Benchmark ADC1 USB A/D Converter
The reference-quality Benchmark ADC1 2-channel 192-kHz 24-bit audio analog-to-digital converter is equipped with Benchmark's UltraLock technology. The ADC1 is designed for maximum transparency and is well suited for the most demanding applications in studios and mastering facilities. A rugged and compact half-wide 1 RU enclosure also makes the ADC1 an excellent choice for location recording, broadcast facilities, and mobile rigs. The internal power supply supports all international voltages and has generous margins for over- and under-voltage conditions.

The Benchmark ADC1 achieves outstanding performance over a wide range of input levels. Each channel has a 41-detent variable gain control, a 10-turn calibration trimmer, and a 3- position first-stage gain switch (0, 10, and 20 dB). Each channel has a two-position toggle switch that selects either the 41-detent pot or the 10-turn trimmer. Both the pot and the trimmer have a 20 dB adjustment range. In combination with the first-stage gain switch, these controls provide exceptional SNR and THD+N performance over a 40 dB adjustment range. The 10-turn calibration trimmer may be used to calibrate the ADC1 to precise studio reference levels. It may also be used to optimize the gain-staging between a microphone preamplifier and the ADC1.

The ADC1 has four digital outputs (1 balanced XLR, 2 coaxial, and 1 optical). The optical output supports AES, ADAT, and ADAT S/MUX. The two coaxial outputs (Main and Aux) can operate simultaneously at different word lengths and even at different sample rates. The ADC1 has the flexibility to allow simultaneous high-resolution and low-resolution recordings. For example, the main outputs of the ADC1 can be set to 192 kHz 24-bits while the auxiliary output is set to 44.1 kHz 16-bits for a safety backup or CDR demo recording. Both the Main and Aux Outputs originate from the same A/D converter. All outputs are professional format.

The ADC1 has a Word Clock output that follows the sample rate of the Main Outputs. The Word Clock output is active in all modes of operation.

A multi-format clock input automatically recognizes AES/EBU, SPDIF, Word Clock, or Super Clock signals. This clock input is used to synchronize the Main Outputs. If desired, the Main Outputs may be driven from internal sources. The ADC1 will automatically revert to an internal clock source when the external clock is lost.

The ADC1 has two clock modes: Auto and Internal. Both modes support 44.1, 48, 88.2, 96, 176.4 and 192 kHz. The Auto mode allows the ADC1 to lock to an external clock reference. In Auto mode, the ADC1 will follow changes in sample rate, and/or changes in the type of reference signal (AES, SPDIF, word clock, or super clock).

When a clock reference is not available, the Internal mode must be used, and a sample rate must be selected (44.1, 48, 88.2, 96,176.4, or 192 kHz). When the Internal mode is active, the ADC1 is acting as clock master, will only operate at the selected sample rate, and will ignore any signal at the clock reference input. If Internal mode is used, all devices connected to the ADC1 digital outputs will need to be configured to lock to the ADC1. Use the clock output on the back of the ADC1 if the connected devices require word clock.

The Benchmark UltraLock system is 100% jitter immune. The A/D conversion clock is totally isolated from the AES/EBU, SPDIF, ADAT, WC, and super clock interfaces. This topology outperforms two-stage PLL designs. In fact, no jitter-induced artifacts can be detected using an Audio Precision System 2 Cascade test set. Measurement limits include detection of artifacts as low as -140 dBFS, application of jitter amplitudes as high as 12.75 unit intervals (UI) and application of jitter over a frequency range of 2 Hz to 200 kHz. A poor-quality clock reference will not degrade the jitter performance of the ADC1. In addition, the AES/EBU receiver IC has been selected for its ability to decode signals in the presence of very high levels of jitter. The Benchmark UltraLock system delivers consistent performance under all operating conditions.

The ADC1 is designed to perform gracefully in the presence of errors and interruptions at the clock reference input. The ADC1 follows an audio-always design philosophy. Audio is present at the outputs shortly after applying power to the unit. The ADC1 will even lock to and AES/EBU signal that has its sample-rate status bits set incorrectly. Sample rate is determined by measuring the incoming signal. Lack of sample rate status bits or incorrectly set status bits will not cause loss of audio.

The ADC1 is phase accurate between channels, and between other ADC1 boxes when locked to AES/EBU or word clock reference signals. The word clock output from one ADC1 may be connected to the clock input on another ADC1 to expand the number of phase-accurate conversion channels.

For mounting options, see RM Kit #485682, RM Coupler #485683, and RM Blank #485683.