The ADL 600 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 600 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 600.
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 ADL600 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 600’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.
Most mic preamps have a fixed microphone-input impedance of between 1 and 2 kΩ. The ADL 600 provides variable microphone-input impedance, which can be set at 150, 300, 900, or 1500Ω.
As the impedance on the ADL 600 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, some microphones are finicky about impedance; with variable impedance, you can make virtually any mic deliver its best performance.
- 2 input channels, each with:
- Mic, Line, and instrument inputs
- High-voltage, Class A, dual-transformer, vacuum-tube preamp
- 3 military-grade vacuum tubes
- Input-source select
- Variable mic-input impedance (150, 300, 900, 1500 Ohms)
- Variable high-pass filter (40, 80, 120Hz)
- 8-position Gain switch
- Variable Trim adjustment for final stage
- 48V phantom power
- -20dB pad
- Polarity-reverse switch
- Backlit VU meter (output level) with -6dB switch (for metering hot signals)
- Input / Output
- 2 unbalanced 1/4" instrument inputs (front panel)
- 2 transformer-balanced XLR line inputs
- 2 transformer-balanced XLR mic inputs
- 2 transformer-balanced XLR line outputs
- 2U 19" rack-mountable, rugged steel chassis
- Internal power supply with standard IEC connector
- Chasis-ground link connectors (lift chassis ground)
- Microphone: Selectable, 150/300/900/1500 Ohms
- Balanced Line: 2000 Ohms
- Instrument: 100 000 Ohms
Maximum Input Level
- Microphone (1500 Ohms, +20dB Pad Out): +5dBu
- Microphone (1500 Ohms, +20dB Pad In): +25dBu
- Balanced Line: +30dBu
- Instrument: +30dBu
- Microphone (1500 Ohms, +20dB Pad Out): 18dB to 72dB
- Balanced Line: -12dB to 40dB
- Instrument: -5dB to 42dB
- Noise Floor (all inputs, minimum gain): -95dBu (A-Weighted)
- Microphone Equivalent Input Noise (EIN): -125dBu (A-Weighted)
- Frequency Response: 10Hz to 45kHz +/- 1dB
- Maximum Output Level: +23dBu (0.5% THD + N)
- Output Impedance: 600 Ohms
- Tube Complement (per channel): 1-12AT7A, 2-6922
- Internal supply, Standard IEC connector: 115 or 230 VAC / 100W
- Dimensions: 2U rackmount
- Height: 88.9mm
- Depth: 431.8mm
- Width: 482.6mm
- Weight: 12.7kg