5. operation
CONTENTS
1.
2.
3.
4.
5.
6.
OVERVIEW ............................................................................................................................. 1
BEFORE YOU START .......................................................................................................... 2
2.1 Utilizing the User Manual ....................................................................................... 2
2.2 Safety Precautions .................................................................................................. 2
2.3 FIG 1: FRONT PANEL ............................................................................................ 2
2.4 FIG 2: REAR PANEL............................................................................................... 2
INSTALLATION....................................................................................................................... 3
3.1 AC Mains Supply...................................................................................................... 3
3.2 Microphone Input. .................................................................................................... 3
3.3 Line Inputs. ............................................................................................................... 3
3.4 Instrument Inputs. .................................................................................................... 4
3.5 Balanced Line Outputs. .......................................................................................... 4
3.6 Unbalanced Line Outputs. ...................................................................................... 4
3.7 Nominal Operating Level. ....................................................................................... 5
GETTING STARTED ............................................................................................................. 5
4.1 Connections in the recording process. ................................................................. 5
4.2 In Use. ....................................................................................................................... 7
OPERATION ........................................................................................................................... 8
5.1 Compression Introduction ...................................................................................... 8
5.2 Input Source Selection............................................................................................ 8
5.3 Mic Gain. ................................................................................................................... 8
5.4 Input Gain. ................................................................................................................ 9
5.5 90 Hz Low Cut Filter. ............................................................................................... 9
5.6 Drive and Peak LEDs.............................................................................................. 9
5.7 Threshold. ............................................................................................................... 10
5.8 Ratio. ....................................................................................................................... 10
5.9 Attack and Release. .............................................................................................. 10
5.10 Gain Make Up. ..................................................................................................... 11
5.11 Knee. ..................................................................................................................... 11
5.12 Compressor On. .................................................................................................. 11
5.13 Output Gain. ......................................................................................................... 12
5.14 Meter. .................................................................................................................... 12
5.15 Meter ‘+10dB’....................................................................................................... 12
SERVICE ............................................................................................................................... 13
1. OVERVIEW
Welcome to purchase the equipment by AC-audio!
The equipment is a signal processor that utilizes both valve and transistor technology.
The audio processing units of equipment can support high quality signal paths, produce
the particular valve audio peculiarity by adopting low noise solid-state electronic
components and perfect valve circuitry. It has the comprehensive and various functions
on controlling sounds, offering users clear, exquisite and high-quality sound.
There are a single balanced mic input and stereo line inputs/outputs on the rear panel,
and stereo instrument inputs on the front panel. The two channels of the equipment work
in ‘linked stereo’ mode, but a mono signal can be applied to channel 1 only, thus can offer
the equipment equally powerful for both mono/stereo tracking and final stereo mix
processing. A single illuminated VU meter monitors the both channels for output level or
the compressor gain reduction.
To satisfy the requirement of performance that low noise, low distortion and wide
bandwidth should be needed, electronically balanced input amplifier appeared. The
preamp stage utilizes 48V phantom power and a high pass 90Hz filter. A Drive LED gives
a visual indication of the signal level through valve stages, monitors the amount of
‘warming’ taking place. The Peak LED warns that overloading is going to be happened.
The Mic input of equipment is provided on an electronically balanced XLR connector,
and the line inputs are provided on balanced TRS stereo 0.25” jack connectors.
Balanced and unbalanced line outputs can be used at the same time, and they are
provided (again on TRS 0.25” jack connectors). The operating level of both the line input
and outputs can be shifted from -10dB to +4dB via a rear panel switch, allowing the
equipment to integrate into any system easily. On the front panel, without the need for a
separate DI box, a pair of high impedance instrument inputs allows keyboards, guitars
and basses to feed into the equipment directly.
1
2. BEFORE YOU START
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2.1 Utilizing the User Manual
l
l
l
l
l
Be sure to read the Safety Precautions before using the product.
Refer to the INSTALLATION when installing your product.
You can easily find any information you are looking for by the CONTENTS.
Using the SPECIFICATIONS, you can easily find detailed parameters of the product.
Please read this manual fully before installing or operating the equipment.
-
2.2 Safety Precautions
For your security and to prevent damage, please read the following Safety instructions
carefully.
