Wohler AMP2-AMVU User manual

Title and Contents .....................................................
Introduction .................................................................................
Section 1: General Features and Specs ................
General Description and Features ...............................................
Applications and General Specifications .....................................
Section 2: Operation ................................................
Installation .................................................................................
Front Panel Features ...................................................................
Rear Panel Features ....................................................................
Section 3: Technical Information ...........................
General Technical Observations ..................................................
PPM Meter Specifications and Level Threshold Settings ............
VU Meter Specifications and Level Threshold Adjustment .........
AMP2-VM Series Interconnect Block Diagram ...........................
AMP2-AM Series
(AMP2-AMVU and AMP2-AMPPM)
2U Analog Monitor Speaker Unit with
Two VU or PPM Mechanical Level Meters,
Two Balanced and Two Unbalanced Inputs,
Two Loop-Thru Outputs, and Phase Indication
Document P/N 821540 Rev. A
1
2
3
4
5
7
9
10
12
15
16
17
17
18
CONTENTS
1
User Manual

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.

© 2002 Wohler Technologies Inc. ALL rights reserved 3
AMP2-AM Series User Manual P/N 821540 Rev-A
Sect. 1: General Features and Specifications
General Features
and Specifications
Description
Features
Applications
Specifications
Section 1

© 2002 Wohler Technologies Inc. ALL rights reserved
4
AMP2-AM Series User Manual P/N 821540 Rev-A
Features
AMP2-AM Series
Featuring Models: AMP2-AMVU and AMP2-AMPPM
Powered Analog Audio Monitor
Description
Section 1: General Features and Specifications
AMP2-AMVU or AMP2-AMPPM Front Panel
The AMP2-AM series analog monitor is a complete, exceptionally high quality analog stereo audio monitoring system in a
compact, two rackspace cabinet. It contains 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 being monitored.
All AMP2 series monitors come equipped with a ganged stereo volume control and balance pot, 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 AMP2-AM series models are specifically intended for those who prefer mechanical level meters when visually monitoring
audio signals. These units are capable of audibly monitoring two analog source channels through their stereo speaker systems while
simultaneously visually monitoring both channels via the two front panel mounted premium quality mechanical level meters. The
AMP2-AMVU model utilizes mechanical meters exhibiting VU ballistic characteristics while the AMP2-AMPPM model utilizes
mechanical meters exhibiting PPM ballistic characteristics with a choice of EBU or BBC scales..
Rear panel features on both models include two analog inputs on balanced XLR connectors, two loop-through outputs on two XLR
connectors, and two analog inputs on unbalanced RCA phono connectors.
• Two analog inputs on unbalanced XLR connectors
• Two analog loop-through outputs on unbalanced XLR
connectors
• Two analog inputs on unbalanced RCA phono connectors
• Headphone output
• Power indication LED
• Thorough magnetic shielding
• Numerous control and input options
• Quick and easy installation: simply slide in the rack and
connect audio and AC power
• 104 dB SPL at two feet
• Only two rack spaces high
• Excellent high frequency response for positive detection of
background whine and noise
• Audible and visual indication of phase/polarity problems
• Two front panel mounted mechanical level meters:
AMP2-PPM
• 2 Premium PPM Meters (EBU or BBC Scales)
AMP2-AMVU
• 2 Premium Quality VU Meters
WOHLER
TECHNOLOGIES
FAST-OUTFAST-IN
PHASE
AVG
AMP2-AM
ANALOG AUDIO
MONITOR PANEL
POWER

