Formula Sound AVC2 User manual

AVC2
AUTOMATIC VOLUME CONTROL
USERS MANUAL
XLR VERSION

GENERALDETAIL
The AVC2 is a stereo unit and performs as an intelligent volume control. The operation is
very simple. If the average operating level is kept below the internally set threshold the AVC2
has no effect. If the average programme level exceeds the threshold AVC2 will reduce its
output level. The level is reduced in discreet steps indicated by the led bargraph meter on
the front panel of the unit. The action of the AVC2 is to fade between these steps and is
almost undetectable in use. The more one tries to increase the volume the more the AVC2
will decrease it so that the system will barely change in perceived level. If driven to maximum
attenuation the output level will be reduced by more than the increase in input level. The
mixer or pre-amp feeding the AVC2 will probably be clipping but the system will actually be at
a lower than normal level. A clip indicator is provided to show when the input stage of the
AVC2 is being over driven. Reducing the input level will gently release the attenuation pro-
vided by the AVC2.
The AVC2 has no external controls for the operator to worry about - just a bargraph meter
and some indicator led’s to inform the operator of the status of the unit.
An external remote warning indicator may be connected to warn the operator that the operat-
ing level is 3dB away from the threshold at which the AVC2 will start to control level.
A mute relay is fitted which can be operated by an external switch to improve system security
or a fire alarm connection to mute the system in case of fire.
A provision is also included to dim the unit by 20dB.
The AVC2 also has provision to connect an external time switch (not supplied) to switch
between two output levels.
As local conditions and noise control specifications can vary these facilities allow the unit to
be used in several ways to comply with regulations.
For more detail see the section on AUXILIARY CONNECTIONS on the next page.
Page 1

INSTALLATION
The unit should normally be installed in the signal chain either between the mixer or pre amp and the
amplifiers, or in larger systems the mixer/ preamp and the electronic crossover.
The unit should ideally be mounted where the operator can see the indicator leds on the front panel or
alternatively a remote indicator could be installed (see auxiliary connections section)
Connections are via XLR connectors for the audio and 2 X 4 way connectors for auxiliary connections.
A tamper proof cover is available which can be sealed. This cover prevents the connectors
from being disconnected and is often a requirement when the unit is installed as a noise
controlling device specified in a licencing application .
The unit features balanced inputs and outputs which are self compensating. Either side may be tied
to the screen for unbalanced operation without loss of level or performance. (N.B. For unbalanced
operation the negative output should be tied to the screen and not left single ended. An unbalanced
connection between positive and screen with no connection to negative will result in a loss of signal
level).
When wiring to balanced circuits for stereo operation both left and right channels should be identical
to maintain phase.
To avoid ground loop problems, the audio common (cable screens) in this equipment is NOT con-
nected to mains earth within the unit. The mains lead earth connection is only connected to the case
and this must always be connected to MAINS EARTH.
As supplied the unit will be detecting the incoming signal to control the output level.
AUXILIARY CONNECTIONS
2 X 4 way connectors are provided for the auxiliary connections. The connectors are labelled 1,2,3,4
for the first connector and 5,6,7,8 for the second connector. The mating halves for these connectors
are supplied with each unit.
The unit is supplied with a link which is fitted between pins 1 and 2. This is the security link and these
two terminals need to be joined for the unit to operate. Removing the link will mute the unit.
Pins 3 and 4 when joined allow the unit to be dimmed by 20dB. When the connection is removed the
unit will fade back to the previous level.
Pins 5 and 6 are provided to allow a warning indicator to be connected to the system. An led indicator
may be connected directly to pins 5 and 6 observing polarity to avoid damaging the led. Alternatively
a conventional effects lighting, switching pack may be connected that is compatible with a 10V D.C.
input to provide larger warning indication. This output provides a current limited 10V D.C. signal 3dB
before the unit starts to control volume levels.
Pins 7 and 8 are provided for switching between two output levels. This function may be controlled by
a time switch if required. (Time switch not supplied).
Alltheauxiliaryconnectionsarelowvoltagelowcurrentconnections,
Whenconnectedtoexternal switchesfirealarmsetc. theymustbetotally
isolatedandfullyfloatingfromany other electricalcircuit.
Page 2

