4 Channel

Auto Compressor

Operation Manual

April 2002

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CONTENTS

1.0 OVERVIEW 4

2.0

DESCRIPTION OF CONTROLS 5-7

2.6 Hard-Soft Knee switch

2.9 Gain Reduction meter

3.1 Side Chain insert

3.2 Input

3.3 Output

8-9

4.0 INSTALLATION 10-11

4.1 Inspection and unpacking Phantom

4.2 Operating Environment +48V indicator

4.3 CE Standard and LVD Pad

4.4 Power Requirement Listen

5.0 WARRANTY 12

7.0 DIMENSIONS 14

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1.0 OVERVIEW

Main Features:

• 4 channels of Auto compression

• Soft or hard knee compression slopes

• Fully variable Threshold, Ratio, Release and Gain

• Auto Attack/Release and Program Dependant Attack with manual Release modes

• Low frequency Program filter

• Side chain inserts

• Balanced Inputs-Outputs with +4dBu/10dBV switching

The C400 is a professional 4 channel compressor that can be operated as 4 separate processors or linked as two independent stereo pairs. In Link mode, Channel 1 and 3 provide Master control and 'rms summing' is used to ensure that signals from both the linked channels affect compression equally.

Each channel has fully variable controls for Threshold, Ratio, Release and Gain.

Compression slope can be switched between Hard or Soft knee, with Hard knee providing tight control of compression Ratio and Soft knee a more progressive style of compression.

Two Attack/Release modes are available; Auto Attack/Release or Program Dependant

Attack with manually adjustable Release. A low frequency Program filter can be switched into the sidechain to reduce the effects of bass heavy material causing over compression.

Each channel also has a sidechain insert on TRS jack to allow connection of external processing such as an equaliser.

Gain Reduction is displayed on an 8 segment LED bargraph. The Bypass and Link switches also have led indicators.

All inputs and outputs are electronically balanced and can be switched between +4dBu and -10dBV operating levels.

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2.0 DESCRIPTION OF CONTROLS

2.1 BYPASS switch

Pressing BYPASS cancels compression by removing the side chain voltage from the voltage controlled amplifier (VCA). The Input-Output and level change circuitry remain in the signal path.

The BYPASS led lights when the compressor is Bypassed.

2.2 PROG. switch

The PROGRAM switch inserts a low-cut filter into the side chain to remove the bass content of the program material which can cause over compression or pumping.

The filter response makes the side chain 6dB less sensitive at 100Hz.

2.3 THRESHOLD control

In HARD knee mode THRESHOLD sets the reference level above which signal compression starts. The RATIO control then adjusts the amount of compression applied to input signals above threshold.

In SOFT knee mode, compression occurs gradually over a 10dB range of input signal level. The indicated THRESHOLD level is approximately in the centre of this range and the slope set by the RATIO control will not be reached until the signal level has increased some way above the threshold - see Fig 2.1 and 2.2.

Control range is -40dBu to +20dB.

2.4 RATIO control

RATIO controls how much compression is applied to an input signal once it has increased above threshold and refers to the final compression slope.

The RATIO markings around the control indicate how many dB the input signal must increase to cause a 1dB rise in output level. A RATIO of 2:1 means the input has to increase by 2dB for a 1dB change of output level. A 4:1 ratio requires a 4dB increase of input level for a 1dB change of output, etc.

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A RATIO of

∞

:1 effectively means that there is no increase in output level once the input signal has reached THRESHOLD reference i.e. limiting. The following diagrams shows the difference between HARD and SOFT knee compression at a number of different RATIOs. THRESHOLD in the diagrams is set to 0dB.

Fig 2.2: SOFT knee compression Fig 2.1: HARD knee compression

2.5 AUTO-MAN switch

In the AUTO mode (switch out), Attack and Release times are automatically adjusted and are dependant on the dynamic content of the input signal.

AUTO mode has been designed to work with a wide range of vocal, instrument and program sources and can therefore be used in most applications without need to adjust attack and release times.

In MAN (manual) mode (switch in) Attack becomes program dependant and the

Release time is manually adjusted using the RELEASE control.

2.6 KNEE switch

Selects between HARD and SOFT knee compression curves - see Fig 2.1 and

Fig 2.2.

SOFT knee gives a gradual onset of compression and can provide subtle and unobtrusive level control.

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HARD knee compression provides tight control over signal levels above threshold and is useful for creative applications or where a large amount of gain reduction, such as limiting, is required.

2.7 RELEASE control

RELEASE is only active in MAN (manual) mode (AUTO-MAN switch in) and adjusts the release time between 40mS and 4S.

2.8 GAIN control

The GAIN control on the C400 allows the output level from the compressor to be attenuated or amplified by up to 20dB. Generally used to compensate for level changes caused by the action of compression.

Please note:

As +20dB of gain can be added to the signal path it is possible to cause clipping.

An 8 stage led bar graph meter that provides a visual indication of the amount of gain reduction being applied to the input signal.

2.10 LINK switch

Pressing the LINK switch couples channels 1&2 and 3&4 for stereo operation.

Channels 1 and 3 become the masters, the controls on channels 2 and 4 are disabled.

The side chain circuitry on the C400 uses true rms summing to ensure that the signals in both the linked channels contribute equally to any gain reduction.

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3.0 EXTERNAL CONNECTIONS

3.1 SIDECHAIN

The Side chain TRS jack allows connection of an external processor such as an equaliser for frequency sensitive compression e.g. de-essing.

