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50/30 dB Gain Switch
The 50/30 dB GAIN switch is an input pad to prevent high output devices from overdriving the input transform-
er of the LA-3A. Setting the switch to the 30dB position will attenuate the incoming signal by 20dB. For studio
use, the normal setting is down (30dB) when not using the MOD function. See MOD Switch below for more info.
MOD Gain Switch
The MOD (modification) GAIN switch improves the signal to noise ratio of a "stock" LA-3A. Typically, both the
MOD switch and the 50/30 dB switch are set in the "up" position. This disengages the 20dB input pad and
drops the output amp's gain by 24 dB. In this configuration, the unit's gain is +26dB and will be less noisy
than when in normal mode with the 50/30 dB switch at 30. In addition, the MOD switch lowers the threshold
point where compression begins and allows a greater amount of overall compression. Many engineers have
performed this mod on vintage LA-3As. The loss of gain is not a problem in most applications as the LA-3A has
about 50dB gain to begin with. The improvement in signal to noise is usually a desirable trade off. We have
supplied this modification as a switchable feature so you can operate with or with out the modification.
Stereo ADJ Control
The STEREO ADJ (adjust) control is used to balance two LA-3As gain reduction when used for stereo operation.
See Stereo Operation on page 6 for more info.
High Frequency Contour Control
The HF CONTOUR control is a high frequency boost of the signal feeding the gain reduction circuit. This control
is NOT an EQ of the audible program material. It's function is to make the compressor more sensitive to high
and high mid frequency content and to compress or attenuate that spectrum more than the mid and low end
frequencies that are being processed by the LA-3A. This control was used specifically for radio broadcasting to
prevent over modulation of high frequency signal content. Typically, this control is left in the FLAT position (full
CCW). Turning the control clockwise will increase compression of frequencies above 1kHz. At the full clockwise
position, the LA-3A will attenuate 15kHz 10dB more than the lower frequencies.
Input/Output XLRs
Standard XLR input and output connectors are provided on the rear panel. Pin 2 is wired positive (hot) on the
LINE INPUT and LINE OUTPUT.
AC Power
The LA-3A uses a standard detachable IEC power cable.
Fuse/Mains
The AC power FUSE is located at the bottom far left corner of the LA-3A rear chassis. Remove the power cord
before checking or changing the fuse.
• 3AG 1/8 amp time delay (slow blow) fuse is required for operation at115 V.
• 3AG 1/16 amp time delay (slow blow) fuse is required for operation at 230 V.
Voltage Select
The LA-3A can operate at 115 V or 230 V. The voltage selector switch is located beneath the power transformer
on the rear chassis. A small slotted screwdriver can be used to slide the switch to the appropriate setting.
6
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