and
AMP2-SDA/APP
Powered Audio Monitors
Description
Section1:Features,Specs,andInstallation
AMP2-SDA/AVUor/APP FrontPanel
The AMP2-SDA/AVU and AMP2-SDA/APP 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-SDA/AVU model features mechanical meters with VU ballistics characteristics and the AMP2-SDA/APP model
features these meters with PPM ballistic characteristics. Toggle switches on the front panel allow selection of SDI or AES input
sources, SDI subgroup 1 or 2(channels 1/2 or 3/4), and a choice of the selected digital source or the analog source inputs. Two LEDs
indicate the presence and error status of the selected AESand/or SDI signals entering the unit.
The rear panel features an SDI input and loop-through on BNC connectors, an AES input on an unbalanced BNC connector, an AES
output (converted from the SDI input) on a BNC connector, analog inputs on two balanced XLR connectors, and a stereo analog
output of the selected digital source on two XLR connectors.
Wohler Technologies proprietary three-LED stereo phase indication feature allows visual monitoring of phase relationships of the
sources selected for monitoring through the speakers.
•Selectanalogorselecteddigitalinputsourceviaafrontpanel
toggleswitch
•SelectAESorSDIinputsourceviaafrontpaneltoggleswitch
• Select SDI subgroup 1 or 2 (of Group I.D. #1) source via
front panel toggle switch
•SDIsignalstatus/errorindication LED
•AESsignalstatus/errorindicationLED
• Headphone output
• Power indication LED
• Numerous control and input options
•Quickandeasyinstallation:simplyslideintherackand
connect audio and AC power
• 104 dB SPL at two feet
• Only two rack spaces high
•Excellent highfrequencyresponseforpositivedetectionof
background whine and noise
•Audibleandvisualindicationofphase/polarityproblems
•Thorough magneticshieldingforplacementnexttovideo
monitors
• Choice of either VU or PPM high quality mechanical level meters
• SDI input and loop-through on unbalanced BNC connectors
• AES/EBU input on unbalanced BNC connector
• AES/EBU output (from SDI input) on BNC connector
• Analog inputs on two balanced XLR connectors
• Stereo analog output of the selected digital source

©2004 WohlerTechnologies Inc. ALL rights reserved 5
AMP2-SDA/AVUandAMP2-SDA/APPUserManual P/N 821576 Rev-A Section1:Features,Specs,andInstallation
Applications
The AMP2-SDA/AVU and AMP2-SDA/APP 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,Analog:XLR
XLR: 40KΩ, balanced
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 AESspecifications.

©2004 WohlerTechnologies Inc. ALL rights reserved
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AMP2-SDA/AVUandAMP2-SDA/APPUserManual P/N 821576 Rev-A
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 22 for clarification of the
general signal paths into and out of the unit.
AES/EBU input is via a female BNC connectors. Digital SDI BNC input is configured for 75 Ωunbalanced connections. Analog inputs
are via two 3-pin female XLR connectors. Analog inputs are configured for 40K 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 WohlerTechnologies Inc. ALL rights reserved 7
AMP2-SDA/AVUandAMP2-SDA/APPUserManual P/N 821576 Rev-A
Operation
Front Panel Features
Rear Panel Features
Audio Amplifier and Speaker Configuration
Balance Control Characteristics
Section 2

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Please refer to Figure-2a on the facing page to familiarize yourself with the front panel features of the AMP2-SDA/AVU and
AMP2-SDA/APP 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-SDA/AVU model uses meters exhibiting VU ballistic characteristics. The AMP2-SDA/APP
model uses meters exhibiting PPM ballistic characteristics. See page 21 for specifications and settings for the VU and
PPM type of mechanical meter.
Power LED
This LED glows GREEN to indicate the unit is connected to mains power and an operation voltage is present.
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 H, 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 Source Select Switch (Item 6).
SDI Subgroup Select Switch (1 or 2)
This 2-position toggle switch allows the operator to choose whether the unit will monitor Subgroup 1 or Subgroup 2 of
the SDI data stream when the AES/SDI Source Select Switch (Item 6) is set to SDI.
Subgroup selections 1and 2are derived from Group I.D. #1 as follows:
• Subgroup 1 = Channels 1and 2
• Subgroup 2 = Channels 3and 4
AES/SDI Source Select Switch
This two position toggle switch allows the operator to choose between the two types of digital input sources provided for
on the rear panel; AES or SDI. It should be noted that in order for the unit to actually monitor the selected digital source,
the Analog/Digital Source Select Switch (Item 4) must be set to DIGITAL.
Headphone Jack
This jack accepts a standard 1/4” phone type stereo plug. Select the headphone audio sources as you would for the internal
speakers. When you plug in headphones, the speakers will mute.
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.
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 forin-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.

