Wohler AMP1-VSD User manual

Title and Contents .............................................................
Introduction ...............................................................................
Section 1: Features, Specs, and Installation ...........
Description and Features .............................................................
Applications and Specifications ...................................................
Installation .................................................................................
Section 2: Operation ........................................................
Front Panel Features ...................................................................
Rear Panel Features ....................................................................
Audio Amplifier and Speaker Configuration ................................
Section 3: Technical Information ................................
General Technical Observations ..................................................
AES to Analog Converter Module (919050 PCB) .........................
AES D/A Gain Calibration Fine Adjustment (919050 PCB) .......
AES Error Indication Jumper Locations (919050 PCB) .................
SDI to AES Converter Module (919096 PCB) ..............................
Level Meter Rear Panel 6-Position DIP Switch Settings ................
Level Meter Internal 10-Position DIP Switch Settings ..................
Level Meter DIP Switch Locations (919174 PCB) .........................
Level Meter Alternative Scales ....................................................
AMP1-VSD Interconnect Block Diagram .....................................
AMP1-VSD
1U Digital Audio Speaker Monitors
with One SDI Input and One SDI Output on BNC,
Two AES Inputs on BNC, Two AES Outputs From SDI
Input on BNC, Two Analog Outputs of the Left/Right Channel
Selections on XLR, Four Analog Outputs From Selected
Digital Source, Summable Channel Assignment,
Four 26-Segment Level Meters, and Phase Indication
Document P/N 821615 Rev-A
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CONTENTS
1
User Manual
© 2004 Wohler Technologies Inc. ALL rights reserved
ECO-2784 (11/17/04)

2© 2007 Wohler Technologies, Inc. ALL rights reserved
Introduction
Congratulations on your selection of a Wohler Technologies product. We are confident it represents the best performance and value
available, and we guarantee your satisfaction with it.
If you have questions or comments you may contact us at:
Wohler Technologies, Inc.
31055 Huntwood Avenue
Hayward, CA 94544
Phone: [phone] Fax: [phone]
US Toll-Free: 1-888-596-4537
www.wohler.com [e-mail]
1) Read these instructions.
2) Keep these instructions.
3) Heed all warnings.
4) Follow all instructions.
5) Do not use this apparatus near water.
6) Clean only with dry cloth.
7) Do not block any ventilation openings. Install in accordance with the manufacturer's instructions.
8) Do not install near any heat source such as radiators, heat registers, stoves, or other apparatus (including
amplifiers) that produce heat.
9) Do not defeat the safety purpose of the polarized or grounding-type plug. A polarized plug has two blades
with one wider than the other. A grounding type plug has two blades and a third grounding prong. The
wide blade or the third prong are provided for your safety. If the provided plug does not fit into your outlet,
consult an electrician for replacement of the obsolete outlet.
10) Protect the power cord from being walked on or pinched, particularly at plugs convenience receptacles
and the point where they exit from the apparatus.
11) Only use attachments/accessories specified by the manufacturer.
12) Use only with the cart stand, tripod, bracket, or table specified by the manufacturer, or sold with the
apparatus. When a cart is used, use caution when moving the cart/apparatus combination to avoid injury
from tip-over.
13) Unplug this apparatus during lightning storms or when unused for long periods of time.
14) Refer all servicing to qualified service personnel. Servicing is required when the apparatus has been
damaged in any way, such as when power-supply cord or plug is damaged, liquid has been spilled or
objects have fallen into the apparatus, the apparatus has been exposed to rain or moisture, does not
operate normally, or has been dropped.
15) Do not expose this apparatus to rain or moisture.
16) The apparatus shall be connected to a mains socket outlet with a protective earthing connection.
Important Safety Instructions
CAUTION!
In products featuring an audio amplifier and speakers, the surface at the side of the
unit, where the audio amplifier heat sink is internally attached, may get very hot after
extended operation. When operating the unit excercise caution when touching this
surface and ensure that external materials which may be adversely affected by heat
are not in contact with it. There is a Hot Surface label (see diagram) attached to the
aforementioned surface of the product.

