UREI LA user manual
Contents
1. 2 7 EXTERNAL CONNECTIONS Input and output signal wires should be shielded cable and connected in accordance with standard wiring practice as indicated on the rear panel barrier strip Section 1 2 contains wiring information which is augmented by the diagrams in Figures 4 and 5 When strapping two units together for stereo operation use low Capacitance shielded cable and restrict the length to under ten feet If the LA 4 is connected to a high impedance circuit we recommend shunting the and COM output terminals with a 620 ohm 1 2 watt resistor This assures proper loading for the LA 4 See section 2 8 regarding input termination In situations where Input and Output will be connected and disconnected frequently we suggest the use of the Model 301 XLR QG Adapter This is a small box containing one male and one female XLR connector for Input and Output It is completely wired and connects quickly to the rear panel barrier strip It mounts over the barrier strip on the rear panel using two screws The Model 301 is available through your UREI dealer OUTPUT GRD INPUT com SS NJ OPTIONAL S FIGURE 4 CONNECTING THE LA 4 WITH BALANCED INPUT AND BALANCED OUTPUT CIRCUITS OUTPUT OUTPUT GRD INPUT com OUTPUT FIGURE 5 CONNECTING THE LA 4 WITH UNBA2. 3 The LA 4 front panel is adjustable to allow optimum alignment of the front panel with the rack extensions For precise alignment loosen the front panel mounting screws as well as the top and bottom cover screws 1 2 turn is adequate Adjust the relative positions of the brackets and panels and then tighten all hardware RACK MOUNTING TWO UNITS DR 1 kit optional allows mounting of two LA 4 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 The QUANTITY DESCRIPTION Joining Plates Rack Mounting Angles Spacer Plates 8 32 Pan Head Screws 8 Lock Washers Aa ANNEN DR 1 Installation Procedure is as follows Refer to Figure 3 Ta Place the two LA 4 s side by side with front panels touching Remove four screws from the top of each unit as illustrated to permit positioning of the joining plate Replace the screws through the plate and covers but do not tighten completely at this time dis Turn the assembly upside down and install the bottom joining plate in the same fashion as the top joining plate step 1 Su Using the 8 32 screws and lock washers mount one angle and one spacer plate to each side of the LA 4 assembly The spacer plates should be located between the angles and the LA 4 chassis The mounting holes
3. Gz MAINS VOLTAGE SELECTOR This recessed switch can be set with a screwdriver for nominal 115 V or 230 V operation be sure it is in the correct mode before connecting the LA 4 to the mains If the unit is switched from one operating voltage to another be certain to exchange the fuse for another of the correct rating D INPUT TERMINALS For balanced or floating sources connect the high side of the line to the terminal the low side of the line to the CON terminal and the shield to the CHASSIS terminal For unbalanced sources connect the high side of line to the 4 terminal and the low side to the COM and CHASSIS terminals E STEREO TERMINAL For stereo operation of two LA 4 s connect a short cable with standard phono plugs between the two connectors on the rear chassis of the two units Older model LA 4 s Black front panel do not have this connector Instead they have two terminals on the barrier strip Connect the center conductor of the single conductor shielded cable to the terminal labeled STEREO and the shield to the terminal labeled CHASSIS On the front panel the switches labeled STEREO must be switched ON to link the gain reduction circuits together Switching either switch to the OFF position disconnects the link between the limiters for independent operation The stereo connecting cable may remain connected as
