Universal Audio LA 4, Operating Instructions Manual

Page 1: ...www SteamPoweredRadio Com model LA 4 COMPRESSOR LIMITER EFFECTIVE WITH SERIAL 3196 UNITED RECORDING ELECTRONICS INDUSTRIES 8460 SAN FERNANDO RD SUN VALLEY CALIFORNIA 91352 818 767 1000 J gcompeny ...

Page 2: ...NG AND SETUP CONSULT UNPACKING AND INSPECTION INSTRUCTIONS ON PAGE 8 model LA 4 COMPRESSOR LIMITER EFFECTIVE WITH SERIAL 3196 United Recording Electronics Industries 8460 SAN FERNANDO ROAD SUN VALLEY CALIFORNIA 91352 818 767 1000 Printed in U S A Copyright 1980 UREI ...

Page 3: ...TING A SINGLE UNIT 2 4 RACK MOUNTING TWO UNITS 2 5 LINE VOLTAGE SWITCH 2 6 POWERING 2 7 EXTERNAL CONNECTIONS 2 8 IMPEDANCE AND TERMINATION 2 9 INPUT AND OUTPUT LEVELS AND OVERLOAD SECTION III OPERATING INSTRUCTIONS 3 1 GENERAL 3 2 CONTROL SETTINGS 3 3 STEREO OPERATION 3 4 VU METER SECTION IV MAINTENANCE 4 1 GENERAL 4 2 GAIN REDUCTION METER ZERO ADJUSTMENT 4 3 G R METER CALIBRATION 4 4 STEREO TRACK...

Page 4: ...nnected by means of a simple rear panel connection switching both STEREO switches ON will strap the gain reduction circuitry in both units to maintain a stable stereo image c OFF POWER This switch turns the LA 4 s AC power ON and No signal flows when power is OFF D METER FUNCTION The outer knob switches the meter function In GR mode the meter rests at O VU until gain reduction occurs then it defle...

Page 5: ...POWER For safety the IEC style receptacle ties the mains ground third prong on the plug to the chassis ground In some instances it may be desirable to temporarily break the mains ground using a 3 prong to 2 prong AC adapter so that hum causing ground loops can be detected See Section 2 6 C MAINS VOLTAGE SELECTOR This recessed switch can be set with a screwdriver for nominal 115 V or 230 V operatio...

Page 6: ...S Connect the high side of a balanced or unbalanced line to the 11 11 terminal Connect the low side of a balanced line or the shield of an unbalanced line to the COM terminal If hum develops with an unbalanced line connect a jumper between the COM and CHASSIS terminals If a high impedance device is connected to the LA 4 output I connect a 620 ohm 1 2 watt load resistor across the and COM terminals...

Page 7: ... a transfonner isolated output assure trouble free patching by avoiding ground loop problems The input sensitivity is switchable to accommodate high level lines nominal O dBm sensitivity or lower level sources nominal 20 dBm sensitivity Input level is monitored by a bri9ht LED indicator that illuminates whenever the incoming signal level is high enough to cause distortion in the first amplifier st...

Page 8: ...hnical terms the input would have a sensitivity of 14 dBm which is the power dissipated by 1 23 volts across 40 kohms However a mixer of 4 dBm nominal output provides the correct voltage to drive the input so the input sensitivity is rated at 4 dBm In fact if a 604 ohm terminating resistor is used the input sensitivity becomes a true 4 dBm The same criteria apply to output level ratings 1 5 DEFINI...

Page 9: ...N RATIO Ref 0 dB 0 775 V rms Balanced bridging differential amplifier 40 kohms used as a balanced input 20 kohms used as an unbalanced single ended input Less than 90 dBm 15 7 kHz band width input and output terminated with 600 ohm load Determined by rear panel switch to allow for optimum operation in different level environments HIGH Range Maximum 20 dB LOW RANGE Maximum O dB Adjustable with fron...

Page 10: ...ge 20 C to 60 C CONNECTIONS Input and output through rear chassis barrier strip Stereo interconnect through phono jack Power through 3 wire IEC style connector V INDICATORS StandarJ VU meter switch selectable to read output level 0 VU reference 4 dBrn or 8 dBm or amount of gain reduction LED indicator for input overload LED power indicator DIMENSIONS 216 mm W x 89 mm H rack panel depth behind pane...

Page 11: ...RETURN PORTION MAILED IMMEDIATELY 2 2 ENVIRONMENTAL CONSIDERATIONS The LA 4 will operate satisfactorily over a wide range of ambient temperatures from 10 to 50 C 45 to 121 F If the unit is installed in an equiment rack that also contains heat producing equipment such as power amplifiers adequate ventilation should be provided This will prolong component life and maximize operational stability Also...