© 2004 Wohler Technologies Inc. ALL rights reserved 3
AMP1-VSD User Manual P/N 821615, Rev-A
Sect. 1: General Features and Specifications
Features, Specs, and Installation
Description
Features
Applications
Specifications
Installation
Section 1

© 2004 Wohler Technologies Inc. ALL rights reserved
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AMP1-VSD User Manual P/N 821615, Rev-A
Features
AMP1-VSD
Powered Digital Audio Monitors
Description
Section 1: Features , Specs, and Installation
AMP1-VSD Front Panel
The rackmountable 1U size AMP1-VSD audio monitor is capable of audibly monitoring up to four audio source channels through
its stereo speaker system while simultaneously visually monitoring the audio levels via four high-resolution 26-segment LED
bargraph level meters. The AMP1-VSD monitors digital SDI and AES audio sources. A toggle switch on the front panel allows
selection between AES or SDI input sources.Two banks of four buttons on the front panel are used to independently assign from
one to four (summed) channels to each of the two (left and right) speaker channels. SDI signal status is indicated by one bi-color
(red/green) LED and AES signal status is indicated by two bi-color (red/green) LEDs. Wohler Technologies proprietary three-LED
stereo phase indication feature allows monitoring of phase relationships between the left and right speaker channels. Other features
include separate volume and balance controls, power indication LED, and headphone output. Output limiter circuits are incorporated
to protect the speakers, and extensive magnetic shielding allows placement immediately adjacent to video monitors with no color
impurities.
The rear panel of the AMP1-VSD features one SDI input and one SDI output on unbalanced BNC connectors, two AES outputs
(de-embedded from the SDI source) on two BNC connectors, two AES inputs on BNC connectors, four analog outputs (de-
embedded from the selected digital source) on four Phoenix connectors, and left and right analog outputs (of the channels
assigned to the left and right speakers) on two balanced XLR connectors.
All AMP1 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 two speakers) that handles
summed Low Frequency (LF) information below the 500 Hz crossover point. The AMP1 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.
• Two banks of four push buttons for assigning single or
summed channels to the left and right speaker
• Headphone output
• Power indication LED
• One SDI input and one SDI re-clocked output on unbalanced
BNC connectors
• Two AES inputs on two unbalanced BNC connectors
• Two AES outputs (converted from the SDI source) on two
BNC connectors
• Four analog outputs (converted from the selected digital
source) on four Phoenix connectors
• Analog outputs (of the sources selected for speaker
monitoring) on two balanced XLR connectors
• One SDI signal status indication LED
• Two AES signal status indication LEDs
• Quick and easy installation: simply slide in the rack and
connect audio and AC power
• Numerous control and input options
• 98 dB SPL at two feet
• Only one rack space high
• Excellent high frequency response for positive detection of
background whine and noise
• Audible and visual indication of phase/polarity problems
• Thorough magnetic shielding for placement next to video
monitors
• Four 26-segment high-resolution tri-color bargraph level meters:
-Selectable Input Referrence Level (0, +4, +6, or +8 dBu)
-Selectable Display Mode (VU Only, VU/PPM, or PPM Only)
-Selectable Peak Hold (Manual, 3-Second, 10-Second, or Off)
-Selectable PPM Ballistics (Type I, Type II, DIN 45406, or
SSRT)
-Selectable alternate Bargraph Scales (Extended VU, VU,
BBC, NORDIC, DIN, or Custom)