This is an unbalanced insert with Ring wired as Send and tip wired as return.

Please note:

Plugging a jack into the side chain connector breaks the control signal path which

must then be completed by the externally connected equipment.

3.2 INPUT

Electronically balanced Input with pin 2 wired hot (signal +).

Unbalanced operation is possible by joining pin 3 to pin 1 (signal ground) and using pin 2 as signal hot (+).

Please note:

To maintain correct signal levels in un-balanced applications, pin 3 must be

joined to pin 1 and not left un-connected.

3.3 OUTPUT

Electronically balanced Output with pin 2 wired hot (signal +).

For un-balanced operation pin 3 can be joined to pin 1 i.e. pin 2 = signal hot and pins 1&3 = ground (screen).

Please note:

To maintain correct signal levels in un-balanced applications, pin 3 must be

joined to pin 1 and not left un-connected.

3.4 LEVEL

These switches select the input and output operating level for each channel between +4dBu (switch out) and -10dBV (switch in).

The Side Chain insert operates at -2dBu in both +4dBu and -10dBV modes.

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3.5 POWER

Mains power switch for C400

Standard IEC mains inlet for use with a detachable mains cable.

See Section 3.4 for details of power requirements and fusing.

Please note:

The mains protection fuse is inside the unit, accessed by removing the top cover.

Ensure that the unit is disconnected from the mains supply before attempting to

replace the fuse.

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4.0 INSTALLATION

4.1

INSPECTION AND UNPACKING

The C400 has been carefully packed at our factory in a carton designed to withstand handling in transit. Should the unit appear to have been damaged in transit, notify your dealer immediately and do not discard any of the packing. The carton should contain -

• The C400

• Power cord - country specific, please check

• Operator Manual (this book)

The C400 is designed to operate between 0°C and 40°C (32-112°F) with relative humidity no more than 80%. Should the units be installed in an equipment rack, ensure that the ambient temperature conforms to these levels.

4.3

CE STANDARDS AND THE LOW VOLTAGE DIRECTIVE (LVD)

The C400 has been designed to comply with the latest Electromagnetic

Compatibility (EMC) regulations. However we recommend you do not operate the unit close to strong emitters of electromagnetic radiation such as power transformers, motors, mobile telephones or radio transmitters.

The unit should only be connected to a power supply of the type described in 4.4

POWER REQUIREMENTS or as marked on the unit. Disconnect the mains supply before removing any cover.

The C400 is factory configured for either 230V 50Hz ac or 115V 60Hz ac mains operation. Please refer to the following diagram which shows the transformer connections for 230V and 115V –

The rating of the rear panel fuse is shown on the cover -

230V

T125mA

115V

T250mA All are slow blow type

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Please note:

If the fuse requires changing at any time please ensure the correct type is fitted.

An incorrect fuse could cause damage to the unit and may constitute a fire hazard.

The detachable IEC mains lead connections to the appliance are coloured in accordance with the following code:

Green-and-Yellow Earth

WARNING: THIS APPLIANCE MUST BE EARTHED

Please note:

A protective earth connection, made by way of the earth conductor in the power

cord, is essential for safe operation.

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5.0 WARRANTY

Your LA Audio C400 has been manufactured to a high standard using quality components. If correctly installed and operated the unit should give years of problem free operation.

However in the event of a defect in material or workmanship causing failure of the unit within 1 year of the date of original purchase we will agree to repair, or at our discretion replace, any defective item without charge for labour or parts. To receive service under this warranty it is necessary to return the unit to an LA

Audio authorised service centre or to the factory with a dated receipt as proof of purchase. After repair the unit will be returned to you free of charge.

Limitations:

This warranty does not cover damage resulting from accident or misuse. The warranty is void unless repairs are carried out by an authorised service centre.

The warranty is void if the unit has been modified other than at the manufacturers instruction. The warranty does not cover components which have a limited life, and which are expected to be periodically replaced for optimal performance. We do not warrant that the unit shall operate in any way other than as described in this manual.

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6.0 TECHNICAL SPECIFICATIONS

ELECTRICAL

Frequency response:

Maximum Input Level:

Input-Output Level:

Max. Output Level:

THD:

Signal to Noise Ratio:

20Hz to 20kHz (+0, -0.5dB)

+20dBu

+4dBu or -10dBV

+20dBu

< 0.05% (1kHz, +4dBu)

> 90dB, +4dBu out, 22Hz- 22kHz

Attack:

Hard knee

Release:

Auto Attack/Release or program dependant

40ms to 4s - manual mode

Program @

Power Requirement:

PHYSICAL

Input Connectors:

Output Connectors:

Power Connection:

Dimensions (mm):

15VA, 115/230V AC, 50/60Hz

XLR 3 pin (Pin 2 hot)

XLR 3 pin (Pin 2 hot)

IEC 3 pin socket, Detachable lead

482 (19") W

164 (6.5") D

44 (1.75") H

Temperature Range: Operating 0ºC to 50ºC

Storage -30ºC to 75ºC

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7.0 DIMENSIONS

In keeping with our policy of continuous improvement LA Audio reserves the right to alter specifications without prior notice.

Manufactured in the UK by LA Audio, 40 Chigwell Lane, Loughton, Essex, IG10 3NY, UK.

Tel: +44 (0)208 418 0778. FAX: +44 (0)208 418 0624.

Web: www.laaudio.co.uk. email: [email protected]

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