Wohler AM-2B User manual

2001 Wohler Technologies, Inc. ALL rights reserved
OPERATION AND MAINTENANCE MANUAL
AM-2B
STEREO PHASE DISPLAY SCOPE
Part Number 821602 Rev B
I. GENERAL DESCRIPTION
II. OPERATING INSTRUCTIONS
III. MAINTENANCE/CALIBRATION
IV. SPECIFICATIONS
V. PARTS LIST
Panorama DTV
711 Grandview Drive
South San Francisco, CA 94080
650 589-5676 Fax: [phone]
web: www.panoramadtv.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.panoramadtv.com [e-mail]

2001 Wohler Technologies, Inc. ALL rights reserved
1
I. GENERAL DESCRIPTION
The AM-2B is a CRT based display system used to verify proper stereo audio phase,
amplitude and separation.
The oscilloscope display shows the phase relationship between the left and right channels.
Channel 1, or left, drives the scope Y-axis and channel 2, or right, drives the X-axis. The
correct phase vector is marked on the graticule with a line and the words "IN PHASE" for
operator convenience.
Measurement of amplitude is done with average reading true VU meters and peak reading
LED meters. The VU meters, one each for left and right audio, meet all electrical and
ballistic specifications established by Bell Laboratories and ANSI as required by broadcast
and sound engineers. The LED peak reading meters, one each for left and right audio, are
full wave rectified, reading both positive and negative peaks. They have a rise time response
of approximately 250 microseconds and a fall time of 300 milliseconds.
Audio inputs are through 3-pin XLR connectors and are balanced and buffered with greater
than 50K ohm input impedance. Inputs can be resistively terminated according to studio
standards.

2001 Wohler Technologies, Inc. ALL rights reserved
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II. OPERATING INSTRUCTIONS
Connect the AM-2B power cord into a grounded 3-pin AC mains power source. If there is
any doubt as to which mains voltage the AM-2B is wired to accept, please refer to the power
transformer wiring details on the AM-2B "Chassis Wiring" schematic and verify that the
power transformer is wired correctly for the local mains voltage standard.
Audio left should be cabled to the rear panel connector labeled CH-1 and audio right to CH-
2.
Proper connection can be verified by supplying a continuous tone of known correct left/right
phase and amplitude to the AM-2B. This will produce a stationary line on the scope along
the "IN PHASE" vector. The phase vector angle displayed is a result of phase and
amplitude. So only a test tone, which has correct phase and equal amplitude left to right will
produce an "IN PHASE" display vector. If in doubt about the phase accuracy of the test
signal, it is best to fabricate a "Y" cable and drive both AM-2B input channels with the same
test tone signal source momentarily to verify proper AM-2B phase display.
The test signal of known amplitude can also be used to verify that the AM-2B is still
calibrated to studio standards on the VU and LED meters.
The AM-2B is useful to inspect the phase integrity of all studio equipment. Not only tape
machines, but also other devices such as audio mixing boards introduce sometimes-
surprising phase errors, for example.

2001 Wohler Technologies, Inc. ALL rights reserved
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WARNING
Hazardous voltages are present at certain points within this product.
SERVICE/MAINTENANCE TO BE PERFORMED BY QUALIFIED SERVICE
PERSONNEL ONLY.
Do not make adjustments or perform any internal service with power on unless
another person capable of offering first aid or resuscitation is present.

2001 Wohler Technologies, Inc. ALL rights reserved
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III. MAINTENANCE AND CALIBRATION
AM-2B units are aligned at the factory to operate at normal studio line levels. However,
occasional transfer of units to another installation in which line level standards are different,
or a "touch up" alignment to compensate for long time aging may require re-calibration
procedures.
CHANGING TO A NEW LINE LEVEL STANDARD
The AM-2B uses precision resistors to correctly scale input buffer amplifiers to various line
level ranges. These resistors, which are incorporated in the AM-2B signal printed circuit
board, are selected by movable jumper plugs to preset the input amplifiers to the range of 0
dBm, +4 dBm and +8 dBm. Final, precise alignment is then set with 20 turn potentiometers
listed on the potentiometer summary. The jumpers only preset to a range, so any jumper
changes require final adjustment with the potentiometers.
CALIBRATION
An audio test set or a test oscillator and an AC voltmeter (preferable calibrated in dBm) are
required to calibrate the AM-2B.
Set the test oscillator to output amplitude equal to the studio reference tone level (+4 dBm,
+8 dBm, etc.). This should be cabled from the test oscillator to the AM-2B with a "Y" cable,
as discussed in the section on operation.
All further adjustments are made with the potentiometer listed on the potentiometer
summary page and the range selection jumpers.
1. Connect the test oscillator input to channel 1, left input, only. Adjust the front panel H
and V position, intensity and focus controls so that a stationary, vertical line trace is
obtained. Using the H position control, move the vertical line trace to the right or left-
hand edge of the CRT.
CAUTION
USE AN INSULATED ADJUSTMENT TOOL FOR THIS ADJUSTMENT
AS CIRCUIT POINTS OF HIGH VOLTAGE ARE NEAR.
1. Adjust R2, which is positioned facing up, mounted on a bracket directly behind the CRT
socket, until the vertical line trace is vertical. This sets trace rotation.