4. 2 9 INPUT AND OUTPUT LEVELS AND OVERLOAD The LA 4 s differential input amplifiers are capable of being driven by signals up to a level of 20 dBm input range switch in HIGH mode or 0 dBm input range switch in LOW mode above which clipping distortion and or slew rate limiting occurs The input overload LED turns on when peak signals exceed the clipping level and will remain on long enough to be seen even if the excess signal is only a brief transient To avoid distortion when the LED indicator 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 150 ohm load 7 75 volts which is actually 26 dBm referenced to 1 milliwatt Average output levels can be monitored with the LA 4 s VU meter but remember that transient peaks may exceed the meter indication by as much as 20 dB The actual output headroom depends on the program material the threshold and the compression ratio selected SECTION OPERATING INSTRUCTIONS 3 1 GENERAL Th
5. he power level For example if an input sensitivity is rated at 4 dBm and the input impedance is 40 kohms the true sensitivity is 1 23 volts 1 23 volts across 600 ohms is 4 dBm In strictly correct technical 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 s dBm In level ra o the input sensitivity is rated at 4 fact if a 600 ohm terminating resistor is used the input sensitivity becomes a true 4 dBm The same criteria apply to output tings FINITION OF COMPRESSOR AND LIMITER Compressor A variable gain amplifier whose gain decreases as its input level increases past the threshold point A compressor uses low compression ratios of approximately 2 1 or 4 1 imiter A compressor with a high compression ratio of Lim approximately 8 1 or greater constant output level despit threshold Compression Ratio The output level change above th compress ion ratio The high ratios maintain essentially increases in input level above the ratio in dB of input level change to reshold A compressor whose output level changes 1 dB for a 2 dB input level change above threshold has a 2 1 Compression Ratio dB for a 4 dB input level ch
6. 2 6 POWERING The LA 4 may be operated from either 110 125 VAC or 220 240 VAC mains 50 or 60 Hz single phase As indicated in section 2 5 the nominal line voltage may be selected with a rear panel switch BE SURE TO VERIFY BOTH THE ACTUAL LINE VOLTAGE AND THE SETTING OF THE VOLTAGE SELECTOR SWITCH BEFORE CONNECTING THE LA 4 TO THE MAINS AC mains power is supplied to the Model LA 4 through an IEC style 3 conductor receptacle mounted on the rear of the chassis and a matching 3 wire power cable The ground pin of the connector is tied to the chassis of the Model LA 4 in order to comply with electrical codes 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 un grounding the AC plug temporarily This un grounds the LA 4 and may cure the hum or buzz but is not a substitute for proper system grounding Be aware that unless the Model LA 4 Compressor Limiter is AC grounded a safety hazard can exist UREI accepts no responsibility for legal actions or for direct incidental or consequential damages that may result from violation of any electrical codes
7. the meter is driven by a completely isolated is minimized All connections are made to a so distortion standard barrier strip The and sound reinforcement However 4 is not transmitters limiter such as the UREI LA 4 is ideal for all phases of recording re recording It is also useful for broadcast production due to its RMS responding gain reduction circuitry the LA recommended for overmodulation protection of broadcast disc or optical recorders unless followed by a peak 1176 LN 1 4 DES GNATION OF INPUT AND OUTPUT LEVELS The term dBm has been commonly misapplied when describing levels in high impedance lines In fact dBm refers to a vel where 0 dBm is equal to 1 milliwatt or 0 775 V across a 600 ohm termination Howeve voltage power le dissipation is negligible interest equal to Unf equal to reason understa The term r in high impedance circuits power and only the voltage level is of ABV woul d be more useful here where 0 dBV is 1 volt across any impedance ortunately 2 2 dBm because 0 the term the term dBm is use aBV 1 volt across a 600 ohm line is dBV can be misleading For this d exclusively in this manual with the nding that in other than 600 ohm circuits the voltage level is the reference not t
