No Compromises—Our Finest Channel Strip!
Stunning high-end sound and incredible versatility are hallmarks of this top-of-the-line, tube-driven channel strip. The ADL 700 integrates a proven, award-winning, boutique-quality preamp; a custom-designed FET compressor; and a custom, four-band, semi-parametric EQ.
Our premium channel strip boasts frequency response from 10 Hz all the way up to 45 kHz and offers all of the features you’d want in a high-end device. And the ADL 700 is a great value — as you expect from PreSonus!
You Asked for It!
We created the ADL 700 because you insisted! The PreSonus ADL 600 two-channel tube mic preamp was such a hit with customers—including such top artists, engineers, and producers as Chuck Ainlay, Jimmy Douglass, Mark Mancina, Demetric Collins, and Victor Wooten—that we were inundated with requests for a single-channel version in a channel strip, with a compressor and EQ that would be up to the preamp’s high standards.
You were right—it was a great idea—so we gave the design job to Robert Creel, the engineering mastermind behind many of PreSonus’ most beloved analog circuits, including the XMAX™ preamp. It took years of hard work but he delivered big-time. The ADL 700 channel strip is everything we—and you—hoped it would be!
Putting the AD in ADL 700
We started with a single-channel version of the ADL 600 preamplifier, which was co-designed by PreSonus and famed tube-circuit designer Anthony DeMaria. The preamp employs a distinctive Class A, discrete design that incorporates two 6922 and one 12AT7 vacuum tubes per channel, operating with ±300V power rails for maximum headroom and superb tone.
The dual-transformer design ensures low-noise operation, with maximum common-mode rejection. This resulted in an ultra-quiet tube preamp with a big, warm, smooth, clear, distinctive sound.
The ADL-series preamplifier runs on power rails of ±300V. Most off-the-shelf, op-amp-based designs run on power rails of 10V to 18V. Higher-voltage power rails deliver more headroom, deeper lows, smoother highs, and a richer overall sound.
We only use genuine transistors, resistors, and capacitors in the ADL 700 because this provides ultra-low noise and transparency. Op-amps add noise, coloration, and harshness to a signal. You won’t find them in the ADL 700.
Power amplifiers are classified primarily by the design of the output stage and are designated Class A, B, AB, D, G, or H. In a Class A preamp, the output circuits are always on for the entire cycle of signal swing or the bias current flows at all times. As a result, Class A preamps have the most linear design, with no crossover distortion, and they deliver purer, clearer, and more musical results than the Class AB designs that are found in many preamps.
The ADL 700 employs large, high quality, custom-wound, shielded input and output transformers. Among other things, these securely decouple the preamp from the outside world (the mic and the A/D or following devices), which is very important in a high-voltage tube design such as this one.
The ADL 700’s Cinemag input transformer sets the stage for the preamp’s nearly ruler-flat/linear and detailed sound; the rest of the preamp amplifies what the Cinemag delivers. No other input transformer sounds like the Cinemag does—and we tried others.
The nickel/iron-core, large-scale output transformer delivers high headroom. It will begin to saturate in a pleasing (some would say “creamy”) manner at very high levels. This adds the bit of finish to the sound.
Beyond superb sound quality, the ADL 700’s preamp is special because of its ease of use and flexibility.
Among the hallmark features of ADL-series preamps are separate, balanced XLR mic, balanced XLR line, and ¼” TS instrument inputs and a single, balanced XLR output. An Input Source Select switch enables you to leave your signal sources connected at all times and choose among sources, patching the selected input through the signal chain and completely bypassing the other two inputs.
The preamp offers a choice of four mic-input impedances: 1500Ω, 900Ω, 300Ω, and 150Ω. Lowering or raising the ADL 700 mic-input impedance can create subtle coloring and filtering effects, enabling you to get a wider variety of tonalities without using the EQ.
Most mic preamps have a fixed microphone-input impedance of between 1 and 2 kΩ. The ADL 700 provides variable microphone-input impedance, which can be set at 150, 300, 900, or 1500Ω.
As the impedance on the ADL 700 preamp is lowered, a resistive load is put on the microphone. This will not damage the microphone but lowering or raising the impedance can create subtle coloring and filtering effects, enabling you to get a wider variety of sounds.
In general, a lower input impedance can add color to the mic to produce effects that simulate a “darker,” or more “closed-in” tone, or that change the mic’s apparent sensitivity. This effect is easier to notice on passive microphones (ribbon or moving coil) than on active microphones (condensers or active ribbons/dynamics).
In addition, the ADL 700 provides variable mic-input gain, employing an 8-position, military-grade, rotary switch that provides 35 dB of gain in stepped, 5 dB increments. A Trim potentiometer (±30 dB) allows you to make fine adjustments to the final preamp stage of the ADL 700 input.
The output stage is controlled by a fully variable attenuator that delivers ±10 dB of fine-tune trim adjustment, enabling you to dial in the perfect gain structure for any application.
A Tight Squeeze
The ADL 700’s FET (Field-Effect Transistor) compressor includes fully variable attack, release, threshold, ratio, makeup gain, and bypass controls. The compressors of two ADL 700s can be stereo linked allowing for more accurate stereo imaging. The ADL 700 compressor has a “soft knee” compression curve.
The term “knee” refers to the way the compression curve bends at the threshold point when represented graphically.
With hard-knee compression, the gain reduction applied to the signal occurs as soon as the signal exceeds the level set by the threshold.
With soft-knee compression, the onset of gain reduction occurs gradually after the signal has exceeded the threshold, producing a more musical response (to some folks).