Page 12: ...1 s side by side in a standard 19 USASI rack The assembly occupies two standard spaces 3 1 2 high The DR 1 kit should contain the following items QUANTITY 2 2 2 4 4 DESCRIPTION Joining Plates Rack Mounting Angles Spacer Plates 8 32 Pan Head Screws 8 Lock Washers The DR 1 Installation Procedure is as follows Refer to Figure 3 1 Place the two LA 4 s side by side with front panels touching Remove fou...

Page 13: ... Adjust the relative positions of the angles and panels and then tighten all hardware 18 32 Pan Head Screw 18 Lock Washer 16 32 Nut 16 Lock Washer 16 32 Oval Head Screw cover screws Angle Rack Extension front panel mounting screws FIGURE 2 MOUNTING DETAILS FOR SR 1 RACK MOUNT KIT 6 911 0 6 cover screws 11 Joining Plate II II 11 0 18 32 Screw II 48 Lock Washer II 0 front panel mounting screws FIGUR...

Page 14: ...es In some installations this may create ground loop problems Ground loops can become very evident as hum and buzz if a significant potential difference exists between the AC conduit ground and the grounded metal enclosure in which the chassis is installed If hum is experienced check for the possibility of ground loops by using a 3 prong to 2 prong AC adapter ungrounding the AC plug temporarily Th...

Page 15: ... ear panel barrier s tr ip It mounts over the barrier strip on the rear panel using two screws The Model 301 i s available I through your UREI dealer OUTPUT GRD INPUT COM COM FIGURE 4 CONNECTING THE LA 4 WITH BALANCED INPUT AND BALANCED OUTPUT CIRCUITS OUTPUT GRD COM INPUT COM FIGURE 5 CONNECTING THE LA 4 WITH UNBALANCED INPUT AND UNBALANCED OUTPUT CIRCU ITS Wi th a bal a nced input and unbalanced...

Page 16: ...reater impedance high impedance sources In most cases it is not necessary to place a 600 ohm terminating resistor across the input of the LA 4 In fact most 600 ohm sources operate normally when bridged by a high impedance acting as though no load were connected to the source device A 604 ohm termination resistor is required at the LA 4 s output only if it is connected to a high impedance line The ...

Page 17: ...r flashes more than occasionally either lower the output level of the source feeding the LA 4 or use an external attenuation pad If the LED is illuminated virtually continuously check the input range switch if it is in LOW mode and the input source is 4 dBm nominal level move the switch to HIGH mode The output amplifier is capable of delivering 24 dBm into a 600 ohm load 12 3 volts or 20 dB into a...

Page 18: ...evel increases very gradually as the input level rises above the threshold point The 2 1 setting automatically lowers the threshold for a gentle overall dynamic range compression It can also be seen that at higher settings of the Ratio control 8 1 through 20 1 there is virtually no incr_ ease in output level as the input level rises above the threshold point 3 2 FIGURE 6 dB OUTPUT LEVEL LA 4 COMPR...

Page 19: ...nally deflect the pointer off scale 5 Set the Threshold control at 0 full counterclockwise so that the threshold is above any input signal Set the Meter switch to GR mode and observe the meter Gradually rotate the Threshold control in a clockwise direction lowering the threshold point until the meter displays 3 dB to 5 dB of gain reduction average with occasional peaks of 10 dB to 20 dB downward d...

Page 20: ...U or 100 corresponds to a voltage output of 4 dBm or 8 dBm depending on the switch setting The position marked GR permits the meter to indicate the amount of gain reduction or peak limiting directly in dB During periods of no gain reduction the pointer will return to O VU on the meter scale The pointer is initially set to this position by means of the screwdriver adjusted control accessible throug...

Page 21: ...nel just to the right of the meter engaging the trimmer located 1 1 4 behind the front panel Turn the screwdriver until the pointer indicates O VU This completes the adjustment 4 3 G R METER CALIBRATION Before proceeding with stereo tracking adjustment the G R meter accuracy should be checked by following this procedure 1 Apply a 1000 Hz signal to the Input at a level between 0 1 and 1 volts 2 Swi...

Page 22: ...initial purchase This limited warranty must be activated at the time of purchase by returning the registry portion of the Warranty Card to the factory Should a malfunction ever occur the dealer from whom the unit was purchased will be glad to handle return for factory repair Please call or write to the factory for a Return Authorization Number which must accompany all repairs For prompt service sh...

Page 23: ...www SteamPoweredRadio Com SECTION V LA 4 SCHEMATIC DIAGRAM ...

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