8. the system is warmed Power Set the M switch should be in the initial Off position switch ter evel your audio input and does not il frequently signal leve system observe the luminate mo or continuo 1 with the or with an INPUT swit 4 Set tch on the compression and some experimentation atten the re Ratio corresponds uation pad con The optimum W Input re us y ill On T up and operating with complete switch to either to the nominal Feed typical program material to the LA 4 tor to ensure it 1 and setup is done wait a few seconds to 4 or operating 8 level Overload than occasionall indicat the indicator even of is uminated output ar panel Ratio after setting the signal present adjust the LA 4 s average meter deflections of 0 VU deflect the pointer off scale 5 clockwise Set the Threshol so that th Set the M Gradually rota direction ter switch te the lowering th displays 3 occasional the Ratio determining the optimu dB to 5 dB peaks of 10 ad control e threshol to GR n Threshold e threshol 1 of gain reduction dB to 20 dB downward def at node Ya LE lower the incoming trol to the desired amount of setting varies wit may be useful Thre
9. BEFORE PROCEEDING WITH COMPLETE UNPACKING AND SETUP CONSULT UNPACKING AND INSPECTION INSTRUCTIONS ON PAGE 8 Model LA 4 COMPRESSOR LIMITER EFFECTIVE WITH SERIAL 3196 Wei United Recording Electronics Industries 8460 SAN FERNANDO ROAD SUN VALLEY CALIFORNIA 91352 818 767 1000 Printed in U S A Copyright 1980 UREI TABLE OF CONTENTS SECTION INTRODUCTION PAGE gall FRONT PANEL 1 2 REAR PANEL 2 3 DESCRIPTION 4 4 DESIGNATION OF INPUT AND OUTPUT LEVELS 5 5 DEFINITION OF COMPRESSOR AND LIMITER 5 6 SPECIFICATIONS 6 SECTION y NSTALLATION 2 1 UNPACKING AND INSPECTION 8 2 2 ENVIRONMENTAL CONSIDERATIONS 8 PE RACK MOUNTING A SINGLE UNIT 8 2 4 RACK MOUNTING TWO UNITS 9 EAR LINE VOLTAGE SWITCH 11 2 6 POWERING Death EXTERNAL CONNECTIONS 2258 IMPEDANCE AND TERMINATION 13 2 9 INPUT AND OUTPUT LEVELS AND OVERLOAD 14 SECTION OPERATING INSTRUCTIONS Bel GENERAL 15 Bad CONTROL SETTINGS 15 3 3 STEREO OPERATION 16 3 4 VU METER 17 SECTION IV MAINTENANCE 4 1 GENERAL 18 4 2 GAIN REDUCTION METER ZERO ADJUSTMENT 18 43 G R METER CALIBRATI
10. LANCED INPUT AND UNBALANCED OUTPUT CIRCUITS With a balanced input and unbalanced output or vice versa just use the appropriate connections suggested by each of the above diagrams 2 8 IMPEDANCE AND TERMINATION This section has been matching and bridging inpu the relationship between a impedance Most electronic outputs work well when terminat load connected to an inpu impedance Outputs are usu impedance that is lower th impedance is nearly the sa provided to better explain ts the use of terminating resist the nature of tors and ctual input impedance and nominal source ted by a t having the same or a higher actual ally overloaded when terminai an the source impedance When th a matching input When an input is 10 times the source or more the input is cons The UREI LA 4 has act ohms when used in a balan in an unbalanced configura This makes the LA 4 s inpu nominal source impedance ted by an input me impedance as the source it is known as idered to be a bridging input ts suitable for use with virt ual input impedances of 40 kohms ced configuration and 20 kohms when used tion they are high impedance inputs y any tual impedance 40 000 low or high The LA 4 s inpu ts will bridge 150 ohm or 600 ohm low impedance sources
11. ON 18 4 4 STEREO TRACKING 18 4 5 REPAIRS AND WARRANTY 19 SECTION V LA 4 SCHEMATIC DIAGRAM SECTION INTRODUCTION 1 1 FRONT PANEL A METER The LA 4 s meter is factory set for OVA 4 dBm 1 23 volts or 8 dBm 1 96 volts output level In G R mode the meter should read 0 dB so long as no gain reduction occurs If the meter rests at some other value it may be calibrated by inserting a small slotted screwdriver through the hole just to the right of the meter B STEREO COUPLER This switch should normally be OFF When two LA 4 s are interconnected 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 Cs POWER This switch turns the LA 4 s AC power ON and OFF No signal flows when power is OFF A 5 second turn on time delay circuit prevents clicks pops or thuds at the LA 4 s output D METER FUNCTION The outer knob switches the meter function In GR mode the meter rests at 0 VU until gain reduction occurs then it deflects down scale corresponding to the number of dB of compression In 4 mode or 8 mode the meter indicate output level where 0 VU respectively equals 4 dbm or 8 dBm output level E OUTPUT LEVEL The inner control adjusts the gain of the LA 4 s output stage This control is independent
