ART USB Dual Tube Pre - User's Manual

Important Safety Instructions

Read First: 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.

⚠️ Electrical Hazard: This symbol indicates the presence of uninsulated dangerous voltage inside the enclosure, sufficient to constitute a risk of shock.

ℹ️ Important Information: This symbol alerts you to important operating and maintenance instructions in the accompanying literature.

Do Not Open: No user-serviceable parts inside. Refer service to qualified personnel.

Power Sources: Connect only to mains power of the type marked on the rear panel, ensuring a good ground connection.

Power Cord: Use the provided plug appropriate for your local supply. Route the cord to prevent it from being walked on, stretched, or pinched.

Grounding: Do not defeat the grounding or polarization means of the power cord plug.

Ventilation: Ensure adequate ventilation, especially when in a rack or furniture. Do not impede airflow.

Moisture: Do not expose to rain, moisture, or damp conditions. Do not place liquid containers on the unit.

Heat: Avoid locations near excessive heat or direct sunlight. Keep away from heat-producing equipment.

Environment: Protect from excessive dirt, dust, heat, and vibration. Avoid tobacco ash, drink spillage, and smoke.

Handling: Avoid rough handling and excessive vibration. Use adequate padding for transit. Exercise care when lifting or moving.

Servicing: Switch off and unplug if exposed to moisture, liquid, foreign objects, or if the cord/plug is damaged. Refer servicing to qualified personnel.

Installation: Install in accordance with the user guide instructions.

Introduction

Thank you for purchasing the ART USB Dual Tube Pre computer interface. This manual will guide you to achieve the best performance from this reliable and easy-to-use device.

The USB Dual Tube Pre is a two-channel professional audio interface designed to connect microphones, instruments, and line-level signals to mixers, audio inputs, or directly to your computer via USB or S/PDIF. It represents the latest in ART's line of tube preamps, building upon the legendary Tube MP series with updated design elements for enhanced performance, a compact, stackable aluminum chassis, and precision LED metering.

This model features two digital interfaces for direct digital audio connection to personal computers. The USB interface is compatible with built-in drivers for Windows (98SE/ME/2000/XP/Vista/7) and Apple (OS9.1/OSX) systems, requiring no special drivers for basic operation. It functions as a USB Audio Device, providing an isolated, low-noise interface for hard disk recording. A separate S/PDIF jack offers a standard digital connection to other audio interfaces.

The unit boasts an ultra low-noise discrete microphone preamp with a flat, wide frequency response, capable of handling a wide range of input signal levels with minimal coloration for a clean, neutral sound. The high-impedance 1/4-inch instrument input bypasses the mic preamp for a clean signal path. A high-quality 12AX7A tube adds warmth, and the external analog power supply minimizes AC line noise. The USB interface is isolated and powered directly from the USB port.

The input Gain control and switch help maximize dynamic range and control tube drive. A switchable Low Cut filter (set at 70Hz) reduces low-frequency rumble and wind noise, preserving bass tonality and time-domain response. Phantom power (+48V DC) is available for XLR inputs, supplied by a low-noise, current-limited internal supply.

An optical Compressor with fast attack and musical release times controls maximum audio output levels, preventing overload and maximizing dynamic range before digital conversion. A Phase Invert switch allows for polarity adjustment at the source, useful for phase cancellation issues when using multiple microphones. The Output control matches the output level to various systems, and Insert Loop jacks with a bypass switch allow for external effects processing and input monitoring.

A high-performance monitor section provides output drive capability to balanced outputs and the headphone jack, allowing for zero-latency monitoring of the signal going to digital, mixed with computer audio via USB.

Key Features

• Two-channel tube-based mic/instrument preamp computer interface
• Extremely low-noise discrete front end with variable input and output controls
• Advanced optical output compressor for simplified recording and overload prevention
• USB connectivity to desktop and laptop computers
• S/PDIF output for expanding digital workstation inputs
• Latency-free Monitoring Mix and Level controls
• Balanced XLR (lo-Z) and 1/4" hi-Z inputs for instrument DI
• Separate Gain, Phase Invert, Low Cut Filter, and Compressor switches per channel
• Selectable Dual or Stereo operation of output controls
• Switchable Inserts on each channel
• Insert jacks provide preamp direct out
• Stereo/Dual operation of Optical Compressor
• Mono switch for single input monitoring
• S/PDIF Sample Rate switch (44.1KHz / 48KHz)
• Precision LED metering for preamp and A/D sections
• Built-in low-noise +48 Volt phantom power supply
• Compact, stackable all-aluminum chassis

Front Panel Controls

LEFT GAIN and RIGHT GAIN knobs: Adjust input preamp gain for each channel, matching signal levels to A/D converters and outputs. Increasing gain drives the tube for warmth and optimizes noise performance, also affecting the Opto Compressor.

