OPERATION AND MAINTENANCE MANUAL AM-3B. STEREO AUDIO PHASE MONITOR Part No Rev B

Transcription

1 OPERATION AND MAINTENANCE MANUAL AM-3B STEREO AUDIO PHASE MONITOR Part No Rev B I. GENERAL DESCRIPTION II. III. IV. OPERATING INSTRUCTIONS MAINTENANCE/CALIBRATION SPECIFICATIONS V. PARTS LIST Wohler Technologies, Panorama DTV Inc. 711 Grandview Drive Huntwood Avenue South San Francisco, CA Hayward, CA Fax: Phone: (510) Fax: (510) web: US Toll-Free: sales@panoramadtv.com sales@panoramadtv.com 1

2 I. GENERAL DESCRIPTION The AM-3B is a CRT based display system used to verify proper audio phase, amplitude, separation and sound of stereo audio signals. The oscilloscope display shows the phase and separation relationship between the left and right inputs from the A or B input groups. The units are shipped so that the left input selected drives scope vertical axis, and the right input selected drives the horizontal axis, this assignment, may be reversed by changing two solder-in jumpers. 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 true VU ballistic analog meters fitted with "peak" LED indicators. The VU meters meet all electrical and ballistic specifications established by Bell Laboratories and ANSI as required by broadcast and sound engineers. The peak warning LED indicators are driven by circuitry that is full wave rectified, reading both positive and negative peaks. They can operate in two optional jumper selectable modes: PEAK FLASH Peak warning LED indicators are on during program peaks only. PEAK HOLD Peak warning LED indicators remain on for approximately 2 seconds after the detection of a program peak level. This mode can assist operators to visually notice short duration peaks that might go otherwise unnoticed. The calibration of the analog VU meters and the peak warning LED indicators are separately adjustable. Because so much stereo audio program material is destined for television or radio broadcasting, operators and engineers must be constantly aware of left to right phase errors which would be received poorly by the vast number of monophonic television and radio receivers. The L + R metering provided on the AM-3B center meter assures additional confidence of mono compatibility. A consistent, mid-scale reading on this meter when switched to the L + R position gives reasonable assurance of meaningful reception by monophonic listeners. This concern about mono compatibility can also be verified by audible monitoring, on speakers or headphones, through the AM-3B monitor amplifier. Front panel controls allow 2

3 listening in Stereo, L + R (for mono compatibility) or to the AUX input. I. GENERAL DESCRIPTION (continued) The AM-3B has two full sets of 3 inputs, A and B, for LEFT, RIGHT, and AUX. An A/B switch located on the front panel of the AM-3B can select these. A studio application might be bridging the channel 1, 2 and 3 audio inputs of a videotape recorder on the A inputs, and bridging the channel 1, 2 and 3 playback outputs on the B inputs. In this manner, an operator could accurately monitor audio signals in record or playback. Transmission engineers might want to connect the A inputs to studio sources, and B inputs to demodulated off-air signals. For more exacting audio monitoring applications requiring large power amplifiers and monitor speakers, the AM-3B provides balanced line level outputs that follow the front panel volume controls. The AM-3B has circuitry that detects the presence of audio on its channels 1 or 2. An internal jumper plug selects whether the CRT display operates full-time, or whether the CRT display extinguishes in the absence of audio signals. See the maintenance section for more information. 3

4 II. OPERATING INSTRUCTIONS Connect the AM-3B power cord into any convenient, grounded AC socket. Units are normally shipped to operate on VAC mains. With proper power transformer strapping, the units can accept mains voltages in the range of VAC. If in doubt as to how any particular unit was shipped from the factory, or in the event of a required change, please examine the power transformer connections table of the chassis-wiring diagram, and compare the transformer connections to the table. Please note that units set for VAC use a 2-amp fuse, while units set for VAC use a 1-amp fuse. Connect input cables required for user s application. Proper connection can be verified by supplying a continuous tone of known correct left/right phase and amplitude to the AM-3B. This will produce a stationary line on the scope along the "IN PHASE" display 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-3B input channels with the same signal source momentarily to verify proper AM-3B phase display. The AM-3B is useful to inspect the phase integrity of all studio equipment. Sometimes surprising phase errors are introduced by not only tape machines, but by other devices such as audio mixing boards. The test signal of known amplitude can also be used to verify that the AM-3B is still calibrated to studio standards on the VU and LED peak indicators. Attach left and right speaker cables, if any. This cable should have 16 gauge conductors or larger. These cables should be as short as practical. The speaker/headphone monitor amplifier is of the integrated circuit type and provides sufficient output power for typical rack mounted monitor speakers. The monitor amplifier is short circuit protected and is thermally protected. If the monitor amplifier is operated for more than a short time at power levels above specification, the amplifiers thermal protect circuits will begin shutting down the amplifier. Operation may be resumed after a short cooloff period. Use of the balanced line out connectors is encouraged if large monitor speakers and amplifiers are required. 4

