Art Project Series User manual

Tube MP/C
Tube Preamp/Opto Compressor-Limiter/DI
Project Series
User’s Manual

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IMPORTANT SAFETY INSTRUCTIONS – READ FIRST
This symbol, wherever it appears, This symbol, wherever it appears, alerts
alerts you to the presence of uninsulated you to important operating and maintenance
dangerous voltage inside the enclosure. Voltage instructions in the accompanying literature.
that may be sufficient to constitute a risk of shock. Please read manual.
Read instructions:
Retain these safety and operating instructions for future reference. Heed all warnings printed here and on the equipment. Follow the operating
instructions printed in this user guide.
Do not open:
Aside from two vacuum tubes, there are no user serviceable parts inside. Refer any service work to qualified technical personnel only.
Power sources:
Only connect the unit to mains power of the type marked on the rear panel. The power source must provide a good ground connection.
Power cord:
Use the power cord with the mains plug appropriate for your local mains supply as provided with the equipment. If the provided plug does not fit into
your outlet consult your service agent. Route the power cord so that it is not likely to be walked on, stretched or pinched by items placed upon or
against.
Grounding:
Do not defeat the grounding and polarization means of the power cord plug. Do not remove or tamper with the ground connection on the power cord.
Ventilation:
Do not position the unit where the air required for ventilation is impeded. If the unit is to be operated in a rack, case or other furniture, ensure that it is
constructed to allow adequate ventilation.
Moisture:
To reduce the risk of fire or electrical shock do not expose the unit to rain, moisture or use in damp or wet conditions. Do not place a container of
liquid on it, which may spill into any openings.
Heat:
Do not locate the unit in a place close to excessive heat or direct sunlight, as this could be a fire hazard. Locate the unit away from any equipment,
which produces heat such as: power supplies, power amplifiers and heaters.
Environment:
Protect from excessive dirt, dust, heat, and vibration when operating and storing. Avoid tobacco ash, drink spillage and smoke, especially that
associated with smoke machines.
Handling:
To prevent damage to the controls and cosmetics avoid rough handling and excessive vibration. Protect the controls from damage during transit. Use
adequate padding if you need to ship the unit. To avoid injury to yourself or damage to the equipment take care when lifting, moving or carrying the
unit.
Servicing:
Switch off the equipment and unplug the power cord immediately if it is exposed to moisture, spilled liquid, objects fallen into opening, or the power
cord or plug becomes damaged during a lightning storm or if smoke odor or noise is noted. Refer servicing to qualified technical personnel only.
Installation:
Install the unit in accordance with the instructions printed in the user guide.

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INTRODUCTION
Thank you for purchasing Applied Research and Technology’s Tube MP/C. You’ve undoubtedly noticed that the
Tube MP/C is as cool sounding as it looks. After getting familiar with the Tube MP/C, you’ll realize what a great
investment you’ve just made. The Tube MP/C may be used everywhere! Anywhere you need level adjustments
(gain or attenuation), and anywhere you need compression - you’ll be using the Tube MP/C. Offering a superb
level of sound quality, the Tube MP/C will enhance the sonic textures of your audio system for years to come.
The Tube MP/C is a unique product. It contains two independent award-winning circuit designs - one of the finest
tube microphone preamplifiers available and one of the finest optical tube compressors available. Developed in
partnership with studio and live sound engineers, the Tube MP/C possesses a “sound” that is not available from
any other product on the market - at any price! The Tube MP/C was designed and constructed with the best
components, assuring a lifetime of quiet, reliable performance.
The Tube MP/C offers:
The award-winning A R T “SOUND”!
Tube-based mic/line preamplifier with up to 70 dB of gain
Hand-selected 12AX7a tube
Optical (VCA-less) compressor circuitry = transparent dynamics control
Bypassable compression circuitry
¼-inch TS unbalanced inputs and outputs
XLR balanced inputs and outputs
Transformer isolated XLR output
Selectable output range for Line/Instrument interface levels
LED meters for Tube Warmth, Gain Reduction and Output level
+48V phantom power
Phase reversal switch
Selectable release time settings
>90dB dynamic range
Universal power supply
Custom extruded aluminum chassis

