ART PRO CHANNEL User Manual
Pro Channel
TUBE MIC PREAMP / COMPRESSOR / EQUALIZER
USER’S GUIDE
Contents
FEATURES......................................................................... 5
OVERVIEW ........................................................................ 6
HY USE AN EXTERNAL PROCESSING CHANNEL? ...............................6
W
D
ESIGN NOTES..................................................................................6
SETTING UP ...................................................................... 7
U
NPACKING ......................................................................................7
AC P
A
OWER HOOKUP.........................................................................7
UDIO CONNECTIONS........................................................................7
INSTALLATION ...................................................................................8
S
AFETY PRECAUTIONS ......................................................................8
P
OWERING UP...................................................................................8
FRONT PANEL CONTROLS AND INDICATORS ................. 9
P
REAMP CIRCUIT...............................................................................9
Gain Control.............................................................................................9
Gain Switch..............................................................................................9
Phantom Switch .......................................................................................9
Phase Switch .........................................................................................10
Tube Drive/Gain Reduction Display....................................................... 10
Preamp Output Control ..........................................................................10
COMPRESSOR CIRCUIT ....................................................................11
Threshold Control ..................................................................................11
Ratio Control..........................................................................................11
Attack Switch .........................................................................................12
Release Switch ......................................................................................12
Type Switch ...........................................................................................12
Comp Bypass Switch .............................................................................12
Compressor Output Control ...................................................................12
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CLIP INDICATOR.............................................................................. 13
E
QUALIZER CIRCUIT........................................................................ 13
Low Control ........................................................................................... 13
Low Switch ............................................................................................ 13
Lo-Mid Control ....................................................................................... 14
Lo-Mid (X 10/Norm) Switch ................................................................... 14
Lo-Mid (Narrow/Wide) Switch................................................................ 14
Hi-Mid Control........................................................................................ 14
Hi-Mid (X 10/Norm) Switch .................................................................... 14
Hi-Mid (Narrow/Wide) Switch ................................................................ 14
High Control........................................................................................... 15
High Switch............................................................................................ 15
EQ Byp Switch....................................................................................... 15
MASTER CONTROLS........................................................................ 16
Master Output Control ........................................................................... 16
VU Meter ............................................................................................... 16
VU Meter Switches ................................................................................ 16
Power .................................................................................................... 16
REAR PANEL CONNECTIONS ..........................................17
NPUT AND OUTPUT CONNECTIONS.................................................. 17
I
Input....................................................................................................... 17
Output.................................................................................................... 17
XLR GND Switch ................................................................................... 17
LOOP INSERTS................................................................................ 17
Preamp - Compressor Loop .................................................................. 18
Compressor - EQ Loop.......................................................................... 18
Loop Connection Examples................................................................... 18
APPLICATIONS ................................................................19
EQ T
IPS ......................................................................................... 19
What is the best way to use EQ? .......................................................... 20
SPECIAL EFFECTS .......................................................................... 21
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GROUNDING ....................................................................................21
TUBE REPLACEMENT ..................................................... 21
WE’RE ON-LINE! .............................................................. 22
WARRANTY AND SERVICE INFORMATION .................... 22
IMITED WARRANTY ........................................................................22
L
SERVICE .........................................................................................22
BLOCK DIAGRAM ............................................................ 24
A R T PRO CHANNEL SPECIFICATIONS ......................... 25
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Features
The Pro Channel is a unique product. It contains three independent, award-winning
circuit designs: one of the finest tube microphone preamplifiers available, one of the
finest optical tube compressors available, and one of the most flexible EQs you’ve ever
used. Developed in partnership with studio and live sound engineers, the Pro Channel
possesses a “sound” that is not available from any other product on the market – at any
price! The Pro Channel was designed and constructed with the best components,
assuring a lifetime of quiet, reliable performance. The Pro Channel offers the following:
• The award winning A R T “SOUND”!
• Very low-noise, tube-based mic/line preamplification with discreet, Class-A solid-
state input circuitry
• Both electro-optical and tube compressor designs
• Tube-based, semi-parametric, four-band equalization with selectable frequency ranges
and Q
• Three hand-selected tubes
• VCA-less compressor circuitry (i.e., transparent dynamics control)
• Unique tube character and gain reduction LED metering
• Large 3” analog VU metering to monitor Output and Send points
• Bypassable compression and equalization circuitry
• XLR balanced inputs and outputs
• ¼” TS unbalanced inputs and outputs
• A rugged steel and aluminum chassis
• ¼” unbalanced insert points between the preamp and compressor and between the
compressor and equalizer
• +48V phantom power
• Phase reversal
• Detented rotary controls
• Variable threshold and compression ratios
• Selectable attack and release time settings
• >90dB of dynamic range
• An internal power supply
• A five year warranty
• Designed in the USA
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Overview
Why use an external processing channel?
The best way to get a signal to tape is by using the shortest signal path. In most cases,
the shortest path is as follows: mic to preamp to compressor to EQ to tape. (The signal
doesn’t even go through a mixer!) This isn’t a new concept, but it has become more
relevant with the availability of affordable mixing consoles.