GAIN switch: Adds 20dB of gain, useful for higher gain requirements or increased Opto Compressor range.

LOW CUT switch: Rolls off signals below 70Hz to reduce low-frequency rumble and wind noise, allowing for more gain before clipping.

PHASE switch: Selects input signal phase to compensate for mic orientation and wiring. Normal position keeps output in phase with input. Reversing phase can prevent hollow sounds from cancellations or increase gain before feedback.

OPTO COMP switch: Activates the Optical Compressor. The switch cap lights green when active and red when gain reduction occurs. Compresses dynamic range to prevent clipping without sounding obtrusive. Compressor threshold is affected by GAIN controls and switches, not LEVEL controls.

LEFT LEVEL and RIGHT LEVEL knobs: Adjust the output level of the preamps. Affected by the STEREO/DUAL switch, they can function as independent controls or as MASTER LEVEL and BALANCE controls.

SIGNAL/CLIP LEDs: Monitor output signal levels for A/D converters and indicate clipping. They show signal at the preamp (pre-LEVEL control) and at the A/D converter (post-LEVEL control). Reducing LEVEL controls to 11 O'clock or less helps isolate input section signal/clip indication.

MONITOR MIX knob: Controls the proportion of preamp signal versus computer (USB) signal in the monitor outputs. Fully counter-clockwise is preamp only; fully clockwise is computer only.

MONITOR LEVEL knob: Sets the master stereo output level for headphone and monitor outputs.

MONITOR HEADPHONES jack: Unbalanced 1/8" mini-phone jack for headphones, mirroring the rear monitor outputs.

STEREO/DUAL switch: Configures the LEFT/RIGHT LEVEL controls. In Stereo mode, they become independent. In Dual mode, they act as Master Volume (left knob) and Balance (right knob).

OPTO link switch: Ties the gain of each channel's Opto Compressor together, essential for maintaining stereo image with stereo sources.

MONITOR switch: Sums both input channels for the MIX control's preamp source. Useful for single-input monitoring through both headphone/monitor outputs while listening to a stereo computer return. Does not affect the signal to the A/D converter or INSERT jacks.

Rear Panel Connections and Controls

INPUT Jacks: XLR (low impedance mic) or 1/4" (high impedance instrument) inputs. Gain is controlled by the front panel GAIN knob.

INSERTS jacks: Allow insertion of external signal processing gear (e.g., EQ) between the preamp output and A/D converter. The adjacent INSERT switch enables/disables external connections. The output is via the tip of a 1/4" plug; the ring is the input. Can also serve as preamp direct output jacks when the INSERT switch is in the Bypass (out) position.

INSERT switch: Enables external processors connected to the INSERTS jacks when depressed. Set to Bypass (out) when using INSERTS as outputs.

MONITOR OUTPUT jacks: Balanced or unbalanced 1/4" outputs for line-level signals. Mixes preamp output with computer audio via USB. Controlled by front panel MONITOR Level and MIX knobs, and the MONITOR switch.

S/PDIF Output: Connects to consumer and professional equipment. Output is 0.5V p-p with 75 Ohm impedance. Controlled by the rear SAMPLE RATE switch. Transmits channel status for sample rate and copyright protection. Equipment should be set to "slave" to this signal for timing synchronization. Front panel SIGNAL/CLIP LEDs help calibrate output levels.

USB jack: Connects to computer for sending and receiving audio. Features a separate A/D for the USB interface, operating at a computer-controlled sample rate. Compliant with USB 2.0, backward compatible with USB 1.0.

9 Volts AC POWER jack: Connects to the supplied power adapter (9-10 Volts AC @ 1000mA). Ensure AC, not DC, if replacing. Internal circuitry converts power for tube and phantom power sections.