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OVERVIEW
The Tube MP/C (Preamplifier/Compressor) is a multi-purpose tool for audio engineering and recording. Enclosed
in a table-top chassis are two independent circuits featuring a tube-based analog preamplifier and a VCA-less
compressor with optical gain reduction control. Used as a mic/line preamp or as a DI (direct) box, the Tube MP/C
is designed to work seamlessly with any recording, sound-reinforcement, or electronic instrument setup. A R T’s
Tube MP/C circuitry is a hybrid design utilizing the latest, most advanced, solid-state and tube technology. The
Tube MP/C maintains exceptional signal integrity and extremely low noise. A tube based opto-compressor circuit
follows the tube preamp. While the preamp is always active, the compressor may be bypassed. The
preamplifier’s active balanced solid-state input provides extremely low noise and excellent CMRR. The 1/4” input
has a high impedance, which prevents the loading of any device connected to it and makes the Tube MP/C
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 causes the tube to overload before the input or output
stage. This allows you to manipulate the tube gain to meet different sonic requirements. The compression circuit
features a VCA-less design and utilizes optical electronics (Vactrol) coupled with a 12AX7a vacuum tube gain
stage for superior musical performance. The compressor is soft knee by design. Although it is capable of
providing a thoroughly “squashed” signal in "Limit" mode, it was designed to excel in areas where transparent
and musical dynamics control is desired. The beauty of the optical/tube design is its ability to apply heavy
amounts of compression without pumping and breathing like VCA-based compressors. In many cases you will
hear the results of the compression without hearing the compressor.
SETTING UP
Unpacking
Your Tube MP/C was packed with care at the factory. The shipping carton was designed to protect it during initial
shipment. Please retain this carton for use in transporting the Tube MP/C, or in the unlikely event that you need
to return your Tube MP/C for servicing.

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AC Power Hook Up
The Tube MP/C has a universal external power supply designed to operate at 100 to 240V AC ~ 50/60
Hz. Only use the adapter that came with the Tube MP/C. If the adapter becomes lost or damaged,
contact ART Customer Service for replacement. If you need to purchase one locally, please refer to the
label on the adapter or the specifications later in this manual for the appropriate power specifications.
Setting Up the Universal power supply
Insert the correct clip adapter to the supply according to country of operation. There are four different
clips included. Please attach the matching clip as per your AC power source.
Insert the supplied 12V DC adapter’s plug into the input labeled 12V DC. Always make sure the output
plug is securely plugged into the rear of the TUBE MP/C, and that the adapter is held firmly in an
electrical outlet. Never operate the TUBE MP/C or power adapter in the rain or in wet locations. lf the
adapter’s cord is ever cut, discontinue use and replace the adapter with a new one. Unplug the adapter
when the TUBE MP/C is not in use.

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Audio Connections
Audio connections to and from the Tube MP/C are balanced XLR (Pin 2 Hot (+), Pin 3 Cold (-), Pin 1 Ground)
and unbalanced ¼-inch (Tip Hot (+), Sleeve Ground.) We recommend using only high-quality cables equipped
with the appropriate connectors.
Installation
The Tube MP/C may be employed in a number of setups including:
Between a microphone and a mixer, digital workstation, or analog recorder.
In a mixer’s channel insert points.
Between a microphone and signal processors.
Between electronic musical instruments (synthesizers, guitars, bass, samplers, acoustic instruments
with pickups) and other gear.
The XLR output is transformer isolated allowing you to connect the outputs to two different systems without
creating ground loop noise.
Powering Up
When the rear panel power switch is turned on, the power indicator LED will illuminate. It is important to
remember to turn the Tube MP/C on before any monitoring levels or power amps are turned on. The Tube MP/C
has the ability to add over 60dB of gain to its input signal. This can cause the Tube MP/C to produce a “thump”
on power up and power down. Note: Like all tube-based equipment, the Tube MP/C needs to warm up before
being used. Allow one to two minutes for the tubes to reach proper operating temperature before using.