©2004 WohlerTechnologies Inc. ALL rights reserved 9
AMP2-SDA/AVUandAMP2-SDA/APPUserManual P/N 821576 Rev-A Section2: Operation
Figure-2a: Front Panel Features

©2004 WohlerTechnologies Inc. ALL rights reserved
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AMP2-SDA/AVUandAMP2-SDA/APPUserManual P/N 821576 Rev-A
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12
10
Section2: Operation
(Continued)
Front Panel Features
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.
AES Signal Status LED
Thisbi-color(GREEN/RED)LED (AES) glows GREEN as long as a valid AES/EBU digital datastream is being received. It
glows RED to indicate errors. By setting a rear panel DIP switch, two types of error detection are available:
• Reception Errors: errors in reception of data or no data stream at all.
• Reception and Data Errors: errors in reception and data errors identified by the sending device (possibly invalid).
See the AES Termination and Error Type DIP Switch (Item C, page 12) for information about setting the error type.
SDI Signal Status LED
This bi-color (GREEN/RED) LED (SDI) glows GREEN as long as a valid SDIdigital 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 WohlerTechnologies Inc. ALL rights reserved 11
AMP2-SDA/AVUandAMP2-SDA/APPUserManual P/N 821576 Rev-A Section2: Operation
Figure-2a: Front Panel Features

©2004 WohlerTechnologies Inc. ALL rights reserved
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AMP2-SDA/AVUandAMP2-SDA/APPUserManual P/N 821576 Rev-A
Please refer to Figure-2bonthefacingpagetofamiliarizeyourselfwiththerear panel features of the AMP2-SDA/AVU andAMP2-SDA/
APPunit. The following sections describe these features and are referenced, by letter, to Figure-2b.
Rear Panel Features Section2: Operation
(Continued)
Terminated
Unterminated 3
143 2 214
ERROR
TERM 1
x
TERM 2
AES Input Termination
TERM 2
TERM 1
x
ERROR
1234
Error/Fault Type = Red LED
AES Error Indication Settings
ERROR
TERM 1
TERM 2
x
Reception
Error (Only)
TERM 2
Reception and
Data Error
14
3
2
x
TERM 1
ERROR
A
B
C
D
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 3, page 8) will glow GREEN to indicate operating voltages are present.
AES Output (From SDI) Connector
The AES/EBU OUT connector outputs an AES signal as converted from the SDI input (Item F, page 14) and as selected
by the SDI Subgroup Select Switch (Item 5, page 8). This connector is configured for an unbalanced, 75 Ωconnection.
AES Termination and Error Type DIP Switch
This 4-position DIP switch is used to set the termination characteristics for the AES input (Item D) and select the AES
signal error indication type.
AES Input Termination:
In the event that the AES input signal is fed to downstream equipment, then DIP switch Section S2 must be placed in the
Unterminated (UP) position. If there is no downstream equipment connected, then Section S2 must be placed in the
Terminated (DOWN) position. See below for diagram of termination settings. Note: Sections S3 and S4 are not used.
AES Error Indication Type:
There are two DIP switch selectable modes of AES error detection that will create a RED error indication in the AES Signal
Status LED on the front panel (Item 11, page 10);
• Reception Errors: errors in reception of data or no data stream at all (S1=DOWN)
• Reception and Data Errors: errors in reception and data errors identified by the sending device (possibly
invalid) (S1= UP).
See below for diagram of AES error DIP switch settings. Note: Sections S3 (x) and S4 (TERM 2) are not used.
AES Input Connector
This AES/EBU IN input (on female BNC connector) is meant to receive standard AES/EBU signals and is configured for
an unbalanced, 75 Ωconnection. Note that the unit will monitor this input only when the Analog/Digital Source Select
Switch (Item 4, page 8) is set to DIGITAL and the AES/SDI Source Select Switch (Item 6, page 8) is set to AES.

©2004 WohlerTechnologies Inc. ALL rights reserved 13
AMP2-SDA/AVUandAMP2-SDA/APPUserManual P/N 821576 Rev-A Section2: Operation
Figure-2b: Rear Panel Features

©2004 WohlerTechnologies Inc. ALL rights reserved
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AMP2-SDA/AVUandAMP2-SDA/APPUserManual P/N 821576 Rev-A
E
F
G
H
I
Rear Panel Features Section2: Operation
(Continued)
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
SDI Output Connector
The SDI OUT loop-through connector outputs a reclocked (regenerated) copy of the signal entering the SDI IN input
connector (Item F) and is configured for unbalanced, 75 Ωconnections.
SDI Input Connector
This SDI IN input (on female BNC connector) is meant to receive standard SDI signals and is configured for unbalanced, 75
Ωconnections. Note that the unit will monitor this SDI input only when the Analog/Digital Source Select Switch (Item 4,
page 8) is set to DIGITAL and the AES/SDI Source Select Switch (Item 6, page 8) is set to SDI.
Selected Analog Output Connectors (from Digital Source)
These two 3-pin male XLR connectors are analog outputs of the selected digital source (not the analog source) as selected
for the left and right speakers and level meters. The left connector outputs the left channel (or channel A) and the right
outputs the right channel (or 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. These connectors continually output the
selected digital source even when the analog inputs are selected for monitoring through the speakers. See Item H for a
diagram of XLR connector pinout assignments.
Analog Input Connectors
These two 3-pin female XLR connectors accept standard analog audio signals and are configured for balanced 40k Ω
connections. Note that the unit will monitor analog signals input on these two connectors only when the Analog/Digital
Source Select switch on the front panel (Item 4, page 8) is set to ANALOG. See below for a diagram of XLR connector
pinout assignments.
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 Gain Calibration settings.

