Wohler AMP1A-4S User manual

Title and Contents ...........................................................
Important Safety Instructions and Introduction ..........................................
Section 1: General Features and Specifications........
Description and Features ......................................................................
Applications, General Specifications, and Other Options ...........................
Installation ..............................................................................................
Section 2: Operation ..................................................................
Front Panel Features ...............................................................................
Rear Panel Features .................................................................................
Section 3: Technical Information .......................................
General Technical Observations ...............................................................
Level Meter Gain Calibration and Display Mode Settings .........................
Bargraph Driver Circuit Description (919017) ..........................................
Level Meter Specifications .......................................................................
Multi-ChannelAnalogSwitchingPCBCircuitDescription(919013).........
Interconnect Block Diagrams ..................................................................
AMP1A Series
AMP1A-4S AMP1A-10S AMP1A-LP4S AMP1A-LP10S
1U Multi-Channel Audio Speaker Monitors
with Four or Ten Analog Audio Inputs,
Stereo Analog Outputs, and Optional Dual
10-Segment Level Meters and Phase Indication
Document P/N 821527 Rev-B
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CONTENTS
User Manual
© 2006 Wohler Technologies Inc. ALL rights reserved 1

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.

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© 2006 Wohler Technologies Inc. ALL rights reserved
AMP1A-4S/-10S/-LP4S/-LP10S User Manual P/N 821527 Rev-B
General Features
and Specifications
Description
Features
Applications
General Specifications
Other Options
Section 1

4© 2006 Wohler Technologies Inc. ALL rights reserved
AMP1A-4S/-10S/-LP4S/-LP10S User Manual P/N 821527 Rev-B
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ANALOG AUDIO
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Features
The AMP-1A Series of audio monitors provides self-powered, full-fidelity stereo monitoring in the smallest rack space possible. All
models in the AMP1A Series contain five high performance transducers driven by three power amplifiers: two amplifier/driver
combinations handle midrange and high frequency information in stereo, while the third center channel reproduces information
below the 500 Hz crossover point.
All AMP-1A models 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 AMP1A-4S model features four pairs (8 channels) of balanced inputs on Phoenix connectors and the AMP1A-10S features ten
pairs (20 channels) of these inputs. Any pair of inputs is selectable for monitoring via a rotary source select switch on the front
panel. An additional pair of XLR connectors output the selected audio signals for connecting to downstream equipment.
The AMP1A-LP4S and AMP1A-LP10S models offer the same input features as the -4S and -10S models with the addition of dual 10-
segment tri-color LED bargraph level meters and Wohlers' proprietary three-LED stereo phase indication feature.
AMP1A SeriesAMP1A Series
AMP1A SeriesAMP1A Series
AMP1A Series
1U Stereo Analog Audio Speaker Monitors
Description
AMP1A-4S
Section 1: General Features and Specifications
• 98 dB SPL at two feet
• Only one rack space high
• Excellent high frequency response for positive detection
of background whine and noise
• Audible indication of phase/polarity problems
• Thorough magnetic shielding for placement next to video
monitors
• Numerous control and input options
• Quick and easy installation: simply slide in the rack and connect
audio and AC power
• 4S and 10S models offer front panel switching between four (8
channels) or ten (20 channels) stereo inputs.
• LP models offer dual level meters and stereo phase indication
LEDs
Including Models: AMP1A-4S AMP1A-10S AMP1A-LP4S AMP1A-LP10S
AMP1A-10S
AMP1A-LP4S
AMP1A-LP10S