Warning:
l This equipment must be earthed.
l All mains wiring should be installed and checked by a qualified electrician with all
power switched off.
l Do not locate it where it will be subject to external heating.
l Do not expose to rain or moisture, as this may present an electric shock hazard.
l Ensure the correct operating voltage is indicated on the rear panel before
connecting to the mains supply.
l Never operate the unit with any cover removed.
l Replace the fuse with the correct type and rating only.
-
2.3 FIG 1: FRONT PANEL
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2.4 FIG 2: REAR PANEL
2
3. INSTALLATION
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3.1 AC Mains Supply.
The equipment is fitted with a 3-pin IEC connector which is approved internationally. A
mating socket with power cord and mains plug is supplied. Before connecting the unit to
the supply, check that the equipment is set for the correct mains voltage. The unit is set
for 110-120V 60Hz or 220-240V 50Hz operation internally, and should only be changed
by an authorized service centre.
The mains fuse required is 20mm anti-surge, 315mA rated at 250V. Sometimes, if it is
necessary to replace the fuse, please use the same type and rating only. The power
consumption of the equipment is 30VA.
Please note that attempted operation on the wrong voltage setting, or with an incorrect
fuse, will invalidate the warranty.
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3.2 Microphone Input.
The microphone input is a via 3 pin female XLR connector, compatible for balanced
microphones. The single microphone input of the equipment is automatically routed to
both channels of the unit.
The mating connector should be wired appropriately as the following way:
Balanced inputs:
l Pin 1 = Ground (screen).
l Pin 2 = Signal Phase (also known as “+” or “hot”).
l Pin 3 = Signal Non-Phase (“-” or “cold”).
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3.3 Line Inputs.
On the rear panel, every channel has a 3 pin TRS jack socket, which will accept
balanced or unbalanced line inputs providing the mating plug is wired suitably:
Balanced inputs:
l Screen = Ground,
l Tip = Signal Phase (“+” or “hot”),
l Ring = Signal Non-Phase (“-” or “cold”).
Unbalanced inputs:
l Screen = Ground,
l Tip = Signal Phase (“+” or “hot”),
l Ring = Ground.
3
The equipment utilizes good quality screened cable, particularly for microphone or low
level sources, So that hum or noise cannot be picked up.
If a mono source is only connected to line input 1, it will be routed to both channels of
the equipment automatically.
Refer to Figure 2 for rear panel connector identification.
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3.4 Instrument Inputs.
On the front panel, each channel has a high impedance (1Mohm) 0.25” instrument
jack socket (see Figure 1). A 2 pin (mono) jack plug is required, which should be wired as
the following way:
- Tip = Signal Phase (“+” or “hot”),
- Screen = Ground.
If a mono source is only connected to instrument input 1, it will be routed to both
channels of the equipment automatically.
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3.5 Balanced Line Outputs.
On the rear panel, the line outputs are via 3 pin TRS jack sockets and may be
configured for balanced or unbalanced connection. Balanced operation is always
preferable to maintain maximum headroom and signal to noise ratio, but can only be
used if the following equipment is also capable of balanced operation:
Balanced outputs:
- Screen = Ground,
- Tip = Signal Phase (“+” or “hot”),
- Ring = Signal Non-Phase (“-” or “cold”).
Unbalanced outputs:
- Screen = Ground,
- Tip = Signal Phase (“+” or “hot”),
- Ring = Ground.
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3.6 Unbalanced Line Outputs.
A dedicated unbalanced line output is provided for each channel, on a 0.25” mono jack
socket.
- Tip = Signal Phase (“+” or “hot”).
- Screen = Ground.
These outputs may be used to the balanced line outputs simultaneously, and are
useful for monitoring purposes particularly in a computer based system where latency
free monitoring is necessary.
4
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3.7 Nominal Operating Level.
A switch on the rear panel allows the line inputs and outputs to be matched to
equipment at a nominal operating level of +4dBu or -10dBu. Most professional
equipment requires +4dBu (approximately 1.2V rms), but some small mixing consoles or
portable tape recorders require -10dBu (approximately 225mV rms). If the operating
level is not known, the switch should be set to the position which results in the best signal
to noise ratio, whilst preserving sufficient headroom.
