ART Tube Channel User Manual

Features

The ART Tube Channel is a unique product featuring three independent, award-winning circuit designs: a tube microphone preamplifier, an optical tube compressor, and a flexible four-band equalizer. Developed with studio and live sound engineers, it offers a distinct "sound" unmatched by other products. Constructed with high-quality components, it ensures quiet, reliable performance. Key features include:

• Award-winning ART "SOUND"
• Tube-based mic/line preamplifier
• Electro-optical compressor design
• Tube-based semi-parametric, four-band equalizer
• Hand-selected preamp tubes
• VCA-less compressor circuitry for transparent dynamics control
• Unique tube drive and gain reduction metering
• VU output level metering
• Bypassable compression and equalization circuitry
• XLR balanced inputs and outputs
• 1/4" TS unbalanced inputs and outputs
• Custom extruded aluminum chassis
• 1/4" unbalanced insert points between preamp/compressor and compressor/equalizer
• +48V phantom power
• Phase reversal
• Over 70dB of gain
• Detented rotary controls
• Selectable compression and limiting ratios
• Selectable release time settings
• >90dB dynamic range
• Internal power supply
• Three-year warranty
• Designed and manufactured in the USA

Overview

Why use an external processing channel?

The principle of the shortest signal path for optimal recording quality (mic to preamp to compressor to EQ to tape deck) remains relevant, especially with the availability of affordable mixing consoles. While these mixers excel at routing, their onboard circuitry may not offer the sonic quality of dedicated external processors. The ART Tube Channel provides a superior sounding and more flexible collection of circuits, allowing engineers to achieve the desired sound before committing it to tape, thus avoiding the need to "fix it in the mix." External processing offers sonic and practical benefits, particularly when recording one or two channels at a time, proving more cost-effective than high-end consoles for budget-conscious users.

Design Notes

The Tube Channel is a versatile tool for audio engineering and recording, housed in a 1U rack space. It integrates a tube-based analog preamplifier, a VCA-less optical compressor, and a semi-parametric, four-band, tube-based equalizer. It functions as a direct recording channel, mic/line preamp, or DI box, seamlessly integrating with various recording, sound-reinforcement, or electronic instrument setups. The circuitry employs a hybrid design combining advanced solid-state and tube technology, featuring a transformerless design for exceptional signal integrity and low noise. The compressor circuit follows the preamp, and the equalizer follows the compressor, though the order can be altered using insert points. The preamp is always active, while the compressor and equalizer can be bypassed. Its active balanced solid-state input offers low noise and excellent CMRR. The 1/4" input provides high impedance, ideal for DI or line-level applications without loading the connected device. The second stage of the preamp utilizes a 12AX7a tube, providing up to 40dB of gain, designed to overload gracefully for sonic manipulation. The optical compressor uses Vactrol electronics for musical dynamics control, offering a soft-knee characteristic that excels in transparent compression without artifacts like pumping or breathing. The tube-based equalizer is designed to address common recording challenges for instruments like kick drums, snares, bass, guitars, and vocals, featuring two overlapping sweepable parametric bands and selectable shelving bands for maximum flexibility.

Setting Up

Unpacking

Your Tube Channel was carefully packed at the factory. Retain the original shipping carton for transport or potential servicing needs.

AC Power Hookup

The unit operates on 100-125VAC, 50-60Hz. Units for international use are modified for local specifications. Never alter the power cable; if damaged, discontinue use and replace with a proper 3-prong type.

Audio Connections

Connections are made via balanced XLR (Pin 2 = Hot (+), Pin 3 = Cold (-), Pin 1 = Ground) and unbalanced 1/4" (Tip = Hot (+), Sleeve = Ground). Insert points between circuits are also 1/4" (Tip = Hot (+), Sleeve = Ground). High-quality cables are recommended.