12. and will match 10 kohm or greater 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 impedanc to the source device A 604 ohm termination only if it is connected to where an input termination manufacturer of the source e acting as though no load were connected resistor is required at the LA 4 s output a high impedance line The only instance resistor may be required is when th terminating resistor is ne special type of output transformer in the source device source device is made of p device specifically states that a cessary In such cases there is usu recision passive components no or th transistors or tubes An example of a unit requiring a termin lizer The terminating resistor assu in that device If a 150 ohm or 600 the source device it should be installed arest the LA 4 in order to minimize resistor is a passive equa optimum frequency response resistor is specified for at the end of the cable ne possible hum noise or sig 600 ohms is not a standar nal losses in the cable e ally a e ating res ohm d resistor value A 604 ohm precision resistor may be used but 620 ohm or 680 ohm resistors are close enough in value to 600 ohms and are more widely available
13. ange above threshold has a 4 1 and so forth A compressor whose output level changes Threshold level is bel amplifier set threshol The level at which compression begins The UREI LA 4 compressor Limiter has an adjustable threshold When the input the set threshold the unit functions as a 1 1 a unity gain device When the input level is above the the unit functions as a compressor or as a limiter depending on the compression ratio selected 1 6 SPEC ELECTRICAL INPUT INPUT IMPE EQUIVALENT MAXIMUM NPUT LEVEL GAIN FREQUENCY RESPONSE ATTACK TI RELEASE T COMPRESSION RATI Ref 0 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 0 dB Adjustable with front panel gain control Maximum 20 dB with input level switch in LOW position or 40 dB with switch in HIGH position 0 5 dB 20 Hz 20 kHz to 10 milliseconds for 63 correction depending on signal waveform 100 milliseconds to 1 second for 63 return depending on duration o
14. completely filling the remaining space Particular attention should be paid to protecting the controls switches etc Tape a note to the top of the unit describing the malfunction and with instructions for return We will pay one way return shipping costs on any in warranty repair Because of specially selected components in this product field repairs are not authorized during the warranty period and attempts to perform repairs may invalidate the warranty vew SV MAT OAI OCA Of Aawi fre A Bo INTE WHE COCA O AL COMED Dome ERAS CLAES STATION AA POLI Cots Aae citada du PAI LISOS factam SALES PERT a F DCTS Cantey comeing DG MOEKE ANA orca Uo ESA AUR ABIL Ges SA EO O LAPA LLES AE A AACA NOTES umes vera srecen COMPRESSOR 7 UMN TER SCMEMATIC
15. e LA 4 Compressor Limiter is designed to prevent an increase in output level beyond a pre determined point the threshold and due to its unique design the unit functions as a compressor or a limiter The effect is illustrated in Figure 6 The point at which the compressed curves break away from the straight No Gain Reduction line is determined by the setting of the Threshold control Incidentally this point is sometimes known as the rotation point or threshold point It can be seen from the curves that at low or moderate settings of the Ratio control 2 or 4 1 the output level increases very gradually as the input level rises above the threshold point The 2 1 setting automatically lowers the threshold for 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 increase in output level as the input level rises above the threshold point FIGURE 6 TYPICAL INPUT VERSUS OUTPUT LEVEL CURVES FOR LA 4 AT VARIOUS COMPRESSION RATIOS 3 2 CONTROL SETTINGS The rear panel Input Range switch should be pre set at the appropriate position High for nominal 4 dBm sources or Low for nominal 20 dBm sources 2 The independent 3a assure stability whichever Turn Stereo if stereo operation is desired tly for each LA 4 the