4. GETTING STARTED
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4.1 Connections in the recording process.
There are many ways to connect the equipment:
1) Connected ahead of the line inputs of a mixing desk/recording device
2) Connected to a channel, group or master insert point
1) Because of the various functions of the equipment, such as a mic preamp, line level
or instrument front end, you can connect the output(s) of the equipment directly to the line
input of your console, recorder or sound card. We do not suggest you to connect line level
outputs to microphone inputs, because this may affect the quality of signal and may cause
level overload on the mixer. The equipment has balanced line outputs for professional
sound quality, but can connect to an unbalanced line input easily. Once the outputs are
connected, feed your chosen source into the relevant input of the equipment simply (mic
will connect to the XLR input on rear panel, line level signals such as mixer or tape
machine outputs will connect to the equipment line inputs, and keyboards, guitars and
basses will use the equipment front panel instrument inputs).
The input selector switch is at the top left of the equipment front panel. Through it, you
can select the relevant input source. ‘Mic 48V’ is necessary for condenser type
microphones that require 48V phantom power. When using dynamic and ribbon type
microphones the ‘Mic’ position only should be selected. Take care not to select the Mic
48V position when using such microphones as the 48 Volt feed could harm the
microphone probably. The equipment will route the microphone signal to both the left and
right output channels. If a mono instrument (or mono line level source) is connected to the
left input (marked 1/mono) the signal will be routed to both left and right channels.
Connecting a mono signal to the right input will send the signal to the right hand output
only. Nowadays, it is a common technique recording direct to the multitrack recorder (thus
bypassing the console), it can keep the signal path shorter, and get the highest quality.
5
2) Insert points allow processors such as dynamics devices and EQs to be patched
in-line into the mixer signal path. Insert points are generally provided on a single TRS
stereo jack socket, wired so that one of the pins is a ‘send’, one is a ‘return’ and the third
pin is the earth. A special cable (called an ‘insert’ or ‘Y’ cable) is required to then patch in
and out of the equipment – this cable will have a stereo jack at one end (the end that
connects to the mixer) and two mono jacks at the other end (the end that connects to the
equipment). Of the two mono jacks, one will be a ‘send’ that connects to the equipment
line input, and the other will be a ‘return’ that connects to the equipment line output. This
way the signal path is routed out of the mixer, through the equipment and back again, and
this is a whole signal path.
After the preamp stage, the channel insert point routes the channel signal out and then
directly back into the desk. This insert point send/return facility is usually before the EQ
section on the desk (‘pre EQ’), but some mixers allow for optional pre or post EQ insert
points. They both send and return signals from the mixer but are different in application
essentially. The auxiliary sends will split the channel signal, allowing it pass through the
channel unaffected as well as being fed out to an effects device, allowing the original and
processed signals to be mixed together to taste. This method is designed for processes
such as reverb, echo and modulation effects.
Insert points is typical to patch in dynamics processors/EQs rather than effects
processors. It is because the entire channel signal would need to be processed by a
compressor/EQ and then returned back to the mixer, thus ensuring that the whole signal is
processed.
Group insert points are used to compress sub-grouped signals. It’s common for an
engineer to mix an entire drum kit or a number of tracks of backing vocals to a stereo
group and then use a pair of group faders to control their overall level. In this way, the
engineer needn’t to adjust each individual drum level. If you wish to compress the overall
stereo kit signal, you can connect the equipment to the relevant group insert points, using
the same ‘send and return’ technique as the channel insert.
You can compress individual tracks when recording. It’s common to apply compression
to the stereo mix while mastering it to 2-track tape, DAT or CD. Doing this will help you
fatten the sound further and control levels. As the channel and groups, the stereo L/R mix
buss will have a pair of insert points to facilitate this normally. If not, the equipment can be
connected ‘in-line’ with the mixer’s main stereo outputs, ahead of the master 2-track
recorder. Using master insert points allows the equipment to be monitored by the mixing
desk’s control room outputs, but to monitor it when using it ‘in-line’ mode, it is normal to
put the 2-track recorder in ‘record’ or ‘record ready’ mode, and have the outputs of the
recorder feeding back into the 2-track return inputs of the mixer. A mixer usually has a
2-track monitor option where you can listen to the output of the 2-track recorder.