5
© 2006 Wohler Technologies Inc. ALL rights reserved
AMP1A-4S/-10S/-LP4S/-LP10S User Manual P/N 821527 Rev-B
Applications
Medium-size SegmentsMedium-size Segments
Medium-size SegmentsMedium-size Segments
Medium-size Segments
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General Specifications
Section 1: General Features and Specifications
The AMP1A 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 AMP1A Series is
backed by a strong warranty and a satisfaction guaranteed return policy.
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:
RMS Bass:
Distortion, Electrical:
Distortion, Acoustic:
Hum and Noise:
Magnetic Shielding:
Input Connectors:
Power Consumption
(Average Maximum):
AC Mains input:
90K Ω (Ohm) balanced
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
Balanced: XLR
35 W
100-240VAC, 50-60 Hz
Level Calibration:
Frequency Response:
Level Meter Type:
LED Color:
Metering Range:
Display Modes:
VU Characteristics,
Rise Time:
Decay Time:
PPM Characteristics,
Attack Time:
Decay Time:
Dimension (h xw xd):
Weight:
-6, 0, +4, +8 dBv
20 Hz to 18 kHz (±0.5 dB)
10-segment tri-color LED bargraph
display
Tricolor (red, amber, green)
23 dB
VU or PPM, Selectable
300 ms to 99% of full indication
300 ms
10 ms
2 seconds, 0 to -20 dB
1.75 x 19 x 12 inches
44.5x 483 x 298 mm
14 lbs. (6.4 kg)
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.
Other Options
Wohler Technologies offers by far the broadest range of standard production audio monitor units. Standard-production models or
special order custom features for the AMP1A Series (1U) units include the following functions (and combinations thereof):
• Multiple stereo input selection, from 2 to 10
• AES/EBU and SDI (SMPTE259) inputs
• Separate channel volume controls
• Mono, mute, and mode switches
• Alternate level meter scales and color maps
• High resolution 26-segment bargraph level meters
• Transformer coupled inputs
• FULL output power DC operation
• External speaker capability
• Multiple input and output connector type choices
Other custom options are possible. Call your dealer or Wohler Technologies to discuss your specific needs.
Level Meter Specifications (-LP)
Physical Specifications
Audio Response
Typical 1/6 Octave Audio Response Curve
B
d
0
-10
-20
-30
+10
Hz
10k5k2k1k50020010050 20k20
`

6© 2006 Wohler Technologies Inc. ALL rights reserved
AMP1A-4S/-10S/-LP4S/-LP10S User Manual P/N 821527 Rev-BSection 1: General Features and Specifications
Installation
Mounting
NOTE: Be sure to set the level meter Gain Calibration and Display Mode DIP switch (accessed through the top cover) BEFORE
installing the unit in the rack or console. See page 15 for setting information.
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 pages 18 and 19 for
clarification of the general signal paths into and out of the AMP1A Series units.
Phoenix connector inputs on the analog switching PCB (919013) are 90K Ω, balanced. Care should be exercised to avoid mis-
matched cable types and other similar causes of undesired reflections in RF signal systems.
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.

7
© 2006 Wohler Technologies Inc. ALL rights reserved
AMP1A-4S/-10S/-LP4S/-LP10S User Manual P/N 821527 Rev-B
Operation
Installation
Front Panel Features
Rear Panel Features
Section 2

8© 2006 Wohler Technologies Inc. ALL rights reserved
AMP1A-4S/-10S/-LP4S/-LP10S User Manual P/N 821527 Rev-B
Please refer to Figure-2a on the following page to familiarize yourself with the front panel features of the AMP1A Series units covered
by this manual. The following sections describe these functions and are referenced, by number, to Figure-2a.
Section 2: Operation
Front Panel Features
1Speakers
The AMP1A Series internal speaker system is comprised of two mid-range tweeter speakers (left and right) and two woofer
speakers (left and right). The two mid-range speakers reproduce, in stereo, only the mid and high frequencies, while the two
woofer speakers monorally reproduce the low frequencies.
2 Volume Control - Rotary 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.
3Headphone Output - 1/4" Jack
Select the headphone audio sources as you would for the internal speakers. When you plug in headphones, the internal
speakers will mute. This jack accepts a standard 1/4” phone type stereo plug.
4Power Indication - Green LED
This LED glows GREEN to indicate the AMP1A Series model is connected to operational mains power.
5Balance Control - Rotary 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.
6Source Select Switch - 4-Position or 10-Position Toggle Switch
This switch selects, from the multi-channel inputs, a single stereo audio source (2 channels) for monitoring through the unit.
The 4S models use a 4-position rotary switch for source selection, while the 10S models use a 10-position rotary switch for this
function.
7Audio Level Meters - 10-Segment LED Bargraph Displays
(AMP1A-LP4S and AMP1A-LP10S Only)
Audio levels are visually displayed via these two 10-segment, tri-color (red, amber, green) LED bargraph display level meters.
Bargraph 1monitors Channel A(left) while Bargraph 2monitors Channel B(right). These meters are able to simultaneously
display signal levels using both PPM and VU standards. Alternate display modes are user selectable via a DIP switch module
accessible through the top cover. See page 15 for settings and page 16 for specifications of these meters .
8Phase Indication - Bi-Color LEDs (red/green)
(AMP1A-LP4S and AMP1A-LP10S Only)
These three LEDs indicate the instantaneous and average phase (polarity) conditions between the pair of channels
selected for monitoring in the Left/Right channel speakers. The larger LED labeled AVG indicates the average phase
condition between the two signal sources. The two smaller LEDs indicate the instantaneous phase relationships.
Indication is as follows:
•The smaller "fast" in-phase (ΦΦ
ΦΦ
Φ+)LED glows (or blinks) GREEN for in-phase signals.
•The smaller "fast" out-of-phase (ΦΦ
ΦΦ
Φ-)LED glows (or blinks) YELLOW for out-of-phase signals.
•The larger AVG LED indicates average phase condition; GREEN for in-phase signals, 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 intermittent 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.

