Wohler AM-2B User manual

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: 650 589-1355

web: www.panoramadtv.com

e-mail: sales@panoramadtv.com

Wohler Technologies, Inc.

31055 Huntwood Avenue

Hayward, CA 94544

Phone: (510) 870-0810 Fax: (510) 870-0811

US Toll-Free: 1-888-596-4537

www.panoramadtv.com sales@panoramadtv.com

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.

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-

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.

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.

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.

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.

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

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.

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

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

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