Installation

The Tube Channel can be used in various setups, including:

• Between a microphone and a mixer, digital multi-track recorder, DAT machine, hard disk recorder, or analog recorder.
• In a mixer's channel insert points.
• Between a microphone and signal processors.
• Between electronic musical instruments (synthesizers, guitars, basses, samplers, acoustic instruments with pickups) and other gear.

Safety Precautions

Warning: To prevent electric shock or fire, do not expose the unit to moisture. Do not remove metal panels or chassis parts, as they expose dangerous high voltages. There are no user-serviceable parts inside; refer all servicing to qualified personnel. Always use the correct (3-prong) power cord.

Powering Up

Turn the Tube Channel on after monitor levels or power amps are turned down or off to prevent "thumping" from high gain settings. Conversely, turn the unit off after monitor levels are down. The VU meter illuminates when power is on. Like all tube equipment, the Tube Channel requires a 1-2 minute warm-up period for the tubes to reach optimal operating temperature. If the unit fails to power up, check the power cord connection. If it still does not operate, turn it off, unplug it, and consult your dealer or ART's Customer Service department.

Front Panel Controls & Indicators

Preamp Circuit

Gain Control

Sets the input gain. Turn clockwise to increase, counterclockwise to decrease. The +20dB gain switch selects the range: +9 to +50dB or -11 to +30dB. The "sweet spot" for tube warmth is indicated by the second "warm" LED in the Tube Drive Array.

Gain Switch

Selects the gain range. "Out" (0dB) provides -11 to +30dB. "In" (+20dB) provides +9 to +50dB. The +20dB setting is often necessary for microphone applications.

Phantom Power Switch

Provides +48V DC phantom power for microphones. Consult your microphone's documentation. Turn phantom power OFF when connecting or disconnecting microphones to avoid "thumping" or potential damage. Allow 30-45 seconds for power to dissipate when disengaging.

Tube Drive/Gain Reduction Display

Four LEDs indicate tube gain affecting the input signal, calibrated to represent tube circuitry output. "Cln" indicates clean output. "Warm" LEDs indicate the optimal operating range for warm tone. "Clip" illuminates approximately 6dB before audible distortion, indicating the tube is beginning to distort pleasingly. Regular flashing of the "Clip" LED can be desirable for certain applications.

Preamp Output

Controls the output level of the preamp section. Typically set around the "0" position (12 o'clock). It offers a range from no output to +16dB gain. This control can be used to add gain when the main Gain control is set low for a clean sound, or to reduce output when the Gain control is pushed for maximum tube warmth.

Optical Compressor Circuit

Slope Switch

Determines the compression ratio. "Out" position: 2.3:1 (mild, musical compression). "In" position: >6:1 (soft limiting, for controlling peak levels).

Speed Switch

Selects compressor release time. "Out" ("fast") allows quick recovery. "In" ("auto") adjusts release based on input signal characteristics. "Fast" is suitable for repetitive signals (drums, vocals), while "auto" is better for varying signals (sustained notes, mix material).

Compressor Bypass Switch

Allows bypassing the compressor. "In" (bypass) position allows signal to pass to the EQ without compression (indicated by a red LED). "Out" (Norm) position engages the compressor. Use this switch to set unity gain by matching active and bypassed levels.

Compressor Threshold and Output Controls

These are ganged on a dual concentric pot. The outer control sets the Threshold; the inner control sets the Output level.

Compressor Threshold Control (outer control)

Sets the point at which compression begins. Turning counterclockwise lowers the threshold (more compression). Turning clockwise raises it. Start with the control fully clockwise, adjust Preamp Output, then slowly turn the Threshold counterclockwise until the yellow (0dB) LED lights. Adjust further for desired compression amount, using the Gain Reduction meter as a guide.

Compressor Output Level Control (inner Control)

Sets the output level from the compressor. Typically used to add gain to compensate for compression. Set for unity gain (no level change when active or bypassed). The control ranges from -20dB attenuation to +20dB gain. For best signal-to-noise ratio, add gain before the compressor if possible. Ensure output levels do not clip subsequent equipment.