5 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. 5

6 III. MAINTENANCE/CALIBRATION AM-3B 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 of unit. CHANGING TO A NEW LINE LEVEL STANDARD The AM-3B uses precision resistors to correctly scale input buffer amplifiers to various line level ranges. These resistors, which are incorporated in the AM-3B 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. These jumpers can be changed by removing the bottom cover and changing the position of all range setting jumpers to the desired line level (0 dbm, +4 dbm or +8 dbm). A total of 12 jumpers must be changed. Do not confuse the range jumpers with the termination jumpers. 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. LINE TERMINATION The AM-3B inputs may be set for resistive termination of 600 ohms, 150 ohms or HI Z. If necessary, change the jumpers by removing the bottom cover and changing the position of all termination jumpers to the desired value. A total of 6 jumpers must be changed. Do not confuse the termination jumpers with the range jumpers. If calibration of the AM-3B inputs is going to be done in parallel fed from one test oscillator, termination jumpers may have to be placed in the HI Z position during calibration if the test oscillator is incapable of developing enough test signal voltage across the termination resistors. CALIBRATION An audio test set or a test oscillator and an AC voltmeter (preferably calibrated in dbm) are required to calibrate the AM-3B. 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-3B with a "Y" cable as discussed in the section on operation. All further adjustments are made with the potentiometers listed on the potentiometer summary page and the range selection jumpers. 6

7 III. MAINTENANCE/CALIBRATION (continued) CAUTION USE AN INSULATED ADJUSTMENT TOOL FOR THIS ADJUSTMENT, AS CIRCUIT POINTS OF HIGH VOLTAGE ARE NEAR. 1. Connect the test oscillator output to the left input. 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. Adjust R1, 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 V calibration potentiometer R1 until the vertical line trace extends from the bottom of the CRT to the diagonal "IN PHASE" graticule line. 3. Connect the test oscillator output to the left and right input. Simultaneously adjust the front panel V position control and the scope H calibration potentiometer R27 until the line trace is perfectly parallel with the "IN PHASE" graticule line. 4. Adjust R59 and R63 to set the left and right VU meters to 0 VU. Connect the test oscillator to the AUX input. Select AUX on the front panel. Adjust R73 to set the center meter and AUX level to 0 VU. Reconnect the test oscillator to the left and right inputs. Select L + R on the front panel. Adjust R70 to set the center meter L + R level to 0 VU. 5. Change the level of the test oscillator to that level which is to be considered a "peak warning" level (+14 dbm, +18 dbm, etc.). Connect the test oscillator to the AM-3B inputs. Measure the voltage on test point 1 on board 1. Adjust R75 for a voltage of 3 VDC at test point 1. Similarly, adjust R96 and R117 for 3 VDC at test points 2 and Place the 3 HOLD/FLASH jumpers in the "FLASH" position. These are on Board 1. Verify the peak warning LED indicators are off. If not, adjust R91, R112 and R133 clockwise until they go off. Rotate R91, R112 and R133 slowly counterclockwise until the peak warning LED indicators are just lighted (on). Place the 3 HOLD/FLASH jumpers in the mode desired. Note that the peak warning LED indicators may be set 0 to +20 db above the analog VU meter 0 VU reference level. 7. Change the level of the test oscillator to -15 db below the reference tone level. The reference tone level is that level which is equal to zero VU on the meters (example: if reference tone level is +4 dbm, set the test oscillator to -11 dbm). 7

8 III. MAINTENANCE/CALIBRATON (continued) 8. Using an oscilloscope, connect a probe to U10, pin 1. Preset R94 and R115 to mid range. 9. Remove the test oscillator signal from the CH-2 input so that only CH-1 is connected. 10. Turn R94 counterclockwise until a square waveform is obtained and adjust for a 50% duty cycle. 11. Now connect the test oscillator to CH-2 only. Turn R115 counterclockwise until a square waveform is obtained. Adjust for 50% duty cycle. 12. On Board 1, a jumper plug is selectable between "BEAM AUTO" or "BEAM ON". When set to "BEAM ON", the CRT display will remain on after audio signals are no longer present at the AM-3B's channel 1 or 2 inputs. This mode is useful for examining phase of extremely low-level signals. If the jumper plug is set to "BEAM AUTO", the CRT display will extinguish after an adjustable hold time. AM-3B units are shipped so that the adjustable CRT beam "BEAM AUTO" hold time is set to maximum, adjusting R137 sets a shorter hold time. 8