©2004 WohlerTechnologies Inc. ALL rights reserved 15
AMP2-SDA/AVUandAMP2-SDA/APPUserManual P/N 821576 Rev-ASection2: Operation
Figure-2b: Rear Panel Features

©2004 WohlerTechnologies Inc. ALL rights reserved
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AMP2-SDA/AVUandAMP2-SDA/APPUserManual P/N 821576 Rev-A 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.
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.
The converse of the above is true if the balance control is rotated to the right.

©2004 WohlerTechnologies Inc. ALL rights reserved 17
AMP2-SDA/AVUandAMP2-SDA/APPUserManual P/N 821576 Rev-A
Technical Information
General Technical Observations
SDI to AES Converter Module PCB (919096)
AES to Analog Converter Module PCB (919117) Description
PPM Level Meter Specifications and Level Threshold Settings
VU Level Meter Specifications and Level Threshold Adjustment
AMP2-SDA/AVU and AMP2-SDA/APP Interconnect Block Diagram
Section 3

©2004 WohlerTechnologies Inc. ALL rights reserved
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AMP2-SDA/AVUandAMP2-SDA/APPUserManual P/N 821576 Rev-A 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 WohlerTechnologies Inc. ALL rights reserved 19
AMP2-SDA/AVUandAMP2-SDA/APPUserManual P/N 821576 Rev-A
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 (919117) is used to convert the AES signal to Analog audio.
In the AMPDigital Series units, channels 1and 2(first subgroup) or channels 3and 4(second subgroup) from SDI Group ID #1
are demuxed before being input to the AES to analog conversion module (919117). 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
400-1000 mV
Component,either525or625linesw/ 48 KHz 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 = signal present
Red = Error
Section3: TechnicalInformation

©2004 WohlerTechnologies Inc. ALL rights reserved
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AMP2-SDA/AVUandAMP2-SDA/APPUserManual P/N 821576 Rev-A Section3: TechnicalInformation
AES to Analog Converter Module PCB (919117) Description
There are four primary and three ancillary sections comprising the 919117 AES digital to analog converter:
1) Input source selection.
2) Audio data extraction.
3) Digital to analog conversion.
4) Analog buffer/output amplifiers.
5) Power suppy, Reset, and Error indication.
Input Source Selection (IC13)
Each of the two selectable signal inputs are transformer-coupled to the inputs of a one-of-two active buffer/switch (IC13). The
output of this switch is applied to the receiver stage of the AES receiver/unframer.
Audio Data Extraction (IC11)
"Header" and ancillary data are removed from the recovered input datastream, yielding a datastream having only alternating left/right
channel audio data which is output on pin 26 of IC11.
Digital to Analog Conversion (IC10)
The "pure" audio datastream, along with a data clock and a channel ID (left/right) clock, are applied to a 20 bit two channel D to A
converter (IC10), where the datastream is converted into left and right analog outputs.
Analog buffer (IC4) / Output Amplifiers (IC8, IC9)
Buffer/amps provide balanced left and right channel outputs as well as single ended outputs. Gain calibration, the analog level which
corresponds to a given digital value, is settable via a DIP switch. The default factory setting is 20 dB below "full code" (digital zero)
to equal +4 dbu (0.775V). The other three settings possible are for -18 dBfs = 0 dBu, -9 dBfs = +6 dBu, and -20 dBfs = +8 dBu.
See page 12 for DIP switch location and settings.
Power Supply
The 24V rail internal to the rest of the unit is converted to +5V for digital portions of the 919117 PCB by switching regulator IC12.
Error Indication
The AES status LED is a bicolor LED (Red/Green). It is green as long as a valid digital data strean is being received. The 8412
receiver is capable of distinguishing two types of error conditions: 1) Faulty data; data identified by the sending device (possibly
invalid), or 2) Faulty reception; errors in reception of data or no data stream at all. The red LED indication may be set to occur for
only faulty reception (section 1 closed) or with either faulty data OR faulty reception (section 1 open). See Item C, page 12 for
more information regarding this setting.
919117 Specifications
DtoAgain calibration,
(dB = dBFS):
AESsamplingrate:
D toA converter:
Convertedanalogout:
(S/N):
Convertedanalogout:
(THD):
AESTermination:
+8 = -20, +4 = -20, +6 = -9,
0=-18(DIPselectable)
32-48KHz,auto-select
24-bitlowjitter
>90dB
<0.008%
Removable(DIPselect)