16. eck the meter on the right hand unit If it is not at 5 adjust R 57 Internal threshold trim on right hand unit for 5 VU reading 4 Switch the Ratios on both units to 20 20 1 Reset the front panel threshold control on the left hand unit to read 5 VU Re trim R 57 on the right hand unit to read 5 VU NOTE In some cases particularly where two units have widely different serial numbers good tracking may be difficult to achieve on the 20 1 ratio If you are tracking a very early LA 4 with a black front panel check that resistor R 28 is 33 K ohm change it if it is not 4 5 REPAIRS AND WARRANTY This product is factory warranted to the original purchaser against defects in material and workmanship for one year after 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 ship the unit prepaid directly to the factor with the R A Number visible on the shipping label Be sure it is well packed ina sturdy carton with shock absorbing material such as foam rubber Styrofoam pellets or bubble pack
17. f limiting Zelda Atl 82 1 T2 t er 20 1 switch selectable from front panel 0 775 V rms THRESHOLD OF LIMITING OUTPUT OUTPUT LOAD POWER OUTP POWER REQU REMENTS W ENVIRONMEN PHYSICAL CONNECTION E 52 barrier strip NDICATORS DIMENS WEIGHT ONS SHIPPING W EIGHT ACCESSORIE Ss Adjustable with front panel threshold control and rear panel input level switch Minimum level 2 dB to achieve 1 dB limiting is RATIO LOW RANGE HIGH RANGE Piss 61 dB 41 dB 4 8 12 20 1 45 dB 2 9 0B Floating transformer isolated 150 ohms or greater 24 dBm into a 600 ohm 20 dB into a 150 ohm 100 to 125 VAC or 200 50 60 Hz switch selectable load 12 8 V load to 250 VAC less than 10 Operating O C to 50 C Storage 20 C to 60 C Input and output through rear chassis Stereo interconnect through phono jack Power through 3 wire IEC style connector Standard VU meter switch selectable to read output level 0 VU reference 4 dBm or 8 dBm or amount of gain reduction LED indicator for input overload LED power indicator 216 mm W x 89 mm H rack panel depth behind panel is 203 mm 8 1 2 W x 3 1 2 H x 8 D Panel is 3 18 mm 1 8 brushed clear anodised aluminum in two s
18. hades Chassis is cadmium plated steel 2 95 kg 6 5 pounds 3 63 kg 8 pounds Single Rack Mount Kit No SR 1 Double Rack Mount Kit No DR 1 Model 301 XLR QG Adapter kit for input and output 2A UNPACK NG AN NSPECT SECT ON NSTALLATION ON Careful Lly examine the contents of the shipping carton for any signs of physical damage which could have occurred in transit Though your LA 4 was carefully packed a container was designed to protect the unit accidents do happen IF DAMAGE S EV DENT DO NOT the factory and the from rough handling DESTROY ANY OF MATE RIAL OR THE CARTON POSS MA The shipment should include a two part BLE CLA M FOR DE BY YOU THE CONS DAMAGE GNEE THE PACKI NG MMED SH ATELY NOTIFY THE PPING DAMAGE CLA CARRIER MS MUST OF BE warranty card bearing LA 4 the same serial number as the LA 4 an instruction manual and the IN ORDER TO ACTIVATE THE ONE YEAR LIMITED WARRANTY THE CARD MUST BE COMPLETED AND THE RETURN PORTION MAILED MMEDIATELY RONMENTAL CONSIDERATIONS 2 2 ENV The LA 4 will operate sai from 10 to temperatures instal equipment
19. in the LA 4 are tapped so nuts are not required Do not tighten the screws at this time 4 The LA 4 front panels are adjustable to allow optimum alignment of the front panels with the rack mounting angles For precise alignment loosen the front panel mounting screws as well as the top and bottom cover screws 1 2 turn is adequate Adjust the relative positions of the angles and panels and then tighten all hardware 8 32 Pan Head Screw 8 Lock Washer EE Angle 6 32 Nut 6 Lock Washer Rack Extension 6 32 Oval Head Screw front panel mounting screws FIGURE 3 MOUNTING DETAILS FOR SR 1 RACK MOUNT KIT cover screws Joining Plate Spacer Plate 8 32 Screw 8 Lock Washer Angle front panel mounting screws FIGURE 3 MOUNTING DETAILS FOR DR 1 RACK MOUNT KIT 2 5 LINE VOLTAGE SWITCH Unless a tag on the line cord specifies otherwise the LA 4 was shipped ready for operation with nominal 115 VAC power mains In order to change this for nominal 230 V 50 or 60 Hz slide the VOLTAGE SELECTOR switch on the rear panel to the 230 position The voltage is visible in a window next to the switch slot Be sure to change the fuse to the correct value 1 8 amp slo blo when changing to 230 V operation or 1 4 amp slo blo for 115 V operation A small screwdriver should be used to move the recessed switch