© 2004 Wohler Technologies Inc. ALL rights reserved 5
AMP1-VSD User Manual P/N 821615, Rev-ASection 1: Features , Specs, and Installation
Applications
The AMP1-VSD is 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., the AMP1-VSD is 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.
Physical Specifications
Audio Response Curve
Typical 1/6 Octave Audio Response Curve
B
d
0
+10
-20
-30
-10
Hz
10k
5k
2k1k50020010050 20k20
10 lbs. (4.53 kg)
3.5 x 19 x 12 inches
(89 x 483 x 305 mm)
Weight:
Dimensions (HxWxD):
For AES specifications see page 19.
For SDI specifications see page 22.
Level Meter Specifications
Level Meter Type:
Bargraph Quantity:
LED Color:
Metering Range:
Reference Level:
Display Mode Select:
Peak Hold Select:
PPM Ballistics Select:
Calibration:
Scale Select:
26-segment tri-color LED bargraph
4 each, vertical
Tricolor (red, amber, green)
62 dB
0, +4, +6, or +8 dBv selectable
VU Only, VU/PPM, or PPM Only
Manual, 3-sec, 10-sec, or OFF
Type I, Type II, DIN 4506, or SSRT
Auto
VU, Extended VU, BBC, NORDIC,
DIN, or Custom
General Specifications
AES Input Connectors:
SDI Input Connectors:
AES Input impedance:
SDI Input impedance:
Input Level for Maximum
Output (Volume Full On):
Input Overload:
Peak Acoustic Output
(@ 2 ft.):
Response, Sixth Octave:
Power output
RMS Each Side (4ΩΩ
ΩΩ
Ω):
RMS Bass (4ΩΩ
ΩΩ
Ω):
Distortion, Electrical:
Distortion, Acoustic:
Hum and Noise:
Magnetic Shielding:
Power Consumption
(Average Maximum):
AC Mains input:
BNC, 2 each
BNC, 1 each
75Ω, unbalanced
75Ω, unbalanced
0 dBv balanced
+26 dBv balanced
98 dB SPL
80 Hz - 16 kHz ± 7 dB)
(-10 dB @ 50 Hz, 22 kHZ)
10 W transient / 5 W continuous
20 W transient / 10 W continuous
Less than 0.15% at any level below
limit threshold
8% or less at worst case frequencies
above 180 Hz including cabinet
resonance; typically less than 2%
Better than -68 dB below full output
Less than 1 Gauss any adjacent
surface
35 W
100-240VAC, 50-60 Hz
Custom combinations of connectors, controls and level meters are available by special order.

© 2004 Wohler Technologies Inc. ALL rights reserved
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AMP1-VSD User Manual P/N 821615, 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 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 40°C (104°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 27 for clarifica-
tion of the general signal paths into and out of the AMP1-VSD unit.
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.
Section 1: Features , Specs, and Installation

© 2004 Wohler Technologies Inc. ALL rights reserved 7
AMP1-VSD User Manual P/N 821615, Rev-A
Operation
Front Panel Features
Rear Panel Features
Audio Amplifier and Speaker Configuration
Balance Control Characteristics
Section 2

© 2004 Wohler Technologies Inc. ALL rights reserved
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AMP1-VSD User Manual P/N 821615, Rev-A
1
2
5
6
7
3
4
Please refer to Figure-2a on the facing page to familiarize yourself with the front panel features of the AMP1-VSD unit. The following
sections describe these features and are referenced, by number, to Figure-2a.
Front Panel Features
Section 2: Operation
(Continued)
Speakers
The AMP1-VSD features two mid-range speakers (left and right) and two woofer speakers. 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 two woofer (bass)
speakers. Note that the woofer channel is NOT a dedicated LFE (subwoofer) or Center channel. See page 16 for more
information concerning the AMP1 Series audio amplifier/speaker configuration.
Headphone Jack
This jack accepts a standard 1/4” phone type stereo plug. When you plug in headphones, the internal speakers will mute.
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.
Audio Level Meter LED Bargraph Displays (1-4)
Audio levels for the four source channels are displayed via these four tri-color LED bargraph meters. All bargraph LED
segments are of the tri-color type (green, amber, red) and the meters are user adjustable for Reference Level,Display
Mode,Peak Hold,PPM Ballistics,Alternate Bargraph Scales, and Phase Correlation via DIP switches on the rear
panel and inside the unit. For factory set and user adjustable level meter DIP switch settings, see pages 23 and 24. For
meter specifications, see page 5.
AES/SDI Source Select Switch
This two position toggle switch selects between the two primary input sources; AES or SDI. When this toggle switch is set
to AES, the unit will monitor the AES source signals as input on the rear panel AES IN BNC connectors (Item F, page 12).
When this toggle switch is set to SDI, the unit will monitor the SDI source signals as input on the rear panel SDI IN BNC
connector (Item C, page 12).
Volume Control Pot
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 in the speakers or headphones.
Power LED
This LED glows GREEN to indicate the unit is connected to mains power and an operation voltage is present.

