ART Pro Channel

PLEASE NOTE: This article has been archived. It first appeared on in February 2000, contributed by then Editor-in-Chief Rip Rowan. We will not be making any updates to the article. Please visit the home page for our latest content. Thank you!

The ART Pro Channel is a tube-based mic preamp, compressor / limiter, and four-band parametric EQ. It combines the essentials from ART’s tube preamp, optical compressor, and EQ into a single, 2U package.

Table of contents


The preamp section is a hybrid tube / solid-state preamp, incorporating a solid-state variable front end feeding a fixed-gain tube circuit. A variable (15 Hz – 150 Hz) low-cut control is provided. The preamp is controlled by two gain knobs and a +20 dB gain switch. The first gain knob and the switch control the solid-state amplification that feeds the tube circuit. The other gain knob is post-tube. The layout allows the user to control the amount of signal hitting the tube circuit.

ART Pro Channel

A calibrated LED VU meter (labeled “Tube Character”) monitors the signal coming off the tube circuit. The Tube Character indicates whether the tube is being run clean, warm, or heavily distorted. The preamp also offers a phase switch and phantom power.

The unique compressor circuit features a dual design. The compressor can function as either an optocompressor or a variable-mu compressor. The optocompressor utilizes the ART Vactrol design found in the ART Pro-VLA. The Vactrol optocompressor is a good choice for vocals and other, more transparent compression roles. The dual-triode variable-mu compressor is fast-acting and very suitable for hard limiting. The compressor features variable threshold and ratio, and switches for “fast” or “slow” attack and “fast” or “auto” release. The compressor contains an output make-up gain knob that offers another 16 dB of tube gain. A 10-segment LED gain reduction meter is provided to monitor the amount of compression.

The four-band EQ circuit is quite flexible. The low and high shelf EQs have a switchable boost frequency (40 Hz / 120 Hz for the bass, and 6 KHz / 18 KHz for the treble). The 2 swept mids cover the entire spectrum and each has a narrow / wide Q control.

Finally, the unit has another tube gain stage and a master output control. A large lighted analog meter is provided to monitor the unit’s output. The meter can also be used to monitor the preamp output or the compressor output.

The Pro Channel offers a very flexible input / output routing scheme. Master inputs and outputs are available as either balanced XLR or unbalanced ¼”. Additionally, each stage of the unit is available as an insert. You can use the inserts, for example, to use the unit as a standalone compressor, or to change the signal routing so that the EQ is ahead of the compressor in the signal chain. With its ability to meter any output in the signal chain, the Pro Channel is capable of functioning like three separate units (preamp, compressor, and EQ).

I found the black faceplate with large white lettering to be very easy to read. The large VU meter is also very easy to read, but it’s also a little slow to respond. Overall I encountered only one usability issue with the Pro Channel, and that was the lack of variable attack and release controls on the compressor. Otherwise the Pro Channel is perfectly executed.


Of course, as my friend Bruce is quick to point out, features are meaningless. Results are priceless. I was curious about the results. I am no big fan of ART’s tube MP preamp or Pro VLA compressor. Would this monster preamp, with its four gain stages, be able to deliver?

I tried the Pro Channel using several mics, including a Shure KSM32, a Neumann U87, and an Audio-Technica 4050 CM5, on both male and female vocalists. What I discovered is that this preamp is capable of producing cleaner sounds than I would have expected. In addition, the many gain stages make for a very useful and versatile coloration tool.

First off, this unit has a serious shitload of gain. By my calculations, over 80 dB of gain. There’s so much gain in the box I’m surprised there’s not sparks shooting out the back. There are FOUR different gain knobs on this unit, and a +20 gain switch. That’s not counting gain resulting from positive equalization. Learning to properly optimize the sound of the Pro Channel was, therefore, a little tricky. The results were, however, worth the effort.

As tube preamps go, the Pro Channel is not as clean as a $2000, world-class tube preamp. But it is capable of being cleaner than some other tube preamps, and actually rivals some transistor units in its class.

To get the best clean sound with the Pro Channel, it’s necessary to run the preamp’s tube at low-to-moderate gain (keeping the “Tube Character” meter in the first four to six segments) and to use all of the remaining gain stages to add a little gain at each stage. With this setup I discovered that I could get a good clean sound that was only lightly colored, especially when I kept the EQ and compression circuits out of the signal path. I used this setup on a female vocalist, and was able to achieve a clean vocal that was delicate, though not “airy.”

What I love about this unit is its ability to go from clean to warm to fuzzy to buzzy. Virtually any kind of distortion is capable with this unit. I even found it to be an excellent front-end for an electric guitar or bass.

For example, one sound that I love is the coveted vintage tube mic sound. This sound comes from more than just the vacuum tube. It comes from a few aging components, including a dried, aged capsule that has lost some flexibility and imparts a kind of compressed and limited sound; poorly biased tubes, and worn-out caps. In the right proportions and combinations, these “defects” become “magic”. The sound is “hot”, “compressed”, and “exciting”.

The Pro Channel, with its various overdrivable gain stages and its vari-mu compressor was able to coax that kind of sound out of an Audio Technica 4050 CM5. No mean feat for such a sterile mic. The sound was really cool. The radical 18 KHz high shelf is perfect for adding a little sheen and gloss to this sound, enhancing and coloring the harmonics produced by the tubes to create a nice sheen.

I was similarly enamored with the Pro Channel on bass guitar. I set up the preamp to add “warmth” to the point of barely audible distortion. I used the Variable mu compressor at 3:1 for about 6-12 dBs of gain reduction. Finally I get into the EQ, using a 40 Hz low shelf boost combined with a 15 Hz low cut on the preamp to get a sound that was surprisingly controlled for its size. The slightly compressed and edgy sound was very amp-like. I loved the sound of bass guitar through the Pro Channel.

Finally, I arrived at a track where the goal was to create a truly crapped-out distorted vocal. I plugged an AKG D1000E into the Pro Channel and started cranking up the gain. You can get distortion anywhere you want in the signal path. For example, you can put a clean sound into the compressor, overdrive the EQ, and lower the master output to get overdriven EQ. Or overdrive the preamp and keep the compressor and EQ clean. Or crank up the whole damn thing and create all kinds of distortion. With tube gain stages all the way though, you can achieve any kind of distortion you can imagine, from subtle to buzzy, and from creamy to screamy.


The Pro Channel is a great front-end for a digital system. You can use a little optocompression to gently ride the loudest peaks, and allow the natural limiting of the tubes to tame anything that might clip your inputs. The result is hot, slightly compressed, and energetic. Or for more limiting, raise the ratio to about 6:1, engage the vari-mu compressor for ultra-fast fast attack and release, and dig into more compression. I love compression, limiting, tubes, and distortion, and this box will pretty much do it all. And, shockingly, it sounds pretty damn good when it isn’t overdriven.

The Pro Channel was the biggest surprise I’ve had with a piece of gear in a long time. I thoroughly expected to dislike it. In fact, I loved the Pro Channel. Its a perfect alternative to the sterile inputs on your mixing board. It’s definitely colored: you would not want to run all your tracks through the Pro Channel. But it’s also surprisingly versatile. This is not a one-trick pony, and it’s a real steal at its price point.