9 AM-3B POTENTIOMETER SUMMARY BOARD 1 R1 R6 R27 R32 R54 R59 R63 R67 R70 R73 R75 R91 R94 R96 R112 R115 R117 R133 R137 Scope V gain Scope V coarse position Scope H gain Scope H coarse position Scope astigmatism adjust Left VU meter cal. Right VU meter cal. L + R monitor level L + R VU meter cal. AUX VU meter cal. TP1 adjust Left LED indicator adjust Left audio detect level TP2 adjust Right LED indicator adjust Right audio detect level TP3 adjust L + R/AUX LED indicator adjust Beam "ON" hold time BOARD 2 CHASSIS NO ADJUSTMENTS R1 Trace rotation 9

10 IV. SPECIFICATIONS PHYSICAL: Height Width Depth Weight 3-1/2 inches 19 inches 14-1/2 inches 17 lbs. The AM-3B is to be installed in an EIA standard 19" rack space and occupies 2 standard rack units. TECHNICAL: Left/Right/Aux: 3 pin XLR female inputs: Pin 1, chassis ground. Pin 2, audio high. Pin 3, audio low. 50K input impedance. NOTE: Inputs can be set for resistive terminations of 600 ohms, 150 ohms or Hi Z with jumper selection. Input Line Levels: Output Line Levels: Out Speaker Levels: Power: Jumper selectable range settings for 0, +4 and +8 dbm line levels. Left and right balanced, 600 ohm outputs. 3-pin XLR male; Pin 1, chassis ground. Pin 2, audio high. Pin 3, audio low. Output level follows front panel controls. 4 watts, peak program per channel into 8 or 16 ohms VAC, fused at 2 amps 230, 240, 250, 260 VAC fused at 1 amp 10

11 VI. PARTS LIST BOARD #1 AM-3B B & B SYMBOL NO. DESCRIPTION PART NO. R1,R27,R59,R63,R70, 10K POT R73,R75,R91,R94,R96, R112,R115,R117,R133 R2-R4,R28-R30 47K, 1/4W R5,R7,R31,R33 43K, 1/4W R6,R32 5K POT R8,R15,R16,R22,R34, 100 OHM, 1/4W R41,R42,R48 R9,R17,R18,R35,R43,R44, 10K, 1/4W R93,R114,R135,R138,R147 R10,R13 1.8K, 1/4W R11,R14,R37,R40,R58, 6.8K, 1/4W R62,R69,R72 R12,R38,R90,R92,R111, 1K, 1/4W R113,R132,R134,R136, R140,R142,R144 R19,R20,R45,R46 12K, 5W R21,R24 3K, 1/4W R23,R OHM, 1/4W R25,R26,R51,R52 150K, 1/4W R36,R39 1.5K, 1/4W R47,R50 2.7K, 1/4W R53 A.O.T. 11

12 BOARD #1 AM-3B (continued) B & B SYMBOL NO. DESCRIPTION PART NO. R54,R K POT R55,R56,R76,R79,R84, 10K, 1/4W R97,R100,R105,R118, R121,R126 R57,R61,R68,R71 2.2K, 1/4W R60,R64,R74 3.6K, 1/4W R65-R67,R88,R109, R130,R145,R146 NOT USED R77,R82,R83,R98,R103, 4.75K, 1/4W R104,R119,R124,R125, R148-R153 R78,R99,R K, 1/4W R80,R86,R101,R107,R122, 100K, 1/4W R128 R81,R85,R102,R106,R123, 22.1K, 1/4W R127 R87,R95,R108,R116,R129 0 OHM R89,R110,R K, 1/4W R139,R141,R K, 1/4W V C19,C20,C22,C26,C28, C32,C36 C2,C4 A.O.T. 12

13 BOARD #1 AM-3B (continued) B & B SYMBOL NO. DESCRIPTION PART NO. 600V C13,C15,C18,C21,C23,. 50V C25,C27,C29,C31 C16,C24,C30 NOT USED C33 16V C34,C35,C37 16V Q1-Q4,Q7-Q10,Q13-Q16 2N Q5,Q6,Q11,Q12 2N U1-U4,U7,U11 MC1458CP U5,U8,U13 MC U6 LM324N U9 LM339N U10,U12 74LS123N D1-D23 1N K1-K