© 2004 Wohler Technologies Inc. ALL rights reserved 9
AMP1-VSD User Manual P/N 821615, Rev-ASection 2: Operation
Figure-2a: Front Panel Features

© 2004 Wohler Technologies Inc. ALL rights reserved
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AMP1-VSD User Manual P/N 821615, Rev-A
9
10
11
8
Section 2: Operation
(Continued)
Phase Indication LEDs
These three LEDs indicate the instantaneous and average phase (polarity) conditions between the source(s) assigned to the
left speaker channel and the source(s) assigned to the right speaker channel. The larger LED labeled AVG indicates the
average phase condition between the left and right speaker channels. The two smaller LEDs labeled FAST indicate the
instantaneous phase relationships. 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.
Bargraph Brightness Trim Pot
This control is recessed into the front panel and can be accessed using a small screwdriver. Turning it clockwise will
increase the relative brightness of all bargraph display LED segments. Adjusting this one control will simultaneously affect
the brightness of all bargraph displays on the front panel.
SDI Signal Status Indication LED
This bi-color (GREEN/RED) LED indicates the SDI signal status. Indication is as follows:
•GREEN = valid SDI datastream received
•RED = invalid SDI datastream or TSR errors in datastream
•Unlit = no datasteam received
This LED continuously monitors the status of the SDI input signals even when the SDI source is not selected for
monitoring.
AES Signal Status Indication LEDs (AES1 and AES2)
These two bi-color (GREEN/RED) LEDs indicate the AES signal status. The AES1 LED indicates status for the AES IN
1input and the AES2 LED indicates status for the AES IN 2 input. Indication is as follows:
•GREEN = valid AES datastream received
•RED = invalid AES datastream or reception errors
•Unlit = no datasteam received
This LED continuously monitors the status of the AES input signals even when the AES source is not selected for
monitoring.
Note: If you wish to disable datastream error indication (and leave only indication of reception errors) you can place
jumpers on H14 and H18 of the AES-to-Analog Converter Module (919050 PCB). See page 21 for component locations.
Balance Control Pot
This adjusts the volume balance between the left and right speakers or headphones. See page 16 for more information about
the AMP1 Series balance control characteristics.
Front Panel Features
12

© 2004 Wohler Technologies Inc. ALL rights reserved 11
AMP1-VSD User Manual P/N 821615, Rev-ASection 2: Operation
Figure-2a: Front Panel Features