© 2002 Wohler Technologies Inc. ALL rights reserved 5
AMP2-AM Series User Manual P/N 821540 Rev-A Section 1: General Features and Specifications
Applications
The AMP2-AM Series 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 AMP2-AM
Series 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
UL and CE. 0 dbV ref. 0.775V RMS. Features and specifications subject to improvement without notice.
General Specifications
Input Connectors:
Peak Acoustic Out (@ 2 ft.):
Power output,
RMS Each Side (4ΩΩ
ΩΩ
Ω):
RMS Bass (4ΩΩ
ΩΩ
Ω):
Frequency Response,
Sixth Octave:
Input Level for Maximum
Output (Volume Full On):
Analog Input impedance:
Hum and Noise (analog):
Distortion, Electrical:
Distortion, Acoustic:
Input Overload:
Converted analog out S/N:
Converted analog out THD:
Magnetic shielding:
Power consumption
(Average Maximum):
AC Mains input:
Weight
Dimensions (HxWxD):
XLR (balanced) and RCA (unbalanced)
104 dB SPL
10 W transient / 14 W continuous
25 W transient / 35 W continuous
80 Hz - 16 kHz ± 5 dB)
(-10 dB @ 40 Hz, 20 kHZ)
0 dBv balanced / -10 dB unbalanced
200K Ω, balanced / 40K Ω, unbalanced
Better than -68 dB below full output
Less than 0.15% at any level below
input threshold
6% or less at worst case frequencies
above 120 Hz, including cabinet
resonance; typically less than 1.5%
+26 dBv balanced
>90 dB
<0.008%
<0.8 Gauss any adjacent surface
45 W
100-240VAC, 50-60 Hz Universal
18 lbs. (8.2 kg)
3.5 x 19 x 12 inches
(89 x 483 x 305 mm)
Audio Response Curve
Typical 1/6 Octave Audio Response Curve
B
d
0
+10
-20
-30
-10
Hz
10k
5k
2k1k50020010050 20k20
Note: See page 17 for level meter specifications

© 2002 Wohler Technologies Inc. ALL rights reserved
6
AMP2-AM Series User Manual P/N 821540 Rev-A

© 2002 Wohler Technologies Inc. ALL rights reserved 7
AMP2-AM Series User Manual P/N 821540 Rev-A
Operation
Installation
Front Panel Features
Rear Panel Features
Section 2

© 2002 Wohler Technologies Inc. ALL rights reserved
8
AMP2-AM Series User Manual P/N 821540 Rev-A Section 2: Operation

© 2002 Wohler Technologies Inc. ALL rights reserved 9
AMP2-AM Series User Manual P/N 821540 Rev-A
Installation
Section 2: Operation
Mounting
The unit should be mounted where convenient for operating persons, ideally at approximately ear level for best high frequency
response. 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 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 18 for clarifica-
tion of the general signal paths into and out of the AMP2-AM series unit.
Electrical Interference
As with any audio equipment, maximum immunity from electrical interference requires the use of shielded cable; however,
satisfactory results can sometimes be obtained without it. The internal circuitry common is connected to the chassis.
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.

© 2002 Wohler Technologies Inc. ALL rights reserved
10
AMP2-AM Series User Manual P/N 821540 Rev-A
Please refer to Figure-2a on the following page to familiarize yourself with the front panel features of the AMP2-AM Series unit.
The following sections describe these features and are referenced, by number, to Figure-2a.
Front Panel Features
Section 2: Operation
2
3
4
(Continued)
1
6
7
Speaker System
The AMP2-AM series internal Speaker System is comprised of two mid-range tweeter speakers (left and right) and one
woofer speaker (center). The two side channel speakers reproduce, in stereo, only the mid and high frequencies. Note that
the woofer speaker (center) is not a dedicated Center nor LFE speaker.
Power Indication LED
This LED glows green to indicate the AMP2-AM Series unit is connected to mains power and an operation voltage is present.
Audio Level Meters (VU or PPM)
Audio levels for the left and right analog sources are visually displayed via these two mechanical level meters. The AMP2-
AMVU model uses meters exhibiting VU ballistic characteristics. The AMP2-AMPPM model uses meters exhibiting PPM
ballistic characteristics. The left and right meters correlate to the left and right analog signals entering the unit..
For information about setting the Threshold Level adjustment and settings for the VU and PPM type of meter see page 17.
Headphone Jack
When headphones are plugged into this jack, the internal speakers will mute. This jack accepts a standard 1/4” phone type
stereo plug.
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.
Phase Indication LEDs
These three LEDs offer instant verification of phase (polarity) conditions in the pair of channels being monitored in the Left/
Right channel speakers. There are three LEDs; the two smaller LEDs labeled "FAST IN and "FAST OUT" show instantaneous
phase relationships in the signal, while the larger LED, labeled "AV G ", will indicate the average phase condition. The small
"FAST IN" LED on the left glows (or blinks) green when signals are in-phase. The small "FAST OUT" LED on the right
glows (or blinks) amber for out-of-phase signals. The larger "AV G " LED indicates the average phase condition by glowing
green for in-phase conditions, or red for out-of-phase conditions. In general, it is sufficient to regard the "AV G " LED
(average phase condition) as adequate for proper phase monitoring. While it is normal for stereo signals to contain some
intermittant instantaneous out-of-phase and in-phase conditions (small LEDs), a steady red glow of the larger LED almost
always indicates an out-of-phase alarm condition.
Balance Control Pot
This pans the volume balance between the left and right speakers. If the balance is adjusted hard left or hard right, a slight left/
right channel mix is retained (only in low bass frequencies) so that phase discrepancies can be discerned.
5

