Inova LA-2A manuel d'utilisation

Model LA-2A Leveling Amp lifier Universal Audio, Inc. www.uaudio.com PO Box 3818 Santa Cruz, CA 95063-3818[...]

ii T eletronix L A -2A by Univer sal Audio Thank you for purchasi ng this reproduction of the Teletro nix LA-2A. The LA-2 A was originally produced in the early 1960s by Teletronix , which was later acquired by Babcock Electronics Corporation. My father purc hased the product rights a nd the name Teletronix from B abcock Engineering in 1967, fo ldi[...]

iii IMPORTANT SAFETY INSTRUCTI ONS Before using this unit, be sure to ca refully re ad the applicable items of these ope rating instructi ons and the safe ty suggestio ns. Afterwa rds keep the m handy fo r future ref erence. Take spe cial care to foll ow the warnings in dicated on the unit itse lf, as well as in the ope rating instruct ions. 1. Wat[...]

iv LA-2A     User’s Guide Universal Audio, Inc. PO Box 3818 Santa Cruz, CA 95063-3818 (831) 454-06 30 voice (831) 454-06 89 fax www.uaudio.com Universal Au dio Part Number LA2 A-M01. Revision 1.3 Noti ce This manua l provide s general informat ion, prepar ation for us e, instal lation and operating i nstructio ns for the Univers a l A[...]

v Table of Contents Teletronix LA-2 A by Universal Audio ................................................................................... ii Specifications ................................................................................................................. ...... 1 Operation of the LA-2 A ............................................[...]

1 Specif ications ! Gain Reduction: up to 40 dB ! Distortion: less than 0.35 % total harmonics at +10 dBm, and less tha n 0.75% total harmonics at +16 dBm output ! Response: +/- 0.1 dB , 30 cycles to 15 kilocycles ! Noise: 75 dB below +10 dBm output level ! Gain: 40 +/- 1dB ! Output Level: +10dBm nominal, +16dBm peaks ! Input Level: +16 dBm maximum[...]

2 Operation of t he L A -2A Input and Output Connections Input and Output connections are made using standard XLR style connectors. Terminal strips are also provided. Output connections Input connectio ns 6) Stereo Link 1) + 600 ohms 7) Ground 2) + 250 ohms 8) + 600 ohms 3) Center tap 9) Center tap 4) - 250 ohms 10) - 600 ohms 5) - 600 ohms Barrier[...]

3 VU Meter Operation The VU Meter is used for both output level monitoring and gai n reduction monitoring. When used to monitor the output level, the user may choose either +4 dB or +10 dB settings. The middle setting is for gain reduction, and the meter reads t he amount of compression in dB. Limit / Compress Switch The Limit/Compress Switch chang[...]

4 Calibration Meter Zero Adjust The zero-adjust of the meter is set by the screw-adjust potentiometer located n ext to the Limit / Compress Switch. To adjust this, put the meter into Gain Reduction mode. Make sure that there is no signal present. Loosen the locking nut and use a screwdriver to adj ust this potentiometer until the meter reads zero. [...]

5 Theor y of Ope ration Compresso r Basics Before we dig in to a description of the LA-2A circuit, it is useful to e xamine the general characteristics of compressors and review some terminology. Figure 1 depicts t he input/output characteristics of a compressor, an expander and a perfect amplifier. When operated within its specified range, an ampl[...]

6 As an aside, an expander is a device which increases the dynamic range of a signal. For example, a 10dB change in the input signal might result in a 20 dB c hange in the output signal, thus “expanding” the dynamic range. There are several other terms related to compression that can be demonst rated by referring to Figure 2. The amount of comp[...]

7 TR I M IN P U T IN P U T TR A N SFO R M ER O PTI C A L A TTEN U A T O R MO D U L E T4 VO L T A G E A M P L IF IE R (1 2 A X 7 A ) CA T HO DE FO L L O W ER (1 2 B H 7 ) PR E - E M PH A S I S VO L T A G E A M P L IF IE R (1 2 A X 7 A ) EL EC TRO LU M I N E S C E N T D R I V E R (6 A Q 5 ) O U T P U T TR A N S FO R M ER OU T P U T N E G A TI V E FEE[...]

8 LA-2A Block Diagram A functional block diagram of the LA-2A is pro vided in Figure 3. A brief overview of the operation will be provided here. The input transformer pro vides isolation and impedance matching. After this t he signal is fed in to both the side-chain circ uit and th e gain red uction circuit. The side-chain is comprised of a voltage[...]

9 stage. To see why th is is true, we can look at the extreme cases. If the resistance is extremely high (this is the case wh en there is a small input signal and the light is off) then the photo-cell does not affect the circuit and there is no gain reduction. The second case we can look at is when there is a large signal present. In this condition[...]

10 The next important aspect is that of the release of the compressor. This is determined almost entirely by the characteristics of the photo-cell. The LA-2A uses cadmium-sulfide photo-cells. The first important aspect of the cell is its “two-stage decay”. After the light is removed from the cell, it releases quickly (40-80 milliseconds) to app[...]

11 Side-Chain Circuit The previously described gain reduction circuit is controlled by the co ntrol vol tage w hich is supplied by the side-chain circuit. The LA-2A is a feed-back style compressor. T h is is due to the fact that the signal that is used to drive the side-chain circuit is affected by the gai n reduced signal. This signal is first fed[...]

12 previously, the gain reduction is controlled by t he photo-cell in the T4 el-op. In order to track the operation of this cell and determine the gain reduction, a second photo-cell is also illuminated by the same EL panel. This photo-cell is ha nd-selected to match the gain reduction photocell and hence gives an accurate indication of the amount [...]

13 legendary Bill Putnam's company, Studio Electronics Corp shortly before he changed t he company’s name to UREI®. Three different versions of the LA-2A were prod uced under t he auspices of these different companies befo re production was discontinued around 1969. Developin g the 1176 It was Bill Putnam himself who, in 1966, was responsib[...]

14 currently mix ing, I'm using both an 1176 an d an LA2 on his voice, wh ich is not unusual f or me. "The 1176 absolutely adds a bright ch aracter to a sound, a nd you can set the attack so it's got a nice bite to it. I usually use them on four to o ne, wi th qui te a lot of gain reduction. I like h ow variable the attack and releas[...]

15 Ken Kess ie Mixer Ken K essie (En Vogue, T ony! Toni! Tone! , Celine Dion) is kno wn for being experimental. " Seems like everybody knows the basic tricks for he 1176," h e says, "But here are two that might be lesser known. If you turn the attack knob fully counterclockwise until it clicks, the 1176 eases to be a compressor and a[...]

16 inconsistent piece to piece than th e 1176s, because of th e tubes and the dif ference in fatigue of the tubes. "My big mentors were Andy Johns and Lee DeCarlo and Ron Nevisio n because they were all Record Plant guys. I learned how to make a rock and roll record from them. Al though over the years it's become my own thing, my style st[...]