© 2004 Wohler Technologies Inc. ALL rights reserved
12
AMP1-VSD User Manual P/N 821615, Rev-A
E
D
A
B
C
G
F
Section 2: Operation
Please refer to Figure-2b on the facing page to familiarize yourself with the rear panel features of the AMP1-VSD unit. The
following sections describe these features and are referenced, by letter, to Figure-2b.
Rear Panel Features
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 7, page 8) will glow GREEN to indicate operating voltages are present.
Unused DIP Switch Module (2-Position)
This 2-position DIP module is reserved for future implementation. Do not use.
SDI Input and Output Connectors
The female BNC SDI IN connector receives industry standard SDI formatted signals and is configured for an unbalanced,
75 Ωimpedance connection. The unit de-embeds and monitors sub-group 1 (channels 1/2) and sub-group 2 (channels 3/
4) of SDI Group ID #1 (see page 22 for more information). Note that the SDI input is monitored only when the AES/SDI
Source Select Switch (Item 5, page 8) is set to SDI.
The female BNC SDI OUT loop-through connector outputs a reclocked (regenerated) copy of the signal entering the SDI
IN input connector and is configured for an unbalanced, 75 Ωconnection.
Level Meter DIP Switch Module (6-Position)
This DIP switch sets the Line Level Calibration,Reference Level, and PPM/VU Display Mode for the level meter LED
bargraph displays on the front panel. See page 23 for for setting information.
Selected Analog Output Connectors (Right [A] and Left [B])
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 (Channel A) 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.
AES Input Connectors (AES IN 1 and AES IN 2)
The AES IN 1 and AES IN 2 input connectors are meant to receive industry standard AES source signals and are configured
for 75Ωimpedance connections. Note that the unit will monitor the AES inputs only when the AES/SDI Source Select
Switch (Item 5, page 8) is set to AES.
AES Output (Converted From SDI Input) Connectors
These two female BNC connectors output AES signals as converted from only the SDI input source (Item C) as follows:
•Left connector = Channels 1and 2(converted from subgroup 1 of SDI Group I.D. #1)
•Right connector = Channels 3and 4(converted from subgroup 2 of SDI Group I.D. #1)
(Continued)
High (+)
Low (-)
Gnd
(Shield)
Pin-1 Pin-2
Pin-3

© 2004 Wohler Technologies Inc. ALL rights reserved 13
AMP1-VSD User Manual P/N 821615, Rev-ASection 2: Operation
Figure-2b: Rear Panel Features

© 2004 Wohler Technologies Inc. ALL rights reserved
14
AMP1-VSD User Manual P/N 821615, Rev-A
H
I
J
AES Input Termination DIP Switch Module (4-Position)
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 = IN 1 and
section 3 = 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.
Digital Input Level Gain Calibration DIP Switch Module (2-Position)
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 settings.
Analog Output (From Selected Digital Source) Connectotrs
These four connectors output analog signals converted from the selected digital input (SDI or AES) as selected by
the AES/SDI Source Select Switch on the front panel (Item 5, page 8). These connectors are 3-pin male Phoenix
terminal block connectors and are configured for low impedance connections. Pinout information is silk-screened
just below output connector 1.
Rear Panel Features
(Continued)
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

© 2004 Wohler Technologies Inc. ALL rights reserved 15
AMP1-VSD User Manual P/N 821615, Rev-A
Figure-2b: Rear Panel Features

© 2004 Wohler Technologies Inc. ALL rights reserved
16
AMP1-VSD User Manual P/N 821615, Rev-ASection 2: 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 two woofer (bass)
speakers. Note that the woofer channel is NOT a dedicated LFE (subwoofer) or Center channel.
Speaker Configuration
All AMP1 (1U) products are configured with two speaker channels (left and right) to reproduce midrange and high-range
audio frequencies (in stereo) and two 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 AMP1 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 Wohler Technologies Inc. ALL rights reserved 17
AMP1-VSD User Manual P/N 821615, Rev-A
Technical Information
•General Technical Observations
• AES to Analog Converter Module (919050 PCB)
• AES D/A Gain Calibration Fine Adjustment (919050 PCB)
• AES Error Indication Jumper Locations (919050 PCB)
• SDI to AES Converter Module (919096 PCB)
• Level Meter Rear Panel 6-Position DIP Switch Settings
• Level Meter Internal 10-Position DIP Switch Settings
• Level Meter DIP Switch Locations (919174 PCB)
• Level Meter Alternative Scales
• AMP1-VSD Interconnect Block Diagram
Section 3