POWER switch: Powers the unit on/off. Allow 1-2 minutes for tube and circuitry to warm up after powering on.

S/PDIF SAMPLE RATE switch: Sets the sample rate for the S/PDIF A/D converter. "Out" position is 44.1KHz; depressed (lit) position is 48KHz.

PHANTOM POWER switch: Applies +48V DC phantom power to XLR inputs for microphones. Slow to turn on/off and current-limited for protection. For microphones requiring phantom power: turn gain down, connect mic, switch on phantom power, then raise gain. This minimizes pops and stress.

Block Diagram Description

The block diagram illustrates the signal path of the ART USB Dual Tube Pre. Input signals enter via LEFT and RIGHT INPUT jacks, which connect to LOW NOISE PREAMP stages. These stages are followed by TUBE/OPTO COMP sections. Each channel has controls for GAIN, LOW CUT, PHASE, and OPTO COMP. The GAIN control affects both preamp gain and compressor drive. The LOW CUT filter operates at 70Hz. The PHASE switch inverts polarity. The OPTO COMP switch activates a compressor, with an OPTO link switch for stereo operation. The SIGNAL/CLIP LEDs monitor levels.

The output of the preamp/compressor stages can be routed through INSERTS jacks, which can also serve as preamp direct outputs. The signal then passes through a STEREO/DUAL switch which affects the LEFT LEVEL and RIGHT LEVEL controls. These controls adjust the output level, with STEREO mode allowing independent control and DUAL mode offering Master Volume and Balance.

The signal is then processed by A/D converters, which can output via S/PDIF (with a SAMPLE RATE switch) or USB to the computer. The USB connection also allows audio from the computer (D/A conversion) to be mixed with the input signal via the MONITOR MIX control. The MONITOR LEVEL knob controls the overall output to the MONITOR OUTPUT jacks and the MONITOR HEADPHONES jack.

Applications

Microphone Pre Amplifier: Suitable for dynamic, condenser, and ribbon microphones. Offers a quality upgrade over budget preamps, providing flexibility and a robust tone. Connect via XLR, apply phantom power for condenser mics, adjust gain, and route output to a mixer, workstation, or computer via 1/4" jacks or USB. Analog output level is adjustable at the unit.

Phantom Power Supply: Provides +48V phantom power for condenser microphones, a critical feature for mixers or interfaces lacking this capability. Connect any microphone to existing equipment.

Instrument DI: Functions as a tube DI for bass, acoustic guitar, and other instruments with 1/4" or XLR outputs. Offers tube warmth and responsiveness preferred by many over standard DI's. Connect instrument output to the unit's input, ensure instrument volume is high. Effects can be patched via INSERTS. Adjust input GAIN and monitor SIGNAL/CLIP LEDs. Route output via 1/4" or USB. Analog outputs and USB port can be used simultaneously.

USB Operation

Connect analog jacks and power supply first. Connect monitor outputs to your system or headphones for low-latency monitoring. Set front panel controls. Connect the USB cable to your computer and the unit.

Upon connection, the computer powers the USB interface and typically sets "USB Audio CODEC" as the default audio device. Manual selection may be needed in system sound settings or audio applications.

Windows Setup:

• Windows 98SE: Settings > Control Panel > Multimedia > Preferred Device: "USB Audio Device"
• Windows XP: Settings > Control Panel > Sounds and Audio Devices > Audio > Mixer Device: "USB Audio CODEC". Alternatively, Programs > Accessories > Entertainment > Volume Control > Options > Properties > Mixer Device: "USB Audio CODEC".
• Windows Vista/7: Settings > Control Panel > Sound > Playback Tab and Record Tab > Choose: "USB Audio CODEC". For Windows 7, adjust settings in "Control Panel > Sound Settings" to 2-channel/16bit/44.1K and reset microphone input gain. Use the "Configure" button to set up the microphone.

Mac OS9.1 or OS X Setup: Control Panels > Sound > Input Device: "USB Audio CODEC"; Output Device: "USB Audio CODEC".

Your computer's audio output will now be routed to the USB Dual Tube Pre. Recording software will manage channel selection and monitoring. Multiple units will appear as "USB Audio CODEC 1", "USB Audio CODEC 2", etc.

