urei_la-4_man 电路图.pdf

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1、 BEFORE PROCEEDING WITH COMPLETE UNPACKING 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. Copyrig

2、ht 1980, UREI RadioFans.CN 收音机爱 好者资料库 TABLE OF CONTENTS SECTION I. INTRODUCTION PAGE 1.1 FRONT PANEL 1 1.2 REAR PANEL 2 1.3 DESCRIPTION 4 1.4 DESIGNATION OF INPUT AND OUTPUT LEVELS 5 1.5 DEFINITION OF COMPRESSOR AND LIMITER 5 1.6 SPECIFICATIONS 6 SECTION II. INSTALLATION 2.1 UNPACKING AND INSPECTION

3、 8 2.2 ENVIRONMENTAL CONSIDERATIONS 8 2.3 RACK MOUNTING A SINGLE UNIT 8 2.4 RACK MOUNTING TWO UNITS 9 2.5 LINE VOLTAGE SWITCH 11 2.6 POWERING 11 2.7 EXTERNAL CONNECTIONS 11 2.8 IMPEDANCE AND TERMINATION 13 2.9 INPUT AND OUTPUT LEVELS AND OVERLOAD 14 SECTION III. OPERATING INSTRUCTIONS 3.1 GENERAL 15

4、 3.2 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 4.3 G.R. METER CALIBRATION 18 4.4 STEREO TRACKING 18 4.5 REPAIRS AND WARRANTY 19 SECTION V. LA-4 SCHEMATIC DIAGRAM RadioFans.CN 收音机爱 好者资料库 SECTION I INT

5、RODUCTION 1.1 FRONT PANEL A. METER. The LA-4s meter is factory set for 0VA = +4 dBm (1. 23 volts), or +8 dBm (l. 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, sl

6、otted screwdriver through the hole just to the right of the meter. B. STEREO COUPLER. This switch should normally be OFF. When two LA-4s 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 mainta

7、in a stable stereo image. C. POWER. This switch turns the LA-4s 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-4s output. D. METER FUNCTION. The outer knob switches the meter function. In GR mode, the meter rests

8、 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-4s o

9、utput stage. This control is independent of the THRESHOLD and RATIO settings. - 1 - RadioFans.CN 收音机爱 好者资料库 F. 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. THRESHOL

10、D. 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) illuminat

11、es 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

12、the rear-panel INPUT RANGE switch is in the HIGH position. 1.2 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. B. POWER. For safety, the IEC style receptacle ties the mains ground (third prong on the plug) to the c

13、hassis 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

14、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

15、 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 + - terminal, and the low side to the COM and CHASSIS terminals. E. STEREO TERMINAL. For stereo operation of two LA-4s, conn

16、ect a short cable with standard phono plugs between the two connectors on the rear chassis of the two units. Older model LA-4s (Black front-panel) do not have this connector. Instead, they have two terminals on the barrier strip. - 2 - Connect the center conductor of the single-conductor shielded ca

17、ble 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 o

18、peration. The stereo connecting cable may remain connected as 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

19、 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-

20、4s input sensitivity. HIGH position corresponds to a nominal input sensitivity of 0 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. - 3 -

21、1.3 DESCRIPTION The UREI LA-4 Compressor/Limiter is a single-channel unit, although two may be strapped for stereo operation. Making use of UREIs patented Electro-Optical Attenuator technology, the LA-4 offers smooth, predictable performance coupled with ease of operation. The gain reduction is acco

22、mplished with an RMS detector, which is the analog of human hearing, so gain reduction is smooth and natural sounding. The detector consists of a light dependent resistor (LDR) and an electroluminescent light source, which is a semiconductor, so it does not change or deteriorate with age. Compressio

23、n 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 limiting. The calibrated ratio switch assures consistent and repeatable results. Threshold is adjustable over a wide range, giving the flexibili

24、ty to limit only the highest amplitudes, or to compress virtually the entire program. A balanced, differential input stage and a transformer-isolated output assure trouble-free patching by avoiding ground loop problem. The input sensitivity is switchable to accommodate high level lines (nominal 0 dB

25、m sensitivity) or lower level sources (nominal -20 dBm sensitivity). Input level is monitored by a bright LED indicator that illuminates whenever the incoming signal level is high enough to cause distortion in the first amplifier stage. Output level is continuously variable. The large, illuminated V

26、U meter can be switched to indicate dB of gain reduction, or output level; front panel switching sets the meter sensitivity for 0 VU = +4 dBm or 0 VU = +8 dBm output level, in accordance with the most widely used recording, sound reinforcement and broadcast standards. In gain reduction mode, the met

27、er is driven by a completely isolated circuit, so distortion is minimized. All connections are made to a standard barrier strip. The LA-4 is ideal for all phases of recording, re-recording, and sound reinforcement. It is also useful for broadcast production. However, due to its RMS-responding gain r

28、eduction circuitry, the LA- 4 is not recommended for overmodulation protection of broadcast transmitters, disc or optical recorders, unless followed by a peak limiter such as the UREI 1176 LN. - 4 - 1.4 DESIGNATION OF INPUT AND OUTPUT LEVELS The term dBm has been commonly misapplied when describing

29、voltage levels in high impedance lines. In fact, dBm refers to a power level, where 0 dBm is equal to 1 milliwatt, or 0.775 V across a 600 ohm termination. However, in high impedance circuits, power dissipation is negligible, and only the voltage level is of interest. The term dBV would be more usef