© 2002 Wohler Technologies Inc. ALL rights reserved 11
AMP2-AM Series User Manual P/N 821540 Rev-A Section 2: Operation
Figure-2a: Front Panel Features
131
4
1
2
5 6 7
2
WOHLER
TECHNOLOGIES
POWER
FAST-OUTFAST-IN
PHASE
AVG
MONITOR PANEL
ANALOG AUDIO
AMP2-AM

© 2002 Wohler Technologies Inc. ALL rights reserved
12
AMP2-AM Series User Manual P/N 821540 Rev-A
Please refer to Figure-2b on the following page to familiarize yourself with the rear panel features of the AMP2-AM series unit. The
following sections describe these features and are referenced, by letter, to Figure-2b.
Rear Panel Features
Section 2: Operation
(Continued)
A
B
D
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 Indication LED (Item 2, page 10) will glow GREEN to indicate operating voltages are present.
Analog Input (BALANCED IN) Connectors
These two 3-pin female XLR connectors (left and right) accept standard analog audio signals and are configured for balanced
200K Ωconnections. Pinout information for these connectors is shown below.
Analog Output (LOOP-THRU) Connectors
These two 3-pin male XLR connectors output an analog audio loop-through of the signals entering the inputs (Items B and D).
Pinout information for these connectors is shown below.
Analog Input (UNBALANCED IN) Connectors
These two RCA Phono connectors accept standard analog audio signals and are configured for unbalanced 40K Ωconnec-
tions. Pinout information is shown below.
Center
(Hot)
Sleeve
(Shield)
Female RCA
Phono Pinout
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

© 2002 Wohler Technologies Inc. ALL rights reserved 13
AMP2-AM Series User Manual P/N 821540 Rev-A Section 2: Operation
Figure-2b: Rear Panel Features
INTERNAL POWER
UNDERWRITERS LABS
LABEL ON SIDE
SEE POWER SUPPLY
50/60 Hz
100-240 VAC
NUMBER
SERIAL
UNBALANCED IN
BALANCED IN LOOP-THRU
CHANNEL A (LEFT)
AMP2A / AMP2A-AMPPM / AMP2A-AMVU
UNBALANCED IN
BALANCED IN LOOP-THRU
CHANNEL B (RIGHT)
253408-01
ABD
C B C D

© 2002 Wohler Technologies Inc. ALL rights reserved
14
AMP2-AM Series User Manual P/N 821540 Rev-A Section 2: Operation

© 2002 Wohler Technologies Inc. ALL rights reserved 15
AMP2-AM Series User Manual P/N 821540 Rev-A
Technical Information
•General Technical Observations
•PPM Meter Specifications and Level Threshold Settings
•VU Meter Specifications and Level Threshold Adjustment
Section 3

© 2002 Wohler Technologies Inc. ALL rights reserved
16
AMP2-AM Series User Manual P/N 821540 Rev-A Section 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 sometimes requires 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