As their name implies, most affordable mixers are optimized for signal routing and
general level mixing. However, they are not necessarily your best option for the actual
recording of tracks. The simple truth is that the Pro Channel has a better sounding and
more flexible collection of circuits. Mixer manufacturers need to make tradeoffs
between price and performance. Imagine the price of your mixer if each channel’s EQ
cost over $200 (we’re not talking to those of you who have a $250,000+ console)! For
those of us on a budget, it just doesn’t make sense to spend a ton of money on a
“Cadillac” console when a budget mixer and a few pieces of external gear is more cost
effective. Even those engineers who regularly work on “big” consoles use external EQs,
compressors, and preamps!
The goal of any recording is to get the sounds right before you commit them to tape.
The Pro Channel helps you get it right so you don’t have to “fix it in the mix.”
Design Notes
The Pro Channel is a multi-purpose tool for audio engineering and recording. Enclosed
in a two rack space (2U) chassis are three independent circuits featuring a tube-based
analog preamplifier, a VCA-less compressor (selectable between optical or tube control
elements), and a semi-parametric, tube-based equalizer.
The Pro Channel is designed to work seamlessly with any recording, soundreinforcement, or electronic instrument setup. A R T’s Pro Channel circuitry is a hybrid
design utilizing the most advanced solid-state and tube technology. With a
transformerless power supply, the Pro Channel maintains exceptional signal integrity
and extremely low noise.
Signal flow within the Pro Channel is from the preamp, to the compressor, to the
equalizer (although you can change the order of the circuits by utilizing the insert
points). While the preamp is always active, the compressor and equalizer may be
individually bypassed. The preamplifier’s active, balanced, solid-state input provides
extremely low noise and excellent CMRR (Common Mode Rejection Ratio).
The ¼” input has a high impedance, which prevents the loading of any device connected
to it and makes the Pro Channel perfect for DI or line level applications. The
preamplifier’s second stage 12AX7a tube runs on a regulated DC voltage, providing an
additional 20dB of gain. Our design enables the tube to overload before the input or
output stage, allowing you to manipulate the tube gain to meet different sonic criteria.
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The compression circuit features a VCA-less design and utilizes either optical
(Vactrol®) or tube, dual triode electronics for superior musical performance. The
compressor is soft knee by design. Although it is capable of providing a thoroughly
“squashed” signal, it was designed to excel in areas where transparent and musical
dynamics control is desired. The beauty of the optical design is its ability to apply heavy
amounts of compression without pumping and breathing like VCA-based compressors.
The tube compressor is capable of smoothly compressing fast-rising signal sources
without undue side effects. In most cases you will hear the results of the compression
without hearing the compressor.
The tube-based equalizer was designed to help “fix” the instruments that give us
headaches when recording (i.e., kick, snare, bass, toms, guitar amps, voice, etc.). The
two sweepable parametric bands and selectable shelving bands have been optimized for
musical instruments. The two sweepable bands overlap each other as well as the high
and low shelving bands, providing you with the ultimate in flexibility. This EQ design
gives you all the control you need to effectively dial in great sounds from even the
poorest of sources.
Setting Up
Unpacking
Your Pro Channel was packed with care at the factory. The shipping carton was
designed to protect the unit during initial shipment. Please retain this carton for use in
transporting the Pro Channel, or in the unlikely event that you need to return your unit
for servicing.
AC Power Hookup
The Pro Channel has an internal power supply designed to operate at 100 to 125VAC,
50 to 60Hz. Units manufactured for use outside of the United States have been modified
to comply with the required electrical specifications. Under no circumstances should the
power cable be altered. If the cable becomes cut or damaged, discontinue use and have
it replaced before operating.
Audio Connections
Audio connections to and from the Pro Channel are balanced XLR (Pin 2 = Hot (+), Pin
3 = Cold (-), Pin 1 = Ground) and unbalanced ¼” (Tip = Hot (+), Sleeve = Ground).
The insert points between the preamp and compressor and the compressor and equalizer
are unbalanced ¼” (Tip = Hot (+), Sleeve = Ground) connectors.
We recommend using only high-quality cables and connectors.
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Installation
The Pro Channel may be employed in a number of setups, including:
• between a microphone and a digital recorder, mixer, or analog recorder;
• in a mixer’s channel insert points;
• between a microphone and signal processors; and
• between electronic musical instruments (synthesizers, guitars, basses, samplers,
acoustic instruments with pickups, etc.) and other gear.
Safety Precautions
WARNING: To avoid the risk of shock or fire, do not expose this unit to moisture. Do
not remove metal panels or chassis parts. Removing any chassis parts exposes
dangerous high voltages. There are no user-serviceable parts inside. Refer all servicing
to qualified personnel.
If your power cord becomes damaged, always replace it with the same type as originally
equipped. Since the cord is detachable, it is possible to replace it with a cord configured
for the wrong voltage. Always refer to the unit’s rear panel to determine the correct
supply voltage, and then choose an appropriate cord.
Powering Up
When the power switch is turned on, the VU meter illuminates. It is important to
remember to turn the Pro Channel on before any monitoring levels or power amps are
turned on. The Pro Channel has the ability to add over 80dB of gain to its input signal
and can cause the unit to produce a “thump” on power up and power down.
Like all tube-based equipment, the Pro Channel needs to warm up before being used.
Allow one to two minutes for the tubes to reach their proper operating temperature. If
the Pro Channel fails to power up when the power switch is turned on, check to see that
its power cord is plugged into an active outlet. If the unit still fails to operate properly,
turn it off and unplug it, and then consult your dealer or A R T’s Customer Service
department.
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