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FRONT PANEL CONTROLS & INDICATORS
Figure 1 - Front view
GAIN control
The Gain control sets the amount of input gain of the Tube MP/C. Turn the control clockwise to increase gain
and counterclockwise to decrease gain. Selection of the gain range is made with the +20dB gain switch. You
may control two ranges of gain with this control, +20 to +60dB and +0 to +40dB. When setting the Gain control,
refer to the four segment Tube Drive display for a visual reference to the Tube MP/C’s internal signal levels
(applied gain). Hint: the “sweet” spot for the Tube MP/C is when the second warm LED in the Tube Drive array
is lit.
GAIN switch
Use the Gain switch to set the range of the Gain control. When the switch is in the out (0db) position the gain
range is +0 to +40dB. Depressing the switch adds 20dB of gain. With the switch in, the gain range is +20 to
+60dB. With most microphone applications you’ll find using the Tube MP/C with the +20dB gain switch in is
needed. Use the setting that best fits your application.
LOW CUT switch
The LOW-CUT switch rolls off the response to signals lower than 70Hz. This helps to cut out low frequency
rumble, wind noise, and all types of very low frequency energy before it is amplified. When recording, this allows
you to get more gain before clipping the preamp, recorder, or computer and in a live situation you get more gain
before clipping your amp.
TUBE DRIVE display
Four LEDs display how the tube gain is affecting the input signal. These LEDs are calibrated with the tube
circuitry to give you an accurate representation of the tube’s output signal (Note: these LEDs measure the signal
level before the output level control). Use this meter as a visual aid for setting the Gain level. The first LED is
labeled “CLEAN”. The tube is producing a clean output when this LED is lit. The next two LEDs are labeled
“WARM.” This is the optimal operating range for the Tube MP/C. At this level, the tube is producing an output
signal which most would term “warm” (Whatever you would like to call it is fine - simmering, toasty, etc.) You’ll
find the output signal has an enhanced bottom to low mid quality with smooth high frequency detail. The last

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LED is labeled “Clip.” This LED will light approximately 6dB before audible distortion occurs. If this light flickers,
do not panic. The unique design of the Tube MP/C allows the tube to distort well before any other gain stage.
When a tube goes into distortion it is a gradual process and tends to sound pleasing for a range before it turns
into a distortion box. After some use, you’ll find the “sweet spot” of the Tube MP/C is with this light flashing fairly
regularly. You may find a “clipped” level is suitable for some applications. Note: Use the Tube Character display
to aid in setting the Gain Control.
THRESHOLD control
The Threshold control sets the point at which the compressor circuit will act on the input signal. Turning this
control counterclockwise lowers the threshold (adding more compression to a signal). Turning this control
clockwise raises the threshold. Setting the Threshold control is dependent on the Gain control. The easiest way
to set the Threshold control is to start with the control fully clockwise. After setting the Gain control, slowly turn
the Threshold control counter-clockwise (lowering the threshold) until you see the yellow (0dB) Threshold LED
light. Now adjust the control (either lower or higher) until you have the amount of compression you desire. Use
the Gain Reduction meter as a visual guide to the amount of compression applied.
SLOPE switch
In its “out” position, the Tube MP/C’s compression ratio is an active 2.3:1 ratio. This means that for every 2.3dB
over the threshold the input signal rises, the compressor’s output will change by 1dB. This is a very mild and
musical compression ratio which is ideal for smoothing all types of signals. In its “in” position, the compression
ratio is greater than 6:1. This is typically called “soft limiting” as it allows only a 1dB change in signal level for any
signal reaching over 6dB over the set threshold. This setting is ideal for applications where exceeding a set level
is undesirable (mixing, popping bass, digital recording, etc.).
SPEED switch
The position of the Speed switch selects the release characteristics of the Tube MP/C’s compressor. The Fast
position allows the compressor to recover quickly once the signal falls below the threshold. The Auto position
allows the compressor to adjust itself depending on the characteristics of the input signal. Use the Fast setting
when the signal has repetitive, consistent characteristics (kick drum, snare, vocals, etc.). Use the Auto setting
when the signal has varying characteristics (long decaying notes alternating with quick notes, mix material, etc.).
PHASE switch
The Phase switch is provided to reverse the phase of a signal. This switch works on Pins 2 and 3 of the XLR
Output jack and also reverses the polarity of the ¼-inch output jack. In the Normal (out) position, the signal is in-
phase. In multiple microphone applications, the placement of the microphones can affect the phase of a signal.
If two microphones pick up the same signal from different locations, the result can be a hollow or frequency
“shifted” sound. In some cases, it may sound as if an instrument disappears if it happens to be 180 degrees out
of phase. Depressing the Phase switch can remedy this problem. Likewise, if a microphone cable is wired