FET-based compressors such as the one in the ADL 700 use transistors to emulate a triode tube’s operation and sound. This type of compressor generally provides a faster attack time and better repeatability than the optical compressors that are more commonly found in channel strips in this price class.
Broadly speaking, there are four types of analog compressor designs: those that use opto-isolators (optical), Field-Effect Transistors (FETs), voltage-controlled amplifiers (VCAs; an example is the PreSonus Studio Channel compressor), and variable-gain compressors. Each has its uses, but we’re going to focus on the two types you’re most likely to find on today’s high-end channel strips: optical and FET.
The majority of today’s high-end channel strips utilize optical compressor circuits. In general, the response time of the optical circuits in these compressors tend to soften the attack and release, which can smooth out uneven volume fluctuations. They often have a distinctive sonic signature, so they can be as much an effect as a gain-control device.
FET compressors use a special transistor to vary gain, emulating a triode-tube sound. Inherently high-impedance devices, FET compressors tend be very clean and reliable and provide a faster attack time than most optical compressors.
To some extent, which you prefer is a matter of taste. You might want the sound of an optical compressor for one application but prefer a FET-based compressor for another application.
However, aside from having a distinctive sound, optical compressors have drawbacks. Most notably, when the components in an optical compressor heat up or cool down, the resulting attack and release times can change considerably. That means you might not get consistent results—even on, say, multiple snare hits in the same song.
Unlike optical compressors, FET compressors such as the one in the ADL 700 are not susceptible to temperature fluctuations, so they provide consistent, repeatable results.
There’s also an environmental issue with optical compressors. Optical circuits contain a small amount of cadmium, a metal that is banned in new electronic equipment under the European Restrictions of Hazardous Substance (RoHS) Directive. Unlike optical compressors and certain professional athletes, the FET compressor in the ADL 700 uses no banned substances. We’re just sayin’….
The ADL 700’s 4-band semi-parametric EQ was designed to match the preamp and compressor, with musicality in mind. It combines isolated filters and optimized, per-band Q to provide subtle signal-shaping without harsh artifacts. All bands have Gain (±16 dB) and Frequency controls, with overlapping frequency ranges and fixed Q (0.55). The low and high bands are switchable between shelving and peak.
The ADL 700 offers Gain controls that range from -16 to +16 dB.
The center-frequency range for the low band goes from 20 to 250 Hz; the low-mid band ranges from 160 Hz to 2 kHz; the high-mid band goes from 800 Hz to 8 kHz, and the high band ranges from 2 to 20 kHz. Note that the bands overlap.
The two mid bands are peak bands. A peak equalizer boosts or cuts a band of frequencies around a center frequency (selected by the Frequency control). The width of the band is variable in a fully parametric EQ, typically using either a bandwidth control or, more often, a Q control. (Q is defined as the ratio of the center frequency to the bandwidth; a lower Q results in a wider frequency band.) A good example is the parametric EQ in the StudioLive 24.4.2 digital mixer.
In a semi-parametric EQ, the Q (and the bandwidth) is fixed. The Q on the ADL 700 is fixed at 0.55, a low value that provides a fairly wide frequency band.
To summarize: In the ADL 700 peak EQ bands, you can boost or cut a wide (Q=0.55) band of frequencies by ±16 dB at a selectable center frequency.
The high and low EQ bands can be switched between peak and shelving operation. When used as peak bands, they behave the same way as the two mid bands, except for their center-frequency ranges.
A shelving EQ attenuates or boosts frequencies above or below a specified cutoff point. In this mode, the band’s Frequency control sets the cutoff frequency rather than the center frequency.
In shelving mode, the ADL 700’s high band becomes a low-pass filter, passing all frequencies below the cutoff frequency, while attenuating all frequencies above the cutoff. The low band becomes a high-pass shelving filter, passing all frequencies above the cutoff frequency, while attenuating everything below. In both bands, the frequencies beyond the cutoff are rolled off, following a predetermined curve—not cut off sharply.
Who’s on First?
Would you rather have the compressor before the EQ in the signal chain or put the EQ first? Placing the compressor before the EQ allows you to make dramatic changes to the EQ settings without needing to alter the compressor setting. However, if you place the EQ before the compressor, you can better control different frequencies, achieving a more natural response.
The ADL 700’s EQ>Comp switch provides the best of both worlds, allowing you the flexibility to chose which signal flow is right for your application at any given time.
You also can independently bypass the compressor and the EQ using front-panel switches.
Of course, you get +48V phantom power, polarity inversion, and a 20 dB pad, controlled by big, sturdy, military-grade switches. You also get a -12 dB/octave high-pass filter, the frequency threshold of which can be set at 20 Hz, 40 Hz, 80 Hz, or 200 Hz—or it can be turned off completely. It’s great for controlling room rumble and low-frequency noise.
We didn’t skimp on metering either. Fast-acting, eight-segment LED meters accurately detect fast transients and peaks. Large, backlit, dual-mode analog VU metering enables monitoring of output and gain-reduction levels. A -6 dB switch offsets the meter for use with hot source signals. A master level control adjusts the overall output from -80 to +6 dB.
Double Your Pleasure
As much as you’ll enjoy having one 2-rackspace ADL 700, you will absolutely love having a pair of them. You can even stereo-link the two compressor sections: When the Threshold control is turned fully counterclockwise to the ST position, the onboard compressor controls are bypassed, and compression is controlled externally, via a Stereo Link connection to a second ADL 700.
With its extensive feature set, ultra-low noise (-100 dB S/N ratio), >73 dB gain, extended frequency response of 10 Hz to 45 kHz, and top-of-the-line sound, the ADL 700 is a superb creative tool for serious recording engineers and musicians.