2001 Wohler Technologies, Inc. ALL rights reserved
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2. Adjust the front panel H position control so that the vertical line trace is in the center of
the CRT. Simultaneously adjust the front panel V position control and the scope Y
calibration pot, R66, until the vertical line trace extends from the bottom of the CRT to
the diagonal "IN PHASE" graticule line.
3. Reconnect the test oscillator input to channel 2, right input. Simultaneously adjust the
front panel V position control and the scope X calibration potentiometer, R90, until the
line trace is perfectly parallel with the "IN PHASE" graticule line.
4. Adjust R62 and R86 to set the left and right VU meters to 0 VU.
5. Set the test oscillator output amplitude equal to the line level, which is considered to be
the studio "clip" or distortion level (+18 dBm, +24 dBm, etc.). Adjust R65 and R89 so
that the top red LED’s on the left and right columns are just lighted.
NOTE: Steps 6 and 7 are to adjust LED column linearity and are not required for "touch up"
or when changing to a new line level standard.
6. Reduce the test oscillator output amplitude by 24 dB. Adjust R114 and R142 so that the
24 dB LED on the left and right LED columns is just lighted.
7. Increase the test oscillator output level by 3 dB. Adjust R113 and R141 so that the 21 dB
LED on the left and right LED columns is just lighted. Repeat steps 5, 6 and 7 until no
further improvement in calibration accuracy can be obtained.

2001 Wohler Technologies, Inc. ALL rights reserved
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MODEL AM-2B POTENTIOMETER SUMMARY
SIGNAL P.C. BOARD
R56 Scope astigmatism adjust
R62 Left VU meter cal.
R65 Left LED column cal.
R66 Scope "Y" cal.
R86 Right VU meter cal.
R89 Right LED column cal.
R90 Scope "X" cal.
R113 21 dB LED adjust, left
R114 24 dB LED adjust, left
R141 21 dB LED adjust, right
R142 24 dB LED adjust, right
CHASSIS
R2 Scope trace rotation

2001 Wohler Technologies, Inc. ALL rights reserved
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IV. SPECIFICATIONS
PHYSICAL:
Height 3-1/2 inches
Width 19 inches
Depth 15 inches
Weight 15lbs.
The AM-2B is intended to be installed in an EIA standard 19" rack space and occupies 2
standard rack units.
TECHNICAL:
CH-1/CH-2: 3-pin XLR, female, 50K ohm, balanced: Pin 1, chassis
ground. Pin 2, audio high. Pin 3, audio low.
NOTE: Inputs can be resistively terminated to studio
standards.
Power: 115, 230, 240, 250 or 260 VAC, 50 watts
In the interest of product improvement, Wohler Technologies, Inc. reserves the right to
change specifications at any time.

2001 Wohler Technologies, Inc. ALL rights reserved
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VI. PARTS LIST
SIGNAL BOARD AM-2B
B&B
SYMBOL NO. DESCRIPTION PART NO.
R1,R28,R61,R85 1K, 1/4W 6-0010
R3-R5,R30-R32 47K, 1/4W 6-0011
R9,R12,R17,R36,R39,R44 100 OHM, 1/4W 6-0012
R10,R18,R19,R37,R45,R46, 10K, 1/4W 6-0013
R67,R70,R75,R91,R94,R99
R11,R16,R107,R135 1.82K, 1/4W 6-0131
R13,R40 200 OHM, 1/4W 6-0007
R14,R15,R41,R42 6.8K, 1/4W 6-0015
R20,R21,R47,R48 12K, 5W 6-0017
R22,R49,R55 A.O.T.
R23,R50 270 OHM, 1/4W 6-0016
R24,R25,R51,R52 3K, 1/4W 6-0021
R26,R27,R53,R54 150K, 1/4W 6-0033
R38,R43,R109,R137 909 Ohm, 1/4W 6-0095
R56 200K POT 6-0181
R57,R58,R81,R82 100K, 1/4W 6-0005
R62,R86,R114,R142 5K POT 6-0046
R63,R69,R73,R74,R87, 4.75K, 1/4W 6-0105
R93,R97,R98
R64,R88 3.6K, 1/4W 6-0062

2001 Wohler Technologies, Inc. ALL rights reserved
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SIGNAL BOARD AM-2B (continued)
B&B
SYMBOL NO. DESCRIPTION PART NO.
R65,R66,R89,R90 10K POT 6-0125
R68,R79,R92,R103,144, 46.4K, 1/4W 6-0106
147,150,153
R71,R76,R95,R100 267K, 1/4W 6-0103
R72,R77,R78,R96,R101, 22.1K, 1/4W 6-0104
R102,R143,R146,R149,R152
R80,R104 180K, 1/4W 6-0100
R105,R133 4.22K, 1/4W 6-0090
R106,R134 2.21K, 1/4W 6-0091
R108,R136 806 OHM, 1/4W 6-0132
R110,R138 549 OHM, 1/4W 6-0133
R111,R139 348 OHM, 1/4W 6-0134
R112,R140 301 OHM, 1/4W 6-0097
R113,R141 500 OHM POT 6-0112
R115,R116 2.7K, 1/4W 6-0025
R117-R132 560 OHM, 1/4W 6-0030
R145,R148,R151,R154 60.4K, 1/4W 6-0128
R2,R6-R8,R29,R33-R35, NOT USED
R59,R60,R83,R84
C1,C2,C5,C6 NOT USED