Clip Indicator

Located in the equalizer circuit, this LED illuminates 6dB before headroom is exceeded, indicating the input level to the equalizer is too high. Reduce the Preamp Output, Compressor Output, or the output of the device feeding the compressor return.

Equalizer Circuit

A tube-based, semi-parametric, four-band equalizer with overlapping bands for flexibility. The "Q" (bandwidth) is wide for a musical sound.

Low Frequency Control

Adjusts a shelving filter with selectable corner frequencies of 40Hz or 120Hz. Boosts or cuts frequencies below the selected corner. Range is +/- 12dB. 40Hz is useful for sub-low enhancement (bass, kick drums) or cleaning up muddy mixes. 120Hz is suitable for low-end weight (guitars, toms, vocals).

Low Shift Switch

Selects the corner frequency for the Low Frequency control: "Out" for 40Hz, "In" for 120Hz.

Lo-Mid Frequency Control

Dual concentric control: outer selects frequency, inner applies +/-12dB gain. Ranges are 20Hz to 200Hz and 200Hz to 2KHz, determined by the Shift x 10 switch.

Lo-Mid Shift x 10 Switch

Selects the frequency range for the Lo-Mid control: "Out" for 20Hz to 200Hz, "In" for 200Hz to 2KHz. Overlap with Low Frequency control is intentional for flexibility.

Hi-Mid Frequency Control

Dual concentric control: outer selects frequency, inner applies +/-12dB gain. Ranges are 200Hz to 2KHz and 2KHz to 20KHz, determined by the Shift x 10 switch.

Hi-Mid Shift x 10 Switch

Selects the frequency range for the Hi-Mid control: "Out" for 200Hz to 2KHz, "In" for 2KHz to 20KHz. Overlap with Lo-Mid control in the 200Hz-2KHz range allows for combined adjustments.

High Frequency Control

Adjusts a shelving filter with selectable corner frequencies of 6KHz or 18KHz. Boosts or cuts frequencies above the selected corner. Range is +/- 12dB. 6KHz adds top-end (guitars, vocals) or softens harshness. 18KHz adds "sizzle" (cymbals) or definition, and cutting it reduces hiss.

High Shift Switch

Selects the corner frequency for the High Frequency control: "Out" for 18KHz, "In" for 6KHz. Overlap with Hi-Mid control offers flexibility for bright, noise-free results.

EQ Bypass Switch

Bypasses the equalizer circuit. "In" (bypass) position allows signal to pass to outputs without EQ (indicated by a red LED). "Out" position activates the EQ. Use to set unity gain through the equalizer.

Master Output Level Control

Sets the overall output level of the Tube Channel, from no output to +10dB gain. Refer to the VU meter or external meters for setting levels.

Phase Switch

Reverses the phase of the output signal. "Out" (Normal) is in-phase. "In" (Reverse) is 180 degrees out of phase. Useful for correcting phase cancellation issues in multi-microphone setups.

Output Level VU Meter

A backlit VU meter displays average output level, calibrated to +4dBm at "0". Use it as a visual reference for signal level, but always prioritize monitoring levels on your mixing console or recorder.

Power

The power switch controls power to the unit. Ensure monitors and power amps are turned down before powering the Tube Channel on or off to prevent "thumping." The Output Level VU meter illuminates when the unit is powered on.

Rear Panel Connections

Input and Output Connections

XLR connectors follow AES standard (Pin 1=Ground, Pin 2=Hot (+), Pin 3=Cold (-)). 1/4" jacks are Tip=Hot (+), Sleeve=Ground.

Input

Use one input jack per channel. The 1/4" jack functions even if the XLR is connected but unloaded. Disconnect unused cables to minimize noise and RF interference.

Output

Both balanced and unbalanced outputs can be used simultaneously. If hum occurs when using both outputs, a ground loop may be the cause. Disconnect the ground wire (Pin 1) from the XLR output cable or use a ground-lifted cable to break the loop.

