PreSonus moves up-market with some of Anthony DeMaria's magic.
by Russ Long, 1.15.2007
Russ Long, a Nashville-based producer/engineer, owns The Carport recording studio. He is a regular contributor to Pro Audio Review.
I've been hearing Anthony DeMaria's name since the early 1990s and it has always been synonymous with high quality, tube-based circuit design. I bought one of his ADL-1000s about 10 years ago and I still use it regularly today. In a collaborative effort with Anthony DeMaria Labs, PreSonus was presented with DeMaria's three dual-triode vacuum tube mic preamp design, which they used as the foundation for the ADL 600. After adding several new features to the design to meet the needs of the target market, they ended up with the ADL 600 stereo microphone preamplifier ($2,295). The “ADL” portion of the product name gives credit to Anthony DeMaria for providing a solid design to build upon. The ADL 600 utilizes a high voltage, Class A discrete design with three vacuum tubes per channel for maximum headroom and tonality. PreSonus builds the mic preamps by hand in the USA utilizing the world's finest components including switched attenuators, military-grade vacuum tubes, analog VU and LED meters, and custom-designed proprietary transformers. This “no expenses spared” approach is carried down to the last polypropylene film capacitor.
Features
FAST FACTS
Applications
Studio, broadcast, post production
Key Features
Two-channel; tube; selectable impedance; three-position high-pass filter; 48V phantom power; phase reverse; 20 dB pad; VU meters
The 28-pound ADL 600 has an attractive look that visually blends classic and modern design. The ADL 600's black aluminum faceplate is accented with a combination of brushed aluminum knobs and large chrome toggle switches. A large brushed aluminum bezel containing an analog VU meter and an eight-segment LED meter for each channel is located in the center of the panel. The front panel is laid out so the controls and metering for Channel 1 are on the left hand side and the controls and metering for Channel 2 are on the right hand side. The box measures 3.5 inches (H) X 17 inches (D) X 19 inches (W).
The Input switch selects the input source (Instrument, Line or Microphone). The microphone input has four different input impedance values to select from (1500 ohms, 900 ohms, 300 ohms or 150 ohms) and a gain range of 18 dB to 72 dB. The Balanced Line Input has an input impedance of 2 Kohm and a gain range of –12 dB to 40 dB. The Instrument Input has an input impedance of 100 Kohm and a gain range of -5 dB to 42 dB. The ADL 600's noise floor (all inputs, minimum gain) is -95 dBu (A-weighted) and the microphone equivalent input noise (EIN) is -125dBu (A-weighted). The box has a frequency response or 10 Hz to 45 kHz ±1 dB and a maximum output level or +23dBu (@ 0.5%THD+N). The unit's output impedance is 600 ohm.
The three-position HP FILT rotary switch selects the frequency for the high-pass filters (40 Hz, 80 Hz or 120 Hz). The filters are 1st-order and provide 6dB/octave rolloff. The HP filter switch inserts the filter into the circuit. When the switch is engaged, all frequencies below the selected HP FILT setting are attenuated by 12 dB. The eight position rotary gain switch provides 35 dB of gain in 5 dB steps and the variable TRIM potentiometer provides an additional ±10 dB fine trim adjustment to the final stage of the box. Ultimately, the microphone gain is adjustable from 18 dB to 72 dB. The 1/4-inch jack provides front panel instrument input. The 48V switch activates phantom power while a POL INV switch reverses the polarity of the signal. The 20 dB pad switch activates the 20 dB pad. The VU METER -6dB switch decreases the VU meter by 6 dB, making it easier to meter loud input sources. XLR connectors for microphone and line inputs and preamp output are located on the rear of the chassis.
The ADL 600's custom-designed input transformer is fully encased in a Mu-metal enclosure that yields excellent noise characteristics and magnetic shielding. The preamp's principle gain stage is provided by the combination of a 12AT7A triode and a 6922 triode. A high endurance Grayhill rotary switch and 1% metal film resistors are used to set this stage's gain in 5 dB steps. Poly film pulse capacitors are used for inter-stage coupling to maintain the highest sonic clarity and poly film capacitors are used for the filters. The output trim potentiometer feeds the input to the second 6922 triode. The ADL 600's power supply begins with a filtered AC input receptacle and ends with a power supply that far exceeds the load requirement. Fast switching diodes are used instead of standard recovery 60 Hz diodes in the regulated high voltage supplies. The custom designed, Mu-metal shielded, toroid power transformer was engineered to be overrated by a factor of four, ensuring superior load regulation and minimizing the transformer flux leakage. All said, the ADL 600 is built to last a lifetime.
In Use
Over the past several months I've been able to use the ADL 600 in a wide variety of situations and have always been impressed with its performance. While tracking Roy Wooten (of Bela Fleck and the Flecktones) on drums I used a pair of AKG C-12s through the ADL 600 on overheads and had amazing results. I have never heard C-12s sound more open or natural. While tracking the St. Louis rockers Ludo, I used an AKG D112 through the ADL 600 on kick drum and again had wonderful results. I attempted to use the preamp along with a Heil PR 20 on snare drum but found that I wasn't able to get enough crack with the tube preamp and ended up switching to a John Hardy M-1. The mic preamp did a great job capturing shaker and tambourine with a Royer Labs SF-1 and congas with a pair of Heil PR-30s. In each instance, I was able to get the desired sound without any equalization.
The ADL 600 did a fantastic job of capturing electric guitars with a Royer R-122 and a Heil PR-40. I also had good results recording keyboards and bass guitar through the front panel's instrument inputs.
All of these positive experiences aside, where I found the mic preamp to truly shine is on acoustic guitar, piano and vocals. The preamp did an exceptional job along with an Earthworks SR-77 capturing the sound of a Taylor 514-CE acoustic guitar. It worked perfectly along with a pair of Audix SCX25 microphones to capture a grand piano. The preamp sounded wonderful with a Sony C-800G while recording female vocals and with a Brauner VM1-KHE to record male vocals. The mic preamp makes vocals sound extremely large and full.
One of my favorite uses of the ADL 600 was as a line level tube stage. While mixing I set up a stereo insert on my Pro Tools session and ran in and out of the ADL 600 at line level. The box added a wonderful texture to my mix, almost as if I was no longer mixing in the box but through a tube console.
My first impression of the ADL 600's metering was that it wasn't necessary to have both LED and VU meters on each channel but - as I used the ADL 600 more and more - I found that the fast acting LED meters are excellent for accurately detecting fast transients and peaks while the VU meters are good for simply metering output level.
All said, I found the ADL 600 to be extremely quick and easy to achieve the desired results and it worked in almost every instance.
Summary
The high-voltage Class A dual-transformer ADL 600 is a fantastic sounding and extremely quiet tube microphone preamplifier packed full of features including over 73 dB of gain, variable microphone input impedance, and both analog VU and fast-acting LED metering. At $2,295, it isn't cheap, but it should receive top consideration of any studio or engineer looking to add a tube mic preamp to their arsenal of gear.
Russ Long has done 5.1 DVD mixes for Allison Moorer and Mercy Me and is an in-demand engineer for live sound recordings, having multitracked live performances for Chris Tomlin, Lisa Loeb, Salvador, and Nichole Nordeman.
Review Setup:
Apple Macintosh 2 GHz dual-processor G5 w/2 GB RAM; Digidesign Pro Tools 7.1; Lucid Gen-X-96 clock; PMC AML-1 monitors.
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