AC-AUDIO Tube G32 User manual

CONTENTS
1. OVERVIEW.............................................................................................................................1
2. 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
3. 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 Nominal Operating Level........................................................................................4
4. GETTING STARTED.............................................................................................................5
5. OPERATION...........................................................................................................................6
-5.1 Input Source Selection............................................................................................6
-5.2 Mic Gain....................................................................................................................6
-5.3 Input Gain.................................................................................................................6
-5.4 90 Hz Low Cut Filter................................................................................................7
-5.5 Drive and Peak LEDs..............................................................................................7
-5.6 Output Gain..............................................................................................................8
-5.7 Meter..........................................................................................................................8
-5.8 Meter ‘+10dB’...........................................................................................................8
6. SERVICE.................................................................................................................................9

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1.OVERVIEW
Welcome to purchase the equipment byAC-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. Two illuminated VU meters monitors the both channels for output level.
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. ADrive 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.

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2. BEFORE YOU START
-2.1 Utilizing the User Manual
lBe sure to read the Safety Precautions before using the product.
lRefer to the INSTALLATION when installing your product.
lYou can easily find any information you are looking for by the CONTENTS.
lUsing the SPECIFICATIONS, you can easily find detailed parameters of the product.
lPlease 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:
lThis equipment must be earthed.
lAll mains wiring should be installed and checked by a qualified electrician with all
power switched off.
lDo not locate it where it will be subject to external heating.
lDo not expose to rain or moisture, as this may present an electric shock hazard.
lEnsure the correct operating voltage is indicated on the rear panel before
connecting to the mains supply.
lNever operate the unit with any cover removed.
lReplace the fuse with the correct type and rating only.
-2.3 FIG 1: FRONT PANEL
-2.4 FIG 2: REAR PANEL

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3. INSTALLATION
-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.
-3.2 Microphone Input.
The microphone input is a via 3 pin female XLR connector, compatible for balanced
microphones.
The mating connector should be wired appropriately as the following way:
Balanced inputs:
lPin 1 = Ground (screen).
lPin 2 = Signal Phase (also known as “+” or “hot”).
lPin 3 = Signal Non-Phase (“-” or “cold”).
-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:
lScreen = Ground,
lTip = Signal Phase (“+” or “hot”),
lRing = Signal Non-Phase (“-” or “cold”).
Unbalanced inputs:
lScreen = Ground,

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lTip = Signal Phase (“+” or “hot”),
lRing = Ground.
The equipment utilizes good quality screened cable, particularly for microphone or low
level sources, So that hum or noise cannot be picked up.
Refer to Figure 2 for rear panel connector identification.
-3.4 Instrument Inputs.
On the front panel, each channel has a high impedance (1Mohm) 0.25” instrument
jack socket (see Figure 1).A2 pin (mono) jack plug is required, which should be wired as
the following way:
- Tip = Signal Phase (“+” or “hot”),
- Screen = Ground.
-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.
-3.6 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.

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4. GETTING STARTED
Connected ahead of the line inputs of a mixing desk/recording device:
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.

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5.OPERATION
-5.1 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.
-5.2 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
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.
-5.3 Input Gain.
The Input Gain control sets the level of the signal 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.

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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.
-5.4 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.
-5.5 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
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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-5.6 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.
-5.7 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.
-5.8 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...........................................................................................