© 2002 Wohler Technologies Inc. ALL rights reserved 17
AMP2-AM Series User Manual P/N 821540 Rev-A Section 3: Technical Information
-6 dB PPM
+8 dB PPM
0 dB PPM
+4 dB PPM
Level Gain Calibration DIP Switch Settings
AMP2-AMPPM Meter Driver PCB (919028)
IC2IC1
179036 rev B Top Side
P1 P2
Left Meter Right Meter
Turn pots clockwise to
increase the display level
threshold (sensitivity) in the
associated meter
AMP2-AMPPM Level Threshold Settings
There are two Level Threshold DIP switches accessible through holes in the top cover of the AMP2-AMPPM unit; one for each of
the two level meters. Each DIP switch is physically located above the level meter to which it is dedicated and each can be independantly
set with a possibility of four settings; -6, 0, +4, or +8 dBv. Factory setting is +4 dBv. See the diagram below for DIP switch settings.
PPM Meter Specifications and Level Threshold Settings
Level Meter Type:
Level Meter Scale:
Level Meter Threshold:
Level Meter Dynamics:
Mechanical
Standard VU
0 to +8 dBv (factory set to +4 dBv),
trim pot adjustable (internal)
VU (full ANSI)
Level Meter Type:
Level Meter Scale:
Level Meter Threshold:
Level Meter Dynamics:
Mechanical
Specify BBC (1 to 7) or EBU type 1
and 2 (specified when ordered)
-6, 0, +4, or +8 dBv: DIP switch
selectable (top cover)
PPM
AMP2-AMVU Level Threshold AdjustmentMVU Level Gain Calibration:
Level Gain Calibration adjustment for the AMP2-AMVU is done by adjusting two trim pots (P1 and P2) on the level meter driver PCB
(919036V). The units top cover must be removed to access this PCB, which is mounted in the center of the chassis bottom.
CAUTION: Be sure to follow basic safety porocedures when making adjustments to internal componants of a powered piece of
electronic equipment.
P1 adjusts the left meter; P2 adjusts the right meter. Clockwise rotation of either meter will increase the level of the associated
meter. Adjustment range for each meter is 0 to +8 dBv.
PPM Level Meter Specifications
VU Meter Specifications and Level Threshold Adjustment
VU Level Meter Specifications
AMP2-AMPPM Meter Driver PCB
Level Threshold DIP Switch Settings

© 2002 Wohler Technologies Inc. ALL rights reserved
18
AMP2-AM Series User Manual P/N 821540 Rev-A
AMP2-AM Series Interconnect Block Diagram
Section 3: Technical Information
CHANNEL A
(LEFT)
Rear
Panel
R
L
Audio Amplifier PCB
919100-2 or 919164
Volume Balance
Phase
Indication
PCB
919084
AMP2-AMVU and AMP2-AMPPM Interconnect Block Diagram
Connector Legend
= XLR-M, 3-Pin, Male = RCA Phono, Female
Rev-A, 08/15/02
= XLR-F, 3-Pin, Female
Right
Side Speaker
Middle
Speaker
(Woofer)
R
L
Left
Side Speaker
Phase
Indication
Analog Input Impedances: XLR = 200K
Ω,
Balanced
RCA = 47K
Ω,
Unbalanced
BALANCED IN
LOOP-THRU
Rear
Panel
Headphones
Mechanical
Level Meter
Driver PCB
UNBALANCED IN
BALANCED IN
LOOP-THRU
CHANNEL B
(RIGHT)
UNBALANCED IN
Right
Level Meter Left Level Meter
PPM = P/N 919028
(AMP2-AMPPM)
LR
R
L
VU = P/N 919036V
(AMP2-AMVU)

© 2002 Wohler Technologies Inc. ALL rights reserved 27
AMP2-AM Series User Manual P/N 821540 Rev-A
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]

© 2002 Wohler Technologies Inc. ALL rights reserved
28
AMP2-AM Series User Manual P/N 821540 Rev-A
Wohler Technologies, Inc.
713 Grandview Drive
South San Francisco, CA 94080
650 589-5676 Fax: [phone]
web: www.wohler.com
e-mail: [e-mail]
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]