Loop Inserts

Two unbalanced 1/4" "send" and "return" loops are provided for connecting external equipment or altering the signal path order (e.g., preamp to EQ to compressor). "Send" jacks pass signal when unpatched; "return" jacks break the signal flow when a cable is inserted.

Preamp - Compressor Loop

Connects the preamp output to the compressor input. The Preamp Send jack is after the Preamp Output control. The Compressor Return jack is before the Threshold control. The connected equipment should have level matching capabilities.

Compressor - EQ Loop

Connects the compressor output to the equalizer input. The Compressor Send jack is after the Compressor Output control. The EQ Return jack is before the equalizer input. The connected equipment should have level matching capabilities.

Loop Connections

To use only the preamp: Plug signal into Input Jacks. Output via Preamp Send or bypass compressor/EQ and use main Output Jacks.

To use only the compressor: Plug signal into Compressor Return Jack. Output via Compressor Send jack.

To use only the equalizer: Plug signal into EQ Return Jack. Output via Tube Channel's main Output Jacks.

To place EQ before compressor: Connect Preamp Send to EQ Return, unbalanced Output to Compressor Return. Use Compressor Send as the main output.

Applications

The Tube Channel serves as a processing channel for microphones, instruments, or line-level sources. For preamp-only use, bypass the compressor and EQ circuits and adjust input/output controls. It is also ideal as a DI box, connecting instruments directly and routing through XLR, 1/4", or both outputs. Experiment with input levels for different textures. The Tube Channel often outperforms console preamps. Connect its output to a mixer's line input. Note: Connecting the XLR output to a mixer's XLR input may result in higher noise if the mixer's internal preamp cannot be bypassed.

Special Effects

Experiment with overdriving the preamp, compressor, and equalizer for unique textures on vocals and instruments. Placing signals out of phase can also yield interesting results. Always ensure output and monitoring levels are turned down before testing new settings. The unit offers significant gain reserves.

EQ Tips

What is the best way to use EQ?

There are two main philosophies: use EQ only as needed to achieve a good sound, or avoid EQ altogether. The best approach is to use your ears and judge subjectively. Always tweak EQ while listening to the instrument within the mix, not in solo, to understand its context. Often, what sounds great solo can sound poor in a mix, and vice-versa. Focus on the overall sonic picture. Many engineers default to boosting frequencies, but often, cutting problematic frequencies can yield better results. To find problem areas, isolate a track, boost a mid-band, and sweep through frequencies until an unpleasant sound is prominent, then cut that frequency. Adjust levels accordingly. When recording, ensure desired frequencies are captured, as they cannot be added later. Monitor "off" tape to verify recorded sound. For kick drums, ensure sufficient low-end "thud" and high-end "click" are present at the source. Be prepared for requests to alter sounds post-recording. Efficient recording and mixing involve blending tracks and managing dynamics, rather than extensive re-EQing. If over-EQing occurs, take a break. Start mixing by listening to groups of instruments (e.g., drum kit, guitars, bass) rather than individual tracks. Remember the mantra: "if it sounds good, print it!"

EQ Frequency Guide

This guide associates sonic characteristics with frequency ranges and instruments:

• Low Frequencies:
• 20Hz-100Hz: "mud" (Electric Guitar), "impact", "power" (Bass), "thud" (Kick Drum), "boxy" (Vocals)
• 100Hz-250Hz: "ring/power" (Electric Guitar), "meat" (Snare Drum), "boxy" (Drum Overheads)
• 250Hz-500Hz: "crack" (Snare Drum), "clack" (Bass)
• Mid Frequencies:
• 500Hz-800Hz: "crick" (Kick Drum), "sibilance" (Vocals)
• 800Hz-1kHz: "sizzle" (Cymbals)
• High Frequencies:
• 1kHz-2.5kHz: "air/open" (Vocals)

Instrument/Source Associations:

• Electric Guitar: "mud", "ring/power", "bees"
• Bass: "impact", "power", "clack"
• Snare Drum: "meat", "crack"
• Kick Drum: "thud", "crick"
• Drum Overheads: "boxy", "sizzle"
• Vocals: "boxy", "sibilance", "air/open"
• Piano
• Organ

Frequency scale: 20Hz, 100Hz, 250Hz, 500Hz, 800Hz, 1KHz, 2.5KHz, 5KHz, 10KHz, 18KHz, 20KHz.