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incorrectly, when used with a properly wired cable the signal will be out of phase. Note: for single microphone
applications, switching the phase switch in and out will produce little to no change in the output signal.
OPTO COMP switch
An Opto Comp Bypass switch is included on the Tube MP/C to enable you to remove the compressor from your
signal chain. When set to its “out” (OFF) position, signal is allowed to pass from the preamp circuitry to the output
level control circuitry with no compression. The LED will glow green when the compressor is engaged. In its “out”
position, the compressor is bypassed. Use the Opto Comp switch when setting the Tube MP/C’s Output Level
to achieve unity (no boost or cut) gain. Unity gain is achieved when the "ON" level is the same as the "OFF"
level.
GAIN REDUCTION display
The Gain Reduction display monitors the compressor gain. As an input signal exceeds the threshold level set by
the user, the compressor reduces its' gain. This Gain reduction is displayed by one of four LEDs. For the most
transparent results, adjust the threshold and slope to limit the average gain reduction to 9dB or less.
OUTPUT control
The Output Level control sets the output level of the Tube MP/C. When the control is fully counterclockwise, the
output is muted. Turning the control clockwise increases the level of the output to a maximum of +20dB of gain.
If the Output Level control is set very low (below the “-3” marking), you can set the Output switch to "Inst." level
to better optimize the TubeMP/C to your system's clip level. This is common when connecting to mic or guitar amp inputs.
OUTPUT LEVEL display
The Output Level LED display indicates the signal level present after the output control but before the Output
switch. The red CLIP LED lights a few dB before the internal circuitry actually clips. The yellow "0" LED lights
when you have 12dB or less of headroom before clipping. Note: The Level switch on the rear panel will shift
the output level without changing the level displayed on the Level display.

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REAR PANEL FUNCTIONS
Figure 2 - Rear view
POWER switch
The Power switch supplies and removes power from the unit. The Tube MP/C should be turned “on” only when
all monitor levels are turned down, or off, to protect against any “thumping” caused by high gain settings.
Likewise, the Tube MP/C should be turned “off” after turning all monitor levels down.
INPUT and OUTPUT connections
The Tube MP/C’s XLR Input connector follows the AES standard: Pin 1 = Ground, Pin 2 = Hot (+), Pin 3 = Cold
(-). The unbalanced ¼-inch phone jacks are typical Tip = Hot (+), Sleeve = Ground.
INPUT
One input jack can be selected at a time. However, because of its design, the Tube MP/C can be hard-wired
without having to disconnect the XLR. If the ¼-inch input is used the unit switches over to this source
automatically. When you plug into the ¼-inch jack, you bypass the balanced amplification input section and go
directly into a high impedance termination that is more appropriate for an instrument. The bottom line on this is
that your electric guitar or bass's character is better maintained.
BALANCED OUTPUT
The Balanced output is a transformer isolated connection using a 3 pin XLR connector. Pins 2 and 3 provide
the output signal. Pin 1 floats, isolating the ground to the unit and preventing ground loops when using both
output jacks. The maximum output level is controlled by the Output switch.
Both balanced and unbalanced output connections may be used simultaneously. This is particularly useful when
using the Tube MP/C as a direct box for instruments or line level signals.
UNBALANCED OUTPUT
The ¼-inch output jack provides signal between the shield and the tip. It is intended for use with 1/4" mono
plugs. The maximum output level is controlled by the Output switch.