6
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4.2 In Use.
If you have connected the equipment, it’s time to use it. Here’s a simple step-by-step
guide:
1)
Firstly, set up the gains of the unit. Start with the Input and Output Gains and Gain
Make-Up at 0dB, meanwhile the compressor switched out.
2)
Secondly, with the Meter set to read ‘Output’, adjust the Input Gain to achieve a peak
reading of around 0VU with the chosen source material.
3)
If more output is required, you should then adjust the Output Level control accordingly.
Now depress the Compressor ‘On’ switch, and depress the Meter switch to read
‘Gain Reduction’.
4)
Now, the meter should register that some gain reduction is taking place. If not, or you
wish more gain reduction to occur, increase the setting of the Input Gain control.
5)
You should notice that the output level is reduced when gain reduction is taking place.
By toggling the Compressor On switch you can compare the levels and the subjective
sound quality of the original and compressed signals. With the Compressor active,
use the Gain Make-Up control to set the level so that when disabling the compressor,
there is no level drop. In this way, You can distinguish the signals without the levels
changing.
6)
Start with the Threshold at +10dB, Ratio at 1:3, Attack and Release at ‘Fast’, and
Knee at ‘Soft’.
7)
Turn the Threshold clockwise towards -20dB gradually while continuing to meter gain
reduction. When you do this you’ll notice that compression will start to take place and
the meter will start to register some gain reduction. The further towards -20dB you
move, the greater the gain reduction occurs.
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5. OPERATION
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5.1 Compression Introduction
Compression can replace manual control, it’s more sensitive and convenient. In
addition, there are other benefits of compression that it can be applied properly. Adding
punch and excitement to music is not the only benefit, it can also fatten up sounds and
creating a more professional sounding recording. With the equipment, you have the
added benefit of valve stages in the signal path, which create a warmth and presence.
Valve compression yields a particularly special sound, it is popular to use in audio flied,
particularly with the widespread use of digital products. The reason valve equipment
sounds special is due to two things: natural compression and harmonic distortion. Valves
will tend to naturally compress an audio signal, particularly as the signal level is
increased. This itself contributes to the warmth produced by the equipment. Secondly,
when the signal through a valve is increased, it tends to generate a particular type of
subtle and desirable distortion, called “second harmonic” distortion. This has the effect of
thickening and warming the sound, and the more the level you feed to the valve stages,
the more of this harmonic distortion will be produced. You could hear this effect when you
increase the Input Gain on the equipment.
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5.2 Input Source Selection.
The input source and phantom power selection are controlled on a four position rotary
switch. The selections are:
MIC +48V: For condenser mics that require 48V phantom power
MIC: For most dynamic or ribbon mics
LINE: Line inputs
INST: Front panel Instrument inputs
CAUTION: Please connect a microphone you need before phantom power applied. Do
not connect or separate mic and equipment when phantom power applied. Furthermore,
Adjust the Monitor/speaker for silent state before phantom power applied. Please wait for
about one minute after phantom power applied, then regulate the output amplify, to
ensure the system can be stable before this.
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5.3 Mic Gain.
The Mic Gain control sets the level of the microphone input signal prior to the Input
Gain control. There are 4-switched level positions: -20, 0, +20 and +40dB, with a further
+/- 20dB available on the Input Gain control.
For normal operation it is recommended to keep the Mic Gain setting at the +40dB
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position, with any fine adjustments to the input signal level made by either boosting or
reducing the Input Gain control. Keeping the Mic Gain at its maximum setting (+40dB)
can help to keep the noise figures as low as possible. In extreme cases, high-level signal
sources such as close-mic’d drums, it may be necessary to reduce the Mic Gain position
to prevent input overload.
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5.4 Input Gain.
The Input Gain control sets the level of the signal fed to the input stage of the
compressor, and is variable between -20dB and +20dB. This allows a wide range of
signals to be fed into the equipment, and also allows the valve stages to be driven to a
variable degree. Each channel of the equipment has a triode valve stage positioned
between the input circuit and the compression stage.
Increasing the input gain pushes more signal level into the valve, thus generating more
harmonic distortion and creating that special “valve sound”. At the same time the output
level can be turned down to preserve the same level at the outputs, so a choice of sounds
is available. For a more pronounced valve sound, turn up the input gain and reduce the
output gain, and vice versa for a cleaner sound.