Latency between audio input and USB output is under 2 milliseconds. Software drivers can introduce more latency. Low-latency ASIO drivers are recommended for Windows if latency is an issue. Resources include www.asio4all.com and www.usb-audio.com.

S/PDIF Operation

The S/PDIF output connects to workstations and audio interfaces, providing two channels of 24-bit digital audio. The digital audio source is the A/D converter. Access the A/D directly via the Insert jacks "Ring" terminal. Ensure connected equipment accepts "consumer" mode digital audio and that sample rates (44.1KHz or 48KHz) match between the unit and your application.

A Brief Note from Customer Service

If experiencing unwanted "noise", ensure the signal is being sent correctly. ART preamps output a LINE LEVEL signal. Sending this to a mixer's or recorder's Mic input (which adds more gain) can result in noise. Treat the output as line level for a clean, warm sound. The same applies to guitarists and bassists; send the signal to a low gain input or "loop return" jack on an amplifier.

Warranty Information

Limited Warranty: Applied Research and Technology (ART) warrants this product to the original purchaser against defects in workmanship and materials for three years from the date of purchase. ART will repair or replace defective parts at its option, free of charge, upon prepaid delivery to a service center with proof of purchase.

Exclusions: Warranty does not cover misuse, abuse, unauthorized alterations, or repairs. Void if the serial number is altered or defaced. ART reserves the right to make design changes without obligation to apply them to previously manufactured products. ART is not liable for consequential damages. Some states may not allow limitations on incidental or consequential damages.

For units purchased outside the United States, service is provided by authorized distributors.

Service

If your unit requires service:

1. Verify the unit is the cause of the problem. Check power, cables, and connections. Consult your dealer for assistance.
2. If the ART unit is at fault, visit www.artproaudio.com for Customer Service or to request a Return Authorization (RA) in the "resources" area.
3. When returning for service, pack the unit in its original or a suitable substitute carton.
4. Include a note with the RA number and your contact information (including a daytime phone number) with the unit.

Specifications

• Input Connections: XLR / 1/4-inch "Combo" jack (XLR balanced, 1/4" unbalanced)
• Input Impedance: 1M Ohms (1/4"), >4K Ohms (XLR), 20K Ohms (Insert)
• Output Connection: 1/4-inch TRS balanced, 1/8-inch TRS headphone mini jack
• Output Impedance: 600 Ohms (1/4" balanced), 300 Ohms (INSERTS), < 50 Ohms (1/8" headphone)
• Frequency Response: 20 Hz – 27K Hz (+0, -1 dB)
• Maximum Gain: +65 dB (balanced in-out), +45dB (unbalanced input, balanced output)
• THD: <0.01% @ 1K Hz
• CMRR: >60 dB
• Equivalent Input Noise: -129 dBu typical ("A" wtd., Shorted XLR balanced input, max gain)
• Maximum Input Level: +16 dBu (unbalanced Inst), +12dBu (balanced mic), +7.5dBu (Insert)
• Max Output Level: +5dBu (unbalanced), +11dBu (balanced), +7.5dBu (insert output)
• Phantom Power: Switch selectable, +48Volts DC, filtered, current limited
• Tube Type: Hand Selected 12AX7A
• Compressor Slope: Progressively increasing, 10:1 max.
• Compressor Range: 28dB attenuation max.
• Low Cut Filter: -3dB @ 70Hz, 6dB/Octave
• USB A/D-D/A: 16 Bit, 44.1K Hz or 48K Hz, USB selectable from computer, 0.4 ms A/D latency @ 44.1K Hz
• S/PDIF A/D: 24 bit, 44.1K or 48KHz switch selectable, 0.4 ms A/D latency @ 44.1K Hz
• Computer Interface: USB 2.0 compliant, Windows 98SE/ME/2000/XP/Vista, Win 7, Apple OS9.1/OSX computers with native USB support
• Chassis Type: All aluminum black anodized with integral rubber sides
• Power Requirements: 9VAC @ 1000mA (external)
• Dimensions: 1.75"H x 5.9"W x 6.5"D (44.5mm x 150mm x 165mm)
• Weight: 2.5 lbs. (1.14 kg) with power supply and packaging
• Note: 0 dBu = 0.775Vrms