14 BOARD #2 AM-3B B & B SYMBOL NO. DESCRIPTION PART NO. R1,R11,R21,R31,R41,R OHM, 1/4w R2,R12,R22,R32,R42,R OHM, 1/4W R3,R4,R13,R14,R23,R24, 100K, 1/4W R33,R34,R43,R44,R53,R54, R78,R79 R5,R8,R15,R18,R25,R28, 46.4K, 1/4W R35,R38,R45,R48,R55,R58 R6,R9,R16,R19,R26,R29, 30.1K, 1/4W R36,R39,R46,R49,R56,R59 R7,R10,R17,R20,R27,R30, 19.1K, 1/4W R37,R40, R47,R50,R57,R60 R61-R66, R69-R74 10K, 1/4W R67, R68, R75, R OHM, 1/4W R77, R K, 1/4W R81,R K, 1/4W R83 2.2K, 5W R84,R OHM, 1/4W C1-C11, C14, C16, C22, 63V C26, C27 C12, C15 25V C13, C17, C18 16V C19, C20 350V

15 BOARD #2 AM-3B (continued) B & B SYMBOL NO. DESCRIPTION PART NO. C21, C23, C25 25V C28-C39 35V U1-U5 MC1458CP U6 LM378N U7 MC7805CT U8 MC7812CK U9 MC7912CK D1-D4 1N D5-D8 MR D9-D12 MR501/1N D13-D14 1N K1,K

16 HIGH VOLTAGE POWER SUPPLY AM-3B B & B SYMBOL NO. DESCRIPTION PART NO. R1 3.6K, 1/4W R2 3.3M, 1W R3,R4,R5 470K, 1/2W R5 68K, 1/2W V V Q1 TIP PS1 H.V. POWER MODULE 16

17 CHASSIS AM-3B B & B SYMBOL NO. DESCRIPTION PART NO. R1 500 OHM POT R2 500 OHM POT R3 1K POT R4,R5 1M POT R6 VOLUME POT R7,R8 91 OHM, 1W R9 BALANCE POT C1,C2 NOT USED 1000V D1-D3 T1, RED LED D4 T1-3/4, GREEN LED D5 T1-3/4, YELLOW LED T1 TRANSFORMER J1,J2 50/100 CARD EDGE J3 8 PIN MOLEX, KK TYPE J4 NOT USED 17

18 CHASSIS AM-3B (continued) B & B SYMBOL NO. DESCRIPTION PART NO. J5-J10 3 PIN XLR, FEMALE J11,J12 3 PIN XLR, MALE J15-J17 3 PIN MOLEX P15-P17 3 PIN MOLEX P18 CRT SOCKET J19 HEADPHONE JACK S1,S2,S4 TOGGLE SWITCH, POS S3 TOGGLE SWITCH, POS L1 ROTATION COIL N/A F.B. FERRITE BEAD

19 MISCELLANEOUS PARTS AM-3B B & B SYMBOL NO. DESCRIPTION PART NO. DS1-DS3 VU METER LAMPS M1-M3 VU METERS CRT FILTER/GRATICULE FS1 FUSE,.5 AMP ( VAC OPERATION) FUSE,.25 AMP ( VAC OPERATION) V-POS, H-POS, 10mm KNOBS INT, FOCUS VOLUME/BALANCE KNOB VOLUME/BALANCE CAP, KNOB

20 WARRANTY THE COMPANY GUARANTEES THIS EQUIPMENT AGAINST ELECTRICAL AND MECHANICAL DEFECTS FOR A PERIOD OF ONE YEAR FROM DATE OF PURCHASE. THIS WARRANTY APPLIES ONLY TO UNITS, WHICH HAVE NOT BEEN MODIFIED, ALTERED OR CHANGED IN ANY MANNER. THE COMPANY'S LIABILITY IS EXPRESSLY LIMITED TO THE REPAIR OR REPLACEMENT OF DEFECTIVE PARTS AT ITS FACTORY. ANY COMPANY REPRESENTATIVE MAY GIVE NO FURTHER WARRANTY, ORAL OR WRITTEN, EXPRESSED OR IMPLIED, TO THE BUYER. IN THE EVENT INFORMATION CONCERNING SERVICE IS NEEDED, CONTACT: Wohler Wohler Technologies, Panorama DTVInc. Inc Grandview Drive Huntwood Avenue South San Francisco, CA Hayward, CA FAX: Fax: Phone: (510) Fax: (510) web: US Toll-Free: sales@panoramadtv.com sales@panoramadtv.com 20