20. intaining a stable the procedure in Section 3 4 VU METER The VU meter serves two functions it indicates output level as well as gain reduction directly in dB When the Meter switch is placed in the 4 or 8 position the meter indicates the output level 0 VU 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 through a hole in the LA 4 front panel 4 LA 4 input warm up 1 GENERAL SECT ON V MAINTENANCE The LA 4 is an all solid state unit only the highest quality components provide years of r ruggedly constructed with As such trouble free use with normal care used are conservatively rated for their application workmanship meets the rigid standards you have learned to expect in UREI products NO SPECIAL PREVENTIVE MAINTENANCE IS REQU GAIN REDUCTION METER ZERO ADJUSTMENT RED When switched to trimmer located 1 1 4 until the pointer indicates 0 VU 4 3 UU G R METER CAL the meter pointer sho rest
21. long as one or both of the STEREO switches is in the OFF position F OUTPUT TERMINALS Connect the high side of a balanced or unbalanced line to the 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 connect a 620 ohm 1 2 watt load resistor across the and COM terminals G INPUT RANGE SWITCH This switch sets the LA 4 s input sensitivity HIGH position corresponds to a nominal input sensitivity of O dBm for most professional lines LOW position corresponds to a nominal input sensitivity of 20 dBm for preamplified instruments very hot condenser microphones or semi professional or hi fi type equipment DESCR EI ON The although URE I s pat UREI LA 4 Compressor Limiter is a single channel unit two may be strapped for stereo operation Making use of nted Electro Optical Attenuator technology the LA 4 offers smooth predictable performance coupled with ease of operation which is and natural sounding The gain reduction is accomplished with an RMS detector the analog of human hearing so gain reduction is smooth The detector consists of a light dependent re
22. of the THRESHOLD and RATIO settings E s COMPRESSION RATIO The outer knob switches the amount of compression to 2 4 8 12 or 20 1 The LA 4 can be considered to be limiting at compression settings of 8 1 or greater G THRESHOLD The inner control adjusts the level above which compression or limiting occurs In conjunction with the rear panel Input Range switch threshold may be set for a wide range of input signal levels and or amounts of compression H INPUT OVERLOAD INDICATOR This LED Light Emitting Diode illuminates when the input level reaches 20 dBm 7 75 volts high enough to cause distortion in the input amplifier Avoid distortion by setting the output level of the source or by using an attenuation pad so the LED does not turn on If a nominal 4 dBm source causes the LED to be constantly ON be sure the rear panel INPUT RANGE switch is in the HIGH position REAR PANEL A FUSE For 110 125 V operation use MDL 1 4 amp slo blo fuse For 220 250 V operation use MDL 1 8 amp slo blo fuse By 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
23. provided This will stability Also led in an equipment 50 while circuitry suscep ld neverthel ro rack that also cont such as power amplifiers y adjacent If 45 to 121 F ss to large powe allows mounting of one LA 4 in a shielded installation shoul locating the LA 4 immediatel motors etc 2 3 RACK MOUNTING A SINGLE UNIT The SR 1 kit optional standard 19 USASI rack 1 2 high QUAN TI BHP BBN ND The SR 1 kit should contain TY DESCR Er ON Rack Adapter Angles Rack Extensions 6 32 Oval Head Screws black 6 Lock Washers 6 32 Nuts 8 32 Pan Head Screws 8 Lock Washers r The unit occupies two standard spaces the following items tisfactorily over a wide range of ambient the unit is tains heat producing adequate ventilation should be prolong component life and maximize operational tible to hum pickup is fully be planned to avoid transformers 3 The SR 1 Installation Procedure is as follows Refer to Figure 2 The ds Using the 96 32 screws lock washers and nuts mount the angles to the backside of the rack extensions Do not tighten the screws at this time Zi Using the 08 32 screws and lock washers mount the angle and rack extension assemblies to the tapped holes in the sides of the IA 4 Do not tighten the screws at this time