30、ul here, where 0 dBV is equal to 1 volt (across any impedance). Unfortunately, because 0 dBV (1 volt) across a 600 ohm line is equal to +2.2 dBm, the term dBV can be misleading. For this reason, the term dBm is used exclusively in this manual, with the understanding that, in other than 600 ohm circu

31、its, the voltage level is the reference, not the 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 sensitivi

32、ty 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 600 ohm terminating resistor is used, the input sensitivity becomes a true

33、 +4 dBm. The same criteria apply to output level ratings. 1.5 DEFINITION 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. Limiter: A compre

34、ssor with a high compression ratio of approximately 8:1 or greater. The high ratios maintain essentially constant output level despite increases in input level above the threshold. Compression Ratio: The ratio, in dB, of input level change to output level change, above threshold. A compressor whose

35、output level changes 1 dB for a 2 dB input level change, above threshold, has a 2:1 Compression Ratio. A compressor whose output level changes 1 dB for a 4 dB input level change above threshold has a 4:1 compression ratio, and so forth. - 5 - Threshold: The level at which compression begins. The URE

36、I LA- 4 compressor/Limiter has an adjustable threshold. When the input level is below the set threshold, the unit functions as a 1:1 amplifier (a unity gain device). When the input level is above the set threshold, the unit functions as a compressor, or as a limiter, depending on the compression rat

37、io selected. 1.6 SPECIFICATIONS ELECTRICAL INPUT: Balanced bridging differential amplifier. INPUT IMPEDANCE: 40 kohms, used as a balanced input. 20 kohms, used as an unbalanced (single-ended) input. EQUIVALENT INPUT NOISE: Less than -90 dBm (15.7 kHz band-width); input and output terminated with 600

38、 ohm load. MAXIMUM INPUT LEVEL: Determined by rear panel switch to allow for optimum operation in different level environments; HIGH Range: Maximum +20 dB* LOW RANGE: Maximum 0 dB* GAIN: Adjustable with front panel gain control. Maximum 20 dB with input level switch in LOW position, or 40 dB with sw

39、itch in HIGH position. FREQUENCY RESPONSE: +0.5 dB, 20 Hz 20 kHz. ATTACK TIME: 1 to 10 milliseconds for 63% correction, depending on signal waveform. RELEASE TIME: 100 milliseconds to 1 second for 63% return, depending on duration of limiting. COMPRESSION RATIO: 2:1, 4:1, 8:1, 12:1 or 20:1; switch s

40、electable from front panel. * Ref. 0 dB = 0.775 V rms. - 6 - THRESHOLD OF LIMITING: 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 2:. -61 dB -41 dB* 4,8,12,20:1 -45 dB* -25 dB* OUTPUT: Fl

41、oating, transformer isolated. OUTPUT LOAD: 150 ohms or greater. POWER OUTPUT: +24 dBm into a 600 ohm load (12. 8 V); +20 dB* into a 150 ohm load. POWER REQUIREMENTS: 100 to 125 VAC or 200 to 250 VAC, 50/60 Hz, switch selectable, less than 10 W. ENVIRONMENT: Operating, +OC to +50 C. Storage, -20C to

42、+60C. PHYSICAL CONNECTIONS: Input and output, through rear chassis barrier strip. Stereo interconnect through phono jack. Power through 3-wire IEC style connector. INDICATORS: Standard VU meter, switch selectable to read output level (0 VU reference +4 dBm or +8 dBm), or amount of gain reduction. LE

43、D indicator for input overload. LED power indicator. DIMENSIONS: 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). FINISH: Panel is 3.18 mm (1/8) brushed, clear anodised aluminum in two shades Chassis is cadmium plated steel. WEIGHT: 2.95 kg (6.5 pounds). SHIPPIN

44、G WEIGHT: 3.63 kg (8 pounds). ACCESSORIES: Single Rack Mount Kit, No. SR-1. Double Rack Mount Kit, No. DR-1. Model 301 XLR/QG Adapter kit for input and output. - 7 - SECTION II INSTALLATION 2.1 UNPACKING AND INSPECTION Carefully examine the contents of the shipping carton for any signs of physical d

45、amage which could have occurred in transit. Though your LA-4 was carefully packed at the factory, and the container was designed to protect the unit from rough handling, accidents do happen. IF DAMAGE IS EVIDENT, DO NOT DESTROY ANY OF THE PACKING MATERIAL OR THE CARTON IMMEDIATELY NOTIFY THE CARRIER

46、 OF POSSIBLE CLAIM FOR DAMAGE SHIPPING DAMAGE CLAIMS MUST BE MADE BY YOU, THE CONSIGNEE. The shipment should include a two-part warranty card bearing the same serial number as the LA-4, an instruction manual, and the LA-4. IN ORDER TO ACTIVATE THE ONE-YEAR LIMITED WARRANTY, THE CARD MUST BE COMPLETE

47、D AND THE 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 equipment rack that also contains heat-producing equipment (such as power ampli

48、fiers), adequate ventilation should be provided. This will prolong component life and maximize operational stability. Also, while circuitry susceptible to hum pickup is fully shielded, installation should nevertheless be planned to avoid locating the LA-4 immediately adjacent to large power transformers, motors, etc. 2.3 RACK MOUNTING A SINGLE UNIT The SR-1 kit (optional) allows mounting of one LA-4 in a standard 19 USASI rack. The unit occupies two standard space