9
© 2006 Wohler Technologies Inc. ALL rights reserved
AMP1A-4S/-10S/-LP4S/-LP10S User Manual P/N 821527 Rev-BSection 2: Operation
Figure-2a: Front Panel Features
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AMP1A-LP4S
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75 76 5
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2 1 3 1 0
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6AMP1A-LP10S
ANALOG AUDIO
MONITOR PANEL
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AMP1A-4S
ANALOG AUDIO
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AMP1A-10S

10 © 2006 Wohler Technologies Inc. ALL rights reserved
AMP1A-4S/-10S/-LP4S/-LP10S User Manual P/N 821527 Rev-B
Please refer to Figure-2b on the following page to familiarize yourself with the rear panel features of the AMP1A Series units. The
following sections describe these features and are referenced, by letter, to Figure-2b.
APower - IEC-320 Connector
Attach a standard IEC-320 power cord between this connector and mains power (100 - 250VAC, 50/60 Hz). The front panel power
LED (Item 4, page 8) will glow GREEN to indicate operating voltages are present.
BBalanced Inputs (Channels 1-4) - 3-Pin Male Phoenix
(AMA1A-4S and ANAP1A-LP4S Only)
These balanced (40K Ω) 3-pin Phoenix connectors (left and right) accept standard analog audio signals. The two banks of
inputs, Channel A (Left) and Channel B (Right), are comprised of four connectors each for a total of eight inputs (four stereo
pairs). Connector pinout information is silk-screened on the rear panel above each connector.
CBalanced Inputs (Channels 1-10) - 3-Pin Male Phoenix
(AMA1A-10S and ANAP1A-LP10S Only)
These balanced (90K Ω) 3-pin Phoenix connectors (left and right) accept standard analog audio signals. The two banks of
inputs, Channel A (Left) and Channel B (Right), are comprised of ten connectors each for a total of twenty inputs (ten stereo
pairs). Connector pinout information is silk-screened on the rear panel between the two rows of connectors.
DSelected Outputs - 3-Pin Male XLR
These two 3-pin male XLR connectors are analog outputs of the audio source as selected by the Source Select Switch on the
front panel (Item 6, page 8). The output is not affected by the volume/balance controls or headphone mute. See below for XLR
connector pinout information.
Rear Panel Features
Section 2: Operation
High (+)
Low (-)
Gnd
(Shield)
Pin-1 Pin-2
Pin-3
Male XLR Pinout

11
© 2006 Wohler Technologies Inc. ALL rights reserved
AMP1A-4S/-10S/-LP4S/-LP10S User Manual P/N 821527 Rev-B
Figure-2b: Rear Panel Features
Section 2: Operation
AMP1A-10S and
AMP1A-LP10S
Rear Panel.
AMP1A-4S and
AMP1A-LP4S
Rear Panel.
AB
D
AC
D
INTERNAL POWER
UNDERWRITERS LABS
LABEL ON SIDE
SEE POWER SUPPLY
4321
CHANNEL A
(LEFT)
+ + + +
100-240 VAC
50/60 Hz
INPUTS
SEL. OUT CH B(R)
SEL. OUT CH A(L)
4321
+ + + +
(RIGHT)
CHANNEL B
AMP1A-LP4S
253829
INPUTS
+
INTERNAL POWER
UNDERWRITERS LABS
LABEL ON SIDE
SEE POWER SUPPLY
CHANNEL B
(RIGHT)
+ + + + +
CHANNEL A
100-240 VAC
50/60 Hz
(LEFT)
1 2 43 5
SEL. OUT CH B(R)
SEL. OUT CH A(L)
+ + + +
AMP1A-LP10S
253828
96 7 8 10