Increasing the Input Gain control setting will tend to push the signal towards and
possibly over the compression threshold setting, so this control will have a pronounced
effect on the amount of compression taking place.
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5.5 90 Hz Low Cut Filter.
The low cut (high pass) filter switch restricts the low frequency response of the preamp,
to remove rumble or LF noise from the signal effectively. The filter is useful in restricting
“popping” on vocals or even low frequencies caused by contact with microphone stands or
microphone cables.
Popping is an undesirable thump that is caused by close-miking certain spoken or sung
letters, such as “P” or “B”. These particular letters cause a sudden expulsion of air that
result in an audible thump. As this thump has a lot of low frequency content the high pass
filter can help to reduce the problem, as using a bop cover suspended in front of the
microphone. The 90Hz filter is active on mic, line and instrument inputs.
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5.6 Drive and Peak LEDs.
The yellow Drive LED provides a visual indication of the signal level through the valve
stages, and therefore the extent of “warming” or valve character being showed. The Drive
LED will illuminate gradually when the input level or gain is increased, over the range 8dB
to +18dB.
The red Peak LED operates as a conventional warning that clipping is about to occur.
The operating level of the entire signal chain is monitored, and the LED illuminates when
9
there is less than 6dB of headroom remaining. Normal operation would be to set the input
gain so that the Drive LED is illuminating regularly, with occasional lighting of the Peak
LED on transients.
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5.7 Threshold.
The equipment functions by reducing the gain of the signal when it rises above a certain
level, known as the Threshold. Any signal below the threshold passes through the unit
unaffected. The equipment has a variable Threshold control, adjustable between +10dBu
and -20dBu.
The Threshold control on the equipment starts at a ‘plus’ value in the counter-clockwise
position, and decreases to a ‘minus’ value as you rotate the control clockwise. The reason
for this is as you turn the Threshold control on the equipment clockwise then the degree of
compression will increase.
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5.8 Ratio.
Once the input signal has crossed the threshold, the degree of gain reduction is
determined by the Ratio control. The Ratio control is calibrated in dBs and is simply the
change in output level that results from a given change in input level. An uncompressed
signal will have a 1:1 compression ratio - every 1dB change in input level results in the
same 1dB change in output level. For instance, a compression ratio of 1:3 means that a
3dB change in input level will only give a 1dB change in output level. For more severe
compression, turn up the Ratio control simply.
The equipment offers a wide range of ratios from 1:1.5 (gentle compression) through to
1:30 (limiting). Limiting effectively clamps the input signal at the threshold level no matter
how much the signal is increased: this can be useful when trying to ensure that the signal
doesn’t exceed a certain level, for instance, to prevent a digital recorder distorting through
overload.
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5.9 Attack and Release.
The Attack and Release switches are used to control how fast the compressor reacts
to the audio signal. The Attack switch governs how quickly the equipment acts to
compress the signal once it has risen above the threshold, while the Release switch
controls how quickly the signal returns to normal once it has dropped back below the
threshold level.
The Attack time of the equipment is switchable between 0.5mS (‘Fast’) and 5mS
(‘Slow’). At 0.5mS attack, the compressor is fast enough to compress a 1kHz signal in less
than half a cycle, effectively preventing the overload of any following equipment which has
limited headroom, such as a digital processor, tape machine or transmitter. Fast attack
times are used to compress a signal quickly, so are suitable for audio signals with sharper
10
transients such as drums. However, if you want the initial leading edge of the signal
retained (for instance the initial click of a bass guitar or bass drum) then a slower attack
time can be employed, and slow attack times can also be useful on sustained sounds like
synth pads.
The Release time of the equipment is switchable between 0.2S (‘Fast’) and 1.5S
(‘Slow’). The Release setting is important, because if it is too short, the compressor gain
recovers too quickly with the result that there is an audible ‘pumping’, ‘breathing’, and
sometimes low frequency distortion. Try to use a slow release time in these cases.
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5.10 Gain Make Up.
The Gain Make-Up control is positioned at the output of the compressor stage, and
allows the signal level to be brought back to the same loudness as the uncompressed
signal.