© 2004 Wohler Technologies Inc. ALL rights reserved
18
AMP1-VSD User Manual P/N 821615, Rev-ASection 3: Technical Information
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. ALL rights reserved 19
AMP1-VSD User Manual P/N 821615, Rev-ASection 3: Technical Information
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 11, page 10 for more information
about error detection and indication.
There are two AES inputs, which can be configured with unbalanced 75 ΩBNC connectors and/or 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, balanced 110 ΩPhoenix connectors, or balanced 110 ΩXLR connectors.
919050 Specifications
Input formats:
Digital-to-AnalogConversion:
Sampling rate:
Termination:
Analog out (of digital source),
S/N:
THD (full output):
Max output of analog out:
D to A gain calibration,
(dB = dBFS):
Standard input connectors:
Optional input connectors:
Standard output connectors:
Optional output connectors:
Error Indication:
AES/EBUor SPDIF
24-bit low jitter
32 kHz to 48 kHz
Removable (DIP switch selectable)
Greater than 96 dB
Less than 0.008%
+24 dBv (0 dBv = 0.775 vRMS)
+8 = -20, +4 = -20, +6 = -9, 0 = -18 (DIP switch selectable)
BNC: 75 Ω, unbalanced
Phoenix or XLR: 110 Ω, balanced
BNC: 75 Ω, unbalanced
Phoenix or XLR: 110 Ω, balanced
Two Bi-Color LEDs (on front panel):
Green = OK
Red = Error, no lock to signal, or no signal.
AES to Analog Converter Module (919050 PCB)

© 2004 Wohler Technologies Inc. ALL rights reserved
20
AMP1-VSD User Manual P/N 821615, Rev-A
AES D/A Gain Calibration Fine Adjustment (919050 PCB)
The digital gain calibration is set at the factory for +4 dB (Analog) = -20 dBFS (Digital). Three other values (+8 = -20, +6 = -9, and
0 = -18) may also be user selected via a DIP switch on the rear panel (Item I, page 14). However, if a fine adjustment of the
calibration is desired, perform the following procedure:
1) Remove the top cover. Save screws for later reassembly.
2) You must remove the 919083 PCB to access the trim pots (P1-P4) on the 919050 PCB (see Figure-3a below for trim pot
locations).
3) Place the AES/SDI Source Select Switch (Item 5, page 8) to the AES position. Connect a digital (AES) source of known
digital amplitude and set the unit’s controls to monitor that source. For convenience sake, it would be best to use your facility’s
digital reference level, but any nearby level may be used with appropriate scaling of output level required.
4) Using an accurate DMM (preferably one having direct reading in dBv/dBu), measure the level on the Analog Out From
Selected Digital Source phoenix connectors (Item J, page 14). Be sure to take a measurement of the FULL balanced output,
NOT just between one of the outputs and ground!
5) Locate trim pots P1,P2,P3, and P4 (see Figure-3a below). Adjust P4 (channel 1) through P1 (channel 4) for the desired
analog level corresponding to the digital signal amplitude being supplied to the unit. For example, if your “house” Analog/Digital
correspondence is for a -18 dBfs digital level to correspond to an Analog level of +0dBu, it would be easiest to set the digital
source to -18 dBfs, set the gain calibration DIP switch for -18dBFS = 0dBu and then set P1 through P4 for 0dBu outputs on the
phoenix Analog Output connectors. But, if a digital source of -20dBfs is applied, even though the facility references are for
-18dBfs, then the analog output levels should be adjusted for a -2.0 dBu analog output level on the phoenix connectors.
Note: If the meter being used to measure the analog output is not so accurate at those relatively low signal levels, you may wish to
increase the digital signal amplitude by some convenient factor like 10 or even 20 dB (but do not increase above digital full scale).
P1 - Adjusts Channel 4
P2 - Adjusts Channel 3
P3 - Adjusts Channel 2
P4 - Adjusts Channel 1
Figure-3a:
AES/EBU to Analog Module PCB (919050)
Digital Gain Calibration Trim Pot Locations
Section 3: Technical Information