12 © 2006 Wohler Technologies Inc. ALL rights reserved
AMP1A-4S/-10S/-LP4S/-LP10S User Manual P/N 821527 Rev-BSection 2: Operation
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© 2006 Wohler Technologies Inc. ALL rights reserved
AMP1A-4S/-10S/-LP4S/-LP10S User Manual P/N 821527 Rev-B
Technical Information
• General Technical Observations
• Level Meter Gain Calibration and Display Mode Settings
• 919017 - Level Meter Bargraph Driver Circuit Description
• Level Meter Specifications
• 919013 - Multi-Channel Analog Switching PCB Circuit Description
• Interconnect Block Diagrams
Section 3

14 © 2006 Wohler Technologies Inc. ALL rights reserved
AMP1A-4S/-10S/-LP4S/-LP10S User Manual P/N 821527 Rev-BSection 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

15
© 2006 Wohler Technologies Inc. ALL rights reserved
AMP1A-4S/-10S/-LP4S/-LP10S User Manual P/N 821527 Rev-B
Level Meter DIP Switch Settings
Two DIP switch modules, accessed through an opening in the top cover, allow the user to set the Bargraph Display Mode and Meter
Input Gain Calibration independently for each of the two bargraph displays. There are four sections (S1, S2, S3, S4) on each DIP switch
module. The first two sections (S1, S2) are for setting the Meter Input Gain Calibration and the second two sections (S3, S4) are for
setting the Bargraph Display Mode.
Meter Input Gain Calibration Settings
DIP switch sections S1 and S2 set the Meter Input Gain Calibration, which determines the level of the input signal that will result in
a "0" reading on the meter bargraphs. The factory setting is +4 dBv, but can instead be set for -6 dBv, 0 dBv, or +8 dBv by the user. See
the diagram below for settings.
Bargraph Display Modes
DIP switch sections S3 and S4 determine how peak levels are displayed (Display Mode) and select either the "PPM" mode or an auto-
reset "VU Peak" mode (NOT the PPM value!). The PPM mode exhibits an attack time of 10 milliseconds and a decay time of 2
seconds from 0 to -20 dB. The VU mode exhibits a 300 millisecond rise to 99% of full indication and a decay of 300 milliseconds.
The factory setting is VU mode. See the diagram below for settings.
Installation Note:
The Meter Input Gain Calibration/Bargraph Display Mode DIP modules are accessible through openings in the top cover of the unit.
Any adjusments to the DIP switch modules should be performed before installing the unit into an enclosed rack.
Level Meter Gain Calibration and Display Mode Settings
AMP1A Analog 10-Segment
Level Meter DIP Switch Settings
Gain Calibration
21
-6 dBv 0 dBv
21
+4 dBv
21
+8 dBv
21
Display Mode
4
PPM
34 3
VU Peak
Section 3: Technical Information

