InovaメーカーLA-2Aの使用説明書/サービス説明書
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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.
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.
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.
v Table of Contents Teletronix LA-2 A by Universal Audio ................................................................................... ii Specifications ............................................................................................
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.
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.
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.
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.
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.
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.
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.
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.
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”.
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.
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.
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.
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.
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.
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.
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