OPERATIONANDSET-UP
As supplied the unit is adjusted to operate at an average nominal programme line level of 0Vu
(+4dBu) and in most cases will not need any adjustment. This is the level that a standard Vu meter
will read before going into the red (end section), therefore the operator can use the readings on the
Vu meters fitted to his mixer to be an indication of maximum permitted volume level.
To achieve the required system volume level adjust the output level of the AVC2 by using the output
pots on the rear panel. The output pot’s are accessible through small holes located between the input
and output connectors and are labelled 1 & 2,
Pot 1 is used normally to set the output level. When level 2 is selected by joining pins 7&8 on the
auxiliary connectors the output is switched via number 2 pot which should then be adjusted to provide
the second required output level.
Check the level by driving the system until the first led illuminates on the attenuation meter located on
the front panel of the AVC2 and readjusting outputs as necessary.
Black plastic snap rivets are provided to blank these holes after the initial set up. If these rivets need
to be removed lift the head by prising with a thin object - finger and thumb nails will usually suffice.
Always refit the snap rivets after adjustments are complete.
For different applications the unit may be set to operate at different levels by internal adjustments.
See later section INTERNAL ADJUSTMENTS.
The “AVC2” is slow acting to differentiate between dynamic peaks of music and an increase in aver-
age level. Bear this in mind when making adjustments.
INTERNAL ADJUSTMENTS
Do not attempt to make any internal adjustments unless you are qualified to do so and you know what
you are doing.
ALWAYS DISCONNECT POWER BEFORE REMOVING COVERS.
Access is gained by removing the top cover. Remove 3 screws from either side of the case. Remove
2 screws from the top and lift top cover off.
When the adjustments are completed refit the case top.
FIG 1.A. Shows the position of the range setting jump plug. This sets high and low operating ranges
for the unit.
FIG 1.B. Shows the position of the sensitivity adjustment preset. This is a multi-turn preset. Use this
if you wish to change the operating threshold of the unit. Use in conjunction with the range setting
jump plug to increase or decrease the sensitivity of the unit.
FIG 1.C. Shows the position of 2 jump plugs. These are used to select the type of control chain used
to trigger the attenuators. This may be set to linear, ‘A’ weighted or both.
The “AVC2” uses two control chains in parallel, one with a flat response and one ‘A’ weighted. The
output of the highest chain is used to control the unit. In special applications either may be selected
by setting the jump plugs as indicated on the P.C.B.
IF YOU ARE NOT SURE OR FOR GENERAL PURPOSE USE LEAVE AS FACTORY SET (BOTH).
ALL OTHER PRESETS AND JUMPERS ARE FOR ALIGNMENT AND TEST PURPOSES
AND ARE FACTORY SET. DO NOT - REPEAT - DO NOT TOUCH!
INCORRECTSETTINGOFANY INTERNAL ADJUSTMENT WILLINVALIDATETHEWARRANTY.
Page 3

AVC2 SPECIFICATIONS
Frequency response 20Hz - 30kHz +/- 0.5dB
Distortion O/P level Attenuation
(THD and noise) freq 1kHz 0dBu 0dB < 0.01%
0dBu 12dB < 0.015%
0dBu 30dB < 0.05%
Noise measured 20Hz-20kHz Equiv. input noise < -90dBu
INPUTS Electronically balanced, connect pins 1 & 3 to screen pin 2 hot for unbalanced use
XLR Connector Pin 1 screen Pin 3 -Ve Non Phase Pin 2 +Ve Phase
Input impedance Balanced 20K ohms
Unbalanced 10K ohms
Maximum input level +22dBu
Clip indicator Indicates @ +20dBu
OUTPUTS Electronically balanced, connect pins 1 & 3 to screen pin 2 hot for unbalanced use
XLR Connector Pin 1 screen Pin 3 -Ve Non Phase Pin 2 +Ve Phase
Source impedance 100 ohms
Minimum load impedance 600 ohms
Operating Threshold Range
High range Average level adjustable +5 dBu -2dBu
Low range Average level adjustable -8 dBu -14dBu
N.B. If a signal generator is used as the source for making adjustments to the operating threshold, the threshold will
be approx. 6dB lower than using a music source due to the averaging measurement which the unit uses for control.
For operation outside the above ranges contact Formula Sound Ltd.
ATTENUATOR RANGE -3dB -6dB -9dB -12dB -15dB -18dB -24dB -30dB
CONTROL CHAIN
A control chain with a flat frequency response Linear, “A” weighted, or a combination of both may be selected to
control the attenuators.
AUX CONNECTIONS 1 & 2 Mute 3 & 4 Dim output -20dB 5 & 6 Remote warning 7 & 8 Level 2 select
POWER
220-240V AC (110V to order) Mains Fuse 250mA slow blow I.E.C. Mains connector
FINISH
Front and Rear panels - Black anodised aluminium with silver notation
Case black plastic-coated steel.
DIMENSIONS
19" Rack mounting 1RU
Width 482mm (19") Depth 200mm (7.9") Height 44mm (1.75")
FORMULA SOUND LTD.
Ashton Road
Bredbury
Stockport
Cheshire
UK
SK6 - 2SR TEL [phone] ([phone]) FAX [phone] ([phone])
Formula Sound reserve the right to alter specifications at any time without notice.