16 © 2006 Wohler Technologies Inc. ALL rights reserved
AMP1A-4S/-10S/-LP4S/-LP10S User Manual P/N 821527 Rev-BSection 3: Technical Information
The "PPM-1" version of the 919017 meter driver input is driven single-ended from the main circuit board. Gain selection via S1 and
S2 of the DIP switch module (page 17) allow the circuit to be configured for an input level of -6, 0, +4, or +8 dB to indicate '0' on the
actual display. The input attenuator network consists of R1-R4, R11, R17, R18, and R19. The buffered signal (and its inversion) are
coupled to half-wave rectifiers IC2a and b.
The two half-wave rectifiers provide full-wave rectification of the AC signal from the input amplifier. IC2a provides output on
negative excursions; IC2b is for positive excusions. C8 is charged via R14 (or R26); the time constant of this resistor-capacitor
combination determines the attack time of the meter. When the input level decreases, C8 discharges through R14, R16, and D1 (R27,
R28, D3); the resulting time constant determines the decay time of the meter. By switching in additional RC (R21, C10) with S3, the
attack time is increased and the decay decreased, to approximate VU characteristics. S4 is closed along with S3 to adjust the
reference voltage to compensate for the voltage dividing effects of R21.
The popular LM3916 10-segment LED bargraph driver has internal voltage comparator references at VU meter intervals. R25 sets
the current for the external reference network and the LED drive current, which is about 10 times the current taken from pin 7. The
top of the internal comparator resistor ladder is connected to pin 6, the bottom to pin 4. The voltage across R23, R24, and P1 is the
reference against which the rectifier output applied to pin 5 is compared. The meter is calibrated by adjusting P1 (PPM) or P2 (VU).
ZD1 sets the voltage at the bottom of the resistor ladder and the bias for the rectifier circuit with C11 as a bypass. NOTE: The driver
PCB connects the LEDs in the bargraph in a SERIES string. The anode of the LED corresponding to the LOWEST input level (-20) is
connected to V+, with the other 9 LEDs following, and the outputs of the 3916 connected to the node between each LED. Only ONE
output of the 3916 is active (LOW) at any one time ("dot" mode), so if the LED string is "broken" (open) at any point, the bargraph will
go OFF whenever the input level is AT OR ABOVE the level corresponding to the break.
Bargraph Driver Circuit Description (919017)
Level Meter Specifications
Level Calibration:
Frequency Response:
Level Meter Type:
LED Colors:
Metering Range:
Display Mode (Ballistics):
VU Characteristics:
Rise Time =
Decay Time =
PPM Characteristics:
Attack Time =
Decay Time =
Bargraph Length:
LED Segment Size:
LED Segment Pitch:
Segment Brightness, (I f = 20 mA):
Segment Brightness, Uniformity:
Adjacent Segment "Off" Brightness:
Peak Emission Wavelength:
-6, 0, +4, +8 dBv, Selectable
20 Hz to 18 kHz (±0.5 dB)
10-segment LED Bargraph Display
Tricolor (red, amber, green)
23 dB
VU or PPM, Selectable
300 millisecond to 99 % of full indication
300 millisecond
10 milliseconds
2 seconds, 0 to -20 dB
2.00" (50.8 mm)
0.152" x 0.305" (3.56 x 7.75 mm)
0.20" (5.08 mm)
5.5 mcd
<8% difference between segments
<1% of brightness of active segment
green: 570 nm red: 630 nm

17
© 2006 Wohler Technologies Inc. ALL rights reserved
AMP1A-4S/-10S/-LP4S/-LP10S User Manual P/N 821527 Rev-BSection 3: Technical Information
Multi-Channel Analog Switching PCB Circuit Description (919013)
Input selection from multiple sources is accomplished via a ten channel analog switch circuit. Connection to each source is
facilitated by installing a three position plug-in "Phoenix" style connector on the end of the source cable. The Phoenix connector has
screw clamps for the ground and a balanced pair. The signal is coupled to the circuit through a capacitor and a 47.5K ohm resistor on
each line in.
Selection of an input is made by pulling the control pins high on a 4053 analog switch. Inputs to the 4053 are normally connected to
a neutral buss (circuit bias supply) until a switch pair is selected at which time the inputs are switched to the signal busses. The 4053
has three SPDT switches, so two ICs are required for every three input pairs. There are two signal summing busses for the balanced
line. The signals are summed into inverting amplifiers and then summed into a differential amplifier, which then drives the audio
monitor in which the board is installed. Balanced outputs are available from the inverting amps for audio routing purposes.
In monaural board versions, two balanced pairs of signal summing busses are joined into one balanced summing pair by solder
bridging pads, and two opamps with their associated components are left off the board. In stereo versions, all opamps are installed
along with enough 4053 switches to accommodate the desired number of inputs. The inputs can be independently selected in the case
of mono sources or simultaneous pairs for stereo sources can be selected by installing jumpers at H3 (channel select pins).
Selection from ten stereo sources is accomplished by stacking two ISS boards and jumpering their select lines together. One board
can select from up to ten mono or five stereo inputs. Channel selection is normally done with a rotary switch mounted on the from
panel of units with the ISS option installed. This switch can be remoted as an option.
Unusual input select configurations (L only, R only, phase invert, etc.), or simultaneous multiple input select, are available as
additional options.
Trouble-Shooting Tips
Since a single-sided 24V supply is used, all opamps are “biased” with a 1/2 supply reference. The CMOS devices are powered from
a separate zener-regulated 15V source on each analog switch board. The analog switch elements are in series with an opamp summing
junction, so they can handle very high input signal levels without any "breakthrough" effect. When not selected, each 4053 input is
shunted to AC ground for improved off isolation. The inverting input of any opamp is sensitive to any stray capacitance to circuit
common. Though the summing amp design includes stabilizing elements, care should taken to avoid capacitive loading of the
summing busses. They are jumpered between switchboards in some configurations. There is an "enable" bus connected to pin 6 of
each 4053. It is available on H3 and H4, pin 12 (for bank switching or other special functions).
If it becomes necessary to disassemble a stacked audio switchboard assembly, insure that the upper board is positioned directly over
the lower one when reassembling. Should it inadvertently be displaced toward either the front or rear, the power connections may
become shorted.
Input:
Impedance:
Maximum input level:
Crosstalk:
Distortion:
Response:
Output gain:
Maximum output:
Power:
Ten balanced
90K ohms, balanced
+ 16 dBv (maximum input level of +26 dB is available with -10 dB gain to balanced output)
-65 dB
<.O5 %
+/- .5 dB 20 Hz - 20 KHz
0 dB balanced, -10 dB unbalanced
+16 dBv
Less than 30 mA with a 24 volt supply
919013 Specifications:

18 © 2006 Wohler Technologies Inc. ALL rights reserved
AMP1A-4S/-10S/-LP4S/-LP10S User Manual P/N 821527 Rev-BSection 3: Technical Information
AMP1A-4S and AMP1A-LP4S Interconnect Block Diagram
AMP1A-4S and AMP1A-LP4S Block Diagram
CH. B (R)
Selected
Output
(XLRM)
CH. A (L)
3
Channel
A (Left)
4 2
1
Stereo Source Select Switch
(Front Panel)
3
4
1
2
4 3 2
1
Channel
B (Right)
3
4 2
1
Rear
Panel
Input Select Switch (ISS)
Analog Switch PCB
919013S
Left
Right
L
R
Balanced Inputs on
Phoenix Connectors
Note: These features on -LP model only.
2
Level
Meters
Phase
Indication
Right
Bargraph
Driver PCB
919017R
Left
Bargraph
Driver PCB
919017L
Phase
Indication
PCB
919084
Audio Amplifier PCB
919100 or 919164
Headphone
BalanceVolume
Left
Side Speaker
Left
Woofer
Speaker
Right
Side Speaker
Right
Woofer
Speaker
Rear
Panel
LR
L
R

19
© 2006 Wohler Technologies Inc. ALL rights reserved
AMP1A-4S/-10S/-LP4S/-LP10S User Manual P/N 821527 Rev-BSection 3: Technical Information
AMP1A-10S and AMP1A-LP10S Interconnect Block Diagram
1
Channel
A (Left)
Inputs
CH. A (L)
Selected
Output
(XLRM) CH. B (R)
Stereo Source Select Switch
Rear
Panel
1
2
3
4
5
6
7 8 9
10
2 3 4
5
6 7
8 9
10
10
9
3
Channel
B (Right)
Inputs 6
7
8 5
4 2 1
2
1
6
10
9 7 8
4
5 3
Input Select Switch
(ISS) Analog Switch
PCB
919013S
4
2
3
10
1
65
SOURCE
7
9
8
Left
Right
Balanced Inputs on
Phoenix Connectors
AMP1A-10S and AMP1A-LP10S Block Diagram
L
R
Note: These features on -LP model only.
Level
Meters
Phase
Indication
Right
Bargraph
Driver PCB
919017R
Left
Bargraph
Driver PCB
919017L
Phase
Indication
PCB
919084
Audio Amplifier PCB
919100 or 919164
Headphone
BalanceVolume
Left
Side Speaker
Left
Woofer
Speaker
Right
Side Speaker
Right
Woofer
Speaker
LR
L
R
2
Rear
Panel

20 © 2006 Wohler Technologies Inc. ALL rights reserved
AMP1A-4S/-10S/-LP4S/-LP10S User Manual P/N 821527 Rev-B
Wohler Technologies, Inc.
31055 Huntwood Avenue
Hayward, CA 94544
Phone: [phone]
Fax: [phone]
US Toll-Free: 1-888-596-4537
web: www.wohler.com
e-mail: [e-mail]
You can now 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]