While the subjective sound quality of the signal can be improved by compression, the
overall signal level will be reduced when gain reduction is taking place. The Gain Make Up
control is designed to boost the compressed signal by between 0 and +20dB, in order to
bring back the level to the same loudness as the uncompressed signal. Without this
control, comparing the original and compressed signals becomes difficult, since there
would be a level drop each time the compressor is switched in: therefore it is normal to
adjust the Gain Make Up control so that when the ‘compressor on’ switch is activated, the
audio signal remains constant in level.
The Gain Make Up control is different from the Output Level control. It can active only
when the ‘compressor on’ switch is engaged. Once the Gain Make Up has been adjusted,
use the Output Level control to set the overall output level of the equipment.
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5.11 Knee.
The Knee switch controls the shape of the equipment compression curve. In “Soft
Knee” mode, the response curve of the compressor around the threshold is gentle, so
that the compression effect is more subtle and musical. In “Hard Knee” mode, the curve
is more severe, so that signals above the threshold are “squashed” more aggressively. It
causes the full compression ratio to be applied immediately the signal has passed the
threshold point. This yields a more audible and pronounced compression effect.
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5.12 Compressor On.
“Compressor On” enables or disables the compressor stage, thus allowing we making a
comparison between the original untreated signal and the compressed signal. An
associated status LED indicates when the compressor is active.
11
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5.13 Output Gain.
This controls the level at the equipment outputs, and is variable between -∞ and +15dB.
This control acts like an output fader effectively, and is very useful when recording direct
to tape or hard disc through the equipment. You may find that some digital recorders
require a good deal of input level in order to register a 0dB reading on their meters. This is
normal, since many digital recorders are designed to preserve headroom and keep the
signal well below the 0dB clip point - thus preventing the recorder distorting. The
equipment provides ample gain to drive digital recorders, but you may find the Output
Gain control has to be set to higher levels because of it.
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5.14 Meter.
The equipment is equipped with an illuminated VU meter. The Meter switch enables the
equipment’s VU meter to monitor one of two parameters. The normal mode allows the
meter to read the audio output level, and is calibrated to read 0VU when a +4dBu signal is
produced at the balanced line outputs of the equipment. Your dealer if required may adjust
the reference point internally.
Increasing the Output Level control on the equipment towards the +15dB setting will
cause the equipment’s meter to move further towards the red area and possibly to the end
of the scale if sufficient gain is applied.
The meter may be switched to indicate the amount of compression occurring by
selecting the ‘G/R’ setting. If the signal is below the threshold, the meter will indicate 0dB:
i.e. no gain reduction. As the signal passes through the threshold, the meter will start to
indicate the gain reduction at the compressor stage. Note that this reading won’t include
any extra gain make-up applied.
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5.15 Meter ‘+10dB’.
Sometimes the output level of the equipment may need to be set to a relatively high
level, particularly when driving a digital recorder. The Meter ‘+10dB’ setting reduces the
normal meter reading by 10dB so that high output levels can be generated without the VU
needle pressing constantly at its end stop. This doesn’t affect the actual output level, but
only the metered reading. This setting also has no effect when the G/R switch is engaged
and the meter is reading the amount of gain reduction.
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6. SERVICE
If you want to require service of the equipment, you must take it or post it to an
authorized dealer with a description of the fault. When claiming service under warranty,
proof of purchase date must be included with the equipment for repair. Please retain the
original packing for possible future use, and ensure that the unit is protected suitably
during transit. The manufacturer cannot accept responsibility for damage caused during
transportation.
The equipment is supported by a limited warranty for a period of one year from the date
of purchase. During this period, any faults due to defective materials or workmanship will
be repaired free of charge. The warranty excludes damage caused by deliberate or
accidental misuse, tampering, operation on the incorrect mains voltage, or without the
correct type and value of fuse fitted. It is the user’s responsibility to ensure fitness for
purpose in any particular application.
The warranty is limited to the original purchase price of the equipment, and excludes
any consequential damage or loss.
Please record the following details, and retain proof of purchase:
Serial Number................................................................................
Region / Country............................................................................
Date purchased..............................................................................
Dealer.............................................................................................
User name......................................................................................
Tel...................................................................................................
Address...........................................................................................
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