24. s at some other position Then insert a small slot LA 4 front panel just to the right behind the front panel This completes the adjustment GR mode uld rest allow about of BRAT ON and with ted screwdriver in no signal appl the LA 4 should All parts and ied to the at O VU Before proceeding with stereo tracking adjustment meter accuracy should be checked by following this procedure T If the pointer 1 2 hour for the LA 4 to the hole on the the meter engaging the Turn the screwdriver the G R Apply a 1000 Hz signal to the Input at a level between 0 1 and lvolts Switch the meter to 4 and adjust the output to read 0 Advance the threshold control to drop the output 5 dB meter reads 5 VU Switch the meter to G R it should read 4 5 to 5 5 VU If so proceed to the stereo tracking calibration Section 4 4 If not adjust R 49 tracking pot to read 5 VU Return to step 2 above and recheck STEREO TRACKI NG Calibrate the meters as described in Sections 4 2 and 4 3 Set the front panel controls as fol Llows Counter clockwise Thresholds Ratio 10 to 8 Meters G aR Stereo Switches ON Outputs Counter clockwise 18 Sa Apply a 1000 Hz signal to the input at a level between 0 1 and 1 volts Advance threshold on the left hand unit until the meter reads 5 VU Ch
25. shold Output Level Peaks may occasional setting STEREO OPERAT ON stereo programs regardless of which channel tha CO stereo image 3 2 separat switches independent th t requires th some experimentat Threshold m se is instigat sam W On W 8 position reduction degr For stereo operation of gain tely for each unit In tly display the o but will bot Meter switch in mode is due to the fact that Stereo units are strapped most gain reduction will drive reduction repeat t and then turn mode the meters utput level th Mei 16 woe ld is above any input signal and observ control in a cl ld point until the meter u may reset the th a typical input control for yo Wit LY full counter the meter lockwise average with lection tion may be useful in tting If two LA 4 Compressor Limiters are to be used in tandem for the gain reduction of each unit can be made equal ting the act tion The channel the other channel both the St in each unit ter switch in tereo t will W 4 or th display the same amount of gain GR position level detection circuits The tracking in GR in both attenuator of the source device and check the position of the th program material As with a A thereby ma
26. sistor semiconductor LDR and an electroluminescent light source which is a so it does not change or deteriorate with age Compression ratio is adjustable by an easily re settable multi position switch that allows effects from a smooth 2 1 compression through a super tight sounding 20 1 The limiting calibrated ratio switch assures consistent and repeatable results Threshold is adjustable over a wide range flexibility to limit only the highest amplitudes giving the or to compress virtually the entire program A balanced differential transformer isolated input stage and a output assure trouble free patching by avoiding ground loop problem The input sensitivity is switchable to accommodate high level nominal sensitivity that illuminates whenever th to cause Output level is continuously variable VU meter level front panel CILECUTE 4 dBm or 0 VU 8 dBm output level widely used recording In gain reduction mode lines O dBm sensitivity or lower level sources nominal 20 dBm Input level is monitored by a bright LED indicator incoming signal level is high enough distortion in the first amplifier stage The large illuminated can be switched to indicate dB of gain reduction or output switching sets the meter sensitivity for 0 VU in accordance with the most sound reinforcement and broadcast standards
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