Tube Replacement

The tubes in the Tube Channel are designed for longevity and are hand-sorted for performance. ART recommends using tubes available from ART for consistent sonic results, as they are matched to the unit. While other brands can be used, ART is not responsible for the resulting sound quality. Unauthorized alterations to the Tube Channel will void the warranty.

Block Diagram

The block diagram illustrates the signal flow through the ART Tube Channel. The signal enters via unbalanced 1/4" or balanced XLR inputs and proceeds to the Preamp section, featuring Gain, Phantom Power (+48V), Tube Drive/Gain Reduction metering, and Preamp Output controls. From the preamp, the signal can be routed through the Preamp/Compressor Insert Loop (Send/Return). The signal then enters the Compressor section, which includes controls for Slope, Speed, Bypass, Threshold, and Output, along with a Detector and a Gain Reduction meter. The compressor's output is then fed to the Compressor/EQ Insert Loop (Send/Return). Following this is the Equalizer section, a 4-Band semi-parametric EQ with controls for Low, Lo-Mid, Hi-Mid, and High frequencies, each with selectable frequency ranges and +/- 12dB gain adjustment, plus an EQ Bypass switch. The final stage includes the Master Output Level control, a Phase switch (Normal/Invert), and an Output Level VU Meter, before exiting through unbalanced 1/4" and balanced XLR outputs. The unit's model number is 259.

ART Tube Channel Specifications

ART retains a policy of constant product improvement. ART reserves the right to make changes in design or make additions to or improvements upon this product without any obligation to install the same on products previously manufactured. Specifications are subject to change without notice. Designed and manufactured in the United States of America.

We're On-line!

For product information, questions, applications, tips, answers, and general discussion with ART employees, visit ART on the Internet. Email artroch@aol.com or check the Web Page at: http://www.artroch.com

Warranty and Service Information

Limited Warranty

Applied Research and Technology, Inc. (ART) warrants this product to the original purchaser to be free from defects in workmanship and materials for three years from the date of purchase. ART will, at its option, repair or replace defective products or components free of charge upon prepaid delivery to the factory service department or an authorized service center, accompanied by a valid sales receipt. EXCLUSIONS: This warranty does not cover misuse, abuse, or unauthorized alterations or repairs. It is void if the serial number is altered, defaced, or removed. ART reserves the right to change designs or make improvements without obligation to apply them to previously manufactured products. ART is not liable for consequential damages, including loss of use. Some states may not allow limitations on incidental or consequential damages. This warranty grants specific rights, and you may have others that vary by state. For products purchased outside the United States, service is provided by authorized ART distributors.

Service

In the unlikely event your unit requires service, follow these procedures for returns within the United States. For service outside the US, contact your authorized ART distributor.

1. Confirm the unit is the cause of the problem. Ensure it has power, all cables are correctly connected and functional.
2. If the unit is at fault, describe the problem, including how and when it occurs.
3. Call the factory for a Return Authorization (RA) number.
4. Pack the unit in its original carton or a suitable substitute. Do not use the original carton as a shipping carton; place it inside another box for shipping. Print the RA number clearly under the address.
5. Include with your unit: a return shipping address (no P.O. Boxes), a copy of your purchase receipt, your daytime phone number, and a description of the problem.
6. Ship the unit to: Applied Research and Technology, Inc., 215 Tremont Street, Rochester, NY 14608, Attn: Repair Department, R.A.# [Space for RA number].
7. Contact Customer Service at (716) 436-2720 for your Return Authorization number or repair inquiries. Customer Service hours are Monday-Friday, 9:00 AM to 5:00 PM Eastern time.

©1998 Applied Research and Technology, Inc.